Sustained swimming and improvements in anti-oxidative stress responses in matrinxa (Brycon amazonicus) exposed to environmental nitrite.

Nitrite is usual in water of intensive rearing systems. Considering its oxidative harmful potential, it was selected to challenge matrinxa Brycon amazonicus reared in sustained swimming (SS) (with flowing water adjusted to speed at 1.0 BL seg^-1 (long-duration aerobic metabolic characteristic) and evaluate any beneficial effect of such rearing system to enhance the fish potential to cope with this oxidant stressor in fish farmings. Some parameters of oxidative stress, intermediary metabolism and hematometry were measured in matrinxa adapted to SS and exposed to the highest environmental nitrite concentration allowed by law. The experiments were performed in two steps. At first, fish were adapted to exercise under SS for 90 days. Subsequently, adapted fish were exposed to environmental nitrite (1.0 mg L^-1) for 24 h in order to evaluate their physiological responses. The results were compared with fish let in the same environment but from motionless water. Glycogen, glucose, pyruvate, lactate, free amino acids and ammonia were quantified in liver, plasma and muscle. Lipid peroxidation (LPO), glutathione peroxidase (GPx) and catalase (CAT) were assayed in liver and white muscle. Hematometry data were obtained using standard procedures. Sustained swimming practice enhance the hematological capacity of fish, improving oxidative metabolic responses; changing the ability to mobilize carbohydrates for energy purposes; facilitating the energy-dependent detoxification process; and minimizing the mobilization of amino acids for this purpose. In conclusion, the potential of matrinxa adapted to SS to cope with oxidative stress caused by environmental nitrite was enhanced.