JOURNAL OF THE}VORLD AQUACULTURE SOCIETY

The cost of feed constitutes approximate-ly 5OVo of the total operational costs ofcommercial hybrid striped bass (HSB) cul-ture operations. Therefore, reducing feedcosts while maintaining high nutritionalquality should result in substantial gains inthe profitability of HSB aquacultural enrer-prises. Fish meal has typically served as theprimary source of protein in commercial di-ets for HSB culture. If appropriate process-ing protocol is followed, then this feedstuff

t Mississippi Agricultural and Forestry ExperimentStation (MAFES) Publication Number J9626.

Vol.31, No. 3September,200O

generally has a high nutritional value as aningredient in formulated diets for carnivo-rous and omnivorous fish. However, thelack of a consistent supply of this feedstuffcauses unexpected increases in the purchaseprice of feed, thereby reducing the marginfor proflt. Moreover, long term availabilityof fishmeal to support the anticipated in-crease in demand is highly questionable.Therefore, dietary protein sources that canserve as complete or partial substitutes forfish meal must be evaluated if commercialaquaculture of hybrid striped bass and otherspecies of flsh is to be sustainable. With theidentification of successful feedstuff alter-

Effects of Reduced Levels of Dietary Protein and MenhadenFish Meal on Production, Dressout, and Biochemical

Composition of Phase III Sunshine Bass Morone chrysops gx M. saxatilis d Cultured in Earthen Pondsl

Lours R. D'AaRAMo, ConrNey L. OHs, eNo Jor+r B. TeylonDepartment Wildlife and Fisheries, Mississippi State University,

Box 969O, Mississippi State, Mississippi 39762 USA

AbstractThe responses of phase tII sunshine bass Morone chrysops I x M. saxatilis d to diets

containing reduced levels of menhaden fish meal (3$-lOVo, dry weight) and crude protein(4O-36Vo, dry weight) were evaluated in two separate experiments. Reductions in fish mealwere compensated by increase in dietary soybean meal, a meat and blood meal product, andadditional amounts of a L:L catfish oil:menhaden oil mixture sprayed on as a top dressing.Fish were cultured in earthen ponds and fed commercially manufactured, extruded diets toapparent satiation. In Experiment I, dietary crude protein was reduc6d from 40 to 36Vo and,the menhaden fish meal ingredient was reduced from 30 to lSVo (dry weight). The meanweight of fish stocked into each pond ranged from 144 to 188 g, the stocking density was864llha, and the duration of the growout was 172 d. In Experiment 2, both dietary treatmentscontained 4OVo crude protein (dry weight) and either SOVo ot 107o menhaden fish meal. Themean weight of fish stocked into each pond ranged from 42 andl 77 g, the stocking de6itywas 8r500/ha, and the duration of the growout was 175 d. Simultaneous reductions in dietarymenhaden fish meal and crude protein resulted in significant decreases in all productionindices except survival and percent weight increase. Weights of filet, carcass, liver and intra-peritoneal fat, expressed as a percent of total body weight, were not significantly different. A66Vo reduction in dietary menhaden fish meal while the crude protein level was maintainedat 40Vo did not significantly affect-growth, production, and weigbts of filet, carcass, liver andintraperitoneal fat, expressed as a percent of total body weight, and represents a 6Vo decreasein the cost of feed. In both experiments, levels of protein, lipid, moisture, and ash of the wholebody and the filet were not significantly different. Fatty acid composition of the filet and liversfrom fish fed the control and experimental diets in Experiment 2 were highly comparable.The comparable level of performance of fish fed diets believed to be deficient in IfUFAsuggests that thb dietary levels reported to be required may not be totally applicable to dietsformulated for pond culture.

O Copyright by the World Aquacultule Society 2OOO

3t6

REDUCED PROTEIN AND FISH MEAL IN FEEDS FOR SUNSHINE BASS 3I7

natives to fish meal, the impact of the aqua-culture industry as a major consumer ofmarine fishery resources will be substan-tially reduced.

Reduction of the fish meal in diets ofboth carnivorous and omnivorous fish sp'e-

cies has met with variable success. A com-bination of soybean meal and dried distill-ers' grains with solubles totally replacedprotein derived from fish meal in diets fedto channel catfish lctalurus punctatus whensupplements of lysine and methionine wereprovided (Webster et al. 1992). Soybeanmeal completely replaced fish meal in dietsfed to blue catfish Ictalurus furcatus with-out affecting weight gain and body com-position (Webster et al. 1995a). Growthrates ofrainbow trout Oncorhynchus mykisswere reduced when fed a diet in which 5OVo

of a fish meal ingredient (dry weight) wasreplaced with soyflour and casein (Kaushiket al. 1995). Dabrowski et a]. (1989) alsoreported a reduction in growth rates of rain-bow trout wllLen 5OVo of the dietary proteinderived from fish meal was replaced withsoybean meal; growth ceased and mortali-ties occurred when all of the fish meal wasreplaced. Growth and feed efficiency of reddrum Sciaenops ocellatus decreased unlessat least l.OVo of the dietary protein was de-rived from fish meal (McGoogan and Gatlin1997\.

Three previous studies have investigatedthe effects of the reduction of menhadenfish meal in diets for HSB. In aquariumstudies, Brown et al. (1993) observed thatdiets containing casein as the primary pro-tein source were unpalatable regardless ofthe level of fish oil (6-l2vo), but were con-sumed if at least IOVo menhaden fish mealwas present in the diet. In two separatefeeding trials, each conducted in tanks andof 12-wk duration, Gallagher (1994) fed ju-venile hybrid striped bass (5 g and 100-150g) diets containing 35Vo crude protein inwhich the level of menhaden fish meal wasreduced from 47Vo to 16.5%o with corre-sponding increases in soybean meal (0-44Vo) that represented O-:75Vo of dietary

protein. No significant differences in weightgain were found with the exception of a sig-nificantly lower weight gain for the 5-g fishfed the diet containing the 34Vo soybeanmeal (5OVo of the dietary protein). Also re-ported were the results of a 14-wk pondstudy evaluating response to diets contain-ing either IOOVo of the dietary protein as

flsh meal, or 5OVo of the dietary proteinfrom each of soybean meal and menhadenfish meal. No significant difference inweight gain of HSB (initial stockingweight, 100-150 g) from the two dietarytreatments was found. Webster et al. (1997)fed palmetto bass (initial weight, approxi-mately 20 g) in cages diets that containeddecreasing levels of.anchovy fish meal (45,30, 15, andoVo, dry weight). The reductionswere compensated by increases in soybeanmeal and menhaden fish oil and decreasesin corn meal. Protein substitution for thediet without anchovy fish meal included theaddition of meat an{ bone meal. After 125

d, growth of fish fed the diet with no an-chovy meal was significantly lower thanthat of fish fed each of the other diets. Thegrowth of fish for each of the other dietarytreatments was not significantly differentwhen compared to each other. The responseof hybrid striped bass to a reduction in di-etary fish meal protein, with or without re-placement with an animal-derived proteinsource, has not been evaluated for the com-plete duration of phase III pond culture.

The results of numerous studies suggestthat the dietary protein requirement ofHSB is between 36 to 4lEo. Brown et al.(1992) used menhaden flsh meal as thesole dietary protein source and reported a

requirement of approximately 4lVo (dryweight), regardless of the salinity of thewater. Swann et al. (1.994) found that fishcultured in cages had a significantly higherweight gain when fed diets containing36%ocrude protein (dry weight) versus 32 or4OVo. Juvenile sunshine bass cultured incages required 4IVo dietary protein (dryweight), or a protein to energy ratio ex-ceeding 99 mg protein/kcal, when 56Vo of

318 D'ABRAMO ET AL.

Tasls 1. Ingredient composition (Vo dry weight) of the contol and experimental diets used in Experiments Iand 2. The number in parentheses next to each feed ingredient is the International Feed Number.

Feed ingredientExperiment I

Control diet dietExperiment 2

diet

Menhaden fish meal (5-02-009)Soybean meal (5-2O-637)Corn meal (4-02-935\Cottonseed meal (5-01-621)ProCon 65 (proprietary blend of meat meal and blood

meal mixtures)uWheat middlingsHybrid striped bass vitamin premixTrace mineral premixCholine chloride-607oVitamin C (Stay-C)Fish oil (1:1, catfish oil:menhaden oil)Dicalcium phosphateAvailable lysine (Vo)b

Available methionine f cystine (7o)b

30.016.2525.015.00.0

to.40.150.15o.250.32.O

0.52.00.98

15.029.7524.510.00.o

15.40.150. l5o.250.34.O

0.51.7o.83

10.022.O

25.O

t5.o15.0

7.150.15o. t5o.250.34.50.5t.90.89

" AIso known by the product name 65 RDB (Mid-South Milling, Memphis, Tennessee, USA).b Based upon values for channel catfish lctalurus punctatus.

the dietary protein was derived from an-chovy meal (Websrer et al. 1995b). Theysuggested that differences in reported pro-tein requirements may be related to differ-ences in culture technique, diet composi-tion, and protein quality. Webster et al.(1999) completely replaced fish meal (307odry weight) with different combinations ofmeat and bone meal, poultry by-productmeal, soybean meal, and distillers' grainswith solubles in some practical diets fed tojuvenile sunshine bass (initial weight, 15g) held in aquaria. After an 8-wk feedingtrial, no adverse effect on either weightgain, growth rate, or body compositionwas observed for most of these diets.When soybean meal was the primary pro-tein-source, at least l5Vo fish meal was stillrequired in the diet. All previously report-ed results of investigations of protein re-quirements and responses to reductions offish meal in practical diets for sunshinebass are limited to studies in aquaria orcages. This study was designed to evaluatethe effect of reductions of protein and fishmeal in diets fed to phase III sunshine bassMorone chrysops I x M. saxatilis 6 inearthen ponds.

Materials and Methods

Experiment IThis experiment was designed to evalu-

ate responses to simultaneous reductions inthe dietary levels of menhaden fish meal(3O-I5Vo dry weight) and crude protein(4O-36Vo dry weight). Phase III sunshinebass were stocked into six 0.05-ha earthenponds at8,64I/ha between 2OMay and27May 1997. Mean weight of fish stockedinto each pond ranged from I44 to 188 g.Fish in the control treatment were fed a lo-cally manufactured (Fish Belt, Itta Bena,Mississippi, USA) extruded HSB diet thatcontained 4OVo crude protein (dry weight)and 3O%o menhaden fish meal (dry weight).The diet for the experimental treatment wasformulated to contain 36Vo crade protein(dry weight) and l5%o menhaden fish meal.The decrease in dietary n-3 highly unsatu-rated fatty acids (HUFA) resulting from thereduction in the menhaden flsh meal wascompensated by a 2Vo inqease in the levelof a 1:1 mixture of menhaden oil and cat-fish oil that was sprayed onto the f,nisheddiet as a top dressing. The ingredient com-position, fatty acid profile, and proximate

REDUCED PROTEIN AND FISH MEAL IN FEEDS FOR SUNSHINE BASS

Tanre 2. Proximate composition (Vo dry weight) and fatty acid composition (Vo of total fatty acids) of the

control and experimental diets used in Experiments I and 2.

Experiment I Experiment 2

Control Exp. Control Exp.

319

Crude proteinCrude lipid (acid hydrolysis)AshCrude fiberNitrogen-free extractMoistureDigestible Energy :Protein

n-3 HUFA'n-6 HUFA22:6 n-3 (DHA)/20:5 n-3 (EPA)Total n-3 fatty acidsTotal n-6 fatty acids

40.19.7

10.44.9

34.98.48.0

ootr.32o.77

12.7626.42

36.3r0.88.04.7

40.28.68.4

9.411.51

0.8211.6524.93

41.29.69.2)-J

34.59.67.8

6.981.94t.t29.84

27.82

41.5

8.98.84.9

35.98.67.3

3.52t.t70.955.70

27.72

" HUFA : Fatty acids with > 20 carbon chain and 3 or more unsaturated bonds

analysis of both the control and experimen-tal diets are presented in Tables I and 2.The desired crude protein and lipid levelsin both the control and experimental dietswere achieved. Dietary levels of n-3 HUFAwere approximately l.OVo. The calculateddigestible energy/protein ratios (kcaVg pro-tein) for the control (8.0) and experimental(8.4) diets were based upon avaitable di-gestible energy values for the feedstuffs(Sullivan and Reigh 1995; D. Gatlin, TexasA&M University, personal communication)and determinations of dietary crude protein(AOAC 1990).

There were tfuee replicates per treatment.All fish were fed to apparent satiation oncedaily from 27 May to 13 August at 0900 h.Thereafter, all fish were fed to apparent sa-tiation twice daily, at 0900 and 1400 h. Theamount of feed fed per feeding was record-ed for each pond. After I72 d, flsh wereseine harvested. Fish that escaped seineharvest were collected after each pond wasdrained completely.

Experiment 2

This experiment was designed to evalu-ate responses to a reduction in dietary men-haden fish meal (3O-I.OVo) while maintain-ing the crude protein level at 4OVo. PhaseIII sunshine bass were stocked into eieht

0.05-ha earthen ponds at 8,5004ra between24 Apil and 26 April 1998. Mean weightof fish stocked in each pond ranged from42 to 77 g. There were two dietary treat-ments. The diet for the control treatmentcontained the same ingredient compositionand was produced by the same feed man-ufacturer in the same manner as the dietused in the control treatment for Experi-ment 1. For the diet used in the experimen-tal treatrnent, the menhaden fish meal in-gredient was reduced from 3OVo (dryweight) or 48.8Vo of the total dietary pro-tein, to loclo (dry weight) or l6.3Vo of thetotal dietary protein. The decrease in the di-etary n-3 HUFA resulting from the reduc-tion in menhaden fish meal was compen-sated by a 2.5Vo increase in the level of a

top dressing oil (catfish oil: menhaden oil,1:1) sprayed on the finished diet. The de-crease in the amount of crude proteincaused by the reduction in menhaden fishmeal was compensated by a 5.75Vo increasein the level of the soybean meal and theinclusion of a commercially available, pro-prietary blend of meat meal and blood medmixtures (ProCon 65, also known by theproduct narne, 65 RDB, Mid-South Milling,Memphis, Tennessee, USA) at l5%o (dryweight). The ingredient composition, fattyacid profile, and proximate analysis of both

the control and experimental diets are pre-sented in Tables I and 2. The crude proteinlevel of both the control and experimentaldiet was approximately 4lVo. The level oflipid in the experimental diet was less thanwhat was intended and consequently the to-tal amount of n-3 HUFA in the experimen-tal diet was O.SVo, approximately 5OVo ofthe level in the control diet. The digestibleenergy/protein ratios (kcaUg protein) for thecontrol (7.8) and experimental (7.3) dietswere based upon available digestible energyvalues for the feedstuffs (Sullivan andReigh 1995; D. Gatlin, Texas A&M Uni-versity, personal communication) and de-terminations of dietary crude protein(AOAC 1990).

There were four replicates per treatment.Fish in all ponds were fed to apparent sa-tiation twice daily, at O90O and 1400 h. Theamount of feed fed per feeding was record-ed for each pond. After 175 d of culture,fish were seine harvested. Fish that escapedseine harvest were collected after each pondwas drained completely.

C ommon Experimental Protocol

Dissolved oxygen and temperature in allponds were monitored at 0800 and 1300 hdaily for the duration of both experiments.Additional dissolved oxygen measurementswere conducted at 22OO and 0500 h whenrapid changes characteristic of seasonalconditions warrant more frequent record-ings. Surface aeration was provided by a0.25-hp vertical pump aerator (Air-O-LaterCorp., Kansas City, Missouri, USA) andtractor driven paddle-wheel when the con-centration of dissolved oxygen declined be-low 7 mglL. Ten fish were subsampled fromthose fish harvested from each pond andsexed. The weights of interperitoneal fat(IPF), filet, and carcass were initially deter-mined and expressed as a percent of totalweight. Proximate analyses were performedon pooled, homogenized samples of filetsand livers of three of the 10 fish subsam-pled from each pond. Crude protein (Lecomethod), crude fat (acid hydrolysis meth-

D'ABRAMO ET AL.

od), ash (furnace combustion), and moisturecontent (oven drying) were determined ac-cording to standard methods (AOAC 1990).Filets and livers obtained from a differentgroup of three fish from the subsample ob-

- tained from each pond were also pooled andhomogenized and fatty acid proflles weredetermined (Woodsen Tenet Laboratories,Memphis, Tennessee, USA; AOAC 969.33modified to include extraction of lipid).

Statistical Analysis

Analysis of variance (ANOVA, Zar1974) by means of the general linear modelof SAS Version 6.11 software (SAS Insti-tute, Inc., Cary, North Carolina, USA) wasused to test for the effpcts of diet on pro-duction characteristics and proximate com-position of sunshine bass. Mean weight atstocking was evaluated as a covariate forthe ANOVA of production characteristics.Data on tissue indices were analyzed usingtwo-way ANOVA with subsampling to testfor the effects of different feeds and sex.Total lipid levels and fatty acid composi-tions of the filet and liver samples were an-alyzed using one-way ANOVA with sub-sampling. Differences were considered sig-nificantatP<0.05.

Results

Experiment IOn June 19 most fish in one of the rep-

licate ponds representing the control dietarytreatment died due to an unexpected andrapid decrease to a lethally low level of dis-solved oxygen. Therefore, results are basedupon two replicate ponds for the control di-etary treatment and three replicate pondsfor the experimental dietary treatment.

The mean individual harvest weight, to-tal production, and feed conversion ratio ofthe control dietary treatment were signifi-cantly greater than those for the experimen-tal dietary treatment (Table 3). The signifi-cantly higher mean production and harvestweight of fish fed the control diet were notdue to the higher mean initial stockingweights that resulted from random assign-

REDUCED PROTEIN AND FISH MEAL IN FEEDS FOR SUNSHINE BASS

Tnst-e 3. Mean x SE values for production characteristics and dressout percentages for fish fed the controland experimental dietary treatments in Experiment 1. (N) : number of replicates. Means in each row followedby dffirent letters dffired at the 0.05 probability level by ANOVA (hr 1974).

Production totals Control (2) Experimental (3)

321

Mean individual weight (g)

Total production (kg/ha)FCRSurvival (7o)

Weight gain (7o)

Dressout percentages

647.7 + 26.5a41320 + 3Oa

3.2 + 3.7a77.3 + 3.7a272 + 42a

Control (2)

533.2 + 23.4b3,084 t 104b

5.7 t 0.lb67.7 + 3.8a227 + 22a

Experimental (3)

FiletCarcassLiverIPF

34.4 + 0.3a62.7 + O.2a

4.1 + O.la5.2 + O.2a

34.7 + O.3a

62.2 + O.2a

3.7 + O.la6.O + 0.2a

ment of ponds to the control treatment.Mean stocking weight used as a co-variatedid not improve the ANOVA and was notincluded in the final model. Percent weightgain for fish fed either the experimental orcontrol diet was not significantly different,most probably due to the small sample size.Survival of fish did not significantly differbetween dietary treatments.

There were no significant differences be-tween fish fed the experimental and controldiets for either filet, carcass, liver, or IPRall expressed as percent of total weight (Ta-ble 3). One difference in tissue indicesbased on sex was found. The IPI expressedas percent total weight, of males (6.lvo)was significantly higher than that of fe-males (5.2Vo). There were no diet depen-dent differences in the levels of protein, lip-id, ash, and moisture for either the filet orwhole body of fish fed the different diets(Table 4). Moisture content of the liver of

fish fed the control diet was significantlyhigher than that of fish fed the experimentaldiet.

Experiment 2

Thirty days after the experimenf began,one pond where fish were fed the experi-mental diet was removed from the studydue to an unexpected decline to a lethallylow level of dissolved oxygen. Therefore,results are based upon four replicate pondsfor the control dietary treatment and threereplicate ponds for the experimental dietarytreatrnent.

Mean stocking weight used as a co-var-iate did not improve the ANOVA and wasnot included in the final model. The meanindividual harvest weight, total production,and feed conversion ratios for the differentdietary treatments were not significantlydifferent. Also, percent survival, and per-

Test-s 4. Mean X SE proxirnate composition (Vo) of filet, liver, and whole body fish fed the experimental andcontrol diets in Experiment 1. Macronutrient composition is reported on a percent as is basis. (N) : namberof replicates. Means in each row for each tissue followed by dffirent letters differed at the 0.05 probabilitylevel b,t ANOVA (Zar 1974).

Filet (3) Liver (3) whole body (3)

Control Exp. Control Exp. Control Exp.

Crude proteinLipidAshMoisture

19.8 + 0.2a 19.8 + 0.5a5.6 + O.4a 6.1 + l.2a0.9 + 0.1a 0.9 I 0.0a

74.0 + 0.8a 73.O ! O.1a

19.1 + l.la 23.9 + O.8a

57.6 + 1.6a 51.8 + 1.0b

17.5 + 0.1a 16.6 + 0.8a12.3 + O.3a 38.4 t O.6a

3.1 + 0.3a 2.5 t O.la67.3 + O.la 67.0 + O.4a

322 D'ABRAMO ET AL.

TABLE 5. Mean t SE values of production characteristics and dressout percentages for fish fed the controland experimental dietary treatments in Experiment 2. There were no significant differences between treatments.(N) : number of replicates.

Production totals Control (4) Experimental (3)

Mean individual weight (g)Total production (kg/ha)FCRSurvival (7o)

Weight gain (7o)

Dressout percentages

347.2 + 48.O

2,507 + 4363.7 + O.9

83.8 + 3.8590 + 160

Control (4)

440.5 + 55.93,217 + 654

2.9 + O.2

84.3 + 6.3588 + 122

Experimental (3)

FiIetCarcassLiverIPF

35.7 + 0.561.8 + 0.32.9 + 0.15.1 + o.2

36.2 + 0.361.5 + O.2

3.0 + 0.15.1 + 0.1

cent weight gain were not significantly dif-ferent (Table 5).

The filet, carcass, liver, and IPF of fishfrom the two dietary treatments were notsignificantly different (Table 5) and, there-fore, the experimental diet would not be ex-pected to have any adverse effects on pro-cessing. No sex-specific differences in thesetissue indices were found.

In general, there were no diet-dependentdifferences revealed from the proximateanalyses of the filets and livers of the fishfed the experimental and control diets (Ta-ble 6). The lipid content of the liver ap-peared to be inversely related to the lipidcontent of the filet of fish fed the differentdiets. There were some significant differ-ences in fatty acid composition of the filetsand livers of fish fed the control or exper-imental diets (Table 7). Although these dif-ferences were not reflected in significantdifferences in either growth or survival of

fish in Experiment 2, they may have a yetto be determined biological significance.The total mean level of n-3 HUFA in thefilet tissue was 5.23Vo for flsh fed the con-trol diet and 2.37Vo for fish fed the experi-mental diet. These levels were reflective ofdifferences in dietary levels (6.98'and3.52Vo, respectively).

Discussion

Under the phase III pond culture condi-tions for sunshine bass in this study, the di-etary level of the menhaden fish meal in-gredient can be reduced from 30 to IOTo(dry weight) without any significant differ-ences in production and dressout character-istics. The similar dressout characteristicsindicate no potential adverse effects on pro-cessing of fish fed the experimental diet.However, comparable production could notbe achieved when the level of dietary crudeprotein and the menhaden fish meal ingre-

T,cnI-B 6. Mean ! SE proximate composition (Vo) of filet and liver of fishfed experimental and control dietsin Experiment 2. Macronutrient coinposition is reported on a percent as is basis. There were no significantdffirences between treatments for filet and liver tissue. (N) : number of replicates.

Filet (3) Liver (3)

Control Experimental Control Experimental

Crude proteinCrude lipid

(acid hydrolysis)AshMoisture

20.o + o.2

6.1 + 0.31.2 + 0.0

73.7 + O.4

19.8 + 0.1

7.3 + 0.61.3 + 0.0

73.4 + 0.6

24.2 + 2.3

57.1 + 1.5

21.5 + 3.8

58.1 + 1.4

REDUCED PROTEIN AND FISH MEAL IN FEEDS FOR SUNSHINE BASS 323

TABLE 7. Fatty acid composition offilets and livers offishfed the control and experimental diets in Experiment

2. (N) : number of replicates; * : not detected. Means in each row for each tissue followed by different

letters differed at the 0.OS probability level by ANOVA (Zar 1974). Means in each row for each tissue nol

followed by a letter were not significantly dffirent.

Filet (3) Liver (3)

Fatty acid Control" Experimental Control Experimental

C14:0Cl4:lC15:0C16:0C16:1Cl6:2C16:3C17:0Cl7:7C18:0C18:1Cl8:2 n-6C18:3 n-3C18:4 n-3C2O:.1

C2O:2C2O:3 lr-6C20:4 n-6C20:5 n-3C22:1C22:5 n-3C22:6 n-3C24:l

n-3 HUFAn-6 HUFAn-3HUFA/n-6 HUFA ratioTotal n-3 fatty acidsTotal n-6 fatty acids

2.53a0.1 1a

o.2019.675.860.28aO.2lao.270.304.35

34.47a16. l3

1.80

O.43a2.O2

1.000.41l.l7a2.37a0.16O.7la2.86a0. l8a

5.941.583.88.17

17.71

2.3lb0.14b0.18

19.675.600.18b0.12b0.250.314.26

37.50b16.57

1.74

0.34b2.tl0.950.400.90b1.48bo.170.49b1.89b0.14b

3.861.303.05.94

17.87

2.22O.l2a0. l3

14.936.76a0.18

o.20o.343.90

44.9013.371.600.35a3.631.30aO.32a1.46

o.2l0.42a1.33a0.14

1.751.781.03.70

15.15

2.490.18b0.1I

t6.o77.84b0.11

0.15o.343.59

46.73

12.t3t.35o.29b3.290.82bo.22b0.88

o.2l0.28b0.86bo.14

t.t41.101.02.78

13.23

dient were together decreased from 40 to36Vo and 30 to lsEo, respectively. Giventhat the primary protein sources of the dietsused in this study, soybean meal and men-haden fish meal, are highly digestible, it ap-pears that pond cultured hybrid striped bass

require 4OVo dietary protein for best growth.This required dietary level is supported bythe results of laboratory studies reported byBrown et al. (1992). The ratio of digestibleenergy to protein (E:P ratio) for both thecontrol and experimental diets used in bothexperiments was close to 8 kcaVg. This ra-tio was found to be optimal for weight gainof HSB and protein efficiency ratio (Ne-matipour et al. 1992), thereby supportingthe conclusion that 4OVo dietary protein is

required. The dietary levels of lysine andthe sulfur amino acids (methionine * cys-tine) in all the control and experimental di-ets in our study exceeded the requirementsfor these amino acids reported by Griffin etal. (1992) and Griffln and Brown (1992),respectively.

Our pond studies, both approximately24.5 wk, are the longest studies conductedrelative to evaluation of response to reduc-tion or elimination of fish meal in diets forhybrid striped bass. The successful reduc-tion of 65.OVo of dietary menhaden fishmeal represents a decrease from 47.3 tol5.7%o in its contribution to the amount oftotal dietary crude protein. As a result, a

more cost-stable formulation is possible

D'ABRAMO ET AL.

and, at the costs of the experimental andcontrol diets purchased for experiment 2, a6Vo reduction in feed costs is realized. As-suming mean production of phase III to be3,000 kglha and a feed conversion ratio(FCR) of 3.0, then US $222 is saved perha. Although the mean decrease of 0.8 inFCR for the experimental diet of Experi-ment 2 was not significantly better than thatof the control diet, this result suggests thatthe feed containing lOVo fist. meal wouldbe economically competitive with other di-ets. This study has shown that the amountof dietary fish meal can be successfully re-duced. However, caution needs to be exer-cised because the positive results are ulti-mately related to the quality, i.e., nutrientvalue, of the other ingredients used as sub-stitutes for the menhaden fish meal ingre-dient.

Whether fish meal can be replaced com-pletely at the 4OVo crude protein level hasnot been determined. Complete substitutionmay be possible if the proper mixture ofalternative sources of dietary protein, i.e.,soybean meal, meat and bone meal and dis-tillers' grains with solubles, or soybeanmeal and a poultry by-product meal areprovided as suggested by the recent resultsof feeding trials in aquaria (Webster et al.1999). However, complete elimination offish meal may not be possible under con-ditions of feeding in ponds because of itspresumed value as an effective attractant. Inaddition, sufficient replacement of losses ofHUFAs through increases in oils may berestricted by the feed manufacturing pro-cess.

Despite the lower level of HUFA in thediet containing the 107o fish meal, growthand survival were unaffected. In fact. for alldiets used in both Experiment 1 and Ex-periment 2, the dietary level of n-3 HUFAswas below the reported requirement of IVoof the diet or 2OVo of the dietary lipid (Ne-matipour and Gatlin 1993>. The results ofour study suggest that levels lower than thedietary requirement estimated from the re-sults of controlled experiments with juve-

niles in aquaria may not be completely ap-plicable to pond culture situations. In fact,the overriding factor relative to growth andsurvival may reside in provision of the ap-propriate ratio of dietary 22:6 n-3 to 2O:-5

rr-3.The comparatively high FCR values for

the phase III growout periods, all > 2.5,may be due to increased energy demandsassociated with high water temperatures.Afternoon pond water temperatures exceed-ed 30 C for almost 5OVo of the total cultureperiods. Growth rates of sunshine bass Mo-rone chrysops 9 X M. saxatilis d in aquar-ium studies have been observed to declinewith increasing temperature despite contin-ued high rates of feed co4sumption (Keem-biyehetty and Wilson 1998). As water tem-perature increased fuom 26.7 C to 32.2 C,energy conversion efficiency declined, sug-gesting an increased energy requirement formaintenance and/or activity of the fistr.Similar effects may have contributed to thehigh FCR values observed in our study.Therefore, improvement in growth atwarmer temperatures through modifi cationsof the nutrient composition of the diet ap-pears unlikely.

Acknowledgments

This research was funded in part throughgrants from the Southern Regional Aqua-culture Center and the Special ResearchGrants Program, United States Departmentof Agriculture. We thank Mr. Mack Fon-dren, Mr. Mark Peterman, and Ms. EllenThornton for their technical assistance andMrs. Holly Ohs, Mr. Shenjie Wu, Mr. Brad-ley Taylor, Mr. Tioy Lindsey and other staffof the Eastern Unit of the Thad CochranNational Warmwater Aquaculture Centerfor feeding the fish and monitoring andmanaging water quality.

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REDUCED PROTEIN AND FISH MEAL IN FEEDS FOR SUNSHINE BASS