Addition of sodium chloride and calcium carbonate in water as an alternative to minimize nitrite toxicity in Pacu Piaractus mesopotamicus juveniles
Pacu Piaractus mesopotamicus is a species with great potential for intensive breeding systems. However, increased stocking density may lead to the accumulation of toxic nitrogen compounds such as nitrite. Management strategies such as increased sodium chloride and calcium concentrations in the water can reduce the toxicity of this compound to fish. Thus, the aim of the present thesis was to verify if the addition of sodium chloride (1 g NaCl.L-1) or calcium carbonate (150 mg CaCO3.L-1) in the water reduces nitrite toxicity to pacu juveniles using zootechnical, blood and oxidative stress parameters as biomarkers. Different time and concentration dependent effects were demonstrated on fish exposed to nitrite. In addition, oxidative stress responses were tissue specific. Nitrite induced increased glutathione-S- transferase activity and lipid peroxidation (LPO) levels and reduced total antioxidant capacity (ACAP). Among the blood parameters, changes in total erythrocyte count, hematocrit, total hemoglobin and hematimetric indices were reported. Increased feed conversion rate (FCR) was also attributed as one of the effects related to nitrite. The use of NaCl was effective in preventing hepatic LPO and reducing muscle ACAP. The addition of CaCO3 prevented the increase in LPO levels in the gills and muscle, and the impairment of FCR. Both compounds also had a beneficial effect in attenuating changes in blood parameters resulting from short-term nitrite exposures. In conclusion, the addition of NaCl or CaCO3 in the proposed quantities was able to reduce nitrite toxicity in pacu juveniles, and may be an interesting strategy for water quality management, especially in intensive production systems.