Optimizing amino acid balance in fish meal-free diets for GIFT strain of Nile tilapia (Oreochromis niloticus) by deletion method

An indoor feeding trial was conducted to optimize the amino acid (AA) profile of the genetically improved farmed tilapia (GIFT) diet using the AA deletion method. Six corn-soy-based isonitrogenous and isoenergetic fishmeal-free diets with different AA profiles were formulated to evaluate the effects of crystalline AA supplementation on the growth performance, whole-body composition, muscle growth-related gene expression and haemato-biochemical responses of juvenile GIFT tilapia. Each diet was randomly assigned to triplicate groups of 30 fish (5.5 +/- 0.3 g) per experimental unit, which were fed three times a day (09:00, 13:00 and 17:00 h) for a period of 60 days. Maximum growth performances and feed utilization were observed in fish fed a balanced diet and a -Trp diet compared with the AA-unsupplemented diet, whereas no significant differences were observed among fish fed -Met, -Lys and -Arg diets. Whole-body proximate composition and amino acid profile of GIFT tilapia were not significantly affected by diets with different amino acid profiles. Similarly, no significant differences were observed in blood biochemical responses, except glucose. However, significant (p < .05) differences were observed in haematological responses and mRNA expression of MyoD,myogenin and myostatin. Based on the growth performance and feed efficiency, the EAA pattern associated with -Trp diet was considered to be the optimum EAA ratio for maximum growth and feed utilization of juvenile GIFT tilapia.