INFLUENCE OF MULTIPLE AMINO-ACID SUPPLEMENTATION ON THE PERFORMANCE OF RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM), FED SOYA BASED DIETS

Using rainbow trout, Oncorhynchus mykiss (Walbaum), of approximately 5 0 g, a 63 day feeding trial was undertaken to evaluate the efficacy of individual and multiple amino acid supplements in diets where soyabea n meal was used as the principle protein source. Iso-nitrogenous diets (45% crude protein) were formulated where the control diet (F) contai ned fishmeal as the reference protein and a solvent extracted soyabean meal (S) replaced approximately 66% of this protein source, The soyab ean containing diets were then supplemented with crystalline amino aci ds thus; methionine only, dual supplemented with two methionine and ly sine levels and finally, a supplement comprising methionine, lysine, t ryptophan, threonine, arginine and histidine. The results showed that soyabean meal (SBM) was inferior to the reference protein when SBM was used to replace 66% of the fishmeal and that no significant restorati on in growth, feed efficiency and apparent net protein utilization was obtained by either methionine only or dual methionine and lysine supp lementation. However, by comparison with the fish fed the unsupplement ed, single and dual supplemented diets, multiple amino acid incorporat ion was associated with significantly improved percentage weight gain, specific growth rate and marginal improvements in apparent net protei n utilization, However, performance was not equal to that of the fish fed the fishmeal based control diet. The results are discussed with re spect to the level of each of the essential amino acids (EAA) as a pro portion of the total EAAs (A/E index) of test diets by reference to th e whole body tissue amino acid profile of rainbow trout.