Anaerobic denitrification is a biological process in which facultative heterotrophic microorganisms, under anoxic conditions, catalyze the sequential reduction of nitrate (NO₃⁻) and nitrite (NO₂⁻) ions to gaseous forms of nitrogen. In aquaculture, the controlled application of anaerobic denitrification contributes to the control of nitrogen compounds, maintaining water quality, reducing the need for water renewal, and the use of chemical additives for the control of dissolved inorganic nitrogen. This study evaluated the effect of different volumes of denitrification reactors (5%, 25%, and 50% of the culture volume) on water quality, zootechnical performance, and histological integrity of Penaeus vannamei cultured for 55 days in a BFT system, compared to a control treatment without denitrification. The experiment was conducted in 12 tanks (500 L) stocked with juveniles (0.94 g ± 0.44; 400 ind/m³). The denitrification reactors received water from the tanks and were activated when nitrate reached 75 mg/L, using common sugar as a carbon source (C/N 3:1). Water quality was monitored periodically, and weekly biometrics allowed the calculation of zootechnical indices. Gill and hepatopancreas samples were collected on day 0, midway, and at the end, processed, and stained with hematoxylin and eosin for histological analysis. There were no significant differences in temperature, dissolved oxygen, ammonia, total suspended solids, and sedimentable solids between treatments (p>0.05). The control had a higher average concentration of nitrate (84.47 mg/L ± 50.73) and accumulated nitrate (162.67 mg/L ± 4.62) compared to the treatments with denitrification, especially 50% (52.81 mg/L ± 27.99 and 71.33 mg/L ± 10.26, respectively). Survival was higher in 50% (85.20% ± 0.03) and lower in the control (74.53% ± 0.01). Regarding histopathological analyses, on day 0, all tissues showed normal morphology. At the end, the control group exhibited severe branchial hyperplasia, necrosis, and lamella fusion, as well as thick epithelium and dilated tubules in the hepatopancreas. The 5% treatment showed tubular dilation and moderate gill hyperplasia; 25% showed less gill hyperplasia than 5%, but still with tubular dilation; 50% had the least hyperplasia observed, although it maintained tubular dilation. Higher denitrification volumes improved water quality, reduced branchial hyperplasia, and minimized tissue changes in Penaeus vannamei, although tubular dilatation in the hepatopancreas persisted. The 50% treatment was the most effective, combining better survival, less histological impact, and control of nitrogen compounds.
Biofloc ➝ Denitrification ➝ Penaeus vannamei ➝ Nitrate ➝ Nitrite