Stocking density of Amazon fish (Colossoma macropomum) farmed in a continental neotropical reservoir with a net cages system

A 60-day experiment was conducted to evaluate the best stocking density (SD) and net cage (NC) size for rearing tambaqui juveniles (Colossoma macropomu) in a continental neotropical reservoir. 57,688 tambaqui juveniles (50.10 ± 1.39 g, mean ± S.E.M.) had been randomly stocked in 16 NC. The experiment was run with a 2 × 2 factorial scheme at two SD (15 kg/m3; 24 kg/m3) and two NC sizes (22.5 m3; 40 m3), with four replications: T1: 15 kg/m3 x 22.5 m3; T2: 24 kg/m3 x 22.5 m3; T3: 15 kg/m3 x 40 m3; T4: 24 kg/m3 x 40 m3. After 60 days, growth performance, biochemical parameters and body composition of fish were evaluated. Individual weight gain, feed conversion ratio, feed efficiency rate, specific growth rate and protein efficiency ratio were better at SD 24 kg/m3. For body composition, the crude protein and lower crude fat values in NC 24 kg/m3 and NC 40 m3 were higher. The biochemical parameters showed no significant difference for total proteins and plasma cholesterol. Triglycerides had higher rates for the fish stored in NC 40 m3. An SD-NC interaction appeared for glucose and cortisol, with higher values for SD 15 kg/m3 in NC 40 m3; the highest values were observed in SD 24 kg/m3 for NC 22.5m3. Therefore, the production of the fish stocked in SD 24 kg/m3 was more efficient as the biochemical parameters had better indices for the fish raised in 40m3. The findings in this study suggest using SD 24 kg/m3 in NC 40 m3 to maximise fish productivity and welfare. •Fish stocked at 24 kg/m3 showed greater growth performance.•Stocking density and net cage size can improve fish productivity and welfare.•Physical area was not a limiting factor for fish growth at the highest stocking density.