PARTIAL SUBSTITUTION OF FISH-MEAL AND FULL-FAT SOYA BEAN MEAL WITH WHEAT GLUTEN AND INFLUENCE OF LYSINE SUPPLEMENTATION IN DIETS FOR RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM)

A 65-day study was undertaken to evaluate the utilization of lysine-su pplemented wheat gluten meal as a protein source for rainbow trout, On corhynchus mykiss (Walbaum), The performance of the trout fed wheat gl uten was compared to that of trout where protein was principally suppl ied using fish meal and full-fat soyabean meal. Six isonitrogenous die ts (approximately 45% crude protein) were formulated. Thus, the refere nce diet (FS) was based on fish meal and full-fat soya bean meal while a further five diets were formulated with a mixture of wheat gluten a nd wheat middlings used to isonitrogenously replace approximately 75% and 57% of the full-fat soya and fish meal respectively. Crystalline L -lysine representing 0.00%, 0.29%, 0.58%, 0.87% and 1.16% of the compl ete diet was then added to the wheat-gluten-based diets, Optimal perfo rmance in terms of weight gain and apparent net protein utilization wa s achieved by the fish fed a wheat-gluten-based diet supplemented with lysine (0.58%) yielding a digestible lysine level of 1.9% of the comp lete feed. Within the range of supplements provided, lysine digestibil ity was high. However, at the highest levels of supplemental lysine th e relationship between uptake and supplement level was not linear. Add itionally arginine digestibility was not affected by the level of lysi ne supplementation. However, amongst the wheat-gluten-based diets, opt imal performance was associated with a lysine:arginine ratio of 1.1:1. Despite a lysine:arginine ratio of approximately 1.1:1, the overall p erformance of the fish fed the fish-meal-soya-based reference diet was poorer than expected. The results are discussed with respect to optim al patterns of gross and digestible amino acids, lysine-arginine antag onism and the possible relationship between antinutritional factors an d the poor performance of the fish fed the fish-meal-soya-based refere nce diet.