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JOURNALOFTHE WORLD AQUACULTURE SOCIETY

Vol. 30, No. 1 March, 1999

Amino Acid Availability of Four Practical Feed Ingredients Fed to Striped Bass Morone saxatilis

BRIAN C. SMALL Department of Animal and Avian Sciences, University of Maryland,

College Park, Maryland 20742 USA

R~CHARD E. AUSTIC Department of Animal Sciences, Cornell University, Ithaca, New York 14850 USA

JOSEPH H. SOARES, JR.' Department of Animal and Avian Sciences, University of Maryland,

College Park, Maryland 20742 USA

Abstract Four dietary protein sources were bio-assayed for amino acid availability, as estimated by

true digestibility, when fed to striped bass Morone suxutilis. Diets were formulated to contain either herring fish meal, soybean meal, corn gluten meal or peanut meal as the sole source of dietary protein. A fifth diet, containing no protein, was fed to estimate the level of endogenous amino acids for calculation of true digestibility. The five dietary treatments were ran- domly assigned to ten tanks of striped bass having an average weight of 150 g per fish. All fish received the assigned diet fed at a rate 1.5% of the biomass per day for a period of 10 d. Fecal samples were collected from anesthetized fish by gentle, manual stripping of the lower digestive tract. Diets and feces were analyzed for dry matter, chromium, nitrogen and amino acid concentrations. There were no statistical differences (P > 0.05) among the protein sources for apparent dry matter digestibility or availability of arginine, threonine, valine and nonessential amino acids with the exception of cysteine. Corn gluten meal had a significantly lower availability coefficient for lysine, and peanut meal had significantly lower availability coefficients for histidine, isoleucine, leucine, and lysine when compared to herring fish meal and soybean meal. Statistically there were no differences between soybean meal and herring fish meal for any nutrient tested. These data suggest that in terms of amino acid availability and overall protein quality, soybean meal could be used to spare herring fish meal in striped bass diets, with corn gluten meal being equally as useful when supplemented with lysine or complemented with other proteins.

Striped bass Morone saxatilis and its hybrids M. saxatilis X M. chrysops are of growing importance in the aquaculture in- dustry. As the quantity of available nutrient requirement data for the striped bass and its hybrids increases, the ability to formulate species specific feeds becomes more feasi- ble. Recently the requirements of striped bass for the ten essential amino acids (EAA) were quantified in our laboratory (Small and Soares 1998). However, the bioavailability of amino acids in practical feed ingredients must also be quantified in order

I Corresponding author.

to optimally formulate nutrient sufficient, least-cost diets for the striped bass.

Bioavailability can be estimated by true digestibility. True digestibility is determined by comparing the quantity of amino acids consumed with those present in the feces, correcting for metabolic fecal amino acids (MFAA). Wilson et al. (1981) described a similar procedure for estimating the amino acid availability of several feed ingredients fed to the channel catfish. Other species of fish for which either apparent or true amino acid digestibility coefficients have been estimated include rainbow trout Oncorhynchus mykiss (Kaushik and Luquet 1976; Hilton and Slinger 1986; Perera et al.

0 Copyright by the World Aquaculture Society 1999

58

AMINO ACID AVAILABILITY OF PROTEINS IN STRIPED BASS DIETS 59

TABLE 1. Composition of diets (gAO0 g as fed) for determining the amino acid availability of herring fish meal (HFM). soybean meal (SBM), corn gluten meal (CGM) and peanut meal ( P M ) when fed to striped bass.

Diets

Ingredients HFM SBM CGM PM Protein free

Test ingredient 50.33 75.50 58.49 78.59 0 Herring fish oil 12.00 17.35 15.00 11.00 20.00 Dextrin 16.80 1.28 7.40 3.70 57.98 Cellulose 17.35 0 11.46 0.6 1 13.20 Vitamin premix' 0.50 0.50 0.50 0.50 0.50 L-Ascorbic acid 0.10 0.10 0.10 0.10 0.10 Choline chloride, 70% 0.40 0.40 0.40 0.40 0.40 Mineral premixh 0.15 0.15 0.15 0.15 0.15 Cr,O, 1 .OO 1 .00 1 .oo 1 .oo 1 .00 NaCl 0.62 1.39 1.34 1.40 1.44 NaHCO, 0.56 0 0.48 0 0.48 K2COj 0.10 0 0.86 0 1.06 MgCO, 0.09 0 0.18 0 0.35 Ca,(PO,), 0 2.33 2.62 2.55 3.33

a mgkg premix: retinyl palmitate, 20; menadione dimethyl pyrimidinol bisulfite, 22; cholecalciferol, 10; dl-a- tocopheryl acetate, 3 120; thiamin HCI, 40; riboflavin, 30; d-Ca-pantothenate, 150; niacinamide, 150; pyridoxine HCI, 20; d-biotin, 3; folk acid, 15; cyanocobalamin (0.1% in mannitol), 200; inositol, 1OOO; ethoxyquin (anti- oxidant), 220.

mgkg premix: MnS04.H20, 315; ZnS0,.7H20, 680; CuS0,.5H20, 6 0 FeSO4.7Hz0, 500; KIO,, 8.5; Na2Se0,, 0.3; NaMoO,.W,O, 8.3.

1995), sea bass Dicentrarchus labrax (Spyridakis et al. 1988), common carp Cy- prinus carpio (Hossain and Jauncey 1989), Atlantic salmon Salmo salur (Anderson et al. 1992) and gilthead seabream Sparus au- rata (Lupatsch et al. 1997). To our knowl- edge, there are no data published on amino acid availability of feed ingredients for the striped bass or its hybrids. The present study was designed to determine the bioavailability of amino acids, as estimated by their true digestibility coefficients, for four practical feed ingredients fed to striped bass.

Materials and Methods Diets were composed of either herring

fish meal (HFM), corn gluten meal (CGM), soybean meal (SBM), or peanut meal (PM) as the sole source of dietary protein. The SBM used in this study was autoclaved to a dye-binding factor of 4.06 prior to incor- poration in the diet to destroy antinutrition- al factors (Ketola and Baltusis 1993). The test ingredients were incorporated into diets

at a level of 36% crude protein. The re- mainder of the diet was formulated to contain 9.0 kcal of metabolizable energy per gram of crude protein (NRC 1993), 1% chromic oxide as an indicator, and a minimum of 0.8% calcium, 0.6% available phosphorus, 0.1 % magnesium, 0.7% sodium, 0.6% potassium, and 0.9% chloride (Table 1). The composition of the protein free diet used to estimate endogenous amino acids in the excreta is also given in Table 1. All diets were mixed and cold pelleted by H. G. Ketola at the U.S. Biological Ser- vice Tunison Laboratory, Cortland, New York, USA.

Juvenile striped bass were obtained from L. C. Woods of the Department of Animal and Avian Sciences hatchery at the Crane Aquaculture Facility, Baltimore, Maryland, USA as fingerlings, and reared in circular fiberglass tanks to an average weight of 150 g. Striped bass were then stocked in 1,000- L tanks at 13 fish per tank. For 1 mo prior to starting both experiments, all fish were fed a commercial hybrid striped bass feed

60 SMALL ET AL.

(Southern States Cooperative, Inc., Rich- mond, Virginia, USA).

Fish were reared in tanks supplied with dechlorinated water in a flow-through system at a rate of two complete turnovers per day. Calcium chloride and sodium chloride (9: l), as a solution, were injected directly into the incoming water line at a continuous rate in order to achieve a minimum concen- tration of 36 mg c a l c i u d in the rearing tanks. A photoperiod of 12L:12D was maintained throughout the experiment. Wa- ter temperature was maintained at 23 C and recorded four times daily via a central com- puterized monitoring system (REES Scien- tific, Trenton, New Jersey, USA). All other parameters were monitored weekly throughout the experiment to insure adequate levels of pH, dissolved oxygen (DO), ammonia, chlorine, and Cahardness. DO and temperature were measured with a YSI model 58 oxygen meter (YSI Incorporated, Yellow Springs, Ohio, USA). pH was monitored with a Coming model 250 Ion ana- lyzer (Coming Incorporated, Coming, New York, USA). Chlorine, both free and total, and ammonia were measured using a Hach DR/700 colorimeter (Hach Company, Loveland, Colorado, USA). Calcium con- centration was determined with a Hach model HA4P hardness test kit and by atomic absorption spectrophotometry using a Perkin-Elmer 5100 PC atomic absorption spectrophotometer (Perkin-Elmer Corpora- tion, Norwalk, Connecticut, USA). Throughout the experiment, environmental conditions were maintained as outlined by Nicholson et al. (1990).

Fish were fed at a rate of 1.5% of tank biomass daily divided into two feedings Monday through Friday and one feeding Saturday and Sunday. The five dietary treatments were fed to ten tanks of striped bass for a period of 10 d prior to fecal collection.

A total of 2.5 h was allowed to pass between feeding and the start of fecal collection. Feces were collected by gentle, manual pressure manipulation of the lower di-

gestive tract from the anal fin to the anus. Caution was taken to avoid contaminating the sample with mucus or urine. In all cas- es, the fish were anaesthetized with 0.2-g tricaine methanesulfonate (MS-222)L prior to handling, the bladder was evacuated by slight pressure, and urine and mucus were wiped from the anal area with a cloth. Feces were collected from all fish in a given tank and pooled by tank for analysis.

Samples of test diets and feces were dried overnight in a forced air oven at 60 C, ground in a CRC micro mill (Chemical Rubber Company, Cleveland, Ohio, USA), and stored in a desiccator for subsequent analysis. Diet and fecal samples were analyzed for chromium, amino acids and nitrogen. Chromium was determined by colori- metric analysis after perchloric acid digestion as described by Saha and Gilbreath (1991). Samples analyzed for amino acid concentrations were first treated with per- formic acid to oxidize methionine and cystine to methionine sulfone and cysteic acid before hydrolysis (Spindler et al. 1984). Samples were then hydrolyzed in duplicate in 6 N HC1 at 110 C for 21 h (Krick et al. 1993) before chromatographic separation using ninhydrin detection and an automated peak integration system (Spectra-Physics, San Jose, California, USA). Tryptophan, phenylalanine and tyrosine, however, were degraded by the acid hydrolysis and per- oxidation procedures, and were not recovered by this method. Crude protein was determined by multiplying the nitrogen con- centration by 6.25.

Apparent digestibility coefficients (ADC) for dry matter and crude protein were calculated as follows:

ADC (%)

= 100 - [lo0 X (Cr,03Food/Cr203Feces)

X (Nutrient,,,, / Nutrient Food)]

(1)

True amino acid digestibility coefficients (TDC) were calculated by correcting the


TABLE 2. Mean apparent dry matter, crude protein and true amino nitrogen digestibility coeficienrs for herring fish meal, soybean meal, corn gluten meal and peanut meal fed to striped bass.

Dry matter Crude protein Amino nitrogen digestibility (%) digestibility (%) digestibility (%)

Herring fish meal 68.4 87.9ab 88.4ah Soybean meal 72.2 92.6a 92.3" Corn gluten meal 70.8 90.7ah 90.8ah Peanut meal 60.3 85.3h 82.7h PSE' 4.5 1.8 2.3

I Pooled standard error. ah Means (N = 2) not sharing similar superscripts within columns are significantly different ( P < 0.05).

apparent amino acid digestibility coefficients for metabolic fecal amino acids as follows:

TDC (%)

= 100 - [loo X ( C r * O ~ ~ o o ~ / C r * O ~ ~ e c ~ ~ )

X ((Amino acidFeces - MFAA)

+ Amino acidFd)] (2) The metabolic fecal amino acids were determined by feeding a protein-free diet. True amino nitrogen digestibility values

TABLE 3. Mean amino acid true digestibility coefi- cients for herring fish meal (HFM), soybean meal (SBM), corn gluten meal (CGM) and peanut meal (PM) fed to striped bass.

True digestibility coefficients (%)

Amino acid HFM SBM CGM PM PSEI

Alanine 90.8 92.1 95.1 86.3 1.7 Arginine 94.4 97.2 94.6 93.4 1.0 Asparagine 81.7 92.3 90.4 85.7 2.7 Cysteine 63Sh 69.6h 87.2' 71.0h 3.9 Glutamate 93.1 95.7 94.7 86.9 2.7 Glycine 84.6 91.0 89.2 78.2 3.7 Histidine 88.5' 92.3" 83.Qh 65.3h 5.8 Isoleucine 90.lUh 94.1" 92.1ah 87.7h 1.6 Leucine 92Sah 94.8" 96.4a 87.Sh 1.7 Lysine 91.5" 94.8" 87.3h 85.2h 1.7 Methionine 89.2ah 92.Q 90.9sh 82.3h 2.4 Pro!ine 89.2 94.4 93.3 87.5 1.8 Serine 88.3 93.6 92.6 85.8 1.9 Threonine 89.9 91.4 93.1 85.4 2.2 Valine 89.7 93.4 92.9 86.5 1.9

I Pooled standard error. ah Means (N = 2) not sharing similar superscripts

within rows are significantly different ( P < 0.05).

were determined by averaging the true amino acid digestibility values with respect to the nitrogen content of each amino acid.

Mean values and pooled standard errors were calculated for each treatment with each tank being a replication (N = 2). Data were analyzed by analysis of variance mixed model procedures (SAS Institute Inc. 1992). Pairwise contrasts were used to identify significant differences at the 5% level between the means of the amino acid digestibility coefficients for different test ingredients.

Results Digestibility coefficients for dry matter,

crude protein and amino nitrogen were calculated using formulas (1) and (2), respectively, and a comparison is presented in Ta- ble 2. The apparent dry matter digestibility ranged from a minimum of 60.3% for peanut meal to a maximum of 72.2% for soybean meal, with no significant ( P > 0.05) differences among test ingredients. Crude protein and amino nitrogen digestibility values were similar except where determined for peanut meal.

Mean amino acid true digestibility (availability) coefficients for the four test ingredients are presented in Table 3. Among the essential amino acids, significant differences (P C 0.05) occurred for histidine, isoleucine, leucine, lysine and methionine across test ingredients. Peanut meal had significantly lower digestibility values for each of these amino acids. Both corn gluten meal

62 SMALL ET AL.

and peanut meal were found to have lower digestibility values for lysine, and corn gluten meal had a significantly higher cysteine digestibility when compared among treatments. Overall, the average availability coefficients of all the amino acids ranged from 63.5% for cysteine in hemng fish meal to 97.2% for arginine in soybean meal, with average amino nitrogen digestibilities of 88.4%, 92.3%, 90.8% and 82.7% for herring fish meal, soybean meal, corn gluten meal and peanut meal, respectively.

Discussion

Methods for determining nutrient digestibility coefficients of fish feedstuffs have been reviewed by several authors. Nose (1960) was the first to use chromic oxide to determine protein digestibility in fish. Inaba et al. (1961) found digestibility coefficients based on feces recovered after being voided into the water were about 10% higher than coefficients based on analysis of feces stripped manually from the fish, indicating the loss of nutrients to the surrounding water or the inclusion of undigested feed in the feces collected by stripping. Cho et al. (1982) suggested forced evacuation would also result in the addition of excess en- zymes, body fluid and intestinal epithelium in the feces. Austreng (1978) reviewed methods of fecal collection after estimating digestibility coefficients on the analysis of feces collected by two stripping methods and dissection from five zones of the ali- mentary canal. It was concluded that protein absorption occurs mainly in the small intestine and that stripping of feces should be limited to the hindmost part of the rec- tum. While none of the methods used for fecal collection are error free, Austreng (1978) concluded that stripping from the ventral fin to the anus was satisfactory for estimating digestibility coefficients of feedstuffs fed to salmonids. While actual values may differ as a result of the method of fecal collection, errors in estimation would be of minimal importance when comparisons are

made among data amassed using similar collection methods.

In the present study, levels of dietary cellulose were varied in order to keep the diets isoenergetic and isonitrogenous. Fish, like other animals, adjust their dietary energy intake according to digestible energy levels (Morales et al. 1994). Dietary protein levels have also been found to effect protein digestibility in fish (Carneiro et al. 1994; Pe- reira-Filho et al. 1994). The effect of dietary fiber on protein digestibility has been well established in the rat. Rats fed increas- ing levels of dietary fiber at a fixed level of dietary protein demonstrated lower digestibilities for protein, dry matter and energy when fed on the high-fiber diet (Zhao et al. 1995). However, when protein levels reached 40% of the diet, dietary fiber levels of 20% did not greatly decrease protein digestion (Saito 1992). Diets fed in the present study were formulated to be in excess of the amino acid requirements for striped bass, thus, the effect of varying energy and crude protein were deemed greater than the effect of varying dietary fiber. While not statistically significant, numerically lower digestibility values for herring fish meal when compared to soybean meal may be a result of the high level of cellulose included in the hemng fish meal diet.

The apparent dry matter digestibility coefficients were similar among the test ingredients, hemng fish meal, soybean meal, corn gluten meal and peanut meal. These are contradictory to results published for hybrid striped bass Morone sanatilis X M. chrysops by Sullivan and Reigh (1995), who reported higher apparent dry matter digestibility coefficients for hybrid striped bass fed ingredients of animal origin as compared to ingredients of plant origin, suggesting poor digestibility of intact starch. The dry matter digestibility coefficient for soybean meal fed to hybrid striped bass was reported as 44.5%. We report 72.2% for the soybean meal fed to pure striped bass in this study. This discrepancy may also be due to processing. Sullivan and


Reigh (1995) did not utilize any type of heat pretreatment, but by autoclaving the soybean meal used in this study, not only was there destruction of anti-nutritional factors, but there may also have been gelati- nization of the starch.

Apparent digestibility coefficients of crude protein were high among the four test ingredients regardless of origin. These results are similar to those reported for the hybrid striped bass (Sullivan and Reigh 1995) and other species of carnivorous fishes. High protein digestibility coefficients of fish meal and plant meals were reported (280%) for rainbow trout (Alexis et al. 1988), Atlantic salmon (Anderson et al. 1992) and yellowtail Seriola quinqueradiara (Masumoto et al. 1996). The high protein digestibility of plant meals suggests that they may be effectively substituted for fish meal in the diets of striped bass and other carnivorous fishes.

The availability, as measured by true digestibility, of amino acids was high among the ingredients, with the exception of cysteine from herring fish meal, soybean meal and peanut meal, possibly due to differences in structural proteins, and histidine from peanut meal. Calculation of amino nitrogen and the associated digestibility coefficients yielded values similar to the crude protein digestibility coefficients for individual protein sources. Amino acid availability values for individual ingredients varied by as much as 27% from crude protein digestibility values. Also, there were significant differences between digestibility coefficients of some of the essential amino acids within a protein source. Thus, amino acid availabilities cannot be estimated from the apparent digestibility coefficients of crude protein. A similar conclusion was suggested by Lupatsch et al. (1997).

In summary, the results of this study in- dicate that both soybean meal and corn gluten meal may be substituted for fish meal in diets formulated for striped bass, as long as the lower availability of lysine in corn gluten meal is taken into account. These

data also suggest that peanut meal is a lower quality protein and thus would not be an adequate substitute per se for fish meal when fed to striped bass. Individual amino acid availabilities are also variable within ingredients. Thus, the use of individual amino acid availability, as opposed to crude protein or average amino nitrogen digestibility values, allows for more accuracy and specificity when determining the protein quality of an ingredient and the need for supplementation of feed formulas. There- fore, use of individual amino acid availability values would improve the ability to formulate nutritious least cost diets for striped bass.

Acknowledgments A special thanks goes to Daniel Brougher

and Kathy Hughes for their help during the conduct of these experiments. We wish also to thank Dr. George Ketola for manufactur- ing the experimental diets and Dr. L. Curry Woods for providing the striped bass. This study was supported by a competitive grant from the Northeastern Regional Aquacul- ture Center (#555502).

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