L-threonine requirement of silver catfish (Rhamdia quelen): growth performance, body composition, plasma and liver metabolites

A feeding trial was performed to evaluate the effects of dietary L-threonine supplementation on growth and body composition of fingerlings Rhamdia quelen (initial weight: 4.47 +/- 0.39 g). Five diets (370 g/kg crude protein and 14.23 MJ / kg of digestible energy) containing levels of L-threonine (16.0, 22.0, 28.0, 34.0, 40.0 g threonine/kg protein) were fed to quadruplicate groups of fishes for 10 weeks. The analysed variables were influenced by the threonine levels. Fish fed with diet containing 16.0 g threonine/kg of CP showed lower growth and body deposition of nutrients. In addition to unsatisfactory performance, the fish subjected to lower levels of threonine presented higher hepatosomatic index scores and changes in the concentrations of some plasmatic metabolites. To determine the ideal level of threonine in the diet, the weight gain, specific growth rate and feed conversion ratio were subjected to broken-line and quadratic regression. The results showed indicate that a diet containing inadequate levels of threonine causes insufficient growth. Dietary threonine requirement of R. quelen was estimated between 24.5 and 32.5 g threonine/ kg of crude dietary protein, corresponding to 9.1 and 12.0 g/ kg threonine in the diet for the initial growth of silver catfish.