Effect of different oxygen tensions on weight gain, feed conversion, and antioxidant status in piapara, Leporinus elongatus (Valenciennes, 1847)

Juvenile piapara (Leporinus elongatus) were progressively exposed to several levels of dissolved oxygen for 28 days, severe hypoxia, moderate hypoxia and normoxia, while weight gain, feed conversion, and some antioxidants and biomarkers of oxidative stress were measured in liver and blood. Fish exposed to severe hypoxia showed lower weight gain and feed conversion (1.6) when compared with moderate hypoxia (2.9) and normoxia (1.8). Lipoperoxidation in liver and blood was higher under moderate hypoxia and normoxia compared with severe hypoxia. Activities of catalase, glutathione reductase, and glutathione peroxidase in both liver and blood showed essentially no differences, while superoxide dismutase activities were higher in liver and blood in piapara exposed to severe hypoxia. Nevertheless, oxidized and total glutathione contents in blood and liver in fish exposed to hypoxia were higher than in fish exposed to normoxia. Liver glutathione S-transferase activity decreased with the increase in oxygen availability, while the level of microsomal cytochrome P450 1A increased with O2 availability. Below a critical O2 content, piapara showed decreased feed consumption, weight gain, and also cellular damage, but the antioxidant status was the same, or in some cases, higher than in normoxia. Despite the energetic limitations in oxidative metabolism under severe hypoxia, piapara appears to maintain essential antioxidant compensatory levels in such circumstances, probably to avoid the oxidative challenge that accompanies the increase in reactive oxygen species generation related to shifts in environmental oxygen availability. The results indicate that the balance between O2 utilization and the antioxidant status in obligatory water-breathing organisms has a great importance for farming purposes.