Colossoma macropomum is the second largest scaled fish of the Amazon. It is economically important for commercial fisheries and for aquaculture, but few studies have examined the diversity and genetic structure of natural populations of this species. The aim of this study was to investigate the levels of genetic variability and connectivity that exist between three natural populations of C. macropomum from the Amazon basin. In total, 247 samples were collected from the municipalities of Tefé, Manaus, and Santarém. The populations were genotyped using a panel of 12 multiplex microsatellite markers. The genetic diversity found in these populations was high and similar to other populations described in the literature. These populations showed a pattern of high gene flow associated with the lack of a genetic structure pattern, indicating that the number of migrants per generation and recent migration rates are high. The values of the F_ST, R_ST, and exact test of differentiation were not significant for pairwise comparisons between populations. The Bayesian population clustering analysis indicated a single population. Thus, the data provide evidence for high genetic diversity and high gene flow among C. macropomum populations in the investigated region of the Amazon basin. This information is important for programs aiming at the conservation of natural populations.

The objective was to evaluate the hematological and biochemical blood parameters and performance of Colossoma macropomum submitted to BFT maturation and under different feeding regimes. BFT maturation was carried out for 60 days (Phase 1). Feeding on six or seven days a week and feeding rates of 4% or 6% of biomass were tested (Phase 2). The water quality parameters were monitored throughout the experimental period. At the end of Phases 1 and 2, blood samples and zootechnical performance were evaluated. In Phase 1, total ammonia was higher on the 17th day (1.25 mg TAN L⁻¹) and stabilized from the 21st day onwards. Nitrite reached a peak (9.67 mg L⁻¹) on the 26th day. There was an increase in nitrate between the 25th and 60th day (1.79 ± 0.01 vs. 5.45 ± 0.01 mg N-NO₃⁻ L⁻¹, respectively). FCR (1.90 ± 0.21), weight gain (9.81 ± 1.08 g), and SGR (1.26 ± 0.12%) were highest at 30 days of phase 1. The glucose level (118.23 ± 26.30 mg dL⁻¹) was highest on the 30th day. The plasmatic protein (5.36 ± 0.30 g dL⁻¹) and alanine aminotransferase (ALT) levels (27.58 ± 6.58 UI mL⁻¹) were highest after 60 days. The hemoglobin level (5.77 ± 0.74 g dL⁻¹) was lowest after 30 days. In Phase 2, the triglycerides, ALT, and hematocrit levels were different at the end of the experiment under all feeding regimes. Histological analysis of gills showed a normal condition for fish under BFT. It was possible to apply a feeding regime of six days a week and 4% biomass for juveniles, with 43 g on average.