Threonine (Thr) is one of the most limiting amino acids in functional ingredients used for diet preparation, and its deficiency can reduce fish growth. This study aimed to estimate the digestible Thr requirement in tambaqui ( Colossoma macropomum ) diets in the fattening stage for 60 days. Diets containing different digestible Thr concentrations (9.40, 10.30, 11.20, 12.10 and 13.00 g/kg) were analysed. The best results for growth performance, body crude protein content and body deposition occurred in fish fed with 10.30 and 11.20 g Thr kg diet ⁻¹ ( p < 0.05). The dietary Thr requirement estimated based on weight gain, the feed conversion ratio and the specific growth rate was 10.64, 10.71 and 10.80 g Thr kg diet ⁻¹ respectively ( p < 0.05). For body deposition, the best values of dietary Thr were between 10.40 and 10.70 g/kg ( p < 0.05). Diets with higher levels of digestible Thr caused an increase in plasma cholesterol, liver glycogen levels and erythrocytes, and a decrease in hepatic aspartate aminotransferase levels and mean corpuscular volume ( p < 0.05). In conclusion, tambaqui require between 10.40 and 10.80 g Thr kg diet ⁻¹ to provide better fish growth performance, body deposition and health.

The aim of this study was to determine the requirement for lysine in the diet of juvenile tambaqui (Colossoma macropomum). In total, 750 juvenile fish (0.34 ± 0.02g) were distributed in tanks arranged in a randomized block design with six treatments, five replications in two blocks, and 25 fish per unit, for 50 d. Six levels of digestible lysine were tested (1.30, 1.48, 1.66, 1.84, 2.02, and 2.20%), in formulated diets based on the ideal protein concept. The performance, feed efficiency, daily deposition of protein and body fat, and nitrogen retention efficiency of the fish were evaluated. The consumption of rations and protein, specific growth rate, body composition, and deposition of body fat were not influenced by the lysine levels tested. The consumption of digestible lysine increased linearly and the efficiency of digestible lysine for weight gain decreased linearly with the increase in lysine levels. The levels of digestible lysine that optimized weight gain and body protein deposition were estimated at 1.73 and 1.78%, respectively. The feed conversion and nitrogen retention efficiency were most improved at 1.66% and 1.84%, respectively. The recommended level of dietary lysine for providing better weight gain and body protein deposition in juvenile tambaqui is 1.78%, equivalent to 2.00% total lysine.

This study evaluated the digestibility of whole mango (Mangifera indica) meal (WMM) and determined the growth performance, intestinal enzyme activity, and metabolic and hematologic responses of tambaqui (Colossoma macropomum) juveniles fed diets containing different proportions of corn meal (CM) substitution by WMM. Fish fed with graded levels of WMM (0 (control), 80, 160, 240, and 320 g kg diet^-1), replacing part of the dietary CM. The apparent digestibility coefficients of WMM were above 96%. Diets with WMM did not affect growth performance or intestinal enzyme activity. However, they showed a positive linear effect on plasma glucose, amino acids, and albumin levels and a negative linear effect on hepatic aspartate aminotransferase activity and hepatic glycogen, plasma cholesterol, and hemoglobin levels. Increased erythrocyte values and decreased plasma triglyceride levels were verified in fish fed 80 and 160 g WMM kg diet^-1. In conclusion, the WMM may be a viable alternative to the tambaqui juveniles’ diet, and WMM could replace up to 16% of CM without harming the growth and health of tambaqui juveniles.

Mango (Mangifera indica) production is expanding in many countries, and its discarded residues have the potential to be used in the manufacture of fish diets. This study evaluated replacing part of the corn meal (CM) with mango meal (MM) in diets for piava (Megaleporinus obtusidens) in terms of zootechnical performance, plasma glucose, and intestinal enzymes. Piavas (n = 160) were distributed in a completely randomized design (four treatments and four replications) and were fed for 45 days with diets containing different levels of MM inclusion (0, 33, 66, and 100%). There was no microbiological contamination (mold, total coliforms, Bacillus cereus, and Salmonellasp.) in MM. The MM diet had higher total phenols and total tannins (P < 0.05). Diets with 100% of the CM replaced by MM reduced the growth performance and increased the feed conversion ratio (FCR) and plasma glucose levels in piava (P < 0.05). According to the second-order regression analysis, the optimal level of MM inclusion in the diet estimated based on weight gain and FCR was 23.68 and 19.75%, respectively (P < 0.05). The gradual increase in MM levels replacing CM in the diet reduced the activity of the intestinal enzymes amylase, lipase, and alkaline protease (P < 0.05). In conclusion, we recommended replacing 19.75-23.68% of CM with MM, which can be used in piava diets.