METHIONINE PLUS CYSTINE TO LYSINE RATIO IN DIETS FOR TAMBAQUI JUVENILES

ABSTRACT The objective of this study was to determine the appropriate ratio of methionine plus cystine to lysine in rations for tambaqui (Colossoma macropomum) juveniles, with initial weights of 0.28 ± 0.08 g and 0.94 ± 0.33 g. A randomized block design consisting of six treatments, five replicates in two blocks, and 20 fish per replicate was implemented. Six isolisinic (1.45%), isoenergetic, isophosphoric, and isocalcic diets, containing different ratios of methionine plus cystine to digestible lysine (50%, 55%, 60%, 65%, 70%, and 75%) were used. Performance and feed efficiency variables, including body composition (moisture, protein, and fat), daily protein deposition rate, daily fat deposition rate, and nitrogen retention efficiency, were evaluated. The specific growth rate and feed conversion presented quadratic effects, with maximum effects from the digestible methionine plus cystine to lysine ratio of 64.4% and 64.8%, respectively. The increase in digestible methionine plus cystine intake resulted in a linear reduction in body fat content with the elevation of the digestible methionine plus cystine to lysine ratio. The digestible methionine plus cystine to lysine ratio recommended in rations for tambaqui fingerlings is 64.8%.