Determination of the effects of the hypoxic and hyperoxic stress exposures on antioxidant enzyme activities and gene expressions on rainbow trout (Oncorhynchus mykiss)

In this study, juvenile rainbow trouts (Oncorhynchus mykiss) were subjected for 28 day to either hypoxic (4,5±0,5 mg O2/L) or hyperoxic (12±1,2 mg O2/L). Liver, kidney and gill were taken 6, 12, 24, 48, 72 hours (acute) in addition to 28 days (chronic), following the sampling times and gene expression and antioxidant responses studied with regard to antioxidant enzyme activities, glutathione status and lipid peroxidation. Biochemical changes were accepted as significant at p<0.05. GSSG, OSI and MDA levels in liver have increased significantly compared to control. The acute effect of hypoxia and hyperoxia significantly reduced SOD, GPx and GR activities and significantly increased CAT activity compared to control. The change in chronic effect varied according to treatment. Although the gene expressions of antioxidant enzymes were high at 24h, as a result of the acute and chronic treatment of hypoxia and hyperoxia was decreased. Glutathione levels in the gill (tGSH, GSH and GSSG) did not change compared to control. Although glutathione levels in kidney were in control levels at the first time, This decreased at 72h and 28d. MDA levels did not changed compared to control in kidney and gill. H2O2 levels were increased compared to control with the chronic effect of both hypoxia and hyperoxia. Antioxidant enzyme activities in kidney and gill generally increased compared to control.The changes in these parameters are an indication that hypoxic and hyperoxic exposures cause oxidative stress development in rainbow trout. This is an irreversible effect in rainbow trout exposure to both hypoxia- and hyperoxia- induced oxidative stress.