Effects of Stocking Densities on the Growth Performance and Physiology of Juvenile Piaractus brachypomus in Recirculating Aquaculture System

The effects of different stocking densities on the growth and physiology of juvenile Piaractus brachypomus were evaluated in two experiments. Experiment I used juveniles weighing 1.5 ± 0.4 g at the following densities for 20 days: D0.68—0.68 kg/m3; D1.45—1.45 kg/m3; D4.41—4.41 kg/m3; and D7.17—7.17 kg/m3. Experiment II used juveniles weighing 6.66 ± 1.3 g at the following densities for 20 days: D1.0—1.00 kg/m3; D1.95—1.95 kg/m3; D5.63—5.63 kg/m3, and D7.90—7.90 kg/m3. Both experiments showed a reduction in dissolved oxygen levels in the water, with Experiment II showing a plateau effect from 2.34 kg/m3 (p < 0.05). Final weight, final length, weight gain, daily weight gain, and specific growth rate were inversely proportional to density (p < 0.05), while final biomass, feed intake, and feed conversion were directly related to density in both experiments (p < 0.05). At the end of Experiment II, plasma triglycerides decreased as stocking density increased (p < 0.05), and hemoglobin and mean corpuscular volume were higher at the lowest density (D1.0) (p < 0.05). High stocking densities reduced dissolved oxygen, characterizing a hypoxic state in both experiments, affecting growth and some physiological parameters. Therefore, studies testing stocking densities for P. brachypomus in normoxic situations are still needed.