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by: Percy Wintheiser


Percy Wintheiser
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This 142 page Class Notes was uploaded by Percy Wintheiser on Wednesday September 9, 2015. The Class Notes belongs to FISH 311 at University of Washington taught by Staff in Fall. Since its upload, it has received 56 views. For similar materials see /class/192253/fish-311-university-of-washington in Aquatic And Fishery Sciences at University of Washington.

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Date Created: 09/09/15
BIOLOGY OF FISHES FISH 311 FORM EXTERNAL ANATOMY BODY SHAPE AND SIZE FINS SPINES AND SCALES EVOLUTIONARY TRENDS IN BODY FORM General topics 1 2 3 4 KI OOOO De nitions quot shquot and quot shesquot External anatomy body structure and form The concept of primitive versus derived Evolutionary trends in sh morphology The primitive sh body plan The derived sh body plan What does it all mean Continental drift and the breakup of Pangaea The development of modernday coralreef communities 1 DEFINITIONS What is a sh Fishes are so numerous and so highly diverse morphologically that a concise and all encompassing de nition is dif cult No one character by itself will do Instead a combination of features is required For example Fishes are animals that are 1 most always aquatic 2 most always coldblooded 3 most always gillbreathing 4 craniates in which 5 ns are usually developed never pentadactyl limbs What s the difference between quot shquot and quot shesquot The classical de nitions of these two terms are a bit complex quotFishquot can be both singular and plural but in all cases refers to a single species quotFishesquot is always plural and always refers to more than one species For example an aquarium full of guppies Poecilia reticulatus is full of sh the ocean is ll of shes 39 Fish versus shes By convention fish refers to one or more indi VIduas of a Single speCIes quotFishesquotis used when discussing more than one species regard less of the number of individuals involved FISH versus FISHES Drawings from Jordan 1905 2 EXTERNAL ANATOMY BODY STRUCTURE AND FORM Variation in body shape among shes is enormous The trick is to try and make some sense out of it to better understand how shes have evolved and how they t into their particular habitat or in other words how they make their living Many textbooks in ichthyology approach this subject by introducing a number of quottypica quot sh body shapes The authors say that most shes fall into one of six broad categories Each one of these categories is characterized by general features of body shape n placement etc Roverpredators streamlined shes with a pointed head terminal mouth narrow caudal peduncle and forked tail always on the move in search of prey pursuit predators examples include trout Salmonidae bass Serranidae tuna and mackerel Scombridae and Salmonidoe bill shes Istiophoridae Xiphiidae 4111711227 i Q J V Serranidae Scombridae lstiophoridae Liein wait predators sheaters designed for capturing fastswimming prey by ambush but these are also elongate streamlined forms often with attened heads large welltoothed mouths the tail n is large dorsal and anal ns placed far back on the body examples include pikes Esocidae barracudas Sphyraenidae needle shes Belonidae and sauries Scomberesocidae K 1 M r 39 gt Scombereaocidac Esocidue Belonidae Sphyrucnldac Surfaceoriented shes typically small shes with dorsally directed mouths attened heads large dorsally directed eyes examples include mosquito shes Q Poeciliidae topminnows and killi shes J Cyprinodontidae halfbeaks and ying shes Exocoetidae P quot d 39 Exocoeiidae Cyprinodontiduc Exocoeh dae Bottom shes wide variety of body shapes all adapted for contact with the bottom most are attened or compressed forms with small often subterminal mouths and small eyes examples are numerous at shes Pleuronectidae cat shes Ictaluridae suckers Catostomidae and some angler shes Lophiidae Pleuronectidae Caioatomidue lcluluridac Deepbodied shes laterally compressed forms with deep bodies dorsal and anal ns typically long pectoral ns high on the body with pelvic ns immediately below small mouths eyes large snout short examples include the huge variety of forms that inhabit coral and rocky reefs kelpbed forests etc Acanthuridac Banjosidac Chuclodonhdac Scutophagiduc Eellike shes elongate bodies blunt heads and tapering or rounded tails paired ns sometimes absent but when present small dorsal and anal ns typically running the length of the body examples include the eels Anguilliformes loaches Cobitidae pricklebacks Stichaeidae and gunnels Pholididae Anguillidae v my MK xvZimmmwwy HIJZWquot EmuM Stichaeidae Pholididue Cobiiiduc This is all right I suppose but it39s important to remember that structural variation in the bOOy plan of shes is a continuum and that it39s impossible to draw sharp boundaries between these six categories or for that matter any set of categories that one might chose One of the best ways to demonstrate this continuum is to look at representative body shapes of shes in cross section as shown here 390 H Representative body shapes in fishes with typical cross sec tionsA Fusiform tuna Scombridae B compressiform sunfish Centrarchi dae C depressitorm skate Fiajidae dorsal view D anguiiliform eel Anguitlidae E fiiiform snipe eei Nemichthyidae F ta eniform gunnel Pholidae G sagittiform pike Esocidae H globiform lumpsucker Cyclop teridae H based on Jordan and Evermann 1900 While again this approach is OK in that it serves to show the great amount of variation in body shape among shes but it is arti cial in the sense that it lacks an underlying scienti c basis for its construction It39s based instead on the whims and biases of its authors if you asked a bunch of ichthyologists independently to take the same approach to classifying shes based on body shape each would no doubt end up with a different result So if this is not the best way to demonstrate the tremendous variation that we see in the external anatomy of shes what is better It seems preferable to place the problem in an evolutionary context For example we could ask As shes have evolved through time can we discern any general structural or morphological trends in sh body shape Are these trends meaningful Do they tell us anything about the evolutionary success of shes An evolutionary approach implies by de nition that something in this case body shape changes with time and if things change in order to talk about it you39ve obviously got to have a picture of what the thing looked like originally and what it looks like now In evolutionary biology we refer to these two end points as the primitive condition and the derived condition 3 CONCEPT OF PRIMITIVE VERSUS DERIVED Relative primitiveness in the evolutionary sense is measured in terms of similarity to a common ancestor the more primitive an organism is the more similar it is to the hypothetical ancestor Derived organisms are those that differ more radically from the ancestor derived forms are also those that appear more recently in the fossil record You should in no way come to think that derived forms are somehow better or more complex than primitive forms Each and every organism is the result of a long evolutionary history and each has acquired its own individual specializations that enable it to survive in its own particular habitat 4 EVOLUTIONARY TRENDS IN FISH MORPHOLOGY Are there any general structural or morphological trends that characterize sh evolution ie are there any sequential structural changes that can be traced throughout the evolutionary history of shes If so what are they and what can they tell us about the evolutionary success of these organisms Evolutionary trends 1 A shift in position of the paired fins pectoral and pelvic ns 2 An increase in overall spinyness eg ns and scales 3 Changes in body shape Shift in position of the pectoral and pelvic fins see gures on the right pelvic ns are abdominal in primitive bony shes but come to lie beneath the pectoral ns thoracic in derived shes Pectoral ns are inserted horizontally and lOW on the body in primitive shes but more vertically and high on the body in derived shes Q A 5 Q t b 6 Q A b 6 Increase in overall spinyness for example acquisition of n spines head spines and spiny scales see gures on the left in primitive bony shes the ns are supported by soft pliable rays in derived forms they are supported by stiff sharp spines Bones of the head are smooth and spineless in primitive shes but become highly spiny in more derived shes a39n Scorpaena scroFa Scales are smooth and spineless in primitive shes cycloid but become highly spiny in derived forms ctenoid annulus radii exposed I ctenii portion 39 I WWWI Mitzii fi 35 llllllllttummnm i a mum tlll l s a gt Mklllllltllllun 11 A 1 ti N J CTENOID Body shape Primitive bony shes are generally long and skinny fusiform in head body and tail with an elongate gut region and vertebral counts that often exceed 50 eg salmon and their relatives trout etc have 5075 vertebrae derived shes are generally short fat and deep bodied with a small compact gut region and low vertebral counts that center on 24 e 1 ano ELOPS AFFINIS SEBAS IODES CARNAI US 5 THE PRIMITIVE FISH BODY PLAN Long skinny head and body ns placed posteriorly without spines generally large adult body size built for speed in open water examples might include tarpon herring sardines anchovies salmon and trout 6 THE DERIVED FISH BODY PLAN Short deep head and body ns placed anteriorly full of spines generally small adult body size built for maneuverability in complex tight crowded habitats examples might include squirrel shes cichlids basses surgeon shes angel and butter y shes So in summary when we look at shes as a whole and concentrate on the big picture it seems evident that over long periods of evolutionary time shes have undergone a major morphological shift from long and skinny to short and fat from soft pliable n rays to stiff spiny n rays from smooth scales to spiny scales and from large body size to small 7 WHAT DOES IT ALL MEAN How can we explain these changes in adaptational and evolutionary terms To understand we need to go back in time some 200 million years or so and take a look at what was happening geologically and environmentally particularly in shallowwater marine habitats of the world We need to look and see what kinds of habitats were available to shes over time One of the most profound global events in the history of the earth was the formation and eventual breakup of Pangaea the socalled super continent 8 CONTINENTAL DRIFT AND THE BREAKUP OF PANGAEA 200 my BP a 135 my BP 65 my 8P Land shallow sea and deep ocean at three pas limes The hatched areas are cpicontinentul seas Plate boundaries are not shown a Pangaea in the Triassic 1 Lane Jurassic or early Cretaceous Northem Pangaea has become Laurasia southern l ungucu after becoming Gondwana has split again into Wcsl Gondwana East Gondwana and India c Late Cretaceous From geophysical and biological evidence we know that a coalition or consolidation of the continents took place at the end of the Permian about 300 million years before present MYBP resulting in the formation of a super continent called Pangaea Approximately 200 MYBP starting with a rift between North America and North Africa Pangaea began to break up into two enormous land masses one in the northern hemisphere called Laurasia and one in the south called Gondwana Laurasia was made up of presentday North America Europe and Asia while Gondwana contained presentday South America Africa India Antarctica Australia About 150 MYBP Gondwana began to break apart First Africa split off from the rest then somewhat later about 140 MYBP or so India broke off and began a long northward journey across what is now the Indian Ocean to its present position as a subcontinent of Asia in the Northern Hemisphere New Zealand broke off as recently as 70 MYBP Australia was the last to separate remaining attached to Antarctica for another 30 million years or so not becoming independent until about 40 MYBP By Miocene times about 25 MYBP the earth had taken on its modernday appearance What were the biological affects of this breakup of Pangaea The splitting of the land masses created a vast increase in the amount of space available to developing marine communities including evolving marine shes a tremendous increase in area and volume in the form of shoreline and shallow seas particularly within warm tropical regions around the world where the rate of speciation is highest This all translates into new and unexploited habitats for shes as well as for the plants and invertebrate animals that shes eat But of particular importance in all this change was the development of organic reefs 9 THE DEVELOPMENT OF MODERNDAY CORALREEF COMMUNITIES Prior to roughly 200 million years ago the primary habitats available particularly to marine shes were vast stretches of open water Under these conditions natural selection favored speed the ability to move quickly to both escape predation and to rundown prey The body plan of primitive shes was well suited to these constraints they are built for speed Long fusiform shes with ns placed posteriorly they are designed like we would build a rocket or an arrow But at about this time 200 million years ago just as more complex kinds of habitats were becoming available through continental drift modernday coral reefs began to ourish in the warm shallow seas of the world will w H n W 2 V W M W nm x 1 62 9 rquot 4 l3 Now for the rst time a threedimensional habitat became available to shes one that not only provided places to hide from predators but also provided vast new food resources that never were there before This tremendous increase in new and complex surface area not only provided habitat for these new food resources invertebrates as well as marine algae but stimulated speciation of prey species of plants and animals as well All this was great for shes but how to exploit these new resources The old body plan designed for speed was no longer optimal The ability to move around ef ciently within this complex crowded habitat became much more important so we begin to see shes designed for greater maneuverability Speed was in a sense sacri ced for greater maneuverability Bodies became shorter and deeper and ns the dorsal and anal ns but particularly the pelvic ns shifted to a more anterior position on the body All changes that make shes better able to control the position of their bodies to make quick turns and to rapidly take off and stop At the same time it39s important to emphasize that shes became generally smaller in size It39s much easier to get around in a tight environment if you39re small Because speed was in a sense sacri ced for this new maneuverability one can imagine that shes were now much more vulnerable to predation One response to this was the development of spines not only spines in the ns but also on the scales and bones of the head Spiny scalation probably also evolved in response to the new rough calcareous habitat to better protect the body against abrasion All of these changes a coupling or coevolution of geological changes environmental changes and morphological changes in shes resulted in a tremendous proliferation explosive radiation of forms during an early period from late Triassic through the Cretaceous or from about 180 to 70 million years ago The result that we see today is a tremendous diversity of shes in the warm shallow seas of the world And what39s important to realize is that nearly all the species that occupy these habitats belong to the most highly evolved group of bony shes a superorder called the Acanthopterygii containing about 14800 species Numerous faunal studies have shown that 75 to 80 percent of the resident shes in coral reef habitats are perchlike shes members of the acanthopterygian order Perciformes a group that contains roughly 10000 species almost a third of all living shes BIOLOGY OF FISHES FISH 311 BIODIVERSITY RESOURCE SHARING AMONG CORAL REEF FISHES COMMUNITY STRUCTURE SPACE SHARING MECHANISMS AND COMMUNITY EVOLUTION General topics 1 2 3 Introduction What are the questions Data collection through direct observation The pioneering work of C Lavett Smith and James C Tyler What species inhabit the reef environment Maj or resources food and living space Mechanisms of space sharing on the reef Community evolution Degrees of specialization among reef dwelling shes Trends in reef community evolution 1 INTRODUCTION WHAT ARE THE QUESTIONS Coralreef sh communities are characterized by high densities of individuals belonging to many species This high biodiversity suggests that there are ne subdivisions of the basic environmental resources particularly of food and space These subdivisions are re ected in structural and behavioral adaptations that enable individual species of shes to utilize aspects of the environment that are not available to other species adaptations that avoid or at least reduce competition In order to understand the origin and maintenance of this high species diversity as well as to explain the spectacular variety of body form coloration color pattern and behavior displayed by these shes we must begin to ask some questions 1 What species inhabit the reef environment 2 How do the different species share the food and space available on the reef 3 How are the species structurally and behaviorally adapted for avoiding interspecific and intraspecific competition through this resource sharing 2 DATA COLLECTION THROUGH DIRECT OBSERVATION To answer these questions it is essential that basic data be obtained through direct observation and because this kind of research is expensive the habitat of interest usually being far away and long periods of eld time required nancial assistance of some kind is usually mandatory So one of the rst things you39d probably want to do is sit down and write a grant proposal Assuming adequate funding the researcher then goes to the tropics obviously some place where reefs are well developed and preferably a locality where human environmental impact has been minimal Because reefs are so complex the non biological structure so intricate and the biodiversity so overwhelming it might be a good idea to pick out a small relatively isolated patch reef instead of trying to record data from larger assemblages Once the speci c study site has been located you must be prepared to sit and watch for long periods of time at least three or four weeks both during the day and at night Before you begin to collect data it is essential that you prepare detailed maps of the patch reef on which distributions of plants and animals can be plotted Fishes would then be identi ed by sight and the numbers of individuals of each species recorded Following the three or four weeks of observation the reef must be collected thoroughly usually by employing some kind of ichthyotoxin eg rotenone This is required for a number of reasons the most important and obvious being 1 Species identifications must be checked and verified 2 Reproductive state must be determined for all individuals 3 Stomachs of all individuals must be examined for diet determinations 3 THE PIONEERING WORK OF SMITH AND TYLER 1972 Numerous studies of this kind have been carried out but perhaps the most important was one done in the early 1970s by two prominent ichthyologists C Lavett Smith of the American Museum of Natural History New York and James C Tyler of the National Museum of Natural History Washington DC Space Resource Sharing in a Coral Reef Fish Community pp 125 178 In B B Collette and S A Earle editors Results of the T ektite Program Ecology of Coral Reef Fishes Nat Hist Mus Los Angeles Co Sci Bull 14 1972 Smith and Tyler chose to investigate how resources were parceled out among shes that occupied a patch reef of approximately 100 m3 in Great Lameshur Bay St John Virgin Islands a roughly triangular patch of coral with a few smaller patches on the periphery which they called quotsatellitesquot at a depth of about 12 m Z 05 Meters 325 Monte r98 A 39 unnu ans Monlastrea 5 cavernosa M 9335 weeth D lorla gbyrinihifcrmis m Por39tes as tecldes porites 0 dead coral if squot Slderastvea radians yum algae was 55353 red lncrustlng sponges m 39193 W7 43 Mgi ekglg a globose sponge A agi lgtes Hnger sponges we Weight seawhlps 30 Muss anourzsa W seafans 5 Mllll alcl grnls tubular sponges The main study reef and its intimately associated satellites as seen from above the bottom being open white sand 4 WHAT SPECIES INHABIT THE REEF ENVIRONMENT After constructing elaborate maps as shown above Smith and Tyler made a detailed survey of the fishes Altogether 691 specimens were identi ed representing 75 species in 47 genera and 27 families TABLE 1 Families and number of genera and species found on a 100 m3 patch reef at St John Virgin Islands The families in boldface all belong to the order Perciformes families indicated by a single asterisk contain plant eaters families indicated by a double asterisk are almost exclusively plant eaters FAMILY GEN SP FAMILY GEN SP FAMILY GEN SP Muraenidae 2 2 Emmelichthyidae l l Scaridae 2 5 Clupeidae l 1 Lutjanidae 2 2 Clinidae 6 6 Synodontidae 1 1 Pomadasyidae 1 2 Blenniidae 1 1 Holocentridae 2 4 Sparidae 1 1 Gobiidae 6 15 Syngnathidae l 1 Mullidae 1 1 Acanthuridae 1 2 Serranidae 2 3 Chaetodontidae 2 2 Scombridae 1 1 Grammistidae 1 1 Pomacentridae 2 5 Balistidae 1 1 Apogonidae 2 7 Cirrhitidae l l Ostracionidae 1 1 Carangidae 2 3 Labridae 2 4 Tetraodontidae 1 1 Through detailed observation using SCUBA Smith and Tyler were able to describe three kinds of sh inhabitants of the patch reef Residents Visitors and Transients Residents were de ned as individuals that actually live on or within or are otherwise intimately associated with the reef It appeared that these are species that remain in the community for periods of at least many weeks and from all available evidence most of them spend their entire juvenile and adult lives in the same patch of reef Of the 75 species identi ed 53 were judged to be residents Visitors were those species whose individuals appear and remain for a few hours or for perhaps a day or two and then move on Of the original 75 species 13 were listed as Visitors Transients were those species whose individuals pass through the area without seeming to be affected by the reef in any recognizable way Of the original 75 species 7 were listed as visitors The behavior of the remaining two species varied to the extent that they were listed as both Visitors and Transients 24 5 g 27 539 12 Pg y 1 9 mtgi iftgm If 30 WW 9391quot 39 9 WW 39 4y i quot 39 The Northwest satellite a rounded mound of Montastrea annularis and Diploria clivosa with a patch of algae covered dead region in between from which arose tall seawhips Residents are within the dashed line and frequent visitors to it outside OK so now we have a pretty good idea of what species are there The next thing that one might ask is What keeps them there What resources does the reef environment provide for these shes 5 MAJOR RESOURCES FOOD AND LIVING SPACE The major resources in any habitat may be divided into two broad categories those related to food and those related to living space It is the partitioning of these two major resources that is studied by ecologists in an effort to understand the origin and maintenance of high diversity communities whether these communities are aquatic or terrestrial The more we study coralreef communities the more we39re beginning to realize that food is seldom in short supply and that space is more often the critical limiting factor This is not to say that food is unimportant but that in high diversity reef communities at least among shes food plays a subordinate role to living space We believe this for a number of reasons 1 The number of shes around the reef is so great that it appears that space is fully utilized If there were a food shortage it would seem likely that open or unused space would be available and that this would be obvious to the scienti c observer It has been shown that plants are much more abundant on the open ats away from the reef than near the reef itself but by far most herbivorous shes are found primarily associated with the reef where plants are relatively sparse This suggests that space the nooks and crannies of the reef are the limiting factor to biodiversity rather than food 2 Fishes seldom exhibit any symptoms of starvation although minor cases of this might go undetected since individuals weakened by the lack of food may fall to predation before the symptoms become Visually obvious 3 The lack of evidence for any large uctuations in the abundance of reef shes throughout a yearly cycle suggests that the limiting factor in the community is not dependent on density Rather the critical factor must be density independent a factor that prevents excessive population build up and resulting crashes husns b DIrlbl mchlhm 000600 N O Number in t o 0 1845 1855 1865 1875 1885 1895 1905 1915 19251935 Time Fluctuations in abundance of lynx and snowshoe hare over a period at ninety years The oscillations oi the lynx population color seem to follow those of the hare population The index of abundance used here vertical axis is the number of pelts received by the Hudson s Bay Company It is likely of course that some species are food limited but most probably these would be the wanderers that is those species that fall within the category of Transient or Visitor rather than Resident OK now that we39ve moreor less eliminated food availability as a factor that limits sh diversity in reef habitats we can concentrate on the sharing of available space 6 MECHANISMS OF SPACE SHARING ON THE REEF Smith and Tyler 1972 identi ed six essential aspects of space sharing all of which they found to be highly developed among shes in the reef community that is resident species in particular are highly speci c in each of these areas each is maximized on the reef to avoid or at least reduce competition for space 1 Hunting and feeding areas 2 Shelter sites 3 Activity cycles 4 Symbiotic relationships 5 Seasonal cycles in reproduction and in the use of space by juveniles 6 Territoriality Hunting and feeding areas Every species needs space within which it searches for and consumes food The volume of feeding space required varies enormously depending on the species and this is generally related to the size of the individuals the largest species and the largest individuals within a species requiring the most space Not surprisingly to avoid or reduce interspeci c competition for food sh species in high diversity reef communities have very speci c areas for feeding Shelter sites Most residents on the reef have speci c shelter sites within the reef structure that they come back to every day or night depending on their speci c activity cycle The shelter site provides a refuge in which the sh is relatively free from either detection or attack by predators The claiming of speci c shelter sites is thus probably a mechanism that functions to stabilize the community Activity cycles One of the primary space sharing mechanisms on the reef is differential times for hunting and feeding The most obvious cycles are daynight transitions On the patch reef studied by Smith and Tyler of the 75 species identi ed 24 were primarily dayactive residents 14 were primarily nightactive residents 16 were primarily dayactive visitors 4 were primarily nightactive visitors and 2 were active both day and night the remaining 15 species were undetermined During the day many nocturnal species hover around the reef misleading some investigators to conclude that the reef is much more active in the day than at night At night the greatest activity is out on the open sand ats away from the reef itself During this time most of the diurnal species have sought shelter in the holes crevices and overhanging ledges of the reef Some of the more conspicuous daynight changes observed by Smith and Tyler are illustrated in the following diagrams A compressiver rearranged rendition of the tunnel region of the main reef with several species of apogonids present during daylight absent at night but with the large specimens of Scams and Camhigaster not present during daylight having arrived and become quiescent for the night he Scams sometimes in a mucous envelope and the Canthigasler always nestled closely atop a black mussellike bivalve The spongedwelling Gobiowmu horxti remains within its tubular sponge both day and night while the smaller Cumhigaxtcr present on the reef during daylight are hypothetically shown quiescent in deep cavities on the reef Numbers cor respond to sh names in Table l3 A day condition B night condition b 331 Night Daytime and night residents of the ramosc form of Monlaxrrea annulan s making up the North and Northeast satellites Residents are within the dashed line and visitors outside Symbiotic relationships The ultimate specializations in high diversity communities are interactions between members of different species that are more intimate than predatorprey interactions and closer than casual associations in which one species uses another for shelter Smith and Tyler recognized four kinds of symbiosis among shes 1 Cleaner fishes that groom other species for parasites 2 Gobies Gobiidae and blennies Blenniidae that live among polyps of living coral 3 Fishes that live within sponges Diagrammatic view of three tubes of lavender candle sponge Verongia archeri on top of the reef opposite the Habitat and the usual niche of three Gobiosama horsti and one Phaeoptyx xenus Sizes of the shes relative to the sponge are much exaggerated 4 A loose association of wrasses Labridae and feeding goatfishes Mullidae the wrasses feeding on organisms dislodged by the goatfishes All of these associations are recognized as mechanisms that evolved to both stabilize the community and to share the available space Seasonal cycles in reproduction and in the use of space by juveniles On the reef nearly all species have a highly speci c breeding season recruitment is intermittent For example juveniles of more than one closely related species may shoal or school together over the highest part of the reef while the subadults may be segregated by species and hover low between coral colonies adults may be somewhere else Thus juveniles subadults and adults occupy different microhabitats and are ecologically separate entities a space sharing mechanism that is true quotspatial sharingquot of space In many cases closely related species may have their spawning seasons adjusted so that juveniles of only a few species utilize the available space at any one time for example the midwater microhabitat might be occupied by different species at different times of the year a case of quottemporal sharingquot of space Territoriality The number of individuals that can live together in a given volume of space depends on at least three factors 1 The amount of microhabitat available 2 The size of the home range required by each individual 3 The extent to which the space can be shared by other individuals of the same or different species Fishes that maintain a xed spatial relationship between each other are called quotterritorialquot Densities among territorial sh species are never as great as those of gregarious species Territoriality is much more obvious and best developed when shes are actively reproducing the result being that the standing crop is limited The fewer the number of individuals the more space is made available to others 7 COMMUNITY EVOLUTION Organic reefs have a fossil record that extends back at least to the Cambrian about 500 MYBP but our modernday coralalgal assemblages are much more recent having a continuous fossil record only since the middle Triassic about 200 MYBP they have been well established only since Jurassic times about 150 MYBP PRESENT REEFS FISHES Spinyrayed fishes 70 MYBP 100 MYBP E 150 MYBP Softrayed fishes 200 MYBP Because true spinyrayed shes Acanthomorpha are unknown before midCretaceous about 100 MYBP it seems that the evolutionary history of these fishes is at least coextensive with the history of modern coralalgal reefs a kind of correlated or coevolutionary increase in diversity of reefs and the more derived teleosts Reef sh communities are unusual for their lack of softrayed shes preacanthomorphs The only nonacanthomorph shes consistently associated with the reef are a few highly specialized types amounting to only about 5 of the number of taxa identi ed by Smith and Tyler such as eels Anguilliformes especially moray eels family Muraenidae some herrings Clupeidae and a few scopelomorphs e g lizard shes family Synodontidae In all these cases the taxa appear to be secondary invaders of the reef environment that is forms that evolved elsewhere and only later become adapted to a reef existence So why wereare softrayed shes unable to adapt effectively to the reef environment You already know the answer the softrayed or nonacanthomorph bodyplan diddoes not permit specialization for a bottomliving benthic life style The long narrow bodyplan of softrayed forms with ns in the primitive position works well in wide open space but not in the close quarters of a reef habitat The lack of n spines important in maneuverability and defense in a reef environment is a deterrent as well The weak easily lost and easily damaged scales of soft rayed shes is a further disadvantage in a rough calcareous benthic environment Modern reef shes have developed either thick resistant scales the skin often studded with specialized armored scales or the scales have become reduced or lost altogether the skin becoming thick and leathery Only the acanthomorph body plan short and deep with ns in the derived position permits the degree of maneuverability required for life on the reef The protrusible upper jaw so well developed in acanthomorphs is another requisite allowing for the development of numerous specializations for benthic feeding 8 DEGREES OF SPECIALIZATION AMONG REEF DWELLING FISHES Most of the softrayed sh species that occupy the reef are midwater forms that is they live well above the bottom and rarely if ever associate with the substrate eg herrings some scopelomorphs Those few softrayed shes that are benthic are obviously secondarily specialized for bottom dwelling e g eels It is signi cant also that nearly all preperciform members of the reef community and many of the least specialized perciforms as well have a resting behavior of hovering near or over the reef instead of being in contact with the bottom substrate These are the least specialized of the reef dwellers Next in order of specialization are those species that feed in midwater or away from the reef but spend their resting periods in contact with the reef often in crevices deep within Finally there are the extremely specialized shes that have greatly restricted home ranges and spend their active as well as inactive periods in actual contact with the reef These are generally small shes most have specialized food habits and some are intimately and symbiotically associated with invertebrates such as coral and sponges 9 TRENDS IN REEF COMMUNITY EVOLUTION In the beginning when modern coralalgal associations arose approximately 200 MYBP there were few shes associated with them only algae and invertebrates But as acanthomorph shes became more numerous and diverse some became specialized for feeding on the plants and invertebrates they were initially no doubt attracted to the reef by these food resources Soon other shes particularly unspecialized carnivores were attracted to the reef to prey on the more specialized types At rst these carnivores visited the reef seeking prey but returned to open water during their resting periods Gradually they began to hover nearer the reef during their inactive periods From this point there was an increased tendency for some shes to rest in contact with the bottom during their inactive period Smaller size and cryptic coloration increased their ability to use the reef and some species became so closely tied to the reef community that they gave up their midwater habits As more species developed specialized habits the diversity of the community increased Continued development of specializations enabled ever ner subdivisions of the resources until it reached its present modemday state Finally diversity was increased even more by secondary invasion of benthic forms that had evolved elsewhere such as eels Anguillformes certain scopelomorphs eg Synodontidae and frog shes Antennariidae BIOLOGY OF FISHES FISH 311 FORM AND FUNCTION SENSORY PERCEPTION II SMELL AND TASTE HEARING AND THE ACOUSTICOLATERALIS SYSTEM General topics 1 2 Chemoreception olfaction and gustation Structure and function of olfactory organs The role of chemoreception in the behavior of shes A B C D Chemical perception of food Reproductive behavior Migration Predator avoidance Acousticolateralis system A B C Sound detection in the inner ear Lateral line system in shes Function of the lateral line system 1 CHEMORECEPTION OLFACTION AND GUSTATION Chemoreception plays a major role in the lives of shes Nearly all aspects of life feeding prey detection predator avoidance species and sex recognition sexual behavior parental behavior and migration are affected or mediated by the ability to detect waterborn chemicals and to react appropriately to these stimuli Chemoreception can be conveniently divided into two basic types that while essentially different show some degree of overlap in their sensitivity to particular substances A Olfaction smell results from stimulation of sensory receptor cells in the olfactory organs which are innervated by the olfactory nerve cranial nerve I cerebellum pineal felencephalon olfactory bulb H medulla pituitary saccus vasculosus inferior lobe Lateral View of the brain and roots of the cranial nerves of a salmon olfactory nerve I optic nerve II oculomotor nerve Il trochlear nerve IV trigeminal nerve W abducens nerve VI facial nerve VII auditory nerve VIlI glossopharyngeal nerve IX and vagus nerve X B Gustation taste mediated by taste buds sensory receptor cells and innervated by the facial glossopharyngeal and vagus nerves cranial nerves VII IX and X Taste buds are found in the mouth cavity as well as in the gill cavity on the gill arches and in some cases on external surfaces of the body barbels anor skin A third type of chemoreception is often recognized usually referred to as a common or general chemical sense It is mediated by sensory receptors located on exposed body surfaces of a fish and better developed in scaleless bottom living forms Taste buds are not involved instead the receptors are free nerve endings supplied by the spinal nerves It is low in sensitivity compared to smell and taste 2 STRUCTURE AND FUNCTION OF CHEMOSENSORY ORGANS The olfactory organs or nares of nearly all shes are paired bilateral structures unpaired and medial in position in hag shes and lampreys that consist of olfactory chambers lined with various numbers of folds of olfactory epithelia called lamellae The presence and structure of these lamellae dramatically increases the surface area of the olfactory chambers This surface area provided by the olfactory lamellae increases with growth over the life of the sh both through an increase in size of individual lamellae as well as by addition of more lamellae quot 39ll lrmllmrjr u liturgy 1me a i Elihu d J iil ii i v I 1 l r h39xquot nll394f r I l A ltm rtl 1 I l W n u r a 95quot l u 1 r I u I y H l39 nlquotuf rpm J uvl na if Anguilla anguilla The exposed olfactory or nasal chamber of a young and an adult European eel Anguilla anguilla HN posterior naris VL anterior naris R raphe The shape of the olfactory chamber and the number of lamellae contained within varies enormously among shes In general a greater number of lamellae is associated with greater olfactory requirements and sensitivity to odors For example the threespine stickleback Gasterasteous aculeatus which relies most heavily on vision to make its way in the world has small rounded olfactory chambers containing few lamellae whereas most eels order Anquilliformes which rely heavily on olfactory cues have large elongate olfactory chambers with numerous gt60 lamellae Species with intermediate sensitivities to chemical odors which make up the vast majority of shes have ovalshaped chambers with an intermediate number of lamellae see gure on page 4 Gasterosteus aculeatus 2 lamellae Esox Iucius 9 18 reduced Iamellae Oncorhynchus mykiss 1 31 8 Perca fluvia tilis 1 318 Phoxinus phoxinus 1 119 Gobio gobio 91 3 Tinca tinca 1529 Barbatula barbatulus 1624 Lota Iota 3032 Anguilla anguilla 6893 The arrangement of olfactory lamellae in ten selected species of shes The observed number of olfactory lamellae for each species is indicated in parentheses The olfactory organs of terrestrial vertebrates pass through the roof of the snout and open into the pharynx We say they have internal nares This passageway allows air and airborn chemical odors to be pulled from the external environment over the olfactory sensory nerve cells that line the nasal passages and into the throat and lungs through the process of respiration In contrast the olfactory organs of nearly all shes are completely closed to the pharynx We say they have external nares anterior and posterior openings called anterior and posterior nares Water along with water born chemical odors is drawn into the anterior naris passed over the sensory receptors of the olfactory lamellae and then forced back out into the external environment by way of the posterior naris Posterior nares Anterior nares Openings of the mandibular sensory canals of the cephalic lateralline system Posterior naris Anterior naris The arrangement of tubular anterior and posterior nares of an eel Water ows into the anterior naris across around and between the numerous olfactory lamellae and back out through the posterior nares Among shes exceptions to this general rule of closed nares include the hag shes Myxini a very few teleosts some uranoscopids and the bathydraconid genus Gymnodraco and of course the lungfishes Dipnoi Representatives of these few groups have internal nares comparable to those of terrestrial vertebrates Circulation of water through the olfactory chamber of the European eel Anguilla anguilla Water is pushed through the nares by various mechanisms In sharks and rays the nares are on the underside of the snout directly in front of the mouth Water is forced or pulled across the nares by the actions of a branchial pump In the case of teleosts most of which have the nares situated on the sides or on top of the snout current that ow across the head and snout produced by swimming are often enough to cause a steady ow of water into and out of the nares In most cases ciliary action within the olfactory chamber helps to move water across the olfactory lamellae Olfactory sensitivity All available evidence points to a great acuity of the sense of smell in many species of shes both with respect to the perception of very low concentrations of odors and to the capability of discriminating two or more odors in a mixture Early research on thresholds involved behavioral experiments in which individuals trained by reward or punishment were conditioned to select or avoid water that held the chosen chemical and then were tested on more and more diluted concentrations More modern methods involve conditioned heart rate electroencephalograms recordings from nerve tracts and other electrophysiological methods Thresholds from various published sources for a number of sh species and chemical substances are shown in the table reproduced on page 7 Olfactory Thresholds of Fishes for Various Substances Substance Fish Threshold Source Amino acids hagfish 1045 to 10 5 M deing and Holmberg 1974 Lmethionine lemon shark 10 8 to 10 7 M Zeiske et al 1986 Amino acids catfishes 10 9 to 104 M Caprio 1982 Methionine grayling 13 x104 M deing and Selset 1980 Bile acids grayling 63 gtlt10 9 M deing and Selset 1980 Bile acids goldfish 10 9 M In Meisami 1991 Steroids goldfish 10 3t010 2 M In Meisami 1991 Phenylethyl alcohol A anguila 29 x1040 M In Little 1983 Phenylethyl alcohol rainbow trout 10 9 M In Little 1983 Sucrose Phoxinus 12 x 10 3 M In Little 1983 You can see that there is considerable variation but in general the olfactory sensitivity of shes is comparable to that of mammals For example the rainbow trout Oncorhynchus mykiss has been shown to detect phenylethyl alcohol at concentrations of 1 X 10399 molar which is on the same order of sensitivity as humans Anguilla anguilla The European eel Anguilla anguilla with its highly developed olfactory chambers and numerous olfactory lamellae can detect phenylethyl alcohol at concentrations of 3 x 103920 molar or about the same concentration detectable by dogs Someone gured out that this olfactory acuity corresponds to 1 ml of alcohol dissolved in a lake of a volume 58 times as great as that of Lake Constance bounded by Germany Austria and Switzerland 207 square miles in area which equates to one or two molecules of alcohol in the olfactory chamber at any one time Gustation the sense of taste is important to shes in the location and identi cation of possible food sources Depending on the ecology of the species it can be a very highly developed sense For example in certain minnows family Cyprinidae the sensitivity to various sugars and salts has been found to be 512 and 184 times higher respectively than those of humans Unlike olfactory sense receptors taste receptors are not restricted to a single location In addition to positions throughout the mouth pharynx gill arches and skin cat shes Siluriforrnes have welldeveloped barbels sometimes longer than the sh itself that bear dense concentrations of taste receptors These barbels are under muscular control and often stiffened and can be used as sweepers to cover a wide searcharea for these often nocturnal species Similarly some species of hake family Gadidae and searobins family Triglidae have taste buds on specialized pectoral n rays Barbels of various shes A a sciaenid or drum genus Pogonias B a cat sh genus Clarias C a mullet genus Mullus and D a cod genus Gadus A searobin genus Prionotus with specialized pectoral fin rays used as feelers to search for food on the bottom but also lined with taste buds the rays are used to taste potential prey 3 THE ROLE OF CHEMORECEPTION IN FISH BEHAVIOR Chemical Perception of Food Chemical perception of food in shes was rst clearly demonstrated experimentally at the turn of the century in elasmobranchs and in many teleosts Aquarium held dogfish Mustelus canis were shown to be unable to recognize the presence of food substances when their nares were plugged with cotton food recognition was regained when the cotton was removed Since then the use of chemoreception in the foraging and directed movements of shes has been demonstrated on numerous occasions 4 v 39 Pathways of an aquariumheld eel Anguilla anguilla in search of an odor phenyl ethyl alcohol to which it has been conditioned A wad of cotton soaked in the odorous solution was placed in the hollow tube In the experiment at the top localization of the source of the odor required 1 minute straightline distance 25 cm in the bottom experiment 4 minutes were required distance 35 cm Pathways of an aquarium held eel Anguilla anguilla following a trail of phenyl ethyl alcohol laid down by means of a pipette leading to the source of the odor in the hollow tube In the experiment at the top localization of the source of the odor required 2 minutes in the bottom experiment 4 minutes were required distance 35 cm Reproductive Behavior Chemoreception is known to play a role in courtship behavior parental behavior and aggressive behavior in breeding shes Males of numerous species have been shown to be attracted to water conditioned by females of their own species and vice versa For example males of such distantly related taxa as the lamprey Petromyzon marinus and rainbow trout Oncorhynchus mykiss have been shown to be attracted to odors of their own females during the breeding season One of the clearest examples of the role of chemoreception in parental behavior comes from work on the cichlid Hemichromis bimaculatus often called the jewel sh Pairs were allowed to spawn in one of four clay owerpots After spawning or hatching the pot containing the eggs and fry was removed and another put in its place The pot with the developing embryos was placed randomly in one of four white cylinders from which water was supplied to the tanks through the clay pots in the tank Once the eggs were hatched the parents always gathered around the pot that came from the cylinder containing their young Further they displayed parental behavior typical of the species even though no young were Visually present The response lasted the full three weeks typical of the period of their parental behavior Finally when the late stage young were replaced with newly hatched embryos the female parent switched her behavior to that appropriate for newly hatched young continually farming the pot and imaginary embryos with her pectoral ns to keep oxygen levels high Filter Experimental arrangement to test the preference of breeding cichlids genus Hemichromis for water carrying the odor of their offspring Increases and decreases in aggressive behavior have been observed in the threespine stickleback Gasterosteous aculeatus when males have been shown to assume aggressive postures and then retreat from the odor of a male in nuptial coloration Similarly male cichlids Haplochromz39s burtom39 responded to water conditioned by ripe females by increasing their aggressive and courtship behavior but not until several days after exposure In this case the smell or pheromones released by the female acted as a primer rather than as a releaser of a particular behavior as was the case in sticklebacks Migration Olfaction has been shown to play key roles in the migration of salmonids and freshwater eels Anguillidae In the former case the speci c odorants are imprinted on the young during development and early rearing Distilled water WFMWW WWMWWWWWWW Tap water Home water w animatinme Nonhome water 2 lWWWmum wwrwmmeMw NonhomewaterS quotW KWWMMWWMWW Effects of infusion of different waters into the olfactory chamber measured by electroencephalogram activity in the olfactory bulb of an adult spawning salmon The American eel Anguilla rostrata also uses its olfactory sense to migrate from the sea to freshwater as they show positive rheotaxis to the later and not the former However in this case the speci c odorants of freshwater are not learned at some earlier lifehistory stage as the parents of these elvers metamorphic stage just before entry into freshwater migrated from freshwater to the sea Sargasso Sea in the Atlantic Ocean to spawn and subsequently died Predator Avoidance One of the best examples of the role that olfaction can play in predator avoidance is the Schreckstoff or alarm substance secreted by specialized epithelial cells of Ostariophysan and various other shes This is an example of predator avoidance through the recognition of injury to conspeci c or closely related species In addition there are numerous examples in shes of prey recognition of the odor of potential predators Such recognition may be learned or innate inherited One of the best examples of What appears to be innate avoidance behavior is seen in the response of Paci c salmon genus Oncorhynchus to extracts from mammalian skin Paci c salmon migrating upstream to spawn stop their upstream movement reverse their direction and show fright behavior when extracts of various mammalian skins are placed in the water upstream Fiftyfour other groups of substances tested gave negative results 539 4quot la quot 9 S la 3 t 3 I t 1quot 3 quot I Ia a a 0 o o 1 0 s s e a 5 t a a 5 s393 e5 15 3941 I fi f ggmtk39lesg sessmccgoga a I u to J e a Q 5 w o 439 0 5 i l c 250 70 1 o o l o so o a R Q MEAN 39 VK O 50 o 2SD 4039 z 3 Lllilllllllllllllllllll i 0 quot30 IBSO ISBO I430 I630 I730 IOSO 1 TIME IN FIFTEEN MINUTE INYERVALS U u o I I SALMON RETURNING DOWNSTREAM MI a 41 2 539 39t Y O 4 l 1 539 g o a o 5 5 7 Y i V Ni v 3 O a r l 1 250 n n mquot r y g ZSD I I u I n i I A I A I n n l I l 1 IIOO ISOO I400 I500 I600 i IZOD TIME IN FIFTEEN NINUYE INTERVALS Oncorhynchus kisutch and O tshawytscha 4 ACOUSTICOLATERALIS SYSTEM The acousticolateralis system includes the sound receptive and equilibrium centers of the inner ear and the free and connected neuromasts of the cephalic and lateral line system Sound detection in the inner ear Humans have known for thousands of years that shes produce sounds and therefore correctly assumed that shes could also hear However it was not until the early 20th century that conclusive evidence of hearing in shes was provided The existence of sound producing and sound receptive devices in shes should not be surprising since sound travels 48 times faster and farther underwater than in air Sound detection is localized in the ventral portion of the inner ear Three liquid lled sacs the utriculus sacculus and lagena each contain a hard stony structure called an otolith suspended by attached nerve cells The three otoliths the lapillus sagitta and asteriscus are dense relative to other parts of the sh and near eld sound Vibrations cause the sh to move relative to the otoliths which lag behind due to inertia These differential movements cause bending of the ne hairlike structure of the sensory cells which in turn produce nervous or electrical signals that are interpreted by the brain as sound Neurocranium bone Brain cavity Otoliths MyodOme Anterior vertical canal Posterior vertical canal LapiIIUS Asteriscus Lagena Utriculus Sacculus Sagitia Diagrammatic representation of the skull of a bony sh with reference to the location of the otoliths in the inner ear l4 Certain groups of shes increase both their sensitivity to far eld sound and higher sound frequencies through various connections of the swimbladder to the inner ear The gas lled swimbladder serves to magnify the sound because gas compresses far more readily than liquids and the pressure wave associated with far eld sound is functionally augmented In ostariophysans minnows characins cat shes etc the swimbladder is mechanically connected to the inner ear by a series of bony ossicles In clupeids herrings and anchovies the swimbladder actually extends into the inner ear via long paired extensions and are directly coupled to the inner ear Damage to the swimbladder in either clupeids or ostariophysans severely reduces their sound detection abilities The lateral line system Fishes possess two sensory modalities for the detection of underwater vibrations l the inner ear and 2 the lateral line system The lateral line system consists of several series of connected or unconnected neuromasts running over the course of the head and body These neuromasts are encapsulated hair cells that produce impulses when bent in one of two directions thus providing directionality to the incoming wave force They are exclusively near eld receptors That is they react to displacement of particles and not pressure waves alone The inner ear can be both a near and far eld detector Lateral line receptors serve a variety of functions independent of hearing these functions range from prey capture to predator avoidance to schooling behavior and obstacle avoidance Trunk conol system Head canal system Lateral line organs may be free neuromasts lying on the surface of the skin or within pits or they may consist of a series of receptors in canals and grooves on the head and body These canals are lled with watery endolymphic uid mucous that picksup and passes vibrations to the neuromasts through a series of openings pores through the scales andor skin of the sh In general the more active the sh or the faster the water ows within the environment in which the sh lives the greater the propensity for the lateral line system to be contained within canals This presumably reduces the extraneous noise of the outside environment There are typically paired lateral lines running down the course of the body as well as numerous tracts running over the head The head of a deepsea sh genus Melanonus showing the arrangement of the neuromasts in the lateral line canals In the diagram above each sense organ shown as a black dot rests in an ovalshaped pit of connective tissue The canals open through pores shown as open circles When currentlike disturbances pass through the pore p a rounded gelatinous cupula c that rests on top of the sensory structure so is caused to move This in turn causes displacement of the ne hair like sensory structure resulting in a nervous impulse that is passed along a nerve n to the brain Displacement of the lateral line in connection with a dorsal position of the pectoral n in the A paradise sh genus Macropodus and B a flounder Pseudorhombus or as an adaptation to special modes of living in the C stargazer Uranoscopus and D flying sh Exocoetus The speci c position and distribution of the lateral line on the body relates to the ecology of the species Fishes that feed at the surface often have lateral lines that run along the ventral margin of the body presumably to warn the sh of rising predators In contrast bottom living shes may have the lateral lines elevated on the body to warn of predators approaching from above Species that use their pectoral ns in swimming usually have lateral lines that are de ected above the pectorals to avoid interfering with the lateral line sensory system Function of the lateral line system The lateral line system has long been known to aid in obstacle avoidance The head of a sh creates a bow wave in front of it as it swims and pressure changes associated with this bow wave hitting oncoming objects informs the sh of their approach t Kg Functions of lateral line and inner ear in the detection of moving objects 1 Near the source the localflow eld is rather complicated the lateral line detects the spatial differences in the particle acceleration eld along the length of the body hydrodynamic detection 2 Farther from the source the localflow eld is predominantly dipolar the inner ear detects the particle acceleration eld properly averaged over the volume of the body near eld hearing 3 At large distances from the source the propa gating sound wave dominates the inner ear may under favorable conditions detect the radial particle acceleration eld far eld hearing In the local flow the accelerations detected by the lateral line and inner ear result from the acceleration eld of the source and from the velocity eld of the source as it moves relative to the receiver Mth the swim bladder acting as a pressureto motion converter where present the acoustic pressure is detected by the inner ear both in the near and in the far elds In higher animals the detec tion of the far eld pressure has become the ruling principle of vertebrate hearing he W Detection of localflow eld produced by dipole source a Near the source the local ow eld is highly nonuniform conspicuous spatial differences in the water motions over the surface of the sh present strong lateral stimuli b Farther from the source the eld is more nearly uniform motions of the whole fish largely deprive the lateral line ofits physical stimulus leaving the detection ofthe local ow eld mainly to a the inner ear 17 The head of a blind cave sh Amblyopsis spelaeus from caves of Kentucky It is this system that allows blind cave sh popular in the aquarium trade to move throughout an aquarium without ever running into the glass Recent work has also shown the importance of lateral line detectors in the maintenance of schools of some schooling species Schematic showing the distribution ofcanal and super cial neuromasts on the body of the mottled sculpin Enlarged drawings outline the dorsal surface of canal neuromasts from the mandible and trunk and of super cial neuromasts on the tail to indi cate the extent to which neuromasts vary in size and shape Stippled areas represent the hair cell sensory surface MD mandibular canal SO supraorbital canal IO infraorbital canal PR preopercular canal TR trunk canal 39 Some of the most fascinating recent work has shown the acuity that lateral line receptors bring to feeding behavior even in the dark For example in sculpins family Cottidae lateral line receptors on the head and trunk have been shown to be very important in the localization and capture of passing zooplankton BIOLOGY OF FISHES FISH 311 BIODIVERSITY I JAWLESS FISHES SHARKS AND THEIR ALLIES EVOLUTIONARY SUCCESSES AND FAILURES General topics 1 Living jawless vertebrates hag shes and lampreys 2 Similarities between hag shes and lampreys 3 Are hag shes and lampreys sister groups 4 Cartilaginous shes sharks and their allies U I Living sharks of the world 6 Living rays of the world 7 Living chimaeras of the world 1 LIVING JAWLESS VERTEBRATES HAGFISHES AND LAMPREYS The living jawless vertebrates hag shes and lampreys are highly specialized remnants of what were once extremely diverse and geographically wideranging groups that are now all extinct These extinct jawless forms are indicated in the phylogenetic tree below by a star a nathans ERA PERIOD 9 1 l QUATERNARY 2 18 l g O S x N 9 E g TERTIARY g g g m Lu k a Q 5 O O E gt 65 e c quot E x o 5 f g o o 0 3 0 3 0 E c Z N C U m C a i 0 U Q Q E gt o 5 U o b 0 0 a o E 8 a a c 3 390 u S o a CRETACEOUS 9 c g g 3 Q 8 g g g g gt is o 0 c 5 a 9 o m E o o E lt o a 0 lt lt m 145 639 m JURASSIC Lu 5 gt 213 TRIASSIC 248 1 PERMIAN 286 i q PENNSYLVANIAN 325 l Mississwmn 0 W360 39 5 i I 3 DEVOMAN 1 m i I i 410 y f x szLumAN x L 442 I we Euteteostom dm39w l v wquot Teleostoml 0RDOVlCIAN J aivquot Gnathostomata En dka I m quot Vertebrate cmam Craniata RAJ Relationships and time of divergence of the major groups of fishes Here s another look at almost the same thing showing another interpretation of relationships Myxini V NdJOUJOpgdSEJald v suuapooeuso gumouiop seleudeo Gnarhostomata39 Although these ancestors did not survive to the present day it is important to recognize that they were enormously successful in their time dominating the scene for some 140 million years from approximately 490 to 350 MYBP Hagfishes are represented today by seven genera and about 70 species all contained within a single family the Myxinidae They are restricted to marine habitats throughout the temperate zones of the world including the gulfs of Mexico and Panama Lampreys are represented by ten genera and 38 species all contained within a single family the Petromyzontidae They are anadromous and freshwater four species are restricted to temperate regions of the southern hemisphere in South America New Zealand and Australia the rest are found in coastal drainages throughout the northern hemisphere Petromyzon 2 SIMILARITIES BETWEEN HAGFISHES AND LAMPREYS Hag shes and lampreys are soft bodied eellike animals that are similar to each other but differ from all other vertebrates in a number of ways particularly in the structure of the mouth and gills 1 They lack jaws Hag shes are scavengers that burrow into the esh of dead or dying shes the mouth which contains a rasping tonguelike structure is surrounded by a series of short tentacles a sucking disk is absent mucles to nostril and lips somitic muscles r a oblique muscles MR1 g l 739 M yxine mucous gland rectus muscles Muscles of the anterior part of the head The eyes are covered by the large longitudinal muscle to the lips Most lampreys are lterfeeders as young but ectoparasitic bloodsuckers as adults the mouth consists of a circular adhesive disk and a rasping tonguelike structure by which the sh attaches to other shes and sucks their blood epibranchial Lampetra cornealis muscles muse gill slits trigeminal nerve 0 9 1 aso penmg 9 hypobranchial muscles Lampetra Muscles of head region 2 They lack gill arches The gills are contained in a series of separate muscular pouches each expanding and contracting during respiration and which open through small circular openings on the side of the body GILLS OF LAMPREY SHARK AND BONY FISH COMPARED Lamprey Shark Bony fish Diagram of gill organization among shes shown in frontal sections ac annular cartilage bbc branchial basket cartilage e esophagus eba external branchial aperture ga gill arch gc gill cover operculum gf gill lament gp pouch gr gill raker ha hyoid arch iba internal branchial aperture ibs interbranchial septum ma mandibular arch ph pharynx rm roof of mouth 3 snout sd sucking disc sp spiracle t teeth 03 Both have a single median nostril A They lack paired fins U They lack bone Although there is evidence that jawless vertebrates evolved from ancestors that had well developed bone characterized most strikingly by a thick armor of dermal plates all remnants of bone have been lost 6 They have a cartilaginous internal skeleton 3 ARE HAGFISHES AND LAMPREYS SISTER GROUPS Up until very recently and because of these common anatomical and behavioral features hag shes and lampreys were thought to be sister groups that is they were believed to have evolved together to the exclusion of all other vertebrates from the same ancient jawless ancestor Many current textbooks associate these two groups together as the Agnathi Latin for no jaws ADVANCE quotquotHRATES r W ANTHRACOSAURS Haglish 53327 5 V cvcmsromss Man39ng I 9 AMPHIBIANS Chimaera NEOPTERYGIANS CHONDFIOSTEANS DI PNOANS AchopTEnyGIANs SARCOPTERYGIANS ray nned sh flesh nned sh CHONDRICHTHYES cartilaginous fish 39 439 v l quot sm s AGNATHANS jawless sh Phylogenetic relationships among different lines of sh The ancestor of each given lineage is not necessarily the species illustrated but is believed to have been similar But recent work has cast doubt on this notion We now recognize that hag shes and lampreys have long and separate evolutionary histories and that they do not represent sister groups Most now believe that lampreys are more closely related to more derived vertebrates that is to jawed shes than they are to hag shes implying that hag shes stand alone as the most primitive of living vertebrate animals EVOLUTION OF MAJOR GROUPS OF LIVING FISHES CHONDRICHTHYES Sharks Rays Ch i maeras CEPHALASPIDOMORPHI SARCOPTERYGII Lampreys Lobefinned shes MYXINI ACTINOPTERYGII Hagfishes Bony or rayfinned fishes What is the evidence Hag shes are characterized by having 1 2 A single semicircular canal They lack vertebrae even embryonic traces are absent They lack neuromast cells They lack extrinsic eye muscles They are incapable of nervous regulation of the heart They are incapable of hyperosmoregulation an inability to control salt and water balance to meet changing environmental conditions Lampreys on the other hand share the following features with all other vertebrates 1 Two or three semicircular canals Welldeveloped neural and haemal arches the beginnings of a vertebral column True neuromast organs distributed along a lateral line Extrinsic eye muscles Capable of providing nervous regulation of the heart QWPWN Capable of hyperosmoregulation In fact the more we compare hag shes and lampreys the more differences we nd The following list was taken from Moyle and Cech 1988 page 195 DIFFERENCES BETWEEN ADULT LAMPREYS AND HAGFISHES Characters Hagfishes Lampreys Dorsal fin None One or two Preanal fin Present Absent Eyes Rudimentary Well developed Extrinsic eye muscles Absent Present Oral disc Absent Present Lateralline system Degenerate Well developed Barbels Three pairs Absent Intestine Unciliated Ciliated Spiral valve intestine Absent Present 39 Absent Present Buccal glands Nostril location Nasohypophysial sac Extemal gill openings Internal gill Openings Cranium Branchial skeleton Vertebrae cartilaginous Number of spinal nerve pairs per body segment Ducts of Cuvier to heart Pronephric kidney Osmoregulation Eggs Cleavage of embryos In front of head Opens into pharynx One to 14 Each enters directly into pharynx Poorly developed Rudimentary Absent One Left only Present Hyper or hypoosmotic Very large with hooks Meroblastic On top of head Does not open into pharynx Seven Unite into a single tube con necting to oral cavity Clearly cartilaginous Well developed Present Two Right only Absent Isosmotic Small without hooks Holoblastic 4 CARTILAGINOUS FISHES SHARKS AND THEIR ALLIES The Chondrichthyes or cartilaginous shes represent the most primitive living jawed vertebrates Unfortunately very little is known about their origin There is an abundant fossil record see page 10 but it consists of mostly fragments the earliest indications of the presence of cartilaginous shes are isolated teeth dermal denticles calci ed jaw cartilages braincases spines and n radials that date to midDevonian about 370 MYBP These remains are interesting in themselves but they tell us little about the kinds of shes that gave rise to them The reason for this lack of wellpreserved whole specimens is of course that cartilage doesn39t fossilize very well For the same reason little is known about the evolutionary interrelationships of modern or presentday groups of cartilaginous shes At present most consider the sharks and rays to be equivalent groups that is they represent each other39s sister group However there are indications that rays may in fact be more closely related to some subgroup of sharks perhaps angel sharks some think saw sharks are a more likely ancestor rather than to sharks as a whole COMPETING HYPOTHESES OF CHONDRICHTHYAN EVOLUTION Sharks Rays Chimaeras All other Angel Sharks Rays Chimaeras sharks Angel sharks are highly specialized raylike sharks that are unique in several ways They differ from other sharks in a number of ways but most striking are the large triangular pectoral lobes In this and in other ways they do resemble rays Squatina A phylogeny of chondri elasmobranchs established and th 10 group but the relationships among Paleozoi elr grouping is largely arbitrary All modern elasmobranches can be traced to a single ancestral c order have not been chthyan fishes showing two successive radiations among the Q PALE OZOlC v MESOZlC CENOZOIC I I MISSIS PENNSYLN SIPPIAN EVANIAN PERMIAN UATERNARY I TERTIARY N c x l g DEVONIAN a TRlASSIC IURASSIC CRETACEOUS 144 213 248 PRISTIOPHOROIDEA ELASMOBRANCHII SQUALOMORPHA MYLlOBATOlDEA Z PRISTOIDEA Rf quot TO RPEDINOIDEA J CARCHARHINOIDEA BATOIDEA PETALODONTIDA wail s QUALORAJOIDEI LAMNOIDEA GAWORPHA 1 i LU Q c I Q t 5 2 o c 05 O HOLOCEPHALI MYRIACANTHOIDEA f CHIMAERIDAE CHIMAERIDA I I I O Q I I ii 9 O 5 E E 67 CHIMAEROIDEA But until we have more information in support of such a radical realignment we39ll consider that cartilaginous shes consist of three primary groups 1 Sharks 2 Rays 3 Chimaeras or ratfishes These three have long been considered closely related that is they share a common ancestor that is thought to have evolved by late Devonian about 350 MYBP Sharks and rays are thought to be more closely related to each other than either is to the chimaeras and are collectively called the elasmobranchs Elasmobranchii Thus the elasmobranchs represent the sister group of the chimaeras All three groups share a number of important morphological characters 1 Cartilaginous skeleton parts of the skeleton may become calci ed 2 Dermal skeleton of denticles with a unique threelayered structure consisting of vitrodentine dentine and underlying basal tissue Shark dermal denticlesA Sectionthrough adenticleB side and surface views of denticle Abbreviations D dentine D dermis E hard enamellike surface of denticle vitrodentine E39 epidermis PC pulp cavity From Dean 3 Airbladder absent 4 Spiral valve in the intestine Racial gland Spiral valve Intestine J V 5 Internal fertilization males of all recent taxa are equipped with claspers although there are some wellpreserved sharks from the Upper Devonian that lack claspers Ischiopubic cartilage Toward head Pelvic n 6 Osmoregulation by retention of urea 5 LIVING SHARKS OF THE WORLD Sharks are primarily marine organisms but a number of species readily enter brackish to almost freshwater estuaries lagoons and bays a few species of the family Carcharinidae occur far up rivers and in freshwater lakes with connections to the sea They vary tremendously in size among the family Squalidae are some of the smallest of living sharks eg genus Squaliolus and Euprotomicrus that mature at a length of 1115 cm In contrast are the gigantic sleeper sharks of the genus Somm39osus attaining a size of over 6 m and the largest of all the whale shark genus Rhiniodon that are said to attain a length of 18 m Shark biodiversity has grown signi cantly in recent years The most recent estimate published in 2006 indicates 403 living species divided into 34 families and nine orders Um WKVWWM Leopard shark Sixgill shark i I Stringray Sawfish Manta ray Head clasper Ratfish 12 HYPOTHESIZED RELATIONSHIPS OF THE ORDERS OF LIVING SHARKS body flattened raylike mouth termina 39 SGUATINIFORMES no anal fin body not raylike PRISTIOPlDRIFORMES mouth ventral SQUALIFORMES 6 or 7 gill slits one dorsal fin I HEXABCHIFDRMES nictitating eyelids spiral or scroll intestinal valve I CARCHARHINIFORMES no nictitating eyelids ring intestinal valve LAMNIFORMES 5 gm slits mouth well in front of eyes 2 dorsal fins ORECTOLOBIFORMES SHARKS mouth behind front of eyes anal fin present lno fin spines lETERIWTIFORMES A CLASSIFICATION OF LIVING SHARKS SUPERORDER GALEOMORPHA galeomorph sharks 4 orders 23 families 1 Order HETERODONTIFORMES bullhead sharks 1 family 1 genus 8 species 1 Family He terodontidae bullhead sharks horn sharks 1 genus 8 species 2 Order ORECTOLOBIFORMES carpet sharks 7 families 14 genera 32 species 2 Family Parascyllidae collared carpet sharks 2 genera 7 species 3 Family Brachaeluridae blind sharks 2 genera 2 species 4 Family Orectolobidae wobbegongs 3 genera 6 species 5 Family Hemiscylliidae bamboo sharks 2 genera 12 species 6 Family Stegostomatidae zebra sharks 1 genus 1 species 7 Family Ginglymostomatidae nurse sharks 3 genera 3 species 8 Family Rhincodontidae whale shark l genus 1 species 3 Order LAMNIFORMES mackerel sharks 7 families 10 genera 15 species 9 Family Odontaspididae sand tiger sharks 2 genera 3 species Family Mitsukurinidae goblin shark 1 genus 1 species Family Pseudocarchariidae crocodile shark 1 genus 1 species Family Megachasmidae megamouth shark 1 genus 1 species Family Alopiidae thresher sharks 1 genus 3 species Family Cetorhinidae basking shark 1 genus 1 species Family Lamnidae mackerel sharks porbeagles white sharks 3 genera 5 species 4 Order CARCHARHINIFORMES ground sharks 8 families 49 genera 224 species Family Scyliorhinidae cat sharks 16 genera 113 species Family Proscylliidae nback cat sharks 3 genera 5 species Family Pseudotriakidae false cat shark 2 genus 2 species Family Leptochariidae barbeled hound shark 1 genus 1 species Family Triakidae hound sharks 9 genera 38 species Family Hemigaleidae weasel sharks 4 genera 7 species Family Carcharhinidae requiem sharks 12 genera 50 species Family Sphyrnidae bonnethead and hammerhead sharks 2 genera 8 species SUPERORDER SQUALOMORPHA squalomorph sharks 5 orders 11 families 5 Order HEXANCHIFORMES frilled and cow sharks 2 families 4 genera 5 species 24 25 Family Chlamydoselachidae frilled sharks 1 genus 1 species Family Hexanchidae cowsharks sixgill and sevengill sharks 3 genera 4 species 6 Order ECHINORHINIFORMES bramble sharks 1 family 1 genus 2 species 26 Echinorhinidae bramble sharks 1 family 1 genus 2 species 7 Order SQUALIFORMES dogfish sharks 6 families 24 genera 97 species Family Squalidae dog sh sharks 2 genera 10 species Family Centrophoridae gulper sharks 2 genera 14 species Family Etmopteridae lantern sharks 5 genera 41 species Family Somniosidae sleeper sharks 7 genera 17 species Family Oxynotidae rough sharks 1 genus 5 species Family Dalatiidae kite n sharks 7 genera 10 species 8 Order SQUATINIFORMES angel sharks 1 family 1 genus 15 species 33 Family Squatinidae angel sharks sand devils 1 genus 15 species 9 Order PRISTIOPHORIFORMES saw sharks 1 family 2 genera 5 species 34 Family Pristiophoridae saw sharks 2 genera 5 species 6 LIVING RAYS OF THE WORLD Rays are rather easy to de ne morphologically they all share numerous unique features the most important of which are 1 Pectoral ns fused to the head over the gill openings 2 Attachment or articulation of the pectoral girdle to the vertebral column The most recent estimate places the number of living species of rays at about 534 Thus rays include about 57 of all living elasmobranchs Six orders 15 families and 72 genera are currently recognized A CLASSIFICATION OF LIVING RAYS 1 Order PRISTIFORMES saw shes 1 family 2 genera about 7 species 1 Family Pristidae saw shes 2 genera about 7 species 2 Order TORPEDINIFORMES electric rays 2 families 12 genera about 59 species 2 Family Torpedinidae torpedo electric rays 3 genera about 22 species 3 Family Narcinidae numb shes or rounded torpedo rays 9 genera about 37 species 3 Order RHINOBATIFORMES guitar shes 3 families 6 genera about 47 species 4 Family Rhinidae bowmouth guitar shes 1 genus 1 species 5 Family Rhinobatidae guitar shes 4 genera about 42 species 6 Family Rhynchobatidae wedge shes or bilobed guitar shes 1 genus 4 species 4 Order RAJIIFORMES skates 1 family 28 genera about 249 species 7 Family Rajiidae skates 28 genera about 249 species 5 Order DASYATIFORMES stingrays 5 families 17 genera 135 species 8 Family Dasyatidae Whiptail stingrays 7 genera about 79 species 9 Family Urolophidae round stingrays 3 genera about 24 species 10 Family Potamotrygonidae freshwater or river stingrays 3 genera 20 species 11 Family Hexatrygonidae six gill stingray 1 genus 1 species 12 Family Gymnuridae butter y rays 3 genera 11 species 6 Order MYLIOBATIFORMES eagle cownose manta rays 3 families 7 genera 37 species 13 Family Myliobatidae eagle rays 4 genera 20 species 14 Family Rhinopteridae cownose rays 1 genus 7 species 15 Family Mobulidae manta rays 2 genera 10 species 15 1 Order PRISTIFORMES saw shes 1 family 2 genera about 7 species 1 Family Pristidae saw shes 2 genera about 7 species Sawshark Genus Pristiophorus The seven recognized species of saw shes are restricted to coastal tropical and warm temperate waters although most have extremely broad ranges within these zones The long toothed rostrum is used to dislodge small benthic invertebrates from the bottom as well as for immobilizing small schooling shes Their striking similarity to sawsharks is one of the best examples of convergent evolution among shes All are viviparous but without placental connection between mother and young Sawfish Genus Pristis 2 Order TORPEDINIFORMES torpedo or electric rays 2 families 12 genera 59 species 2 Family Torpedinidae truncate torpedo rays 3 genera about 22 species 3 Family Narcinidae rounded torpedo rays 9 genera about 37 species The torpedo rays are primitive in a number of respects and very specialized in others The 59 or so species range from tropical to temperate waters from near the shoreline to the edge of the continental shelf The group is distinguished by the presence of huge electric organs along the lateral margin of the disc which are used both to stun prey and to defend against attack by predators All species are viviparous with or without placental connection between mother and Young Torpedo 16 3 Order RHINOBATIFORMES guitar shes 3 families 6 genera about 47 species 4 Family Rhinidae bowmouth guitar shes l genus 1 species 5 Family Rhinobatidae guitar shes 4 genera about 42 species 6 Family Rhynchobatidae wedgefishes or bilobed guitarfishes l genus 4 species The guitar shes are primitive in their body shape but specialized in their gill arches They range in body shape from sharklike with relatively small pectoral ns to truly raylike forms with widely expanded pectorals All are benthic and generally associated with muddy to sandy bottoms in all major tropical seas of the world but some also venture into brackish and occasionally fresh waters All species are viviparous without placental connection between mother and young Rhinobatus 4 Order RAJIIFORMES skates 1 family 28 genera about 249 species 6 Family Rajiidae skates 28 genera about 230 species The skates are thought by many to be the sister group of the guitar shes The are generally depressed with a relatively long slender tail The trunk or disc is formed by the broad connection between the head and the greatly expanded pectoral ns They are distinguished by having paired electric organs along the sides of the tail and by clawlike spines along the lateral extremes of the disc They are the most widespread of the rays occurring on the bottom from the tropics to polar latitudes and from the shoreline to depths of 3000 m Skates are oviparous that is they lay eggs in sharp contrast to all other rays which are Viviparous l7 5 Order DASYATIFORMES stingrays 5 families 17 genera 135 species 8 Family Dasyatidae whiptail stingrays 7 genera about 79 species 9 Family Urolophidae round stingrays 3 genera about 24 species 10 Family Potamotrygonidae freshwater or river stingrays 3 genera 20 species 11 Family Hexatrygonidae sixgill stingray l genus 1 species 12 Family Gymnuridae butter y rays 3 genera 11 species The stingrays resemble the skates in body shape except that the tail is more slender and generally whiplike In addition they usually possess one or more serrated spines near the base of the tail They are found around the world nearly all in tropical to warm temperate seas but the Pomatotrygonidae or freshwater stingrays are found only in the tropical fresh waters of South America All species are Viviparous without placental connection between mother and young Round ray Genus Urolophus Freshwater stingray Genus Pomatotrygon 1 Butterfly ray Genus Gymnurus l8 6 Order MYLIOBATIFORMES eagle cownose manta rays 3 families 7 genera 37 species 13 Family Myliobatidae eagle rays 4 genera 20 species 14 Family Rhinopteridae cownose rays 1 genus 7 species 15 Family Mobulidae manta rays 2 genera 10 species Eagle cownose and manta rays are highly specialized for active swimming some are considered to be epipelagic The pectoral ns rmly attached to the vertebral column by a ball and socket arrangement resemble bird wings and are moved through the water in a manner similar to birds apping their wings during ight As a result of these adaptations most species are rather wide ranging in tropical seas All members of the order are Viviparous with or without placental connection between mother and tA r Eagle ray Genus Aetiobatus young Cownose ray Genus Rhinopterus Manta ray Genus Mobula 7 LIVING CHIMAERAS OF THE WORLD Besides the elasmobranchs another group of modern cartilaginous shes can be traced back to Carboniferous times approximately 300 MYBP these are the chimaeras sometimes called the rat shes or rabbit shes but of cially they belong to the infraclass Holocephali Holocephalans have long been considered relatives of the sharks and rays because of similarities in the architecture of the cartilaginous skeleton as well as similarities in their soft anatomy These similarities are so striking that paleontologists are convinced that holocephalans arose from the same ancient stock of early jawed shes as the elasmobranchs Nevertheless each having evolved independently from one another for some 300 million years holocephalans are unique in a number of ways 1 They have large permanent slowgrowing tooth plates rather than separate replaceable teeth like sharks 2 Their upper jaw palatoquadrate is fused to the cranium not suspended from the cranium as in elasmobranchs Modemday holocephalans include a single order six genera and 33 species Many authors place all species within a single family Chimaeridae but most recognize three families Order CHIMAERIFORMES Family Callorhynchidae plownose chimaeras l genus 3species Plownose chimaeras are characterized by having a long exible hooklike process on the snout and a sharklike heterocercal tail They range throughout the southern hemisphere off southern South America New Zealand southern Australia and southern Africa Callorhynchus 20 Family Rhinochimaeridae longnose chimaeras Atlantic and Paci c oceans 3 genera 8 species The longnose chimaeras are similar to the shortnose chimaeras in the structure of the tail but the snout is long and pointed They are Widespread throughout the Atlantic and Paci c oceans Rhinochimaera Family Chimaeridae shortnose chimaeras or rat shes 2 genera 22 species The snout of shortnose chimaeras is short and rounded the tail is long thin and tapering a poison gland is associated with the dorsal n spine and the venom is painful to humans They are found throughout the Atlantic and Paci c oceans H ydrolagus 21 BIOLOGY OF FISHES FISH 311 FORM AND FUNCTION OSMOREGULATION WATER AND IONIC BALANCE IN DIVERSE AQUATIC ENVIRONMENTS General topics 1 2 3 De nitions the Laws of Diffusion and Osmosis Functional components of the vertebrate kidney Osmoregulation in freshwater shes Osmoregulation in marine shes Osmoregulation in diadromous and euryhaline shes Osmoregulation in elasmobranch shes Osmoregulation in tetrapods 1 DEFINITIONS THE LAWS OF DIFFUSION AND OSMOSIS Diffusion the movement of ions and molecules through a medium from a region of high concentration to a region of low concentration Or crysth Diffusion Molecules tend to move om high concentration Osmosis When separated by a semipermeable membrane to lower concentrations In A a crystal of salt is placed at the water tends to move from a region of lesser concentration to a bottom of a cylinder of water It immediately begins to dis region of greater concentration of solutes This diagrammatic solve that is the molecules mingle with those of the water view shows why the membrane is permeable to water but not Equilibrium is established at some later time as shown in B to sugar Osmosis the movement of water across a semi permeable membrane when the concentration of solutes is greater on one side of the membrane than the other the net movement of water will be from the region of lesser concentration to region of greater concentration of solutes For the most part marine invertebrates are in osmotic equilibrium with the seawater That is their salty internal uids hold as much salts as does the surrounding aquatic medium Stated another way the principal ions that are found in the uids that bathe the cells of the body are the same and occur in approximately the same concentrations as those found in seawater Thus there is no problem of water balance the rate of diffusion of water into the body is the same as the rate at which water diffuses out Under conditions such as this we say the animals exist in an isotonic environment iso means the same hyperl39onlc Isotomc hypofomc The effect of salt solutions of various concentrations on a red blood cell We assume that this isotonic situation is the way it was for the chordate ancestor of the vertebrates as well as for the earliest of vertebrates that lived in marine environments the primitive kidney of these organisms functioned solely to rid the body of waste materials it had little or nothing to do with water and salt balance In other words it was excretory in function rather than osmoregulatory But what about those early vertebrates that took to freshwater In these forms osmotic equilibrium was disrupted because of the Law of Osmosis any animal submerged in freshwater with body uids in greater concentration than the surrounding water inevitably takes in excess water That is it tends to become waterlogged either by 1 Absorption through the delicate epithelium covering the gill laments and mucous membranes of the mouth and pharyngeal cavity or by 2 Swallowing water along with food So very early on in the evolutionary history of vertebrates there was a need for some kind of mechanism to rid the body of excess water At the same time salts are scarce in freshwater environments the only source being food Therefore because of the Law of Diffusion there was also a need for some mechanism to prevent the loss of salts from the body What evolved to take care of these problems was the vertebrate kidney also called the glomerular kidney A device that functions to both eliminate excess water from the body and to reclaim salts 2 FUNCTIONAL COMPONENTS OF THE VERTEBRATE KIDNEY The vertebrate kidney is made up of thousands of individual tubular structures called nephrons Each nephron has three components 1 Glomerulus 2 Convoluted or nephric tubule 3 Longitudinal collecting duct Each glomerulus is a tuft of blood capillaries surrounded by a capsule of tissue called Bowman s capsule Together the glomerulus and capsule are called a renal corpuscle The glomerulus with the help of blood pressure functions to lter water and certain other uid substances out of the blood stream The ltered substances are called the glomerular ltrate Supplying each glomerulus is an afferent renal arteriole and an efferent renal arteriole proximal convoluted tubule renal portal venule afferent arteriole distal convoluted tubule Bowman s capsule glomerulus efferent arteriole renal venules v collecting duct i The convoluted tubule differentiated into a number of discrete segments is a duct that collects the glomerular ltrate from the glomerulus and transports it to the longitudinal collecting duct All along the length of each tubule many substances are reabsorbed by the blood by means of a second capillary bed that surrounds the tubule This capillary network is supplied by an afferent renal venule and drained by an efferent renal venule Other substances may be secreted into the tubule from the blood The Longitudinal collecting duct receives all the glomerular ltrate from the thousands of tubules of the kidney and dumps it into the urinary bladder Critical to the functioning of each nephron there are two sets of capillaries AFFEREVT ARTEHOLE CONVOLUTED TUE5 Glomerular mass embedded within Bowman s capsule that with the aid of blood pressure acts as a lter to remove excess water and other substances and a Reabsorptive mass that surrounds the convoluted tubule and functions to reabsorb water and other valuable substances while it reabsorbs or excretes salts EFFERENT AFTEROLE GLOMEPULUS BOWMAN39S CAPSULE then is So this the vertebrate or glomerular kidney a wonderful device that takes care of the water problem and at the same time functions to retain glucose salts and other valuable materials by reabsorption through an elaborate system of nephric tubules The basic structure is rather simple but it s important to realize that there is huge variation among fishes in the number size complexity and arrangement of the glomeruli and tubules distal convoluted tubule proximal convoluted tubule branch of renal loop of Henle collecting tubule The human nephron 3 OSMOREGULATION IN A FRESHWATER FISH Let s turn now to the shes themselves and see how the problems of osmoregulation compare in freshwater habitats and in marine habitats A sh submerged in freshwater with body uids in greater concentration than the surrounding water tends to take on water and lose valuable salts to the environment It takes on water primarily by absorbing it through the gills and skin by simple passive diffusion Under these conditions we say the animal exists in a hypotonic environment hypo means less referring to the lower solute concentration of the surrounding water It must be able to eliminate excess water and retain salts How does it do this absorbs water through gills and skin obtains salts through salts Chloride Ceus 39 gins lost removes much water and and With f d via feces some salt via dilute urine Osmoregulation in a freshwater teleost The concentration of solutes in the body uids is much greater than in the outside medium Open arrows indicate movement of substances by passive diffusion closed arrows indicate movement of substances by active transport mechanisms 1 Drinks very little water 2 Has numerous large welldeveloped glomeruli 3 Reabsorbs salts along the length of its convoluted tubules 4 Produces large amounts of very dilute urine 512 of body weight per day To better understand how osmoregulation works in shes living in diverse aquatic habitats it s necessary to take a more detailed look at the functional components of the kidney As an example let s look closely at the kidney of a common freshwater sh the carp Cyprinus carpio which has a kidney that is as complex as a sh kidney gets an almost identical pattern is found in amphibians Basically excess water is ltered from the blood through the glomeruli carrying all kinds of substances in addition to the water such as salts and sugars which are reabsorbed into the blood stream through the epithelium of the kidney tubules Glomerulus G A typical kidney of a freshwater sh has tens of thousands of large glomeruli each with a welldeveloped blood supply Great amounts of water pass through them The glomerulus then is a device that provides a ltrate that can be modi ed selectively by the kidney tubule Neck Region The neck region is lined with cilia The ciliary action plays an important role in aiding movement of materials into the tubule This is particularly important in the lowpressure ltration systems of shes First Proximal Segment PSI Here is where reabsorption of many macro molecules such as glucose and proteins takes place but also excretion of organic acids Second Proximal Segment PSII This is the largest region of the tubule where there is high metabolic activity ie active transport mechanisms that are responsible for the reabsorption of many salts such as Mg 804 Ca P Na Clquot and HCO339 Distal Segment DS this portion of the tubule participates in active reabsorption of Na and some Cl39 It is also a highly ciliated area that assists in propulsion of uid along the tubule In a freshwater sh it is important to move the uid through the length of the tubule as fast as possible to minimize passive reaborbtion of water Collecting Tubule or Duct CT functions primarily to reabsorp monovalent ions mostly Na and Cl39 key Bowman s capsule neck 39 proximal segment active transport proximal segment ll gt diffusion of water or other substance distal tubule as indicated collecting tubule urine 59 collecting duct 4 organic acids gt glucose Na I macromolecules water lt creatine H gt Mgjr 80339 Catt P Nat Cl HCOg Nat cr Nat Clquot 20 mOsml What is left is a dilute urine that contains mostly water but also some creatine and creatinine alkaloids some amino acids and little urea and ammonia So some nitrogenous waste is lost by way of the urine but this amounts to only 7 to 25 of the total nitrogen excreted by a freshwater sh The bulk passes out through the gills in the form of ammonia The remainder is probably urea and other simple compounds of nitrogen that also leave the body by way of the gills The kidney alone cannot reabsorb enough salts to maintain osmoregularity To compensate for this de ciency the gills and oral membranes have evolved the ability to absorb ions by active transport mechanisms in special cells called chloride cells All kinds of ions are absorbed in this way acid phosphate HPO439 bromine Br39 calcium Ca chloride Cl39 lithium Li sodium Na sulfate 804 ions etc v w at if v e r 9 chloride cell gt e 39 as 13951 w W A w a 7 39 fquot i it 3 a d 39 i Q lamellar a e x quotwe quot I as u channel r 91 a 3quot 9 4 erythrocytes quot 543 3 i a 3 39 l g 1 f j I chloride cell 9 a X at N g I if 39 3 3 433 B Photomicrographs of sections along gill laments of rainbow trout Oncorhynchus mykiss showing A arrangement of secondary lamella to form numerous channels with great surface area and B closeup showing erythrocytes and chloride cells Just how this is done that is the identity of the speci c sites of active ion absorption against a concentration gradient is still controversial and not well understood 4 OSMOREGULATION IN MARINE FISHES Marine shes have problems too Their body uids although consisting of the same ions as seawater have a total quantity of salts that is less than that of the same volume of seawater some marine teleosts have as little as onethird the osmotic concentration of seawater Because their body uids are less concentrated than seawater they tend to lose water through their membranes Under these conditions we say the animal exists in a hypertonic environment hyper means more referring to the higher solute concentration of the surrounding water They are forced by osmotic conditions to conserve water and to get rid of excess salts How do they do this loses water through gills and skin removes salts via chloride cells in gills gains water and salts by salts swallowmg seawater and food lost salts and little water via feces lost via scant urine Osmoregulation in a marine teleost The concentration of solutes in the body fluids is much less than in the outside medium Open arrows indicate movement of substances by passive diffusion closed arrows indicate movement of substances by active transport mechanisms 1 Drink seawater 2 Have fewer and smaller glomeruli 3 Excrete salts along the length of its convoluted tubules 4 Produce small amount of very concentrated urine as little as 25 ml per kg of body weight per day Nearly all marine bony shes show a reduction in the number and size of glomeruli culminating in some forms that have completely lost glomeruli In addition to their ability to produce a highly concentrated urine specialized tissues in the gill region have evolved to actively excrete large amounts of salt Glomerulus G Thus as you might expect the glomeruli of marine teleosts are small poorly vascularized and blood pressure in the glomeruli is low Forms in which glomeruli are small and degenerate are called pauciglomerular Some forms thrive with no glomeruli at all these are called aglomerular Examples include the midshipmen genus Porichthys and the monk sh genus Lophius Neck Region This region may be lost altogether especially in the case of aglomerular species 4 organic acids gt glucose Na Cl macromolecules First Proximal Segment PSI Here water just as in freshwater shes there is H reabsorption of macromolecules such as 39139 Mg 804 a glucose and proteins Cay lt organlc acnds Second Proximal Segment PSII water urea Mgf 804quot Ca Instead of act1ve reabsorpt1on of many uric acid 5 P H NHB TMAO salts as we saw in freshwater shes this ne creatine part of the nephron is a site of active crea secretion of salts such as Mg 804 lt3 Naa Cl K Ca P Na Cl39 and HCOg39 It is also responsible for active secretion of nitrogenous waste produce like urea 410 mOsm l creatinine and creatine Distal Segment DS This portion which in freshwater forms is heavily 4 organic acids ciliated and assists in propelling uid megaer gt g quot Mg 804 along the tubule is absent in marine uric Acid Ca P H NH TMAO shes The requirement here is to slow creating creg ne the movement of uid so that there is Na Cl39 time for the maximum amount of passive diffusion of water back into the blood Na Cl Collecting Tubule or Duct CT N or K participates in some reabsorption of Na v lt3 I a and C1quot M 400 mOsml What s left is a small volume of strong concentrated urine containing creatinine creatine some urea and some ammonia plus other miscellaneous nitrogenous compounds but 90 percent of the nitrogenous waste products are not excreted by the kidneys but eliminated by the gills as ammonia and urea Again just as in freshwater shes the gills are very important in ionic balance The kidneys alone cannot eliminate all the excess salts Whatever they can t handle is excreted by the gills so that the bulk of monovalent ions especially chloride ions pass out through the gills This is done by a process of active transport that takes place in the special secreting cells called chloride cells see page 8 not such a good name because they are responsible for the secretion of other ions as well These chloride cells are rich in mitochondria a site of great metabolic activity PASSIVE ACTIVE TRANSPORT O O TRANSPORT O 0 dissolved substance O No ion 0 water 0 carrier Highly schematic representation of how particles migrate through membranes 5 OSMOREGULATION IN DIADROMOUS AND EURYHALINE FISHES So far we have been talking only about shes that live strictly in either freshwater or salt water that is shes that have a very narrow tolerance to salt These are called stenohaline forms from the Greek stenos meaning narrow and the Greek hals or halos meaning salt or sea Many shes however have a wide tolerance to salt and can live in freshwater brackish water or salt water and can move freely among these different habitats These are called euryhaline forms from the Greek eurys meaning broad or widespread Some species have split life histories spending part of their lives in freshwater the other part in the marine habitat These are called diadromous the Greek dzquot means two and dromos refers to running Diadromy takes three general forms 1 Anadromy Adults spawn in freshwater juveniles move to saltwater for several years of feeding and growth and then migrate back to freshwater to spawn Catadromy Adults spawn at sea juveniles migrate to freshwater for several years to feed and then return to the sea to spawn Amphidromy Spawning may occur in either freshwater or saltwater larvae migrate to the other habitat for an initial feeding and growth period then migrate to the original habitat as juveniles or adults where they remain for additional feeding and growth prior to spawning FRESHWATER SEA MIGRATION B G Anadromy R f j I F B Q C G Catadromy r R l B G I a R G J O Amphidromy quot r B G G gtR Three forms of diadromy B birth G growth and R reproduction 12 Families of known diadromous shes Anadromous Catadromous Amphidromous Petmmyzontidae lampreys Anguillidae true eels Plecoglossidae ayu Georriidae southern lampreys Galaxiidaegalaxiids Prototroctidae southern graylings Mordaciidae southern lampreys Scorpaenidae scorpion shes Aplochitonidae whitebaits Adpenseridae sturgeons Moronidae temperate basses Galaxiidae galaxiids Clupeidae herrings Centropomidaesnooks Clupeidae herrings Salmonidae salmons Kuhliidaeaholeholes Cottidae sculpins Osmeridaesmelts Mugilidae mullet Mugiloididae sandperches Salangidaeice shes Retropinnidae New Zealand smelts Gobiidae gobies Aplochitonidae whitebaits Ariidae sea cat shes Soleldae soles Gasterosteidae sticklebacks Gadidae cods Moronidae temperate basses Cottidae sculpins Gobiidae gobies Bovichthyidae bovichthyids Pleuronectidae righteye ou nd ers Eleotridae sleepers Syngnathida e pipe shes Species with a Wide tolerance for salt in general are called euryhaline These forms must of course be able to regulate their osmotic balance according to varying environmental needs All have welldeveloped glomerular kidneys that can adjust to differences in urine volumes due to different salinities They also possess gill and oral membranes capable of coping with both uptake and secretion of certain ions against different diffusion gradients 6 ELASMOBRANCH FISHES What about sharks and rays Marine elasmobranchs have solved the problem of osmoregulation in an entirely different way They have evolved a specialized segment of the nephron that reabsorbs urea and returns it to the blood gills block loss of urea and TMAO water absorbed by gills and skin ingests salts with food most urea and TMAO retained by kidney divalent ions excreted in urine sodium excreted by rectal gland Osmoregulation in a marine shark The concentration of solutes in the body uids is greater than in the outside medium Open arrows indicate movement of substances by passive diffusion closed arrows indicate movement of substances by active transport mechanisms This in ux of urea a toxic nitrogenous waste produce for most vertebrates raises the osmotic pressure of the blood to a level just above that of sea water so that water actually ows into the body of the shark Marine sharks thus act just like freshwater shes they have numerous welldeveloped glomeruli and they excrete large amounts of dilute urine water 800 mOsml M lt organic acids gt glucose Na Cl39 macromolecules 4 divalent ions I Mg 804quot lt gt gt P H lt3 lt2 lt1 II Nat Clquot Number And Size of Glomeruli in Selected Fishes Relative Volume Number of Average mm of Glameruli Weight Glameruli in Diameter of per ml of Body Species g One Kidney Glomeruli pm Surface Freshwater Teleosts Ameiurus nebuosus 89 18160 100 1265 Cyprinus carpio 221 24310 82 508 Perca favescens 116 4870 102 30 Marine Teleosts 39 Gadus morhua calarias 670 16250 37 149 Lutjanus griseus 544 31860 55 1099 Pseudopleuronectes americanus 160 5300 50 314 Elasmobranchs Musteus canis 485 4400 185 6093 Raja erinacea 1060 1200 190 1038 7 OSMOREGULATION IN TETRAPODS True terrestrial vertebrates also have water conservation problems Like marine teleosts the kidneys of reptiles and birds have very reduced glomeruli although no aglomerular kidneys are found As a further aid water is reabsorbed by the walls of a cloaca The result is very dry feces consisting primarily of uric acid In addition birds have a specialized segment of the nephron that reabsorps water Marine turtles the marine iguanas of the Galapagos and marine birds have solved the problem slightly differently These forms drink seawater Desalting of the water and retention of freshwater is accomplished by special salt excreting glands in the head Salt is dumped into ducts that empty into the nasal cavities or directly to the outside In mammals a large section of the nephric tubule has become adapted solely to reabsorb water The glomerulus actually allows more than 100 times the amount of water to lter from the blood as would be excreted in the urine that leaves the other end of the tubule All of this extra water is reabsorbed or pushed back into the blood by the activity of this elongate tubule called the Loop of Henle see picture lower right page 5 BIOLOGY OF FISHES FISH 311 BIODIVERSITY V TELEOST EVOLUTION CONTINUED PERCOMORPH FISHES AND DERIVATIVE ORDERS MORPHOLOGY ECOLOGY AND CO EVOLUTION General topics 1 LIIFUJN 00O Percomorpha perches and perch derivatives Order Lampriformes ribbon shes and their allies Order Beryciformes squirrel shes and their allies Order Zeiformes dories and oreos Order Gasterosteiformes sticklebacks and their allies Order Synbranchiformes the swampeels Order Scorpaeniforrnes the mailchecked shes Order Perciformes the perches Order Pleuronectiformes the at shes 10 Order Tetraodontiforrnes trigger shes puffers and their allies 1 PERCOMORPHA THE PERCHES AND PERCH DERIVATIVES OK we still have lots of shes to describe all of which reside in this largest of all groups the Percomorpha nine orders 245 families 2212 genera and about 13173 species Nearly half of all living shes belong to this group We39ll say something about the following nine orders ORDER LAMPRIFORMES ORDER BERYCIFORMES ORDER ZEIFORMES Preperciform orders ORDER GASTEROSTEIFORMES ORDER SYNBRANCHIFORMES ORDER SCORPAENIFORMES ORDER PERCIFORMES ORDER TETRAODONTIFORMES Perciform derivatives ORDER PLEURONECTIFORMES RELATIONSHIPS OF THE MAJOR GROUPS OF PERCOMORPH FISHES 39 TETRAODONTIFORMES PLEURONECTIFORMES l l PERCIFORMES SYNBRANCHlFORMES to GASTEROSTEIFORMES SCORPAENIFORMES ZEIFORMESto LAMPRIFORMES 2 ORDER LAMPRIFORMES THE RIBBONFISHES AND THEIR ALLIES The lampriform shes make up a strange morphologically diverse assemblage of sevenlies 12 genera and about 21 species ranging in body shape from short and deep to highly elongate and eellike All are marine and found throughout the world39s oceans in rather deep water Common names for these include the opah crestfishes ribbonfishes oarfishes tubeeye or threadtail and other rare representatives for which common names haven39t been created Trachiphridue Lampridae LophoHdac Siylcphoridac All share a peculiar and unique modi cation of the upper jaw that allows for protrusion of both premaxillae and maxillae together the maxillae instead of being ligamentously attaChed to the ethmoid and palatine slides in and outwith the highly protractile premaxillae 3 ORDER BERYCIFORMES SQUIRRELFISHES AND THEIR ALLIES This is a very poorly understood group of 16 families 57 genera and about 219 species Most believe that it is probably an arti cial assemblage of unrelated taxa that are thrown together for convenience only ie we don39t know what else to do there are no convincing characters that tie all members together Common names include pinecone fishes slimeheads lanterneye fishes spinyfins fangtooth alfonsinos squirrelfishes soldierfishes beardfishes pricklefishes bigscales fishes gibberfishes and whalefishes f7 EJEO Shphunabcryciduc Melamphocidoc Bcrycidac Gibberichlhyidac Monoccnfridac Anomalopidac Calamimiduc 9 Barbourisijduo Konogushriduc 4 ORDER ZEIFORMES THE DORIES AND OREOS Another very poorly known group of largely deepwater marine forms found throughout the world 6 families 21 genera and only about 36 species Common names include dories oreos grammicolepidids and the boar shes Zciduc Macrurocyih dac Orcosomulidqc Caproidao 5 ORDER GASTEROSTEIFORMES STICKLEBACKS AND THEIR ALLIES This order consists of two rather different looking suborders the Gasterosteoidei including the sticklebacks tubesnouts and their allies and the Syngnathoidei containing the pipe shes seahorses and their allies In faCt these suborders are so different that many ichthyologists prefer to treat them as separate orders It contains 11 families 71 genera and 278 species Suborder Gasterosteoidei sticklebacks tubesnouts and the sandeel primarily marine but also brackish and freshwater restricted to the Northern Hemisphere four families nine genera and about 14 species The recognition of only seven species in the family Gasterosteidae fails to account for the enormous genetic diversity and biological species that exist in the Gasterosteus aculeatus complex and perhaps also in the Pungitius pungitius complex but the taxonomic and systematic problems in assigning species status to populations are formidable l k J I Aulorhynchidae Gasterosteidae Suborder Syngnathoidei seamoths pipefishes seahorses trumpet shes cornet shes snipefishes shrimpfishes and ghost shrimp shes primarily marine forms but some are found in brackish water a few in freshwater distributed in all tropical subtropical and temperate seas of the world seven families 62 genera and about 264 species Auloa omidac Syngnalhidae Pegusldae Solenoslomidue 6 ORDER SYNBRANCHIFORMES THE SWAMPEELS Synbranchiform shes look just like eels and up until the late 19th century they were classi ed with the true eels But the resemblance to anguilliform shes is only super cial Known as the swampeels and highly evolved as airbreathers these are primarily tropical and subtropical freshwater shes although some species occasionally enter brackish water they are distributed throughout west Africa Liberia Asia the IndoAustralian Archipelago Mexico and Central and South America three families 15 genera and 99 species Synbrunchidae Maslocembelidoe sea 397 Chuudhuriidae The body is eellike pectoral and pelvic ns are absent and the dorsal and anal ns are reduced to a rayless ridge The major distinguishing character however is found in the structure of the gills the gill openings on each side of the head are continuous with each other beneath the throat so that there appears to be a single transverse slit 7 ORDER SCORPAENIFORMES THE MAILCHEEKED FISHES The scorpaeniform shes consisting of 26 families 279 genera and about 1477 species are usually divided into ve suborders but keep in mind that the classi cation of the order is very provisional Suborder Scorpaenoidei scorpionfishes rock shes stone shes velvetfishes pigfishes and searobins marine rarely brackish and freshwater found in all tropical and temperate seas six families 82 genera and about 473 species Scorpuznidu Palaecidcu Triglidae Caracanfhidae Congiopodidac Synancejidae Suborder Platycephaloidei flatheads marine rarely brackish water con ned to the Indo Paci c Ocean ve families 38 genera and about 226 species Pluiycephalidac Hoplich39hyida Suborder Anoplopomatoidei sablefish or blackcod and the skil sh marine North Paci c a single family two genera and two species Anoplopoma mbria and Erilepis zonifer Anoplopomaiidae Suborder Hexagrammoidei greenlings lingcod and comb shes marine North Paci c a single family ve genera and 12 species Hexagrommidae Zuniolcpididao Suborder Cottoidei sculpins poachers oilfishes lumpfishes lumpsuckers and snail shes marine and freshwater all major oceans and seas of the world some freshwater forms with highly restricted distributions eg Lake Baikal families Cottocomephoridae and Comephoridae Eleven families about 149 genera and 756 species 0 I Agonidaz Cycloptcridac Cycloptcridac Cottocomephoridae Psychrolutiduc The evolutionary relationships among these ve suborders of the Scorpaeniformes are completely unknown they remain unde ned and serve only to group families thought to bear a closer relationship With one another than With those placed in other suborders The arrangement of families and family boundaries is subject to much disagreement Even common descent for the order as a whole is open to question There is only one character that provides evidence of shared ancestry the socalled suborbital stay a posterior extension of the third circumorbital bone SO3 that extends across the cheek to the posterior margin of the preopercle Some argue rather effectively that the suborbital stay differs so much among major groups that it could well have evolved independently cori I t Ophiodon elongatum lO Cottu octodtcimxpinomx Bull Fish Sci Hokkaido Univ 533 107 128 2002 Demise of the Scorpaeniformes Actinopterygii Percomorpha An Alternative Phylogenetic Hypothesis Hisashi IMAMURA and Mamoru YABEZ Received 13 September 2002 Accepted ll October 2002 Abstract The Scorpaeniformes has been de ned by two synapomorphies the presence of a suborbital stay and a bony parietal structure supporting the sensory canal but monophyly for the order is still uncertain Two monophyletic groups of scorpaeniform shes are currently recognized a scorpaenoid lineage including the suborders Scor paenoidei and Platycephaloidei and a cottoid lineage containing suborders Anoplopomatoidei Zaniolepidoidei Hexagrammoidei and Cottoidei Synapornorphies that support the monophyly of these two lineages four in the case of the scorpaenoid lineage and 13 for the cottoid lineage are reviewed and reevaluated Comparison of these two sets of synapomorphies with those that de ne percomorph taxa provides evidence to support the following phylogenetic hypotheses 1 the scorpaenoid lineage and percoid family Serranidae have a close relationship supported by two synapomorphies and 2 the cottoid lineage and perciform suborder Zoarcoidei have a sister relationship supported by 13 synapomorphies The order Scorpaeniformes as currently recognized is thus hypoth esized to be polyphyletic We propose reallocation of both lineages to the order Perciformes recognizing a suborder Scorpaenoidei to contain the scorpaenoid lineage plus Serranidae and a suborder Cottoidei closely aligned with the Zoarcoidei to contain the cottoid lineage Scorpaenoid lineage Serranidae Zoarcoidei Cottoid lineage l 4 Suborbital stay Extrinsic muscle derived from epaxlalis Absence of basisphenoid Single pair of nostrils SS 1 Single postocular spine in larval stage SS 3 Extrinsic muscle derived from obliquus superioris Parietal sensory canal with spines Absence of dorsal and anal tin stays ss 2 Backwardrydireded opemular spine Parasphenoid connected with pterosphenold CS 2 Six branchiostegal rays 38 4 I F Presence of adductor dorsalis cs 3 Third epibranchial without toothed plate CS 4 Lateral extrascapular comprised of two elements CS 5 No supraneurals CS 6 Dorsal pterygiophores arranged singly in each intemeural space CS 7 Absence of anal spines with robust pterygiophores CS 8 A3 located medial surtace of levator arcus palatini CS 9 Levator operculi comprised of two elements CS 10 Circular element of transversus dorsalis anterior CS 11 Presence of adductores llll CS 12 Absence of swimbladder Parietal sensory canal without spines Proposed phylogenetic relationships of the former Scorpaeniformes and related taxa 8 ORDER PERCIFORMES THE PERCHES Now we turn to the great pinnacle of teleost evolution the perciform shes the largest and most diversi ed of all sh orders and for that matter the largest order of vertebrates Perciforms are by far the dominate vertebrates in marine habitats as well as the dominate sh group in many tropical and subtropical freshwaters The classi cation of the order is controversial some ichthyologists would like to include other groups eg Scorpaeniformes considering them to be percoid derivatives while excluding others eg the Mugiloidei mullets barracudas and thread ns Common ancestry for the group is by no means certain Most families are basically very similar morphologically and remain unde ned ie no unique characters are available Although they form a morphologically and ecologically diverse group with all kinds of secondary losses and gains the level of evolution reached as contrasted with preacanthopterygian teleosts can be generalized as follows but be aware that many exceptions to these generalizations occur eg many perciforms have cycloid scales A COMPARISON OF PERCIFORM FISHES WITH LESS DERIVED TELEOSTS Lower teleosts Perciformes Spines in ns Absent Present Dorsal n number One adipose n may also Two never an adipose n be present Scales Cycloid Ctenoid or absent Pelvic n position Abdominal If present thoracic or Pelvic n rays Pectoral n base Upper jaw bordered by Swim bladder Orbitosphenoid Mesocoracoid Intermuscular bones Bone cells in bone of adult Principal caudal n ray number Six or more soft rays Ventral and horizontal Premaxilla and maxilla Duct present physos tomes Present Present Present Present Often 18 or 19 jugular One spine and ve soft rays sometimes fewer Lateral and vertical Premaxilla Duct absent physoclists Absent Absent Absent Absent Never more than 17 often fewer The order Perciformes contains 20 suborders 160 families about 1539 genera and about 10033 species They constitute the dominate marine shore shes of the world about 75 of all perciforms are marine shore shes while about 14 mostly cichlids and percids normally occur only in freshwater We can39t possible talk about all 20 perciform suborders but we will say a little about the largest and most diverse Suborder Percoidei includes hundreds of common names 79 families 549 genera and about 3176 species Of the 79 families 26 contain a single genus ten have only a single species and ten have 100 or more species The ten largest families Serranidae Apogonidae Sciaenidae Percidae Haemulidae Carangidae Chaetodontidae Pseudochromidae Sparidae and Lutjanidae contain about 62 of the species By far most are marine only about 380 or 12 of the species normally occur only in freshwater The Percoidei seems to be the basal evolutionary group from which the other perciform suborders have been derived as well as the two perciform derivatives orders yet to be described Pseudcplesiopidue Anisochramidue Sarranidae Glaucosomidae Thnruponiduc Sillaginiduc Banjoaidac Grummidaa Lacfnriidac anuiomiduc Rachycnkrida Echcneiduc Q Coryphaoniduc Menidue Gerridac CarisHiduc Pomudaayidaa thriniduc Sparidac Mullidal Godopsiduo 16 9 ORDER PLEURONECTIFORMES THE FLATFISHES In contrast to all the other groups we39ve talked about today this order the Pleuronectiformes is a wellde ned highly distinctive group We have little doubt that all members of the group were derived from a common ancestor Young at shes are bilaterally symmetrical and swim upright but early in their development one eye migrates across the top of the skull to lie adjacent to the eye on the other side They then lie and swim on the eyeless side The change involves a complex modi cation of skull bones nerves and muscles that leaves one side of the sh blind and the other side with two eyes The upper side is darkly pigmented whereas the under side is usually white Asymmetry is usually also re ected in other characters such as dentition scalation and paired ns Most species have both eyes on the right side and lie on their left side dextral or have both eyes on the left and lie on the right sinistral In some species both dextral and sinistral individuals occur Among the latter species the starry flounder Platichthys stellatus is especially interesting because of the varying frequency of dextral and sinistral forms that occurs over its range in the North Paci c from California to southeast Alaska the two forms dextral and sinistral are about equal in frequency around Kodiak Island and the Alaskan Peninsula about 70 are sinistral but almost 100 of the catch from Japan is sinistral The difference between sinistral and dextral starry ounders appears to be largely under genetic control but there are no convincing arguments for any advantage to being lefteyed or righteyed Most authors recognize 14 families of at shes within which are distributed about 134 genera and 681 species There are three suborders Suborder Psettodoidei spiny turbots marine west Africa and IndoPaci c Ocean a single family one genus and three species Dorsal n not extending out onto the head spines present in the anterior parts of dorsal and anal ns palatine bone well toothed Psettodidae Suborder Pleuronectoidei ounders lefteye ounders family Bothidae righteye ounders family Pleuronectidae marine present in all oceans of the world ten families 95 genera and about 421 species Dorsal n extending out onto the head reaching at least to the eyes dorsal and anal n spines absent palatine toothless Cilharidac Bon due Pleuronecfidae Suborder Soleoidei tonguefishes and soles primarily marine some in freshwater tropical and subtropical seas two families 38 genera and about 257 species Always lefteyed dorsal and anal ns con uent with a pointed caudal n Soleidae Cynoglossidae 10 TETRAODONTIFORMES TRIGGERFISHES AND THEIR ALLIES This last of the major groups of teleost shes is like the Pleuronectiformes a well de ned group Many of the characters that tie tetraodontiforms together are loss characters many bony parts have dropped out altogether or have become fused to other elements For example all members of the group lack parietals nasals circumorbital bones and usually lower ribs the posttemporal if present is fused to the pterotic bone the hyomandibula and palatine are rmly attached to the cranium and the maxilla is usually rmly united or fused with the premaxilla Most ichthyologists recognize nine families with approximately 101 genera and 357 species all divided among two suborders Suborder Balistoidei spikefishes triplespines leatherjaekets triggerfishes filefishes boxfishes cow shes and trunkfishes marine tropical and subtropical seas and oceans of the world ve families 72 genera and 203 species Oslracion dal Baliaiidae Triacanlhidue Suborder Tetraodontoideiz puffers porcupine shes and molas primarily marine a few species entering and occurring in brackish and freshwater all tropical and subtropical seas and oceans of the world four families 29 genera and 154 species Triodoniidae Tetracdontiduc Molidue BIOLOGY OF FISHES FISH 311 FORM AND FUNCTION SENSORY MECHANISMS III EYES AND VISION VISUAL PIGMENTS COLOR VISION General topics 1 Eye structure 2 Image formation and accommodation 3 Light and dark adaptations 4 Visual pigments and color Vision EYES AND VISION 1 EYE STRUCTURE The eyes of vertebrates are all built on the same basic plan but those of shes are characterized by a number of unique structural adaptations that allow them to function properly in an aquatic medium The major features of the eye include an anterior chamber lled with a liquid called aqueous humor an iris a lens and a posterior chamber containing a liquid called vitreous humor lined by a multilayered network of lightsensitive cells called the retina The spherical lens protruding through the pupil and forming a boundary between the anterior and posterior chambers is nearly in contact with the cornea which is essentially a transparent section of the outer layer or scleroid coat of the eyeball The lens is suspended above and held in place by a suspensory ligament scleral cartilage ganglion cells gt bipolar cells visual cells pigment epithelium nerve fibers dermal layer scleral layer ll lens b l choroid body subscleral v 39 I faloiform process ligament ascular choroidal vitreous chamber tissue Diagram of vertical section of teleost eye not drawn to scale showing the relationships of its parts Between the retina and the scleroid coat sclera is a highly vascularized choroid layer which functions primarily to nourish the retina but also serves to absorb stray light or in some species to re ect light back through the retina A choroid body or quotglandquot actually a rete mirabile is prominent in the choroid layer of many teleosts as well as the bow n its structure and function is similar to that of the gas gland of the teleost swimbladder serving to provide a high partial pressure of oxygen to the retina Fishes have no eyelids and thus cannot close their eyes except for the nictitating membranes of certain sharks A few elasmobranchs can control the opening of the pupil by means of muscles associated with the iris but most shes lack this control or have it only poorly developed The retina consists of an outer pigmented epithelium the visual cells rods and cones a layer of bipolar cells and closest to the posterior chamber the ganglion cells and the nerve fibers leading to the optic nerve 2 IMAGE FORMATION AND ACCOMMODATION Fishes live in a medium that has greatly different optical properties than that of air Depending on the angle of incidence of light a calm water surface can re ect up to 80 of the light striking it If the water is rough there is great variation in the transmission of light regardless of the angle of incidence The refraction or bending of light rays entering water is such that a sh in water with a perfectly smooth surface Views objects above the water through a circle subtended by a 9720 cone above each eye Diagram showing refraction of light entering water with a perfectly flat surface XY Because of the bending of the light rays the fish s eye E does not receive light striking the surface above the shaded area The bird at C directly above E is seen in its actual position The insect at B is perceived as if at B and the angles EDF and EGH cause the plant to be seen as if the top were at F and the bottom at H39 Nearly all objects from horizon to horizon appear in the circle which is surrounded by the re ective undersurface seen beyond the limits of the cone In rough water the circular window in the surface is broken up and light is transmitted through everchanging patterns Vision of underwater objects is a different story In most shes the maximum eld of view is achieved by placement of the lens so that it bulges through the opening of the pupil and nearly touches the cornea The lens can thus gather light practically from an entire hemisphere The index of refraction of the cornea is about the same as that of water 133 thus it does not bend light Refraction and image formation therefore depend almost entirely on the lens The lens is spherical with a very high index of refraction about 167 In contrast to tetrapod eyes in which accommodation for near and far vision is accomplished by changes in the shape of the lens the eyes of shes accommodate by slight anterior and posterior movements of the lens that change the distance between the lens and the retina The process by which the distance between lens and retina is modi ed differs among the major groups of shes Lampreys have a unique corneal muscle that inserts on the outer transparent covering of the eye When it contracts the cornea is attened pushing the lens inward closer to the retina and bringing more distant objects into focus Lampreys are thus thought of as being myopic or nearsighted In elasmobranchs there are smooth muscle bers protractor muscles located in the anterior part of the choroid layer that pull the lens outward away from the retina and closer to the cornea thus accommodation serves to bring near objects into focus Elasmobranchs are thus thought of as being hyperopic or farsighted In teleosts while the shape of the lens is spherical or nearly so the shape of the posterior chamber is such that the retina takes on an ellipsoid The effect achieved is that relatively distant objects lateral to the sh are in focus but close objects are not Anteriorly near objects in the binocular eld are in better focus than more distant obj ects A Diagram of eyeball shape and placement of lens in relation to retina in many teleosts Close objects in the an terior field can be in sharp focus whereas the lateral field is adapted to more distant vision 8 Diagram of elliptical eye shape Girellidae that allows for a large anterior field of vision by a laterally placed eye Di rectly in front of the eye is a groove that facilitates forward vision In teleosts accommodation to distant vision in the anterior eld is accomplished by moving the lens backward by means of a retractor muscle retractor lentis Teleosts are thus thought of as being hyperopic or farsighted being myopic or nearsighted anterior lt gt posteriot I xs B Fig 2 A Diagrammatic horizontal section of the left eye in relation to the longitudinal axis of the sh s body lt gt Position of the lens at rest solid line and in full accommodation broken line B Diagrammatic39 representation of the horizontal visual eld of a sh eyes unaccommodated showing the area in focus diagonal lines The triangular open area in front of the sh lies beyond the fa point the circular open area to the sides is within the locus of the near point interrupted posteriorly by the shadow of the sh s body The ability to accommodate for near and far vision varies considerably among teleosts in general most marine teleosts have well developed lens muscles and accommodate very well most freshwater species have less welldeveloped muscles and only moderate powers of accommodation 3 LIGHT AND DARK ADAPTATIONS Regulation of light as it enters or after it enters the eye and adaptation to light or dark are accomplished in a number of ways 1 One means of regulating light that enter the eye is to swim to or away from the source of illumination 2 Some shes have pigment in the cornea or lens that acts as a lter to eliminate certain wavelengths 3 Most elasmobranchs and a few teleosts have contractile irises that control the amount of light entering the eye 4 Most rays many at shes stargazers family Uranoscopidae and some cat shes have a pupillary operculum that can expand and cut off most of the light reaching the pupil 5 Some sharks have nictitating membranes that can be drawn across the eye to reduce excessive illumination 6 Light and dark adaptation in teleosts is largely accomplished by movements of pigment and visual cells rods and cones LIGHT AND DARK ADAPTATION IN TELEOSTS ldirection of light Tquot 73 Tintema limiting 39 39 39 membrane a external limiting membrane rods darkadapted lightadapted Diagram illustrating movement of rods cones and pigment in the retina of teleosts In light adaptation right the rods are moved away from the light and are protected by forward movement of pigment Pigment cells in the outer layer of the retina contain processes through which melanin can move to or from the outer parts of the visual cells Under bright illumination the eye adapts by movement of melanin toward the Visual cells and by movement of the outer segments of the rods into the pigmented area where they are shielded from the light In dim light the pigment is drawn back and the contractile part of the rods pulls them away exposing them to the light Movement of the cones is opposite that of the rods but the cones are not usually hidden by the pigment The time required for the shifting of pigment and visual cells in teleosts is cpnsiderable generally about 30 minutes for light adaptation and an hour or more for dark adaptation 4 VISUAL PIGMENTS AND COLOR VISION The distribution of solar radiation that strikes the earth is relatively homogeneous While the atmosphere does absorb light at the high and low ends of the Visual spectrum its effect is much less signi cant than that of water RADIATION SPECTRUM OF THE SUN quotax WAVE LENGTH IN XNGSTROM UNITS APPROX GAMMA ULTRA RADIO RADAR I RAYS x RAYSIVIOLEE 39NFRA RED I TELEVISION LEss THANl I Ioo I00 3000 9ooo 5000000 MORE THAN 5000000 9 quot MORE ENERGY LESS ENERGY 3000E4000 5000 ZGOOOE7000E8000 LIGHT VISIBLE TO MAN VIOLET BLUE GREEN YELLOW ORANGE RED Wavelength Relative spectral distribution of solar energy in di erent types of sea water Ordinate in relative energy units expressed as percentage of the maximum energy incident at earth s surface Water in contrast to air absorbs light rapidly and differentially with colors at the long or red end of the visual spectrum attenuating rapidly and those at the short or blue end penetrating to relatively great depths Thus unlike terrestrial animals shes live in a Wide range of Visual environments varying particularly in spectral quality and turbidity E E1 000 quot21 03 ES GO 50 a n a P 5 E E as a E 54 T 7 391 2 go as E w 9 8 S 2 S c 939 ca m 8 I in m m as m H quot 60 a g 0 1 g 4 13 g a S I V o 2 o a 39U a 3 m a n a 3 gt m as c quoti 2 E u e E 2 t 5 E gtlt 2 gt E 2 g gtE E g u H an 5 w gt 2 g 4 O U U Transmission of VlSlble I light In the ocean I Depth m 100 250 TRANSMISSION OF VISIBLE LIGHT IN THE OCEAN Pigments called visual pigments or retinenes associated With the photoreceptor cells ie rods and cones are responsible for absorbing light different pigments absorb different wavelengths of light the distribution of pigments present in the retina of a sh determines its sensitivity to various colors 10 5 5 08 3 an 3 06W hum Q 2 E 04 D o 02 Green Yellow Red 400 560 660 760 Wavelength mp l i 7 39 l l 5 l l t l I00 ibo 39 39 39 39 l 39 per per cent Scomber b I 50 so 2 x39 39quotl3 39 I 39 u 49l l I l I l I O o u U I l I l I I I I l J I I I l I 400 500 600 mp 400 500 600 my WOVEIWQ39h Wavelength Visual sensitivity curves for the normal human eye upper an intertidal marine fish Paralabrax clathratus lower left and a marine epipelagic species Scomberjaponicus lower right Many studies have attempted to relate the visual pigments of different species of shes to the visual tasks they face in their particular environments While these studies have revealed an enormous amount of complexity and variation even in some cases within individuals of the same species some general rules appear to hold 1 Deepsea species have rod pigments that absorb maximally at relatively short wavelengths roughly 470 to 490 nm compared with shallowwater and freshwater species This is correlated with the predominantly short wavelengths of light that penetrate into their environment In most cases all the receptors have the same visual pigment but in a few species two pigments are present segregated into separate rods These paired pigment species are usually dark in color as opposed to silvery and often have specialized bioluminescent organs emitting light of relatively long wavelength and it has been suggested that the presence of two pigments is related to these factors Marine fishes living at intermediate depths in coastal waters usually have two cone pigments apart from the rod pigments that absorb maximally at around 460 and 540 nm respectively Freshwater fishes living near or on the bottom particularly if they are crepuscular or nocturnal also often have two cone pigments absorbing maximally at around 530 and 620 nm In both cases the long wavelength cones match the spectral quality of the light fairly well Freshwater fishes living in shallow waters have three cone pigments two of them similar to those of the deeperliving forms but with a blue sensitive cone in addition absorbing maximally at around 430 nm The presence of three as opposed to two cone types covering a wider range of the spectrum presumably correlates with the wider spectrum of light available to them Fishes inhabiting very shallow fresh waters or marine tide pools also usually have three cone pigments but compared with group 4 above the quotgreenquot and quotredquot cone pigments are shifted towards short wavelengths and are comparable in their spectral positions to the cones of terrestrial animals The light environment in very shallow water is of course similar to that of terrestrial animals since the ltering effect of the water will be small A number of species have cones sensitive in the ultraviolet range with an absorption maximum that lies around 355 360 nm Ultraviolet light is heavily absorbed by water present at any intensity only in the surface layers and in some species ultraviolet sensitivity correlates with living near the surface It is not known what use sh make of their ultraviolet sensitivity BIOLOGY OF FISHES FISH 311 BIODIVERSITY ADAPTATIONS OF DEEPSEA FISHES THE 1934 NATIONAL GEOGRAPHIC DEEPSEA EXPEDITION OF WILLIAM BEEBE General topics 1 2 3 Classi cation of the marine environment Vertical distribution of oceanic shes Vertical distribution of oceanic shes in relation to physical parameters Organ systems of deep sea shes Communication among deepsea shes The 1934 Deepsea Expedition of William Beebe 1 CLASSIFICATION OF THE MARINE ENVIRONMENT We can conveniently divide the oceans into two basic units the water itself is the pelagic environment the ocean bottom constitutes the benthic environment The pelagic environment is further divided into two zones Neritic Zone extending from the intertidal region seaward including all water overlying the ocean bottom less than 200 m in depth which corresponds on average to the margin of the continental shelf Oceanic Zone including all water overlying the ocean bottom beyond the margin of the continental shelf n 539 Hulk Oceanic H E i 5121 ic Eu hotic 1 13 quot Equotg p T 200m Low tide Inner Outer 39 d 3 393 f M sob aglcgiplsp39hoti 1000m Z athyp lagic 39Aphotic Supralittoral Abyssopelagic 6000m Littoral Abyssal Had I on iiiiiii m n ppsea mmquot um su 339 Benthic The Oceanic Zone including water having a great range in depth from the surface to the bottom of the deepest ocean trenches is further subdivided on the basis of depth to include 1 Epipelagic Zone from the surface to 200 m a depth that corresponds on average to the margin of the continental slope which is approximately equivalent to the lower limit of photosynthesis often called the Euphotic Zone Mesopelagic Zone from 200 to 1000 m the greater depth corresponding to the limit of penetration of solar radiation often called the twilight zone or Disphotic Zone Bathypelagic Zone from 1000 to 4000 m below the extent of solar radiation often called the Aphotic Zone Abyssopelagic Zone all the deepest parts of the ocean below 4000 m 2 VERTICAL DISTRIBUTION OF OCEANIC FISHES Epipelagic Zone provides habitat for approximately 250 resident sh species including many large predaceous forms like the tunas and mackerals dolphin shes bill shes and pelagic oceanic sharks It also serves as a nursery ground for tons of eggs and larvae of deeper living forms FAMILIES AND REPRESENTATIVE SPECIES PRESENT IN THE EPIPELAGIC ZONE Family Species Remarks Lamnidae Cetorhinidae Alopiidae Rhiniodontidae Carcharinidae Clupeidae Eng raulidae Salmonidae Myctophidae Exocoetidae Scomberesocidae Lamprididae Echeneidae Carangidae Coryphaenidae Bramidae Gempylidae Scombridae Xiphiidae Luvaridae lstiophoridae Stromateidae Centrolophinae Nomeinae Tetragonurinae Molidae White shark Carcharodon carcharias Salmon shark Lamna ditropis Basking shark Cetorhinus maxmus Thresher shark Alopias vupinus Whale shark Rhiniodon Rhincodon typus Tiger shark Gaeocerdo cuvier Herring Clupea harengus Sardine Sardinops sagax Anchovy Engrauis encrasicous Northern anchovy E mordax Atlantic salmon Salmo salar Chinook salmon Oncorhynchus tshawytscha Numerous species of lanterntishes migrate into epipelagic at night from below Oceanic flyingfish Exocoelus obtusirostris California tlylngfish Cypseurus californicus Pacific saury Coloabis saira Atlantic saury Scomberesox saurus Opah Lampris regius Remora Remora remora Pilot sh Naucrates ductor Scad Trachurus trachurus Dolphin Coryphaenus hippurus Bigscale pomfret Taractes Iongipinnis Escolar Lepidocybium flavobrunneum Frigate mackerel Auxis thazard Albacore Thunnus alalunga Swordfish Xiphias gladius Louvar Luvarus imperials White marlin Tetrapturus albidus Medusa sh Icichthys Iockingtoni Silver drifttish Psenes maculatus Bigeye squaretail Tetragonurus atanticus Ocean sunfish Moa moa Slender mola Ranzana laevis Holopelagic neritic Holopelagic Holopelagic neritic Holopelagic neritic Meropelagic Holopelagic neritic Meropelagic Holopelagic neritic Holoepipelagic neritic Holoepipelagic neritic Meropelagic Meropelagic Holopelagic Holopelagic neritic Holopelagic Holopelagic Holopelagic Holopelagic Holopelagic Holopelagic neritic Holopelagic neritic Holopelagic Holopelagic Holopelagic neritic Holopelagic neritic Holopelagic Holopelagic Holopelagic Holopelagic Holopelagic Holopelagic Holopelagic Holopelagic Mesopelagic Zone supports approximately 850 species of mostly silvery forms with large eyes nearly all of which are bioluminescent FAMILIES AND REPRESENTATIVE SPECIES PRESENT IN THE MESOPELAGIC ZONE Family Species Remarks Squalidae Alepocephalidae Argentinidae Bathylagidae Opisthoproctidae Gonostomatidae Stemoptychidae Melanostomiatidae Chauliodontidae Stomiatidae Idiacanthidae Chlorophthalmidae Paralepididae Alepisauridae Anotopteridae Myctophidae Scopelarchidae Synaphobranchidae Nemichthyidae Bregmacerotidae Trachipteridae Gempylidae Etmopterus hiIianus Isstius brasiliensis Slickhead Alepocephaus bairdi Pacific argentine Argentina siais California smoothtongue Bathylagus stibius Barreleye Macropinna microstoma Lightfish Gonostoma Anglemouth Cyclothone microdon Interzonal shallow Interzonal deep Hatchetfish Argyropeecus olfersi Interzonal Longfin dragonfish Tactostoma macropus Interzonal Pacific viperfish Chauiodus macouni Boafish lchthyococcus ovatus Stalkeyed fish Idiacanthus fasciaa Shortnose greeneye Chlorophthalmus agassizi Paralepis atlanficus Interzonal Longnose lancetfish Alepisaurus ferox Interzonal Daggertooth Anotopterus pharao Interzonal Lanternfish Myctophum punctatum Interzonal Northern lampfish Stenobrachius Ieucopsaurus Interzonal Numerous additional genera and species Northern pearleye Benthalbela dentata Atlantic deepsea eel Synaphobranchus infernalis Slender snipe eel Nemichthys scoopaceus Antenna codlet Bregmaceros atantcus Dealfish Trachipferus arcticus Oilfish Ruvettus pretiosus Bathypelagic Zone contains about 280 species of mostly black fishes with small or degenerate eyes poorly developed musculature and weakly ossified skeletons REPRESENTATIVE FAMILIES AND SPECIES IN PELAGIC ZONES BELOW 1000 METERS Family Species Bathylagidae Gonostomatidae Malacosteidae ldiacanthidae Evermannellidae Paralepididae Giganturidae Saccopharyngidae Eurypharyngidae Nemichthyidae Chiasmodontidae Caulophrynidae Ceratiidae Blacksmelt Bathylagus euryops Veiled anglemouth Cyclothone microdon Loosejaw Malacosteus niger Stalkeyed fish Idiacanthus fasciaa Evermannela atrata Slender barracudina Lestidium ringens Gianttall Gigantura vorax Gulper Saccopharynx ampullaceus Gulper Eurypharynx pelecanoides Snipe eel Nemichthys scoopaceus Great swallower Chiasmodon niger Seadevil Caulophryne poynema Warted seadevil Cryptopsaras couesi Abyssopelagic Zone provides habitat for approximately 1350 species including hag shes certain squaloid sharks deepsea skates some chimaeras deepsea cods Moridae eelpouts Zoarcidae snail shes Cyclopteridae brotulas Ophidiidae and Brotulidae rattails Macrouridae deepsea eels Halosauridae and Notacanthidae etc 3 VERTICAL DISTRIBUTION OF OCEANIC FISHES IN RELATION TO PHYSICAL PARAMETERS It39s well known that certain environmental parameters change with increasing depth We all know what these parameters are but their effects on organisms occupying these environments are not well understood What are the parameters 1 Rapid reduction in the amount of solar radiation even in the clearest waters photosynthesis generally does not occur below 200 m all solar energy disappears at depths of about 1000 m 2 Decrease in primary organic production the biomass of plankton on the surface is generally 10 to 100 times greater than at levels below 1000 meters 3 Decrease in temperature ambient temperature at depth range from 1 30C 10C in polar regions 4 Increase in pressure an atmosphere for every 10 meters ZONES DVM BIOMASS LIGHT TEMPERATURE 5 1039 15 20 C 1 v EEFEELAGCiiwi1 quot 39 39 n MESOPELAGIC f f l Permanent Thermocllne f 1000 l BATHYPELAGIC DEPTH 2000 2000 In metres i L 3000 5 3000 l Connnd V V emal COntlnental P Shequot Slope Commenta 56 L 4000 4000 ABYssAL LAiN39 2 BENTHIC The lack of sunlight and consequent loss of primary organic production must lead to a restriction of the food supply and a consequent reduction in the total vertebrate biomass that can be supported Fish biomass may be reduced in a number of ways 1 Decrease the size of individuals 2 Decrease the size of populations Both of these approaches are common in the deep sea deepsea fish populations are known to be sparse compared to those living in upper layers and individuals are for the most part small Another possible adaptation to the restricted deepwater food supply is a reduction in the energy requirements of the shes themselves All indications show that such reduction has occurred but the extent to which it has occurred is unknown for a number of reasons determinations of metabolic rates of deepsea shes are almost nonexistent and very little is known about age structure growth rates and mortality 4 ORGAN SYSTEMS OF DEEPSEA FISHES Most deepsea shes are thought to be less active than surface forms and in general have poorly ossified skeletons soft degenerate muscles and reduced organ systems Reduction is clearly re ected in many sensory systems as well as the central nervous system The only element of these systems that is not markedly reduced in bathypelagic forms is the lateralline or acoustico lateralis complex The cerebellum which is a particularly good indicator of the overall elaboration of shes is poorly developed in bathypelagic forms reduced in size The steady increase of pressure with depth 1 atmosphere for every 10 meters is less a strain on shes than has often been supposed In the deepsea the swimbladder functions just as well as a hydrostatic organ as it does in coastal seas It is present in 75 or more of the individuals and in about half of the species of mesopelagic fishes A welldeveloped swimbladder is also present in those shes closely associated with but not strictly living on the bottom forms called benthopelagic fishes Bathypelagic and truly benthic deep sea shes have no swimbladder This is understandable in benthic forms that spend their entire lives resting on the deepsea oor Like benthic forms in coastal waters deepsea bottom shes have no need for a hydrostatic organ The loss or regression of the swimbladder in bathypelagic shes many of which live at considerably lesser depths than some benthic forms is apparently a result of their foodpoor environments Swimbladders are metabolically expensive to operate and in the deepsea economy in all things is the name of the game So by reducing nearly all organ systems particularly muscles and skeleton bathypelagic shes have not only gotten rid of structures that are energetically expensive to build and to maintain but also achieve neutral buoyancy by lightening the load all this without the use of a swimbladder 5 COMMUNICATION IN DEEPSEA FISHES How are populations maintained in the deepsea How do individuals nd each other in this vast dark environment Coherence of any population is due at least in part to communication between its members How do deepsea shes communicate COMMUNICATION IN THE MESOPELAGIC ZONE In the mesopelagic or twilight zone communication is predominantly through the use of a remarkable diversity of lightorgan systems 95 of all mesopelagic shes have bioluminescent organs photophores of some kind They also have large sensitive eyes In fact many forms have independently evolved large tubular eyes set close together in parallel to provide wideangle binocular vision either in an upward or forward direction These eyes are not only more sensitive but provide better means of judging the position of nearby organisms How do these light organs or photophores function What selective advantage do they provide Numerous functions have been attributed to photophores In most species it is highly probable that luminous tissues or organs are multifunctional Intraspecific functions interactions between members of the same species 1 To attract potential mates 2 To select conspeci c mates photophores and photophore patterns are often species speci c 3 To aid in forming shoals aggregations or schools 4 Use in courtship displays 5 To space individuals evenly to avoid competition for food or other resources not possible to establish territories in midwater where there are no xed reference points Interspeci c functions interactions between members of different species 1 Food acquisition to lure prey illuminate prey or illuminate retina to adapt the eye so it will not be blinded by bright ashes emitted by other luminous organisms 2 Predator avoidance to startle or confuse predators to mislead predators through mimicry eg pelvic structures of Kasidoron simulating a coelenterate with nematocysts Kasidoron edom holotype 212 mm in standard length In swimming position with left pelvic tree in arrange ment as seen in movie sequences right pelvic tree reconstructed to match Smaller drawing about natural size with pelvxc apparatus reconstructed but with some sacs and entire apparatus of right side omitted for clarity So bioluminescent structures are multifunctional there are probably many uses not yet discovered or thought of They seem to be the most important way for shes to communicate in the mesopelagic zone COMMUNICATION IN THE BATHYPELAGIC ZONE In deeper strata below 1000 meters biomass drops considerably Biomass per cubic meter falls to well below a tenth of the amount that exists in the mesopelagic Fishes are less diverse the bathypelagic supports only about 280 species of shes about 30 of those found in the mesopelagic The diversity of shes with light organs drops considerably so that the only light is from the lures of deepsea anglerfishes In response to this almost total lack of light eyes degenerate and in some forms become covered over with skin Light in the bathypelagic zone is not nearly so important as it is in the mesopelagic zone Eyes are expensive to build to maintain and to operate they become a great metabolic burden to a sh trying to cope in the food poor bathypelagic zone Olfactory organs and brain of Cyclothone microdon From top to bottom female male head of male cc corpus cerebelli eg eminentia granularis d diencephalon fb forebrain 0b olfactory bulb 00 olfactory organ or optic tectum Fishes in these deeper waters most likely communicate much less than mesopelagic species Individuals are farther apart very few forms are gregarious few aggregations or schools are formed There is little need to warn fellow members of your species that predators are near Each individual is more or less on its own The problems of communication involve mostly getting members of the opposite sex together In this olfaction seems to have developed as a mechanism for males to locate females Nearly all males of bathypelagic shes more than 80 of the species are macrosmatic that is they have greatly enlarged olfactory organs On the other hand these organs are small or regressed in females of all species we call these forms microsmatic This is a unique example of sexual dimorphism not found in mesopelagic shes Males tend also to be smaller than conspeci c females a dwarfism that reaches the ultimate in ceratioid angler shes in which the male is only a small fraction of the size of the female The smaller macrosmatic males are assumed to be attracted to chemical communicants or phermones produced by their much larger partners each smell being biochemically unique for each species In the bathypelagic zone males may be aided in this tracking down of females by smell by a number of factors 1 Mature males may be considerably more numerous than ripe females 2 Low levels of turbulence at great depths 3 Restricted activities of females Females of bathypelagic species although lacking welldeveloped eyes and olfactory organs have an extremely well developed acousticolateralis system with which they essentially feel their environment 10 COMMUNICATION IN BENTHOPELAGIC SPECIES Moving down into still deeper waters and approaching life near the deepsea oor we nd benthopelagic species that have retained a welldeveloped swimbladder These forms root around in the oozes which they take into their mouths and strain through their gillrakers retaining small oozedwelling worms bivalves and other small animals The swimbladder of many of these shes is not simply a hydrostatic organ Nearly all macrourids and brotulids which make up well over half the benthopelagic fauna have drumming or sonic muscles on the swimbladder In some cases these drumming muscles are found only in the males It seems that the deepsea oor is a very noisy place and that sound plays an extremely important role in communication particularly during the breeding season In contrast to the mesopelagic zone there is no great profusion of light organs On the other hand the swimbladders of mesopelagic forms are not equipped with drumming muscles making it unlikely that sound is important in these upper layers The absence of swimbladders and drumming muscles in bathypelagic shes also suggests that this deeper layer is a silent region In summary 1 At mesopelagic depths a vast array of lightorgans are used by shes that have well developed eyes Bioluminescence is thus the most important means of communication at these levels 2 In the bathypelagic zone reproductive activities are related to differences in olfactory structures with the laying of scent trails by females being the most ef cient means by which males and females get together in pitchblack slowly moving waters 3 Near the bottom of the deep ocean the dominant shes have evolved sonic mechanisms in some way associated with reproductive activities 6 VOL LXVI No 6 WASHINGTON THE 1934 DEEPSEA EXPEDITION OF WILLIAM BEEBE DECEMBER 1934 narllbiNAst GE GRAPHU MAGAZHNE COPYRIGHT 1934 BY NATIONAL GEOGRAPHIC SOCIETY WASHINGTON D 0 INTERNATIONAL COP FIGHT SECURED A HALF MILE DOWN Strange Creatures Beautiful and Grotesque as F igments of Fancy Reveal Themselves at Windows of the Bathysphere BY WILLIAM BEEBE The deepsea investigations of Dr William Beebe oceanographic naturalist during the season of 1934 nanced and sponsored by the members of the National Geographic Society are described by the leader of the expedition who this year successfully established a new depth record of 3028 feet in Bermuda waters HE Bathysphere lived throughout I the spring summer and autumn of 1933 quietly in the Hall of Science of A Century of Progress Exposition at Chi cago In this time half a million people thrust their heads within the narrow door way and murmured Thank Heaven we don t have to go under water in this Being only an inanimate mass of quartz and steel she would remain the static creator of vicarious thrills until the Hall of Science passed avVay unless some activity more potent than slow corrosion and rust was brought to bear THE CALL TO ACTION COMES The summons came at the end of her year when her paint was still undimmed her quartz eyes steadily watching it came to me in a letter saying that the National Geographic Society would be glad to spon sor a new dive Four years ago Mr Otis Barton and I had reached and returned from a depth of a quarter of a mile and later we had made a still deeper dive However knowing that See A Round Trip to Davy Jones s Lockerquot by William Beebe in the NATIONAL GEOGRAPHIC MAGAZINE for June 1931 my interest in the work lay only in scienti c observations the National Geographic So ciety made no stipulation of a record Friendly arrangements were speedily effected between the National Geographic and New York Zoblogical Societies and early in March the new expedition was well under way the twentieth of my Department of Tropical Research and the sixth year of oceanographic work off Bermuda The large blue sphere was roused from her long reverie one day and hoisted upon a freight car The next time I saw her she was squatting disconsolately amid an enor mous jumble of intricate machinery whirl ing belts and ying sparks in a factory at Roselle New Jersey She had returned to the place of her birth for a thorough over hauling As the Bathysphere rested on her present bed of steel lings she seemed as staunch and sturdy as ever I would willingly have scrambled inside and trusted her to carry me down and back safely to any depth I chose but the doctors of mechanics gath ered in consultation were more skeptical and they began to assemble what in hu man hospitals would be stethoscopes and sphygmometers BIOLOGY OF FISHES FISH 311 BIODIVERSITY II PRIMITIVE BONY FISHES AND THE RISE OF MODERN TELEOSTS General topics 1 2 3 Actinopterygians What are they The bichirs and reed sh The sturgeons and paddle shes The gars The bow n The rise of teleosts The success of teleosts 1 ACTINOPTERYGIANS WHAT ARE THEY Actinopterygians are the socalled bony or rayfinned shes They are called quotbonyquot because of all the major groups of living shes they are for the most part the only taxon that has retained the ability to ossify the skeleton There are however a number of actinopterygians that don39t quite t this de nition for example sturgeons and paddle shes have a largely cartilaginous skeleton They are called quotrayfinnedquot because their ns are fully rayed from the base eg the extinct sturgeonlike genus Palaeom39scus pictured below as opposed to the lobed ns of sarcopterygian shes eg Latimeria also illustrated below Again this de nition is problematical because bichirs family Polypteridae usually but not always placed with the Actinopterygii have their pectoral ns mounted on lobes n 3 k s i gg x w m b 394 2e v 4 Q 39 F hquot s 2155 Latmaria Part of the problem is that these common names quotbonyquot and quotrayfinnedquot were coined more than a century ago when we knew much less about these animals particularly about their internal structure and evolutionary relationships The group contains ve primary taxa that together encompass about 96 of all living shes In addition to presentday species the Actinopterygii includes a Whole host of fossil forms a rich fossil history that is so diverse and complex that paleontologists have had great dif culty making sense of all of it see page 4 The museums of the world are lled with fossils not only those of actinopterygians that don39t quite t some that don39t t at all So it39s important to realize how much of our evolutionary history is unknown ACTINOPTERYGIAN EVOLUTION 9 95 e g e 0 Rep 95 165 g f 256 60 a equot e0 0 0 o 99 97gt 5 Qco 99 7gt q o QC 1 7 39 9 95 eg 0 dogs 5 lt9 3 equot e9 9quot S 0 0 9Q 130 MYBP 225 MYBP 375 MYBP 390 MYBP group the teleosm whose mayor radiation occurred in the late Cretaceous and early Cenozoic and the neopterygians which are rst known in the Upper Permian Most living bony sh belong to a single neopterygian PALEOZOIC MESOZOIC CENOZOIC Silurian lt3 1 co Devonian h I I w N N gt0 Permian g TriaSSIc I MISSIS Wl ennsylvquot c vanian n I 3 sippian Ch 11 Tertiary Isolated Races be divided into two major groups the chondrosteans which were dominant in the Paleozoic and have a few living descendants have become progressively more diverse Today THE PHYLOGENY OF THE ACTINOPTERYGII Ray nned sh are rare until the end of the Devonian but they include more species than any other group of vertebrates They may 7quot Prycholepiformes Dorypterld Saurichrhyiformes zi I I Palaeoniscoidea Platysomoidci ph lchlhynd l a I PholldOpleunforme a Luganonformes CHONDROSTEANS u Perleidiformes Redfieldiformes x x 7 z I Peltopleunformcs Semionotida 39 NEOI FERYGIANS TELEOSTS 06 l l y A IE jurassuc I Cretaceous l Semionotiformes Macrosemiiformes Pachycormiformes Aspidorhynchiformes Polypteriformes quot Acipenseriformes Lepisosteiformes Pycnodontiformes Amiiformes Percomorpha Because of this complexity it39s been extremely dif cult for ichthyologists to de ne precisely What we mean by actinopterygianwwhat are the limits of the Actinopterygii There are a number of characters that help but the best seems to be the unique structure of the ganoid scale Primitively all actinopterygians share a threelayered scale that consists of an outer lamellar layer of an enamellike substance called ganoine a central layer of dentine lled with vascular canals and a deep or innermost layer of spongy bone Typically these scales are rhomboid in shape and arranged in sloping diagonal rows along the body dentine layer LJ 01mm w oggc mt 31 6 2quot 4quot0 as 12quotquot w h i w v4ll aeavaquotuquottquotp ewo39i39 quot39 amp I 3 mmW I I I IIII 10mm Aeduella blaz39nvillei Restoration in lateral View These ganoid scales are found in all the primitive members of the group ie covering the body of bichirs and the reed sh forming the rows of scutes on the body of sturgeons represented by a small patch of scales on the caudal peduncle of paddle shes and covering the body of gars However the scales of the bow n and of all living teleosts are clearly derived consisting of only a single layer of bone scales that are called leptoid 2 THE BICHIRS AND REEDFISH The bichirs and reedfish together represent a small living remnant of an ancient lineage that dates back to about 390 MYBP never a large group but remarkably success ll if for nothing else than its ability to compete and survive to the present day in the face of rapidly proliferating groups of more derived shes In addition to an extensive fossil record we have 16 living species in two genera united Within a single family the Polypteridae all con ned to tropical freshwaters of Africa All members of the group have lungs and breathe atmospheric oxygen thus allowing them to inhabit water of very low oxygen levels The dorsal n is strange completely unlike that of any other group in that it is composed of a number 518 of small nlets each containing one stiff ray and one or more soft secondary rays plus a membrane behind Also strange are the pectoral ns that are born on lobes reminiscent of Latimeria and the lungfishes these supporting structures however differ so much from those of sarcopterygian shes that most believe they evolved separately Fifteen species of bichirs genus Polypterus are found in slowly owing streams and still waters throughout tropical Africa Small pelvic ns are present A not so peaceful aquaria sh down right quarrelsome according to some authorities The largest of the 15 species the Nile bichir Polypterus bichir grows to a length of about 70 cm or 28 inches A l i I eavwg gs m 9 O 6 mg asquot V ag was 3 ovo ovo ooM39o orr39 The reed sh or rope sh Calamoichthys calabaricus is restricted to slowly owing streams and still waters of West Africa primarily the Niger Delta in Nigeria and the Cameroons The body is eellike cylindrical not depressed pelvic ns are absent A hardy and peaceful aquaria sh Reaches a length of about 90 cm or 3 feet weein hE rE iss mwxm 4 quot L5 7 I r v e ainius Wagages 39 Kieaifi wzewzr g 39 k wax u su m 931 E is gk 230quot fo 394 2 39 J 1 kaj f AKA quot S39aquot 1 v z n A JRA r 1393 w a quot s 5 rawi r 39 A further curiosity is the strange larvae of the bichirs which have large feathery external gills that give it a rather amphibianlike appearance Anterior portion of Polypterus showing external gills of larva The evolutionary position of the polypterids has been somewhat controversial There are two schools of thought 1 Some argue that they are most closely related to the lungfishes Within the Sarcopterygii The evidence usually cited for this are the lobed pectoral ns of polypterids 2 Others by far most contend that they are actinopterygians citing among other characters the welldeveloped ganoid scales which are like those of other actinopterygians and quite different from the cosmoid scales of sarcopterygians They argue at the same time that the lobed pectoral tins of polypterids are essentially different from those of sarcopterygians and any similarity is due to convergent evolution rather than common descent OK so we39ll go along with the majority and conclude that the bichirs and the reed sh are actinopterygians and further that they represent the most primitive members of the group ie they are the sister group of all other actinopterygians 3 STURGEONS AND PADDLEFISHES This next group collectively known as the Chondrostei is also made up of small remnants the sturgeons and paddle shes of a once large highly diverse group The fossil record is complex providing evidence of the former existence of no less than 13 orders the earliest of which order Palaeonisciformes dates back at least to early Devonian approximately 390 MYBP A 14th order called the Acipenseriformes contains all the surviving members of this once large assemblage only 27 species in six genera and two families Characteristics include a largely cartilaginous internal skeleton absence of vertebral centra and a shark like heterocercal tail The sturgeons family Acipenseridae four genera and 25 species anadromous and freshwater found throughout the Northern Hemisphere Beluga Huso huso These are all characterized by having ve rows of bony scutes on the body an inferior mouth without teeth at least in the adults four barbels in front of the mouth and a large swimbladder Members of the genus Huso Beluga are among the largest if not the largest shes in fresh water de nitely reaching lengths of 5 m or about 16 feet although much greater lengths have been reported eg 9 m and a weight of 1500 kg Large specimens may be 100 years old and carry over 7 million eggs The paddlefishes family Polyodontidae two genera and two species are con ned to freshwater and are found only in China and the Mississippi River Basin Paddlefishes are characterized most strikingly by the paddlelike snout but other important features include a naked body scales are absent except for a few on the caudal peduncle minute barbels on the snout gill rakers extremely long and present in the hundreds in the planktonfeeding Polyodon Their teeth are minute and the gill cover is greatly expanded posteriorly Like their sister group the sturgeons the caudal n is strongly asymmetrical ie heterocercal The American Paddlefish Polyodon spathula is a filterfeeder described by some as a living planktonnet it sweeps through the water with its lower jaw dropped down and the side of the head expanded outward to form a giant funnel Any planktonic organisms such as small crustaceans are swept into the mouth and ltered out by long dense gill rakers It reaches a length of 2 m or about 65 feet In contrast the other living paddle sh Psephurus gladius sometimes called the Chinese Paddlefish and found only in the lower reaches of the Yangtze River is a sh eater It has a long attened bony snout and a mouth that opens to an enormous capacity but its food appears to be smaller fishes It is said to reach a length of 7 m or about 23 feet Although it is commercially exploited and its esh is highly valued as food very little is known about its biology Its present abundance in the Yangtze River is unknown 4 THE GARS The gars or garpikes of cially referred to as the Ginglymodi consist of a single family one living genus and seven species These are heavily armored predaceous shes usually found in shallow weedy areas in freshwater occasionally brackish and very rarely marine habitats Their distribution is primarily eastern North American but they also extend into Central America as far south as Costa Rica One species Lepisosteus tristoechus is found on the island of Cuba The alligator gar Lepisosteus spatula attains a length of 3 m or about 10 feet but the other species grow to less than half this size Lepisosteus Gars are highly modi ed relative to other primitive actinopterygians particularly in the structure of their snout and jaws Both upper and lower jaws are elongate and are armed with several rows of strong sharp teeth they are highly voracious carnivores The dorsal and anal ns are set far back on the body and the caudal n is heterocercal but not so strongly asymmetrical as that of the more primitive actinopterygians eg sturgeons and paddle shes a kind of tail we call abbreviate heterocercal Gars differ from all other living shes except for the blenny genus Andamia but similar to some reptiles in having vertebrae that are convex anteriorly and concave posteriorly a kind of vertebrae called opisthocoelous The vertebrae of all other shes are concave on both ends vertebrae we call amphicoelous The signi cance of this difference in the shape of the vertebrae is unknown gquot 51 Diagrammatic longitudinal sections through vertebrae to show various types of centra Anterior is to the left A Primitive amphicelous type in this case with the centrum pierced by an opening for a continuous notochord B the opisthocelous type C the procelous type D an essentially acelous type but with the centre slightly biconcave to allow room for an intervertebral disc 5 THE BOWFIN The bowfin Amia calva of the family Amiidae is the only living representative of a once widespread and diverse order called the Amiiformes While some of its ancestors were marine the bow n is restricted to freshwater and found only in the eastern United States ranging from the Great Lakes southward throughout the Mississippi River Basin and drainages of the southeast coast Females may reach a length of 1 meter but individuals of about 60 cm are much more common The bow n differs from all more primitive living actinopterygians in having single layered cycloid scales that lack ganoine in this way they are similar to the more derived teleosts but it should be remembered that the scales of extinct amiids had ganoid scales Like the gars their caudal fin is abbreviate heterocercal Thus the gars and the bow n are intermediate between the more primitive actinopterygians and teleosts in tail structure the sturgeons and paddle shes having strongly asymmetrical tails the teleosts characterized by having symmetrical or homocercal tails 6 THE RISE OF TELEOSTS Finally we come to the teleosts this huge diverse assemblage that contains about 95 of all living shes To help understand why teleosts have been so successful it helps to know something about teleost ancestry What kind of a sh gave rise to presentday teleosts What was it about this animal that paved the way for the explosive radiation of forms that was to follow If we look to living shes to nd answers to these questions we don39t get much help Certainly gars are far too specialized to be anything like a teleost ancestor It turns out that even Amia the bowfin is an unlikely candidate We do get some help however when we turn to fossils Among a wide assortment of Amialike fossils there39s one order that stands out as a likely teleost ancestor a group of late Triassic and early Jurassic fossils called Pholidophoriformes u 34 1amp2 2 3 2 2 5 5 1 1 331 5quot quot 39OO con aveaz razki i u ampy oliilcti39l IlllIlll I39ll a 9 g gmlllll l l l 391 Y0 s39393939 c 5395 quotquot 3375 n quota T raj 2 O Q E m wmm a 39 e io a V imx39vmww39gga39n a ugnus u rag a 6363 I I 39 f V Wc 2 r t v 1 quot A All evidence indicates that these are the earliest known teleosts Most members of this group were relatively small fusiform shes but some were as long as 40 cm Many had large teeth which suggest that they had active predaceous life styles The tail was nearly symmetrical in shape The scales of most species retained a thin layer of ganoine So somewhere out of this pholidophoriform assemblage or if not pholidophoriforms something close to them arose all of the teleosts that we know today Early teleosts seem to have been so well adapted for feeding and swimming that they increased in number and variety at an unprecedented rate so quickly in fact that we can hardly follow their evolution Teleosts rst appear as rare forms in middle Triassic deposits about 200 MYBP During the Jurassic and early Cretaceous there occurred a major proliferation of shes so that by the end of the Cretaceous about 70 or 80 MYBP all major groups of teleosts that is families and many modernday genera had evolved Modern times All modernday species 28000 Early Cenozoic 50 MYBP Nearly all modernday genera 4400 Late Cretaceous 70 MYBP All modernday families 515 Middle Cretaceous 100 MYBP Six major orders Late Jurassic 150 MYBP Explosive radiation Late Triassic 200 MYBP First appearance 7 THE SUCCESS OF TELEOSTS Radiations of teleosts during this early period were explosive They far outcompeted other sh groups so that today 95 of all living shes are teleosts The question is why Why should this particular group be able to diversify so extensively while other groups were relatively unsuccessful In answer to this question ichthyologists cite major structural innovations in two character complexes 1 Caudal fin locomotory complex homocercal tails 2 Feeding mechanisms upper jaw mobility Greater upper jaw mobility opened up new trophic possibilities for teleosts allowing for an enormous increase in the evolutionary potential of the mouth parts which in turn allowed for an enormous variety of specialized predaceous and nonpredaceous feeding types The evolution of this new jaw mechanism particularly the protrusible upper jaw of perciform shes prompted highly successful exploitation of food resources that were previously unavailable to Actinopterygian shes But structural changes in the rst of these two character complexes that is the caudal fin locomotory complex are thought by some to have been even more important than changes in feeding mechanisms As we move along through actinopterygian evolution from primitive to derived one of the most striking modi cations is a progressive change in the shape of the caudal n from strongly asymmetrical heterocercal in sturgeons and paddle shes to moderately asymmetrical abbreviate heterocercal in gars and the bow n to more or less symmetrical homocercal in teleosts 2366 Sturgeon Paddlefish Bowfin Teleost Let39s compare the two extremes A heterocercal tail is designed to provide lift something that a thickscaled heavily armored primitive actinopterygian requires to get off the bottom ie to provide at least some pelagic existence The axis of rotation of the tail is oblique thus it pushes down as well as back The result is an upward and forward rotation of the rear end of the sh The somersault effect is counteracted by the large horizontally inserted pectoral ns that serve as planing devices Somersault counteracted by planing pectoral fins Llft provrded by asymmetrical tall gravity With this kind of body plan all movement in the vertical plane must be accomplished by the paired ns primarily the pectorals The position and shape of these ns depends on the shape of the caudal n so this body plan results in rather formidable functional constraints that translate into limited maneuverability a case of a single parameter controlling many other features because of mutual interdependence The homocercal tail of teleosts operates quite differently Its axis of rotation is vertical so that it pushes directly backward the result being that the sh moves directly forward A Purely horizontal thrust provided by symmetrical tail gravity OK what are the advantages to having a homocercal tail There are at least two The rst is greatly increased efficiency in horizontal swimming because the thrust provided by the locomotory organ the tail is purely horizontal Of course it39s important to point out that the acquisition of the homocercal tail appears to have been closely associated with two other changes taking place in actinopterygian evolution 1 The loss of heavy bony armor and heavy scalation no longer requiring a body plan that provides lift 2 Modification of lungs to act as hydrostatic organs ie the evolution of the swimbladder again making a body plan that provides lift obsolete The second is greatly increased versatility the paired ns especially the pectoral ns are now freed from their constraint of serving as planing devices and can now evolve to take on other locomotory functions The result is that pectorals move in an evolutionary sense from a horizontal insertion low on the body to a vertical insertion high on the body Where they can now function to provide greater maneuverability


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