www.elsevier.nlrlocateraqua-online
The effect of dietary feeding stimulants on growth
performance of striped bass, Morone saxatilis,
fed-a-plant feedstuff-based diet
Elias Papatryphon, Joseph H. Soares Jr.
)Graduate Program in Marine-Estuarine and EnÕironmental Sciences, Department of Animal and AÕian
Sciences, UniÕersity of Maryland, College Park, MD 20742-2311, USA
Accepted 29 October 1999
Abstract
An experiment was conducted to evaluate the effects of a previously identified feeding
Ž . X
stimulant FS mixture, which contained L-alanine, L-serine, inosine-5 -monophosphate and
be-taine, on growth performance of striped bass, fed-a-plant feedstuff-based diet. Three diets were fed to striped bass for a period of 6 weeks: a plant feedstuff-based basal, and the basal
Ž . Ž . Ž
supplemented with either a low 2% or a high 4% level of the FS mixture 2% FS and 4% FS,
.
respectively . A significant improvement in feed intake was observed for fish fed the 4% FS when
Ž .
compared to fish fed the basal diet after 4 weeks PF0.02 and this difference was increased
Ž . Ž .
after 6 weeks PF0.0009 . Fish fed the 2% FS had significantly higher PF0.05 feed intake
Ž .
than fish fed the basal at 6 weeks, but lower feed intake PF0.05 than fish fed the 4% FS. Weight gain was significantly improved in fish fed the 4% FS when compared to fish fed the basal
Ž .
diet at 4 and 6 weeks PF0.02 and PF0.0005, respectively , and when compared to fish fed the
Ž .
2% FS at 6 weeks PF0.05 . Feeding the 2% FS diet resulted in a significant increase in weight
Ž .
gain over fish fed the basal diet only at week 6 PF0.02 of the experiment. Feed conversion ratio was significantly improved in fish fed both levels of the FS mixture when compared to that
Ž .
of fish fed the basal diet at week 4 PF0.05 and remained significantly improved after 6 weeks
Ž .
of feeding PF0.03 . These results indicate that using FS as a supplement in plant-based diets may be useful in improving feed acceptability and growth performance of cultured striped bass fed low cost, plant-based diets.q2000 Elsevier Science B.V. All rights reserved.
Keywords: Feeding; Stimulants; Striped bass; Intake; Plant ingredients; Palatability; Growth
)Corresponding author. Tel.:q1-301-405-5785; fax:q1-301-314-9059.
Ž .
E-mail address: js89@umail.umd.edu J.H. Soares .
0044-8486r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved.
Ž .
1. Introduction
Although a substantial amount of research has been conducted on the identification of
Ž .
feeding stimulants FS for fish, there are only a few cases where FS have been applied to practically formulated diets. FS can be of immediate practical importance in
enhanc-. Ž
ing the acceptance of: 1 artificial feeds by first feeding larvae and fry Metailler et al., 1983; Person-Le Ruyet et al., 1983; Hughes, 1991; Kamstra and Heinsbroek, 1991;
. .
Heinsbroek and Kreuger, 1992 and 2 diets containing low cost feedstuffs of low
Ž .
palatability Takeda and Takii, 1992 .
Currently, the diets used for feeding striped bass contain high levels of animal protein
Ž .
in general and fish meal in particular Gatlin, 1997 . Such diets are not only costly, but contribute to the eutrophication of receiving waters because of excessively high levels of
Ž .
phosphorus excreted from the fish Ketola and Harland, 1993 . Moreover, future
supplies of fish meal are expected to decrease, or at best remain constant, while
Ž
aquaculture production is increasing at a steady rate Food and Agriculture Organization,
.
1999 . The three factors mentioned above necessitate the identification of new protein sources to partially or totally replace fish meal in diets for cultured fish.
It has already been suggested that a means to reduce the cost of diets for carnivorous
Ž
fish is to use plant feedstuffs as replacements of expensive animal proteins Cho et al.,
.
1974; Tacon, 1994 . A major obstacle in using high levels of plant feedstuffs, besides nutrient composition and availability, is poor acceptance of the diets. A decrease in feed
Ž
intake has been reported with inclusion of soybean meal in diets for rainbow trout Cho
. Ž . Ž
et al., 1974 , red drum Reigh and Ellis, 1992 , channel catfish Mohsen and Lovell,
. Ž . Ž .
1990 and largemouth bass Kubitza et al., 1997 . In addition, Davis et al. 1995 reported that soy protein did not have acceptable palatability properties for red drum. In
Ž .
a subsequent study, McGoogan and Gatlin 1997 reported that glycine supplementation enhanced growth and feed efficiency of red drum fed soybean meal-based diets. Gomes
Ž .
et al. 1997 showed that both soy protein concentrate-based diets, as well as corn gluten meal-based diets, reduced feed intake of European sea bass. Furthermore, it was demonstrated in the same study that addition of an amino acid attractant mixture improved feed intake, growth and feed efficiency of fish fed the soy protein concentrate-based diets.
Ž .
FS for striped bass have been recently identified Papatryphon and Soares, in press . Furthermore, it was demonstrated that maximum feeding stimulation was accomplished
with a mixture ofL-alanine,L-serine, inosine-5X-monophosphate and betaine, which is in
agreement with previous studies suggesting that mixtures are more effective than
Ž .
individual compounds Carr and Derby, 1986 . The advantages of using these com-pounds in practical applications, however, remains to be shown.
2. Materials and methods
2.1. EnÕironmental
Municipal water was supplied to each tank via a flow through system, where incoming water was filtered through an in-line particulate filter and an activated carbon
Ž .
filter to remove chlorine. An electrolyte solution of CaCl :NaCl 9r1, wrw was added2
continuously to increase the electrolyte concentration and maintain a hardness of
approximately 170 mgrl and a Ca2q concentration of approximately 40 mgrl.
Supple-mental aeration was provided via airstone diffusers to reach a dissolved oxygen concentration of at least 7.0 mgrl dissolved oxygen. The temperature was maintained at
22–248C. Hardness, pH, ammonia, chlorine, temperature and dissolved oxygen were
measured weekly. Water conditions were closely maintained at levels recommended for
Ž .
the striped bass Nicholson et al., 1990 . The photoperiod was set at 12-h light:12-h dark. Tanks were cleaned of solid debris twice a week. Animal handling and rearing conditions followed an approved protocol by the University of Maryland Animal Care and Use Committee.
2.2. Diets
Three dietary treatments were fed to 10 tanks of striped bass for a period of 6 weeks
Ž .
in a completely randomized design. The basal diet Table 1 , which was fed to four replicate tanks of fish, was nutritionally complete and was based on plant feedstuffs. The two test diets were fed to three replicate tanks each and were identical to the basal diet
Ž . Ž . Ž
with the exception that 2% 2% FS and 4% 4% FS of the plant feedstuffs isolated
.
soy protein, soybean meal, corn gluten meal and wheat middlings were replaced by an
Ž . X
isocaloric and isonitrogenous by calculation mixture ofL-alanine, Lserine, inosine5
-Ž .
monophosphate and betaine Table 1 . The diets were formulated to meet all known
Ž .
nutrient requirements for Morone species Gatlin, 1997; Small and Soares, 1998 . The
Ž .
nutrient requirements established for chinook salmon NRC, 1993 were used where information on striped bass was lacking. The dietary ingredients were mixed and cold
Ž .
pelleted in a laboratory pellet mill CPM, San Francisco, CA . The four chemicals were
Ž
added to the diets at equimolar concentrations to reach 2% and 4% of the diet 0.03 and
.
0.06 M, respectively . Just prior to pelleting, the chemicals were dissolved in distilled
Ž .
water 20% by weight of the diet and mixed into the diet. Following pelleting, the diets
were dried overnight in a forced-draft oven at 608C.
2.3. Experimental animals
Ž .
Striped bass Morone saxatilis were obtained from the Blackwater Fisheries
Re-Ž .
search and Development Center Holt, FL and were acclimated in our tanks for a period
Ž .
of 30 days. Striped bass initial mean weight: 11.8 g were stocked in ten 400 l tanks at
Ž .
a density of 38 fishrtank biomass: 1.12 grl . Fish were fed twice daily to satiation
Table 1
Ž . Ž .
Ingredient composition %, as fed and calculated protein and digestible energy levels dry matter of the
Ž . Ž .
basal, 2% feeding stimulant mix 2% FS , and 4% feeding stimulant mix 4% FS supplemented diets fed to striped bass for 6 weeks
Ingredients Basal 2% SM 4% SM
Wheat middlings 21.00 20.50 20.00
Soybean meal 20.70 20.20 19.70
Corn gluten meal 20.25 19.75 19.25
Ž .
Soybean protein concentrate 70% 6.00 5.50 5.00
Feather meal 10.00 10.00 10.00
Choline chloride 77% 0.25 0.25 0.25
Lysine HCl 0.60 0.60 0.60
Digestible energy kcalrkg 3827 3829 3830
a Ž .
Vitamin mix contains mgrkg of diet : ascorbic acid, 400.0; inositol, 440.0; Santoquin, 140.0; niacin, 170.0; alpha-tocopheryl acetate, 500.0; phylloquinone, 15.0; riboflavin, 23.0; thiamin, 14.0; pantothenic acid,
Ž .
56.0; pyridoxine, 14.0; folic acid, 6.0; biotin, 5.0; cyanocobalamin 3000 ugrg , 19.5 ugrkg; retinol ester
Ž500,000 Urg , 2750; cholecalciferol, 5 ug. rkg; cerelose as a filler.
d Ž . X
Stimulant mix in 2% FS contains grkg of diet :L-alanine, 2.71;L-serine, 3.20; inosine-5 -monophos-phate, 10.53; betaine, 3.56.
e Ž . X
Stimulant mix in 4% FS contains grkg of diet :L-alanine, 5.42;L-serine, 6.40; inosine-5 -monophos-phate, 21.06; betaine, 7.12.
f Ž .
Calculated from published values NRC, 1993 .
beginning of the study and every 2 weeks thereafter. Feed intake, growth and feed
Ž .
conversion ratios FCR were calculated throughout the course of the study.
2.4. Experimental design and statistical analyses
A completely randomized design was used. Data were analyzed by one-way ANOVA
Ž .
using SAS software SAS Institute, 1992 . The data were examined for meeting the
Ž . Ž .
assumptions of the analysis of variance ANOVA Sokal and Rohlf, 1987 . For the feed
intake and weight gain data, a repeated measures ANOVA was performed and LSD pairwise contrasts were used to compare the means at each period. Pairwise contrasts
ŽLSD were also used for the FCR data..
3. Results
Ž
The feed intake data of striped bass fed the three experimental diets basal, 2% FS,
.
and 4% FS are shown in Fig. 1a. Feed intake was higher for fish fed the FS-supple-mented diets when compared to fish fed the basal diet, although the magnitude of the increase was greater in fish fed the 4% SM diet. Specifically, feed intake of fish fed the 2% FS diet was significantly higher than fish fed the basal at 6 weeks of feeding
ŽPF0.05 , whereas in fish fed the 4% FS diet, significant improvements are evident at.
Ž . Ž .
4 PF0.02 and 6 PF0.0009 weeks of feeding. In addition, feed intake of fish fed
Ž .
the 4% FS diet was also increased PF0.05 when compared to fish fed the 2% FS diet
Ž .
after 6 weeks of feeding. Significant increases in weight gain Fig. 1b were achieved in
Ž .
fish fed the 2% FS diet at 6 weeks of feeding PF0.02 and fish fed the 4% FS diet at
Ž . Ž .
4 PF0.02 and 6 PF0.0005 weeks of feeding when compared to fish fed the basal
diet. Fish fed the 4% FS diet had significantly improved weight gain when compared to
Ž .
fish fed the 2% FS diet at 6 weeks PF0.05 . A significant improvement in FCR in fish
fed the 2% FS and 4% FS diets over fish fed the basal diet was first evident at 4 weeks
Ž . Ž . Ž . Ž .
Fig. 1. a Feed intake grfish and b Growth grfish of striped bass fed the basal, 2% feeding stimulant
Ž . Ž . Ž .
mix 2% FS and 4% feeding stimulant mix 4% FS diets for 6 weeks. Means vertical bars indicate"S.E.
Ž .
Table 2
Ž . Ž .
Feed conversion ratios FCR of striped bass fed the basal, 2% feeding stimulant mix 2% FS and 4% feeding
Ž . a Ž .
stimulant mix 4% FS diets for 6 weeks. Means numbers in parentheses indicate S.E. sharing the same
Ž .
letter within a period are not significantly different by LSD comparison P-0.05
Period FCR
Basal 2% FS 4% FS
Ž . Ž . Ž .
0–2 weeks 1.45 0.08 1.31 0.09 1.39 0.09
a b b
Ž . Ž . Ž .
0–4 weeks 1.58 0.05 1.38 0.06 1.40 0.06
a b b
Ž . Ž . Ž .
0–6 weeks 1.53 0.04 1.36 0.05 1.32 0.05
a
ns4 for the Basal; ns3 for 2% FS and 4% FS treatments.
Ž .
of feeding PF0.04 and PF0.05, respectively; Table 2 and remained significant
Ž .
throughout the completion of the experiment PF0.03 and PF0.01, respectively .
4. Discussion
Most studies conducted so far with FS for fish have focused on short-term feed intake data neglecting the importance of prolonged studies in growth trials. Long-term studies can better describe the effect of a FS mixture in a practical growout operation. It has already been suggested that FS lose their potency if fed in diets for prolonged periods,
Ž .
especially when feeding at high levels Kamstra and Heinsbroek, 1991 . Results from our studies indicate that supplementation of the plant-based basal diet with a FS mixture improved the performance of striped bass. Feed intake was significantly improved by the fourth week of the experiment for the group receiving the 4% FS diet and by 6 weeks for fish fed the 2% FS diet. By the end of the experiment, feed consumption of fish fed the 2% FS and 4% FS diets was improved by 10.5% and 21.8%, respectively, when compared to the consumption rates of fish fed the basal diet.
Similarly, weight gain was significantly improved by the fourth week of the experiment in fish fed the 4% FS diet and by 6 weeks for fish fed the 2% FS diet. In addition, the final weight of fish fed the 2% FS and 4% FS diets, when compared to fish fed the basal diet, was improved by 9.7% and 17.5%, respectively. The similarity in the patterns between the feed intake and weight gain data support the hypothesis that the mixture added to the basal diet acts directly as a FS. The effectiveness of the FS supplementation on weight gain is better demonstrated when the data are expressed as a percent weight gain, which results in: 81.6% for fish fed the basal diet, 99.2% for fish fed the 2% FS diet and 113.3% weight gain for fish fed the 4% FS diet. Although
Ž .
this experiment if 4% supplementation yields the maximum response. Furthermore, the optimum level would most probably vary in response with the composition of the basal diet. One would also have to take into account the cost for incorporating the FS into the diet as counterbalanced by the prospective increases in production.
The lack of precision in quantifying the exact amount fish will consume when fed to satiation, and the potential bias in manual feeding, have been a common criticism when conducting feed intake studies with fish. In the present study, however, the feed intake, weight gain and FCR data corroborate the conclusion that feeding was not biased. It is of interest to note that FS supplementation did not only have an effect on FI and subsequently weight gain, but also effected FCR, indicating an overall increase in the efficiency of the diet. The lower FCR values attained with fish fed the FS-supplemented diets could be due, at least partly, to the feed intakermaintenance requirement ratio. If this was the sole reason, however, one would also expect a difference in FCR between the two FS-supplemented diets. It has been suggested that an increase in the palatability of a diet will result in better dietary utilization as a response to the cephalic reflex
ŽGiduck et al., 1987 . Fange and Grove 1979 suggested that the cephalic reflex occurs. Ž .
Ž .
in fish as well as in mammals. Takii et al. 1986a,b observed significant increases in the activity of several digestive and hepatic enzymes in eels fed a FS-supplemented diet when compared to fish fed an unsupplemented basal diet. Perhaps the increased performance of striped bass in our study was not only a result of increased feed intake but of additional improvements in the digestive andror metabolic capabilities. This postulate is only hypothetical, however, because we currently have no data on cephalic reflex responses in striped bass.
Improvements in feed intake, weight gain and feed efficiency as a result of FS
Ž .
supplementation have been previously observed in Japanese eel Takii et al., 1986a ,
Ž . Ž .
gilthead bream Tandler et al., 1982 and European seabass Gomes et al., 1997 .
Ž .
Addition of betaine to diets for prawns, Macrobrachium rosenbergii Harpaz, 1997 resulted in increased feed consumption and growth rate and addition of a betaineramino
Ž .
acid mix in diets for shrimp, Penaeus monodon Dy Penaflorida and Virtanen, 1996 , resulted in increases in feed intake, weight gain, SGR and FCR. Betaine is believed to have a response as a palatability enhancer as well as a methyl donor and osmoprotectant.
Ž
In our study, all diets had adequate levels of choline calculated at 3204, 3174 and 3144
.
mgrkg for the basal, 2% SM and 4% SM diets, respectively and an effect of betaine as a precursor of choline seems unlikely. On the other hand, betaine has been characterized
Ž
as an osmoprotectant in salmon and trout Virtanen et al., 1989, 1994; Clarke et al.,
.
1994; Castro et al., 1998 and, as such, it could also have a positive effect on striped bass. However, the positive effects of betaine in the salmonids were evident only during seawater adaptation and thereafter, whereas no significant effects were observed during the freshwater stage, which was the environment of our experiment.
there are several studies with hybrid striped bass of similar initial size that have reported
Ž .
higher growth rates Nematipour et al., 1992; Keembiyehetty and Wilson, 1998 , our
Ž .
growth rates are comparable to the highest ones attained by Berger and Halver 1987 , who used similar sized striped bass fed a herring meal-based diet. In addition, our
Ž
highest growth rates are similar to reported values for hybrid striped bass Gallagher,
.
1994, 1995 fed a high fish meal-based diet. Therefore, there is promise that FS-supple-mented plant feedstuff-based diets may become important in the future.
In order to use plant protein sources for the development of less costly, ‘‘environmen-tally friendly’’ diets for striped bass, it is necessary to find ways to improve the low palatability of plant feedstuff-based diets. We believe that the data presented here suggest that cost-effective FS will be of importance in enhancing the acceptance and utilization of more economical but nutrient sufficient diets for the striped bass and perhaps other finfish.
Acknowledgements
Special thanks to Sara Pollack, Laura Ellestad, Jeannine Washington and Dan Brougher for their help during the conduct of the experiment. Appreciation is extended
Ž
to Dave Yeager at the Blackwater Fisheries Research and Development Center Holt,
. Ž .
FL for supplying the fish and Omega Protein Corporation Reedville, VA for donating the fish oil. This research was supported by a grant from the Maryland Agriculture
Ž .
Experiment Station MD-AQUA-97-03 .
References
Berger, A., Halver, J.E., 1987. Effect of dietary protein, lipid and carbohydrate content on the growth, feed
Ž .
efficiency and carcass composition of striped bass, Morone saxatilis Walbaum , fingerlings. Aquacult. Fish. Manage. 18, 345–356.
Carr, W.E.S., Derby, C.D., 1986. Behavioral chemoattractants for the shrimp, Palaemonetes pugio: identifica-tion of active components in food extracts and evidence of synergistic mixture interacidentifica-tions. Chem. Senses 11, 49–64.
Castro, H., Battaglia, J., Virtanen, E., 1998. Effects of FinnStim on growth and sea water adaptation of coho salmon. Aquaculture 168, 423–429.
Cho, C.Y., Bayley, H.S., Slinger, S.J., 1974. Partial replacement of herring meal with soybean meal and other
Ž .
changes in a diet for rainbow trout Salmo gairdneri . Fish. Res. Board Can. 31, 1523–1528.
Clarke, W.C., Virtanen, E., Blackburn, J., Higgs, D.A., 1994. Effects of a dietary betaineramino acid additive on growth and seawater adaptation in yearling chinook salmon. Aquaculture 121, 137–145.
Davis, D.A., Jirsa, D., Arnold, C.R., 1995. Evaluation of soybean proteins as replacement for menhaden fish meal in practical diets for red drum Sciaenops ocellatus. J. World Aquacult. Soc. 26, 48–58.
Ž
Dy Penaflorida, V., Virtanen, E., 1996. Growth, survival and feed conversion of juvenile shrimp Penaus
.
monodon fed a betaineramino acid additive. Isr. J. Aquacult. 48, 3–9.
Ž .
Fange, R., Grove, D., 1979. Digestion. In: Hoar, W.S., Randal, D.J., Brett, J.R. Eds. , Fish Physiology Vol. VIII Academic Press, New York, NY, pp. 162–260.
Ž .
Gallagher, M.L., 1994. The use of soybean meal as a replacement for fish meal in diets for hybrid striped bass
ŽMorone saxatilis=M. chrysops . Aquaculture 126, 119–127..
Ž
Gallagher, M.L., 1995. Interactions of carbohydrate and lipid in diets for hybrid striped bass Morone
.
chrysops=M. saxatilis . J. Appl. Aquacult. 5, 53–59.
Ž .
Gatlin, D.M. III, 1997. Nutrition and feeding of striped bass and hybrid striped bass. In: Harrell, R.M. Ed. , Striped Bass and Other Morone Culture. Elsevier, Amsterdam, pp. 235–251.
Giduck, S.A., Threatte, R.M., Kare, M.R., 1987. Cephalic reflexes: their role in digestion and possible roles in absorption and metabolism. J. Nutr. 117, 1191–1196.
Gomes, E., Dias, J., Kaushik, S.J., 1997. Improvement of feed intake through supplementation with an attractant mix in European sea bass fed plant protein rich diets. Aquat. Living Resour. 10, 385–389. Harpaz, S., 1997. Enhancement of growth in juvenile freshwater prawns, Macrobrachium rosenbergii, through
the use of a chemoattractant. Aquaculture 156, 221–227.
Heinsbroek, L.T.N., Krueger, J.G., 1992. Feeding and growth of glass eels, Anguilla anguilla L.: the effect of feeding stimulants on feed intake, energy metabolism and growth. Aquacult. Fish. Manage. 23, 327–336. Hughes, S.G., 1991. Response of first-feeding chinook salmon to four potential chemical modifiers of feed
intake. Prog. Fish-Cult. 53, 15–17.
Kamstra, A., Heinsbroek, L.T.N., 1991. Effects of attractants on start feeding of glass eels, Anguilla anguilla L. Aquacult. Fish. Manage. 22, 47–56.
Keembiyehetty, C.N., Wilson, R.P., 1998. Effect of water temperature on growth and nutrient utilization of
Ž .
sunshine bass Morone chrysopsY=Morone saxatilis? fed diets containing different energyrprotein ratios. Aquaculture 166, 151–162.
Ketola, H.G., Harland, B.F., 1993. Influence of phosphorus in rainbow trout diets on phosphorus discharges in effluent water. Trans. Am. Fish. Soc. 122, 1120–1126.
Kubitza, F., Lovshin, L.L., Lovell, R.T., 1997. Identification of feed enhancers for juvenile largemouth bass, Micropterus salmoides. Aquaculture 148, 191–200.
McGoogan, B.B., Gatlin, D.M. III, 1997. Effects of replacing fish meal with soybean meal in diets for red drum Sciaenops ocellatus and potential for palatability enhancement. J. World Aquacult. Soc. 28, 374–385.
Metailler, R., Cadena-Roa, M., Ruyet, J.P., 1983. Attractive chemical substances for the weaning of Dover sole, SoleaÕulgaris. Qualitative and quantitative approach. J. World Maric. Soc. 14, 679–684.
Mohsen, A.A., Lovell, R.T., 1990. Partial substitution of soybean meal with animal protein sources in diets for channel catfish. Aquaculture 90, 303–311.
Nematipour, G.R., Brown, M.L., Gatlin, D.B., 1992. Effects of dietary energy:protein ratio on growth characteristics and body composition of hybrid striped bass, Morone chrysops=M. saxatilis. Aquaculture 107, 359–368.
Nicholson, L.C., Woods, L.C. III, Woiwode, J.G., 1990. Intensive culture techniques for the striped bass and
Ž .
its hybrids. In: Harrell, R.M., Kerby, J.H., Minton, R.V. Eds. , Culture and Propagation of Striped Bass and its Hybrids. American Fisheries Society, Bethesda, pp. 141–157.
Ž .
NRC National Research Council , 1993. Nutrient Requirements of Fish. National Academy Press, Washing-ton, DC, 114 pp.
Person-Le Ruyet, T., Menu, B., Cadena-Roa, M., Metailler, R., 1983. Use of expanded pellets supplemented with attractive chemical substances for the weaning of turbot, Scopthalmus maximus. J. World Maric. Soc. 14, 676–678.
Reigh, R.C., Ellis, S.C., 1992. Effects of dietary soybean and fish–protein ratios on growth and body
Ž .
composition of red drum Sciaenops ocellatus fed isonitrogenous diets. Aquaculture 104, 279–292. SAS Institute, 1992. Technical Report P-229, SASrSTAT Software: Changes and Enhancements, release 6.07.
SAS Institute, Cary, NC.
Small, B.C., Soares, J.H. Jr., 1998. Estimating the quantitative essential amino acid requirements of the striped bass, Morone saxatilis, using filet ArE ratios. Aquacult. Nutr. 4, 225–232.
Sokal, R.R., Rohlf, F.J., 1987. Introduction to Biostatistics. Freeman, New York, 363 pp.
Tacon, A.G.J., 1994. Feed ingredients for carnivorous fish species alternatives to fishmeal and other fishery resources. FAO Fish. Circ. 881, 35 pp.
Ž .
Takii, K., Shimeno, S., Takeda, M., 1986a. The effect of feeding stimulants in diet on some hepatic enzyme activities of eel. Bull. Jpn. Soc. Sci. Fish. 52, 2131–2134.
Takii, K., Shimeno, S., Takeda, M., Kamekawa, K., 1986b. The effect of feeding stimulants in diet on digestive enzyme activities of eel. Bull. Jpn. Soc. Sci. Fish. 52, 1449–1454.
Tandler, A., Berg, B.A., Kissil, G.W., Mackie, A.M., 1982. Effect of food attractants on appetite and growth rate of gilthead bream, Sparus aurata L. J. Fish Biol. 20, 673–681.
Virtanen, E., Junnila, M., Soivio, A., 1989. Effects of food containing betaineramino acid additive on the osmotic adaptation of young Atlantic salmon, Salmo salar L. Aquaculture 83, 109–122.
Virtanen, E., Hole, R., Resink, J.W., Slinning, K.E., Junnila, M., 1994. Betaineramino acid additive enhances
Ž .
