Responses of superoxide dismutase, glutathione peroxidase and reduced glutathione antioxidant defenses in gills of the freshwater catfish ( Heteropneustes fossilis) to short-term elevated temperature

Superoxide anion radical ( O 2 −) has been hypothesized as one of the possible factors involved in the oxidative stress in aquatic animals. The antioxidant enzymes superoxide dismutase (SOD; EC 1.15.1.1) catalyzes the conversion of O 2 − to hydrogen peroxide (H 2O 2) whilst glutathione peroxidase (GSH-Px; EC 1.11.1.9) metabolizes the H 2O 2 to H 2O in part of the cell (cytosol and endoplasmic reticulum). Reduced glutathione (GSH) is an important antioxidant which serves, in part, to set the redox status in tissues. In the present study the patterns of SOD and GSH-Px activities and GSH content were investigated, in an experimental model of elevated temperature, in gills of the fish Heteropneustes fossilis in order to investigate whether temperature elevation for 1–4 h may alter the antioxidant system. After an elevated temperature exposure from 25 (control) to 37°C, the SOD activity increased while GSH-Px activity and GSH content decreased significantly (p < 0.05) at 32 and 37°C at 1–4 h in comparison to control. Nevertheless a transient increase in GSH-Px activity was observed at 1 and 2 h at 32°C. The results at 27°C temperature were non-significant (P < 0.05) in comparison to control. During the extended hours (1 to 4 h) of each elevated temperature, a general trend of increase in SOD activity at 32 and 37°C was observed. However, GSH-Px activity and GSH content were not changed significantly for most of the extended period of elevated temperature. In conclusion, the elevated temperature caused changes in SOD and GSH-Px activities and GSH (thiol) content in gills.