Piaractus mesopotamicus is hypoxia tolerant and performs antioxidant adjustments after rapid reoxygenation at low temperature

Abstract This study aimed to evaluate the effects of the different temperature interactions and reoxygenation rates on parameters of antioxidant defense and oxidative stress in pacu ( Piaractus mesopotamicus ) juveniles. The fish were exposed to 12 h of hypoxia (~2 mg O 2 L −1 ) with subsequent rapid or gradual reoxygenation (with a return to normoxic levels in 0.5 or 5 h, respectively) in interaction with three different temperatures (~18, ~23, and ~28ºC). A control group in normoxia (~7 mg O 2 L −1 ) was also evaluated for each temperature, which was neither submitted to hypoxia nor reoxygenation, totaling nine treatments in triplicate. After 1 and 12 h of the end of the reoxygenation period, samples of gills and liver were collected to determine the total antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (LPO), and protein thiol content (PSH). Results showed temporary changes in ACAP in both organs, where, in general, the lowest levels were found at 18 and 28 o C at 1 and 12 h after recovery, respectively. A reduction of LPO levels in gills occurred in interactions between 18°C and rapid reoxygenation and 23 o C and gradual reoxygenation after recovery (1 and 12 h). Liver LPO levels were higher at 23 o C at 1 and 12 h after recovery. In general, gills PSH content was lower at 18 than at 23 o C at 1 h after recovery. Liver PSH content was higher at 23°C after recovery (1 and 12 h). In conclusion, pacu juveniles are hypoxia tolerant and cope better with rapid reoxygenation at 18 o C. Furthermore, the adjustments of the antioxidant system performed by the fish were sufficient for the partial resumption of homeostasis 12 h after recovery.