Effect of CO2 exposure on the antioxidant enzymes activity and gill histology of adult zebrafish (Danio rerio)

Increase in carbon dioxide level is considered as a threat to all living organisms and in particular aquatic organisms are vulnerable. Although a number of studies were carried out to predict the effect of increased CO2 with marine organisms, fresh water fish were the least concerned ones. Therefore, the aim of this study was to study the effect of antioxidant enzymes in zebrafish exposed to acute concentration of CO2 (based on prediction for 2300). Three ranges of pH were selected below the range where no fatality was observed, 6.0 – 6.5, 5.5 – 6.0 and 5.0 – 5.5. Antioxidant enzyme analysis of superoxide dismutase (SOD), catalase (CAT), lipid peroxidation (LP), glutathione reductase (GR) and glutathione peroxidase (GPx) was performed for the tissues, liver, gills and muscles. Although a significant decrease in SOD activity was observed in all three tissues, only a slight variation in CAT activity was found in all the tissues. MDA content which is an indicator of lipid peroxidation showed an increasing pattern in all the tissues. A slight increase in GR activity was found in all the tissues; however, a significant decrease in GPx activity was noted. Further, the histology of gills exposed to CO2 showed marked damage and injury including lamellar fusion and necrosis. Our study concludes that exposure to CO2 has led to oxidative stress which has resulted in cellular injury and damage