Freshwater Fish Culture
Freshwater Fish Culture BIOL 372
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This 11 page Class Notes was uploaded by Urban Bauch on Tuesday October 13, 2015. The Class Notes belongs to BIOL 372 at Lake Superior State University taught by Geoffrey Steinhart in Fall. Since its upload, it has received 10 views. For similar materials see /class/222330/biol-372-lake-superior-state-university in Biology at Lake Superior State University.
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Date Created: 10/13/15
Fish Health Management for Intensive Fish Farming George W Klontz DVM Professor of Aquaculture Department of Fish and Wildlife Resources University of Idaho Moscow Idaho USA 83843 INTRODUCTION During the past three decades the raising of sh for human consumption has been increasing dramatically especially in the sociologically and industrially developed countries of North America and Europe The increased production has come about largely as a result of consumer awareness that sh and shell sh are nutritionally bene cial to health Unfortunately the production increase in some countries has been so great that the supply of propagated food sh has exceeded the demand in the marketplace Attendant to the increased production of food sh under intensive culture conditions has been the increased loss of production potential through infectious and noninfectious disease processes In many cases the episodes have been so severe that 4555 of the numbers of sh at the beginning of the rearing process have died before they became ready for market Table 1 However the loss of production potential has not been re ected as dead sh only Perhaps the greatest impact has been reduced vitality which has been recorded as reduced growth rate and increased feed conversion The costs incurred from this have been in the opinions of many quite signi cant Table 1 Average loss data in the freshwater food sh industry Food Fish Production Loss Number Green Eggs 1000000 7 Eyed Eggs 930000 5 Hatchout 883500 6 Swimup 848160 1 Growout 839678 25 Processing 629759 5 Distribution 598271 The economics of food sh production have not been documented with precision and perhaps there is no way to do so because of the diversity of the food sh raising community However a generalized picture of the costs incurred in food sh production can be presented Table 2 These data suggest quite convincingly that the greatest portion of the costs in producing a pound of sh under intensive culture systems is feed Thus it would seem quite logical to assume that to pay considerable attention to that component would or could reduce loss of production potential For example weight gain in a group of sh at a feed conversion of 19 kg feed per kg gain is 266 more expensive in terms of feed costs than is the same group of sh at a feed conversion of 15 kg feed per kg gain In this regard it is beyond the comprehension of many that several sh farmers are apparently content with a 191 feed conversion when the commercially available diets all can yield a 131 conversion with very little effort Two of the prime factors in reduced feed conversion are subclinical respiratory gill diseases and asymptomatic infections of bacteria and viruses In this regard perhaps the most signi cant impediment to reducing the mortality rate and to increasing the feed conversion is due to having more concern for disease rather than health The poultry and livestock sheep cattle and swine industries have learned that herd health management through application of the principles of preventive medicine is economically sound In other words these industries start with healthy animals and strive to keep them in that state through monitoring growth rates behavior production milk eggs etc and environmental conditions This could be termed preventive medicine Table 2 An economic overview of the freshwater food sh industry Economics of gross Egg Cost 321 Feed Cost 5705 Labor Cost 1111 Disease Treatment 470 Mortality 641 Overhead 17 52 10000 The foregoing is not a new concept or revelation to the majority of people in the aquaculture community All have attempted at one time or another in some fashion to implement these ideas But the enormity of the task is often mindboggling for an individual person The adopting of the term quotfish healthquot as opposed to quot sh diseasequot in our professional jargon has helped a great deal Then wherein lies the problem I think the problem of our collective inabilities to do much more than quotput out the brush firesquot stems from the absence of a good or adequate base of knowledge of health and its change into subclinical and then clinical disease The term quothealthquot as it applies to an individual or a population of fish either freeliving or con ned should denote that the animal is able to conduct all its physiological activities without impediments Its oxygen demand is met its nutritional energy demand is met its reproductive capacity is realized its behavioral needs are met and so forth ie it is quotnormalquot a term I despise but use too frequently It is my opinion that when any one of the physiological functions of a fish are comprised for whatever reasons extrinsic or intrinsic a state of disease ensues This disease state may be subclinical ie not noticed by the observer or it may be clinical ie quite apparent to the observer In the preceding paragraph I used the terms quotextrinsicquot and quotintrinsicquot These are epidemiological terms to categorize identifiable factors involved in the disease process which originate in the environment ie extrinsic and those which originate within the animal ie intrinsic EXTRINSIC FACTORS AFFECTING FISH HEALTH The extrinsic or environmental factors which are known to compromise the health status of sh individually or collectively can be grouped into the following categories according to their location within the system 1 2 at r 39 J 2 p nd 39 J 3 nutriti n 39 J 4 managementassociated To some this classi cation scheme may seem somewhat simplistic andor conceptual Nonetheless the process of investigating the nature of a disease episode has been enhanced by identifying and quantifying the associated factors The quantitative evaluation of the prime factors has permitted the raising of fish with a minimum of problems l Waterassociated factors Among waterrelated factors identified as affecting the productivity of aquaculture systems water temperature and dissolved oxygen content have the most significant insidious effects on fish health They are inherent in all water supplies and are subject to uctuations to which the fish in the system must adapt The physiological effects of the uctuations are very broad ranging from a change in metabolic rate to altering the susceptibility to pathogens In this regard the documentation of environmental changes and the occurrences of infectious and noninfectious disease processes could be an invaluable aid in predicting the likelihood of a subsequent disease episode Examples of this are legion but not sufficient to be a widespread practice 2 Pondassociated factors The primary effect here is requiring a particular fish to live in a pond configuration which does not meet its behavioral requirements 3 Nutritionassociated factors One would think that in this day and age of high quality commercial diets nutritional problems would not occur but they do all too frequently Our studies over the past 45 years on production forecasting have shown the health of fish can be compromised when the fish are fed at a rate permitting less than 80 of the Allowable Growth Rate We have found growth rate to be a very reliable indicator of the health of the population Deviations of as little as 1 from the expected growth rate can be measured quite accurately and evaluated with a high degree of statistical validity Overfeeding a population is another healthcompromising situation In this case there are frequently abnormal amounts of abdominal fat and hepatic glycogen deposits The effects are not often seen immediately but can be implicated in the milieu of casual factors of an unhealthy state 4 Managementassociated factors The primary healththreatening factors in this category emanate from exceeding one or more of the pond carrying capacities from inadequate housekeeping practices from inadequate recordkeeping practices and from undue physical stressors INTRINSIC FACTORS AFFECTING FISH HEALTH The intrinsic or somatic factors originate within the sh itself They are largely governed by the genetic makeup which by and large dictates the physiological and psychological responses of the sh to the extrinsic factors Perhaps the major intrinsic factor which sh health managers have some control over is the generation of endogenous ammonia NH4 We all know that free ammonia N H3 in the system is deleterious to the health of sh when speci ed limits are exceeded The main impact as we now understand it is on the gill lamellae in the form of epithelial hypertrophy and hyperplasia which reduce the oxygen uptake by the sh thus impacting the physiological wellbeing of the sh The control of this process is to reduce the dietary protein or to decrease the retention time of ammonia in the pond by increasing the water ow or to reduce the population of sh in the pond or to reduce the water temperature or to decrease the pH of the system Any one of the foregoing will serve to preserve the health of sh within limits A second intrinsic factor over which we can exercise some control is the healthy or chronic asymptomatic carrier of infectious agents It is apparent from our studies with Renibacterium salmoninarum and Aeromonas salmonicida carriers that the presence of these bacteria within the sh negatively impact their growth potential and represent a measurable threat to the uninfected portion of the population SUMMARY AND CONCLUSIONS Up to this point this presentation has been rather gloomy in my opinion But we must face reality we could do better with preserving the health of our sh if we only would To that end I would offer the following as food for thought and hope llly subsequent action by both the sh fa1ming community and the sh health management profession collectively 1 Practice preventive medicine through detection and elimination of the carrier states of bacterial and viral pathogens through mass immunization of sh against pathogens through implementation and maintenance of healthpreserving management practices and through implementation and enforcement of live sh transportation regulations 2 Apply the principles of epidemiology to investigations of disease occurrences 3 Maintain open lines of communication among all facets of the aquaculture community AQUACULTURE INFORMATION SERIES NO 7 INTERPRETING THE FEED CONVERSION RATIO The feed conversion ratio the FCR is perhaps the most misused and farmers are discussing mutual concerns One says quotThis past year I fed Alpha brand feed and got a feed conversion of 16 and I am not too happy about thatquot The other replies quotI fed Beta brand feed and got an over all conversion of 12quot So the first fish farmer switches to Beta feed and guess what The resultant FCR is 17 Now this chap is quite concerned that the other fellow did not know what he was talking about or he lied about the 12 feed conversion On the surface of it one might think I have resorted to fictitious humor to make a point Not in the least I hear stories such as this quite frequently especially during continuing education workshops and fish farming trade shows In the foregoing example there is another concerned participant th representative for A pha Feeds This individual has been touting the feed as being thoroughly evaluated and energywise can generate a feed conversion of 11 1 His credibility could be somewhat in question as well as the reliability of the manufacturer The main problem in the example is that the one and perhaps both fish farmers as well as the feed company representative did not fully realize that the feed conversion ratio is more than just feeding fish and measuring the weight gain T ere are at many perhaps more than 20 factors intrinsic to an aquaculture system which can affect the FOR ten of which will be discussed It should be stated that the majority of high quality high energy commercial trout and salmon feeds are formulated to provide an FOR o 11 to 12 if fed properly Considering each of the major causal factors affecting the FCR and suggesting remedial measures should be an all inclusive process Each should be considered as an individual and also as part of the whole 1 Factor Overestimating or underestimating the biomass of fish being fed If the biomass is greater than that being fed for the weight gain will less than expected and the FCR will be acceptable On the other hand if the biomass is less than that being fed for the weight gain as well as the FCR will be less than expected Solution The majority of cases of over or underestimating the biomass andor growth rate stem from not acquiring reliable inventory data Cf Aquaculture Information Series No The inventory process should begin when the pond is stocked Determine the number per kg and weigh the fish into the pon A the completion of the pond stocking determine the number per kg again Also anesthetize a group of 40 fish for individual lengths and weights Calculate the mean median midrange and standard deviation values for lengths and weights Also calculate the mean condition factor This will detect size bias from the original population to the new population It will also facilitate constructing the daily feeding regimen If performance data are used to their fullest advantage the FCR39s should improve and the production costs reduced accordingly Factor Feeding in conditions of less than optimal dissolved oxygen Solution The partial pressure of dissolved in the water at the outfall of each pond should be not less than 90 mm Hg For most facilities in this represents 60 65 of saturation Table l Table l Dissolved oxygen content mgl of water when the p02 is 90 mm Hg Water Temperature DC Dissolved Oxygen mgl O 832 l 8lO 2 788 3 766 4 745 5 728 6 7lO 7 692 8 676 9 660 lo 645 ll 63l l2 6l7 l3 604 l4 59l l5 579 l6 567 l7 556 l8 546 l9 535 20 525 Factor Overestimating or underestimating the temperature dependent growth rate mmday length increase Solution Prepare an annual average weekly or at least monthly water temperature chart Use this in conjunction with either the historical length increase or the length increase from an appropriate table Factor Improper calculation of the daily feeding rate Solution There are two reliable methods of calculating the daily feeding rate for salmonids One is the daily length increase method of Haskell and the other is the prepared feeding chart provided by feed manufacturers The daily increase method uses the temperature dependent daily length increase the delta l the feed conversion ratio and a length weight conversion factor Its main shortcoming is that it presumes a constant condition factor Thus the observed length at the end of the feeding period approximates the expected length However the observed weight is usually greater than the expected because of the increase in condition factor The feeding chart provided by most suppliers contains a built in feed conversion ratio which in most cases is greater than what occurs Thus the population is very often somewhat overfed the growth is often what is expected but the feed conversions are often quite quotlousyquot to say the least The Silver Cup Feed Chart does not contain built in feed conversio ratios The farmer multiplies the chart value body weight to be fed by the historical feed conversion ratio to get the proper daily feeding rate Factor Not weighing the feed accurately Solution Prepare daily feeding amounts for each pond For hand feeding weigh the feed into properly labeled containers For demand feeding weigh the bag of feed before loading the feeder For bulk feeding on at least weekly intervals calibrate the scale on the feeder Factor Poor presentation of the feed Solution For hand feeding this is a management problem which can be corrected by proper instruction For demand feeding adjust the trigger such that the wind cannot activate the feeder Also perhaps more feeders per pond are warranted Factor Feeding out of date feed Solution Do not purchase feed for more than a 3 month period Beyond that the quality becomes questionable due to the potential for vitamin degradation and fat rancidity And do not use last year39s starter feeds for this year39s fish Factor High retention times for ammonia NH3 and solids in the ponds Solution Raceways especially those arranged for multiple pass of the water should have retention times of 20 30 minutes In circulating ponds a 95 water replacement time should not exceed 180 minutes In this case unlike a raceway the incoming quotnewquot water mixes with outgoing quotoldquot water thus providing a dilution effect Factor Feeding at less than optimal times of day Solution On facilities having significant daily quotswingsquot in water temperature and dissolved oxygen the optimal times for feeding are in the early morning and at dusk Heavy noon feedings should be avoided Factor Feeding an improper pellet size Solution In populations having a large variation in sizes the best pellet size is that which is suited for the smallest fish in the population In addition contrary to the recommendations of most feed manufacturers the largest optimal pellet size is 18quot 3 mm The main reason for this is that there are more pellets available and less dusting than with larger pellets Thus more fish get fed and less feed gets wasted S ummary The presented 10 fish husbandry factors affecting the feed conversion ratio are the more common It stands to reason that an improvement in feed efficiency the reciprocal of feed conversion would generate an improvement in costs of production In the following example Table 2 the cost 0 production is based upon feed costs being 57 of the production costs and feeding a 055kg formulation Table 2 Costs per kg weight gain based upon the feed conversion ra io Feed Conversion kg weight gain F F H H H H H H H egaot w mps LLLLLLLLL F F H H H H H H o Q In this example it should be clear that to optimize the FCR is economically more wise that attempting to economize with abor saving devices Finally the most efficient method to improve over all production in terms of fish quality and production costs is to utilize the suggeste performance indicators Table 3 to their fullest advantage
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