Determinação da exigência de triptofano em dietas para pacus (Piaractus mesopotamicus)

Abstract

The Pacu (Piaractus mesopotamicus) is one of the fish with the highest development rate in national fish farming, in addition to producing meat with excellent nutritional value, being one of the most produced native fish in Brazil. Feed is the most expensive item in animal production, reaching up to 70% depending on the species of farming, with protein (amino acids) being the most expensive nutrient. Therefore, this study aimed to analyze the use of tryptophan by fish and evaluate the effect of adding this amino acid to practical diets. Three hundred juvenile tilapia with an initial average weight of 12.15 ± 0.15 grams were used, distributed in 20 experimental boxes containing 150 liters of water under continuous aeration and supply, and fed twice a day for a period of 60 days. Five types of diets with different levels of tryptophan inclusion (1.31; 1.96; 2.55; 3.15 and 3.79 g kg-1) were formulated. After the end of the study, the performance variables such as weight gain (g) and feed conversion rates (g/g) were calculated, which were respectively 5.53 (2.49); 6.88 (1.76); 7.42 (1.75); 8.27 (1.53) and 10.07 (1.29), for the tryptophan inclusion levels (1.31; 1.96; 2.55; 3.15 and 3.79 g kg-1). The best values (p<0.05) of weight gain and feed conversion were found for the fish that received the diet with 2.55 g kg-1. To estimate the ideal tryptophan level in the diet (12 to 25 g), the quadratic polynomial model was applied based on weight gain, obtaining the following equation: y = -2.2145x2 + 11.406x – 5.4099; R² = 0.82, thus, the best tryptophan level for maximum weight gain was estimated at 2.58 g kg-1. It is concluded that the optimal level of digestible tryptophan in diets for Pacus juveniles for better performance and nutritional efficiency was determined at 2.58 g kg-1 DM (0.92% of dietary protein) based on quadratic regression analysis for the fish weight gain variable.