Effects of stocking density on water quality, survival, blood parameters and growth performance of juvenile matrinxa ( Brycon amazonicus ) in the biofloc system

Biofloc technology (BFT) may be a promising alternative to reduce aggressive behavior of juvenile matrinx & atilde; Brycon amazonicus. This study evaluated the effects of different stocking densities on water quality, survival, blood parameters and growth performance of matrinx & atilde; juveniles in the biofloc system. Juveniles of 5.89 +/- 0.11 g were randomly distributed in five stocking densities (50, 140, 230, 320 and 410 fish m(-3)), in triplicates, in BFT. Commercial extruded feed (36% crude protein) was offered to apparent satiety four times per day for 61 days. In general, the increase of stocking density resulted in a reduction in dissolved oxygen, pH and alkalinity. Although nitrogenous compounds, total suspended solids, settleable solids, and turbidity were increased in higher stocking densities, water quality parameters were within the recommended range for matrinx & atilde; in all treatments. A quadratic regression over the range from 50 to 410 fish m-3 (x = stocking densities) were fitted to specific growth rate (%/day) (0.0000127x2 - 0.0074487x + 4.4884021; R-2= 0.73); daily weight gain (g) (0.000007966x2 - 0.004646x + 1.5352; R-2= 0.75); and mean final body weight (g) (0.0004847x2 - 0.2828035x + 87.3270312; R-2= 0.75). On the other hand, a positive linear regression model over the evaluated stocking densities were fitted to final stocking density (kg m(-3)) (0.0508x - 1.285; R-2= 0.92); and feed conversion ratio (0.0006037x - 1.1431; R-2= 0.52). Survival rate was above 90% at stocking densities above 230 fish m(-3). We found a lower concentration of erythrocytes in matrinx & atilde; juvenile at lowest stocking density (50 fish m(-3)), and the lymphocyte concentration was higher in the fish from treatment 140 fish m(-3) compared to 410 fish m(-3), and there was no difference among the other treatments. In conclusion, matrinx & atilde; juveniles can be efficiently produced in BFT at stocking densities of 291-293 fish m-3 or 13.50-13.60 kg m(-3). Although the increase in stocking density is favorable for increasing the biomass and survival of matrinx & atilde;s, an intensive management of solids and nitrate, and alkalinity corrections are necessary to ensure proper functioning of the production and to avoid mortality of fish due inadequate water quality.