Channel Catfish: Dietary Effects on Body Compostion and ... · maintenance. Choosing the right feed plays an important role in de-termining the productivity and profitability of aquaculture

May 1993

Dietary Effects on

Catfish diets must provide enoughenergy, protein, vitamins and min-erals in the proper proportions forfast, efficient growth and healthmaintenance. Choosing the rightfeed plays an important role in de-termining the productivity andprofitability of aquaculture opera-tions. But, producers aren’t theonly people who are interested indiet quality. Certain characteristicsof the diet influence the quality ofcatfish products during processingand storage. As a result, catfishprocessors, wholesale marketersand retailers also depend onproper feed quality to yield desir-able results.

Effects of dietary protein

Because excess fat decreases thedress-out yield and potential shelf-life of processed catfish, questionsregarding the impact of diet com-position on product quality havearisen. Research projects evaluatedthe effects of dietary protein con-tent on body composition of vari-ous-sized catfish in differentproduction systems.

Catfish grow-out in ponds

At Kentucky State University, fin-gerlings stocked in intensivelymanaged ponds were fed commer-cial-type diets containing 34 or 38percent protein to satiation once ortwice daily. At the end of 170 days

SRAC Publication No. 186

SouthernRegionalAquacultureCenter

Channel Catfish

Body Composition and Storage Quality

The Southern Regional AquacultureCenter has supported research to deter-mine how diet affects the compositionand quality of processed channel catfishproducts. The results of-these researchprojects should help producers and pro-cessors modify management practices toimprove the value and marketability oftheir products. This publication wascompiled by James T. Davis, D.M. Gatlin, III and Max R. Alleger, based on re-search conducted at Auburn University,University of Georgia, Kentucky StateUniversity and Texas A&M University,Details are available from the applicablepublications listed.

the fish weighed an average of 1pound. Results of this experimentindicated that neither feeding fre-quency nor protein content of the

diet within this range affectedgrowth or important body compo-sition characteristics such as fatcontent or fillet yield.

In an Auburn University study,fingerlings were fed commercial-type diets containing 26,32 or 36percent protein for 125 days oneither a restricted basis or to satia-tion. Dressing percentage in-creased as dietary protein wasincreased from 26 to 32 percent,but then decreased as protein con-centration was increased to 36 per-cent. Whether fed on a restrictedbasis or to satiation, body fat de-creased as the diet’s protein levelincreased. Body fat content of fishfed to satiation was higher thanthose fed on a restricted basis,

Choosing the right feed plays an important part in profitability of aquacultureoperations.

suggesting that feeding rate doesinfluence important body composi-tion variables.

Another study conducted atAuburn University measured theeffects of feeding commercial-typediets containing 24,28,32,36 or 40percent protein to fingerlings inponds. Fingerlings were fed to anaverage of 1 pound in 151 days.They were fed to satiation oncedaily during the growing season.Dressing percentage increased asdietary protein was increasedfrom 24 to 36 percent, but de-creased when increased to 40 per-cent. Fat content in filletsdecreased, while protein and mois-ture increased when dietary pro-tein was increased.

Conclusions

These studies suggest that filletyield may improve as dietary pro-tein is increased up to 36 percent,and that feeding to satiation mayincrease body fat concentrations.However, the same studies sug-gest that producers can savemoney without sacrificing weightgain by feeding diets that containmuch less than 36 percent protein.These trade-offs betweeneconomic savings and potentialchanges in product quality de-serve further attention, especiallyif fat content and other body com-position characteristics are provento reduce the quality and con-sumer acceptance of catfish pro-ducts.

Catfish grow-out in cages

Cage culture offers an opportunityto produce fish in ponds that maybe poorly suited for conventionalpond culture because of their size,depth or the presence of other fish.However, successful cage culturealso provides unique managementchallenges to the producer.

A study conducted at KentuckyState University focused on the nu-tritional needs of fingerling chan-nel catfish stocked in cages. Fish incages were fed to satiation once ortwice daily for 105 days with com-plete, commercial-type feeds con-

taining either 34 or 38 percent pro-tein.

Body composition of fingerlings inthis study was not affected by feed-ing frequency or dietary proteinlevel. Fish grew faster on thehigher protein diet, and fish fedtwice daily had a higher dressingpercentage than those fed onlyonce per day.

Grow-out of third-year fish inponds

Little information is available re-garding how diet affects thegrowth or body composition ofthird-year fish. Studies conductedat Auburn University and Ken-tucky State University measuredthe effects of feeding commercial-type diets containing various con-centrations of protein to third-yearcatfish in ponds. Results of thesestudies indicate that, althoughbody fat decreases when dietaryprotein is increased, fish growthand dressing percentage were un-affected. It remains unclearwhether diets containing morethan 32 percent protein improvethe quality of fillets from third-year fish enough to justify the ac-companying higher feed costs.

Supplementing aminoacids in catfish diets

Amino acids are the buildingblocks of protein; they are essen-tial for good fish growth andweight gain. Several research pro-jects have focused on the effects ofspecific amino acid supplementsin catfish diets. These studies wereconducted with catfish fingerlingsin aquaria maintained under opti-mum conditions.

Lysine is one of ten amino acidsthat must be provided by the diet;it is also the least abundant aminoacid in many feedstuffs. As a re-sult, extra care must be taken toprovide enough lysine when for-mulating catfish diets containing alarge percentage of protein fromplant sources. Also, lysine supple-mentation above requirement lev-els has been shown to reduce body

fat of some terrestrial animals. Re-searchers at Texas A&M Univer-sity compared diets that containedeither 25 or 30 percent proteinfrom soy isolate or casein and gela-tin, and either 0 or 0.5 percent sup-plemental lysine. Fingerlings feddiets with protein from casein andgelatin gained more weight thanthose fed diets containing soy-based protein. Also, fish fed soy-based diets contained more lipidand less protein than those fed thecasein-based diet.

Supplemental lysine improvedprotein conversion efficiency andfeed efficiency of catfish fed soy-based diets, but not of those fed ca-sein-based diets. Fish fed a 30percent protein soy-based dietwithout added lysine performedbetter than those fed a 25 percentprotein soy-based diet with extralysine. However, supplementally-sine did not influence body compo-sition characteristics at any proteinlevel.

Results suggest that both thesource and concentration of die-tary protein impact catfish per-formance, and that supplementallysine does not influence bodycomposition.

Carnitine is a naturally-occurringcompound that animals typicallyproduce from lysine. Some re-search suggests that providingsupplemental carnitine in the dietincreases the quality of processedanimal products by reducing fatcontent. A study conducted at theUniversity of Georgia comparedthe benefits of feeding diets thatcontained 0.1 percent carnitineand 1.1, 1.4 or 1.7 percent lysine.Feeding diets that included bothsupplemental carnitine and lysineproved most beneficial. When car-nitine was added to diets contain-ing lysine close to or above therequired dietary level (1.4 and 1.7percent, respectively), fat contentin the viscera and dark muscle tis-sue decreased and whole-fish pro-tein levels increased.

Results indicate that feeding high-quality diets supplemented with

carnitine may reduce body fat con-tent.

Effects of vitaminfortification

Improved storage quality dependson management practices duringgrow-out, as well as procedurescarried out during and afterprocessing. Storage quality of poul-try and some kinds of fish hasbeen improved by feeding dietsthat increased concentrations of vi-tamin E in muscle tissues prior toprocessing. Vitamin E, and similarsynthetic products, are called anti-oxidant because they help reducelipid oxidation and maintain thefreshness of products during stor-age.

Researchers at Texas A&M Univer-sity evaluated the benefits of ad-ding synthetic and naturalantioxidants to channel catfishdiets. Fingerling catfish were fedexperimental-type diets that satis-fied all known requirements andcontained one of two concentra-tions of vitamin E (60 or 240mg/kg), either alone, or in combi-nation with one of four syntheticantioxidants. None of the syntheticantioxidants affected weight gain,feed efficiency, survival or tissuecomposition. Fillet samples fromfish receiving each diet were fro-zen at -10°F for six months. TheTBA number, a measure of rancid-ity caused by oxidation, was deter-mined for fillets to assess howstability during frozen storage wasaffected by diet composition. Fishfed the higher level of vitamin Ehad reduced TBA numbers, butsynthetic antioxidants did not af-fect this measure of storage quality.

Fortification of catfish diets withhigh levels of vitamin E probablyoffers an effective means of main-taining fillet stability during fro-zen storage. Results from anotherstudy indicate that maximumbenefits from vitamin E supple-mentation are achieved within 2weeks of feeding a diet fortifiedwith 1,000 mg vitamin E/kg. Feed-ing diets fortified with this highlevel of vitamin E throughout the

Dietary protein concentration does not appear to affect storage quality of catfishfillets.

grow-out period may be unneces-sary.

Vitamin C is essential for normalfish growth and has some proper-ties that allow food products to re-sist oxidation. Rutin, a compoundclassified as a bioflavonoid, mayproduce beneficial responses simi-lar to vitamin C when available inthe diet. A Texas A&M Universitystudy compared diets containingvarious concentrations of vitaminC and rutin. By the end of eightweeks, no differences in weightgain, feed efficiency or survivaldue to diet were observed. But,within 10 weeks, fish fed dietswithout supplemental vitamin Cor rutin had developed deformedspinal columns, external hemor-rhages and eroded fins. By week12, fish receiving supplementalrutin but no vitamin C showed thesame symptoms. By the end of 16weeks all fish that had not re-ceived supplemental vitamin Chad reduced weight gain and feedefficiency and decreased survival.Rutin had no significant effect onweight gain, feed efficiency orother variables, either alone orwhen fed with added vitamin C.

According to this study, high con-centrations of supplemental vita-min C (1,500 and 3,000 mg/kg)improved the oxidative stability ofchannel catfish fillets, but supple-mental rutin was not beneficial.

Dietary impacts onstorage quality

Studies at the University of Geor-gia focused on how dietary pro-tein concentration and packagingmethod may affect the quality offrozen catfish fillets. Year-2 andyear-3 catfish stocked in researchponds were fed diets containing24,28,32,36 or 40 percent proteinto an average harvest weight of 3.3pounds. Upon processing, filletswere packaged using PVDC filmoverwrapping, vacuum packagingwith Eva bags or vacuum skinpackaging and stored at -10°F. Fil-lets were removed from frozenstorage after O, 30 and 90 days forchemical analysis and sensoryevaluation. Chemical analyses in-cluded pH, TBA number, ammo-nia and free fatty acid content. Aconsumer panel evaluated broiledsamples for off-flavor, greasinessand texture. Although lower die-tary protein increased fillet fat con-tent, it did not directly affect TBAnumber, pH or sensory attributes.Sensory panelists reported that allfillets became tougher, but greasi-ness decreased as storage time in-creased. Packaging treatment didnot impact the free fatty acid char-acteristics of fillets.

Results indicate that lower proteindiets may increase the fat contentof catfish fillets, but not to a de-gree that reduces consumer satis-faction. Also, current processingand packaging methods for catfishprovide adequate quality protec-tion for up to 3 months of frozenstorage.

Another University of Georgiastudy evaluated the impact of die-tary protein on channel catfishstored on ice. Fish were fed to anaverage size of 3.3 pounds on com-mercial-type diets containingeither 24, 28, 32, 36 or 40 percentprotein in production ponds. Fishwere processed upon harvest, andfillets were placed on polystyrenetrays overwrapped with plasticwrap and stored in drained icechests.

Sensory and chemical evaluationsof iced fillets were conducted after1,7,14 and 21 days. Catfish fedthe lowest-protein diet had morebody fat than those fed higher-pro-tein diets, but fillet fat content hadno direct effects on free fatty acidcontent during storage. Also, die-tary protein did not affect ammo-nia concentration, pH, TBAnumber or bacterial counts of fil-lets stored on ice for up to 2weeks. Sensory panelists reportedthat the texture of fish fed the 32percent protein diet was superiorto those fed 36 percent proteinafter 1 day of storage. After 1week, fish fed 28 percent proteinwere more greasy than those fedthe other diets, but other differ-ences were not detected.

Results suggest that dietary pro-tein does not influence importantquality attributes of channel cat-fish fillets, and that fillets can bestored on ice for up to 2 weekswithout compromising quality.

References

Bai, S. C. and D. M. Gatlin III.1993. Effects of L-lysine supple-mentation of diets with differ-ent protein levels and sourceson channel catfish. aquacultureand Fisheries Management, inpress.

Bai, S. C. and D. M. Gatlin III.1992. Dietary vitamin E concen-tration and duration of feedingaffect tissue or alpha-tocopherolconcentrations of channel cat-fish. Aquaculture in press.

Bai, S. C. and D. M. Gatlin III.1992. Dietary rutin has limitedsynergistic effects on vitamin Cnutrition of fingerling channelcatfish. Fish Physiology and Bio-chemistry 10:183-188.

Burtle, G. J. and Q. Liu. 1992. Die-tary carnitine and lysine affectcatfish lipid and protein con-tent. Journal of the WorldAquaculture Society (in review).

Gatlin, D. M. III, Bai, S. C., and M.C. Erickson. 1992. Effects of di-etary vitamin E and syntheticantioxidants on compositionand storage quality of channelcatfish. Aquaculture 106:323-332.

Huang, Y. W., R. R. Eitenmiller, D.A. Lillard and P.E. Koehler.1991. Storage quality of icedchannel catfish fed different pro-tein levels. Journal of FoodQuality 14:345-354.

Huang, Y. W., D.A. Lillard, P. E.Koehler and R. R. Eitenmiller.1992. Chemical changes and

sensory evaluation of channelcatfish as affected by diet, pack-aging method and frozen stor-age. Journal of Food Quality15:129-138.

Li, M. and R. T. Lovell. 1992. Com-parison of satiate feeding andrestricted feeding of channel cat-fish with various concentrationsof dietary protein in productionponds. Aquaculture 103:165-175.

Li, M. and R. T. Lovell. 1992.Growth, feed efficiency andbody composition of second-and third-year channel catfishfed various concentrations ofdietary protein to satiety in pro-duction ponds. Aquaculture103:153-163.

Webster, C. D., J. H. Tidwell, J. A.Clark and D. H. Yancey. 1992.Effects of feeding diets contain-ing 34 or 38 percent protein attwo feeding frequencies ongrowth and body compositionof channel catfish. Journal ofApplied Aquaculture 1:67-69.

Webster, C. D., J. H. Tidwell andD. H. Yancey. 1992. Effect ofprotein level and feeding fre-quency on growth and bodycomposition of cage rearedchannel catfish. The ProgressiveFish-Culturist 54:92-96.

Webster, C. D., J. H. Tidwell, L. S.Goodgame, J. A. Clark and D.H. Yancey. 1992. Effects of pro-tein level and feeding frequencyon growth and body composi-tion of third-year channel cat-fish reared in ponds. Journal ofApplied Aquaculture, in press.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 89-38500-4516 from the UnitedStates Department of Agriculture.