EFFECTS OF SUBSTITUITION OF PROTEIN BY CRYSTALLINE AMINOACIDS ON DEVELOPMENT AND FREE AMINO ACIDS OF SKELETAL MUSCLE OF TAMBAQUI Colossoma macropomum JUVENILES¹

One of the biggest challenges for intensive aquaculture is the reduction of the inclusion levels of fishmeal in diet formulations, because the more available substitutes are usually deficient in limiting indispensable amino acids. The aim of this study was to determine the maximum level of protein replacement by crystalline amino acids without impairing muscle development in tambaqui at early stages of growth. The experiment was conducted in 100 L tanks, in a completely randomized design with six treatments, four replicates and 2520 tambaqui juveniles (0.2 ± 0.05 g and 2.1 ± 0.2 cm), during 60 days. Diet with 31.9 % of crude protein was used as a basal diet. Total amino acids profile present in protein (casein-gelatin) was matched by mixtures of crystalline amino acids at levels of 0, 25, 50, 75 and 90% replacement (D0, D25, D50, D75 and D90, respectively). Additionally, a control diet with fishmeal (DFM) as protein source was used. Free amino acids profile in skeletal muscle and morphometric analysis of skeletal muscle fibers were evaluated. At the end of the experiment, fish weights (g) were 4,3±1,0^b, 3,2±0,8^bcd, 3,3±0,3^bc, 2,5±0,4^cd, 1,5±0,2^d, and 9,9±0,7^a in treatments D0, D25, D50, D75, D90 and DFM, respectively. The total percentage of IAA (indispensable amino acids) decreased with the increasing levels of replacement. On the other hand, the inverse was observed regarding the total percentage of DAA (dispensable amino acids) (Fig. 1). Morphometric analysis did not show differences in fibers diameter frequency between treatments D0 to D90 (P>0.05), except for class 10 (p<0.05) (Fig. 2). The results of this study show that substitution up to 50 % can be useful for future studies to determine the appropriate amino acid profile in diets for tambaqui during early stage of development. Additionally, the results open new avenues to provide increased productivity through the use ideal diet for this fish species.