Dietary leucine requirement of Juvenile Nile tilapia, Oreochromis niloticus

An 8-week feeding trial was conducted to evaluate the effects of dietary leucine on growth performance, feed utilization, body composition and non-specific immune responses of juvenile Nile tilapia. Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L-leucine (5.3, 8.1, 10.9, 13.2, 15.6 and 18.1 g kg(-1) diet, respectively) from dietary ingredients and crystalline L-leucine. Each diet was randomly assigned to triplicate groups of 20 juvenile fish (1.94 +/- 0.01 g) three times daily to apparent satiation. Results showed that the weight gain (WG) and specific growth rate (SGR) increased as dietary leucine concentrations increased from 5.3 to 13.2 g kg(-1) and then decreased slightly with further increase in dietary leucine concentrations. Quadratic regression analysis (y = -522.6x(2) + 1304.x + 132.6, R-2 = 0.684) on weight gain against dietary leucine levels indicated that the optimal dietary leucine requirement was estimated to be 12.5 g kg(-1) diet (corresponding to 43.1 g kg(-1) of dietary protein). Leucine supplementation had no impact on the survival and body composition of tilapia. Serum lysozyme activity of fish fed diet containing 13.2 g kg(-1) leucine significantly increased compared to fish fed diet containing 5.3 g kg(-1). Serum superoxide dismutase activity and immunoglobulin M (IgM) concentration were not significantly affected by dietary leucine supplementation.