The aim of this study was to determine the nutritional need of lysine in diets for juvenile Nile tilapia (Oreochromis niloticus). Seven hundred and twenty masculinized fish (7.30±0.11g) were fed for 30 days with eight diets (26.81% of digestible protein and 3090 kcal/kg digestible energy of feed) containing increasing levels of lysine (1.24, 1.36, 1.48, 1.60, 1.72, 1.84, 1.96 and 2.08%). The tilapia were distributed in a completely randomized design with eight treatments and six replicates of 15 fish per experimental unit. We evaluated the performance variables (weight gain, specific growth rate, survival rate, feed intake, digestible lysine intake, feed conversion, protein efficiency for gain, efficiency of lysine for gain and efficiency of retention nitrogen) and body composition (moisture, fat, protein, ash body and deposition rates of daily protein and fat). The high levels of dietary lysine did not affect (P>0.05) feed intake, the survival rate and the moisture and ash body, but improved (P<0.05) other parameters, except for lysine intake and efficiency of lysine for gain, which increased and decreased, respectively, linearly (P<0.05). It is recommended that diets for juvenile Nile tilapia should contain 1.84% digestible lysine for maximum weight gain.
digestible amino acids; Oreochromis niloticus; protein nutrition; synthetic lysine
