Determination of tryptophan requirements for juvenile silver catfish (Rhamdia quelen) and its effects on growth performance, plasma and hepatic metabolites and digestive enzymes activity

Abstract The knowledge about nutritional requirements of fish is essential to improve utilization of nutrients. This study was conducted to estimate tryptophan requirements for silver catfish. Groups of 30 fish (4.65 ± 0.68 g) were stored in tanks (125 L) and fed mixed diets containing different tryptophan concentrations (1.0, 1.8, 2.6, 3.4 and 4.2 g/kg of diet) until apparent satiation. After 60 days, growth performance, body composition, nutrient retention, plasma and liver metabolites and digestive enzymes were determined. The data were evaluated with nonlinear and polynomial regressions, and a highly significant effect of tryptophan ( P