Suplementação de metionina e/ou lisina em rações com níveis decrescentes dos teores de proteína para juvenis de Tambaqui, Colossoma macropomum

Abstract

The aim of this study was to evaluate the effects of the reduction crude protein level (CP), and lysine and methionine supplementation on fish performance and total ammonia nitrogen excretion in tambaqui juveniles ( ). Three hundred and thirty six fish (64,5 ± 1,06g) were uniformly distributed in 24 tanks (120 L), and in a complete randomized design with two levels of protein content (20% and 25% CP) and four levels of amino acid supplementation: a) Dl-methionine (0% of CP) and L-lysine (0% of CP), b) Dl-methionine (3% of CP), c) L-lysine (5% of CP), d) Dl-methionine (3% of CP) + L-lysine (5% of CP) were evaluated by a two-way ANOVA (p>0.05). All diets were isocalorics (300kcal/100g) and hand-fed twice a day for tambaqui juveniles to apparent saciety for 55 days. No differences were observed on water quality parameters. No effects (p>0,05) of protein levels were observed in weight gain, feed conversion ratio, specific growth rate and net protein utilization with exception of protein efficiency ratio, witch showed best results with 20% CP. Lysine supplementation treatments did show better results on fish performance. Methionine supplementation did not improve fish performance. Total ammonia excretion decreased 28,4% when protein levels were reduced from 25% to 20%, however, the lysine and methionine supplementation did not influence this factor.