EFFECT OF HIGH PHOSPHATE LEVELS ON ZOOTECHNICAL PERFORMANCE AND OXIDATIVE STRESS IN GILL, LIVER, AND BRAIN OF JUVENILE PACU (Piaractus mesopotamicus) IN THE BFT SYSTEM

Biofloc technology (BFT) system is intensive and, along with the lack of water renewal, leads to the accumulation of various pollutants, such as phosphate, making it one of the main limiting factors in water reuse between cultivation cycles. Evaluating the effect of phosphate concentrations in water of 0, 100, 200, 300, and 500 mg L-1 in triplicate, for 38 days, on zootechnical performance and oxidative stress (total antioxidant capacity (ACAP), lipid peroxidation, glutathione S-transferase, protein thiols, and non-protein thiols) in the gills, liver, and brain of 225 pacu (20 fish/EU) (22.6 ± 5.3 g) in tanks with 120 L of water with bioflocs, maintained under constant aeration and controlled temperature. There were no deaths or differences in zootechnical performance between treatments. The ACAP (relative area) values of the liver at P100, P200, and P300 were higher than at P0 and lower than at P500. The ACAP (antioxidant activity of the gills) in P300 and P500 was higher than in the other treatments, which did not differ from each other. ACAP in the brain was higher in P300 than in P0 and P100, with no difference between the other treatments. The other biomarkers of oxidative stress did not show differences between treatments. In P300, the antioxidant activity of the liver likely became insufficient to prevent oxidative stress in the gills and brain. The brain demonstrated greater resilience and adaptability. ACAP, especially in the liver, proved to be a suitable biomarker for phosphate toxicity. The positive relationships between zootechnical performance and ACAP levels in the brain suggest that a low level of stress can stimulate fish metabolism and growth. Finally, phosphate concentrations of up to 500 mg L⁻¹ did not harm the development of pacu, indicating the suitability of the species for closed aquaculture systems.