Digestible methionine plus cystine requirement in tambaqui (Colossoma macropomum) diets: Growth performance and plasma biochemistry

Most animals require methionine as an indispensable amino acid in their dietary protein, the normal growth of animals being affected by any deficiency or excess of methionine and cystine in the diet. The current study aimed to determine the digestible methionine plus cystine requirement in diets for tambaqui (Colossoma macropomum). A total of 288 tambaqui with an initial body weight of 54.53 ± 0.15 g were used in a dose-response experiment with five levels of digestible methionine plus cystine (0.400; 0.600; 0.800; 1.000; 1.200 %) and four replicates per treatment. The results showed that increasing the dietary digestible methionine plus cystine level influenced all growth performance variables evaluated in the study, except feed intake. Methionine plus cystine intake increased linearly (P < 0.05). Quadratic effects on weight gain, specific growth rate, and feed conversion ratio were observed, with estimated requirements being 0.876 %, 0.883 % and 0.907 % of digestible methionine plus cystine, respectively. The deposition of body protein, body fat, and body ash also showed a quadratic response with requirements estimated at 0.920 %, 1.124 % and 0.879 % of digestible methionine plus cystine, respectively. The methionine plus cystine levels evaluated influenced plasma biochemistry, except glucose. The requirement for digestible methionine plus cystine in the diet for tambaqui was determined as 0.920 % (0.297 g/Mcal of digestible energy), as it allows greater deposition of body protein