The effects of soybean-based diets, with and without amino acid supplementation, on growth and biochemical composition of juvenile American lobster, Homarus americanus

The feasibility of feeding soy-based diets for the pound culture of the Ame rican lobster was investigated in a factorial study using diets (40% protei n) containing various proportions of extruded-expelled, low-fat soybean mea l (SBM) (0%, 25%, 50%, 75%, 87.5% and 100% of dietary protein) and fish mea l (FM), with and without amino acid supplementation (arginine, leucine, met hionine and tryptophan), in a 60-day feeding trial using late Stage 5 juven iles. The supplemental amino acids were added at levels to simulate the ess ential amino acid (EAA) profile of juvenile lobsters. The 0% SBM diet appro ximated salted fish and fish racks, the industry diet for pounded lobsters. A diet of fresh blue mussel, a component of the lobster's natural diet, wa s included for comparison. Supplementation and SBM levels of not more than 50% of dietary protein significantly resulted in higher body weight gains ( BWGs) than diets without supplementation or with higher SBM levels. Surviva l was not significantly different for juveniles fed the supplemented diets and the non-supplemented diets containing FM. Juveniles fed the non-supplem ented 100% SBM diet suffered early mortality. Supplementation significantly shortened molting cycles and was crucial for survival in juveniles fed the 100% SBM diet. Interactions between supplementation and level of dietary S BM on survival, BWG and duration of the molting cycle were significant. Gro wth performance of juveniles fed blue mussel were comparable to those of ju veniles fed the supplemented 50% SBM diet. The levels (% of protein) of arg inine, phenylalanine and tryptophan were significantly higher in juveniles fed the supplemented diets, while tyrosine, aspartate, glutamate and serine were significantly higher in juveniles fed the non-supplemented diets. Arg inine levels in juveniles fed the supplemented diets were nearly twice thos e of juveniles fed the non-supplemented diets. Interactions between SBM lev el and supplementation on lobster amino acid profile were not significant. Supplementation and decreasing levels of dietary SBM (lower content of 18:2 n - 6, the major polyunsaturated fatty acid (PUFA) in SBM) were associated with better growth and resulted in increasing proportions (% of total) of 2 0:5n - 3, 22:6n - 3 and n - 3/n - 6 PUFA ratios in juvenile carcass. Based on weight gain, replacement of fish protein with SBM in practical diets at no more than 50% of dietary protein appears feasible, with multiple amino a cid supplementation significantly enhancing growth performance. (C) 2000 El sevier Science B.V. All rights reserved.