Exigência de metionina + cistina para alevinos de Tilápia do Nilo (Oreochromis niloticus)

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.