This study was carried out to determine the methionine + cystine requirement for Nile tilápia, fingerlings (2.61 ± 0.14g). A randomized block designs, with six treatments, three replicates and five fish by experimental unit was used. Basal diet was utilized with 28% crude protein and 3173DE kcal kg-1 of digestible energy, supplemented with DL-methionine, resulting in diets with 0.87; 0.95; 1.03; 1.11; 1.19 and 1.27% of methionine + cystine. Diets were fed to satiation during 41 days. No effects (P>0.05) of methionine + cystine levels on survival rate and hepatosomatic index were observed. A quadratic effect (P<0.05) for weight gain was observed, which increased up to 1.22% methionine + cystine in the diet. Feed conversion ratio and protein efficiency ratio increased (P<0.05) up to 1.00% of methionine + cystine. A quadratic effect (P<0.05) of methionine + cystine level on carcass yield was observed, which increased up to 1.13% of methionine + cystine. The concentration of 1.00% methionine + cystine corresponding to 3.54% crude protein, in the presence of 0.54% methionine in the diet, showed the best njperformance.
performance; requirement; juvenile; methionine + cystine; Nile tilapia
