Oxidative stress mediated antioxidant enzyme responses in tilapia (Oreochromis mossambicus) and silver carp (Hypophthalmichthys molitrix) fingerlings during hypoxic transportation and reoxygenation

Fish fingerling mortality due to transportation stress is one of the major problems in fisheries sector of Bangladesh. The present study aimed to understand the stress responses of fish fingerlings transported in a traditional way in Bangladesh. As indicators of oxidative stress, we monitored the production of hydrogen peroxide (H2O2) and activity of two antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase (GPx) during hypoxic transportation and after reoxygenation events. Tilapia (Oreochromis mossambicus) and silver carp (Hypophthalmichthys molitrix) fingerlings were transported in hypoxic condition for 6 hours in aluminum vessels and subsequently released into normoxic (DO>5.0 mgL-1) condition and reared for 16 days to observe delayed mortality. We found that Silver carp fingerlings were most susceptible to mortality during transportation and delayed mortality (51.93±8.06%) was found even higher than the Tilapia fingerlings. During hypoxic transportation H2O2 production was significantly (p<0.05) higher but SOD and GPx activities were found significantly (p<0.05) lower. However, at normoxic condition after initial increase up to 12 hours theH2O2 production gradually decreased while the GPx and the SOD activity increased gradually in the transported fingerlings. Our findings suggest that fish fingerlings transported in the traditional system suffer from oxidative stress, playing role in their early and delayed mortality even after release to normoxic condition.