Gene Expression and Activities of Antioxidant Enzymes in Liver of Hybrid Tilapia, Oreochromis niloticus × Oreochromis aureus, Under Acute pH Stress

Gene expression levels and enzymatic activities of copper/zinc superoxide dismutase (Cu/Zn-SOD), catalase (CAT), and glutathione peroxidase (GPx) in liver of hybrid tilapia, Oreochromis niloticus × Oreochromis aureus were analyzed after 12–72 h exposure to acidic and alkaline pH. Results showed that, compared with the control pH (pH 6.8), acidic pH exposure (pH 4.8 and 5.8) induced the expression levels and enzymatic activities of antioxidant enzymes. Slight alkaline exposure (pH 7.8) increased the transcript levels of CAT and GPx and the activity of GPx. Strong alkalization (pH 8.8) presented an inhibition on the antioxidant enzyme system, suggesting alkaline exposure may be more harmful to antioxidant activity in liver of hybrid tilapia than acidic exposure. Moreover, under acidic and slight alkaline exposure, mRNA expressions and activities of Cu/Zn-SOD were significantly induced after 12 h exposure, whereas CAT and GPx reached the highest levels later, indicating Cu/Zn-SOD play the dominant role at the initial stage, whereas CAT and GPx work later.