Influence of reoxygenation at different temperatures on growth, hematological and oxidative stress parameters in Piaractus mesopotamicus.

This study aimed to evaluate the effects of the interaction between different temperatures and reoxygenation rates on growth performance, as well as hematological and oxidative stress parameters in pacu (Piaractus mesopotamicus) juveniles. The animals were exposed to 8 h of severe hypoxia on the 15th day and 30th day (0.8 mg L-1) followed by abrupt reoxygenation or gradual, at two temperatures (24.11 ± 0.10 and 27.08 ± 0.05 ºC). A control treatment was established for each temperature, maintained at normoxia (≥ 7.0 mg L-1) throughout the experimental period (45 days). Final biometry was performed, as well as the collection of blood and tissues (gills, brain, liver, and muscle) to determine growth performance, hematological parameters, total antioxidant capacity against peroxyl radicals (ACAP), and lipid peroxidation (LPO). Results showed that the growth parameters were higher at 27 ºC. At this temperature, the animals showed higher levels of hyperglycemia compared to juveniles kept at 24 ºC. Fish subjected to different reoxygenation rates at 27 ºC showed a reduction in hemoglobin and the number of erythrocytes, in addition to a higher mean corpuscular volume (MCV) compared to the normoxic treatment at the same temperature and animals exposed to the same reoxygenation rates at 24 ºC. Lower ACAP levels were observed in the liver and muscle of fish kept at 24 ºC compared to animals kept at 27 ºC. Higher LPO levels in all tissues were induced by the interaction of 24 ºC with normoxia and gradual reoxygenation, and 27 ºC with abrupt reoxygenation. In conclusion, the growth of the species is optimized at 27 ºC. Moreover, at this temperature, the animals present better physiological conditions in the face of gradual reoxygenation and can be considered tolerant to hypoxia and reoxygenation when exposed to this situation in the farming environment.