Changes in environmental salinity are responsible for a variety of physiological stress responses in aquatic organisms. Induced stress is associated with enhanced reactive oxygen species generation, which caused oxidative damage. In the present study, the effects of different environmental salinities on the antioxidant status in the gills of the yellowfin seabream, Acanthopagrus sheim, were assayed. Fish adapted to salinity of 20 ppt for 14 days, then suddenly challenged with experimental salinities including 5, 12 and 34 ppt and kept in new salinities for 14 days. Each treatment was done in three replicates. In each replicate, 12 fishes with an average initial weight of 100 ± 10 g were placed in 300-L tanks. Fish were fed 3 times daily 3% body weight. Gill samples were taken after 2 weeks. Catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX) activity and malondialdehyde (MDA) content were assayed in gill tissue. CAT, SOD and GPX activity did not show a significant difference between experimental groups. Like antioxidant enzymes, MDA content of gill was not significantly different between experimental groups. Our finding showed that salinity challenge as a stressor did not affect antioxidant–prooxidant equilibrium or a new equilibrium was created and did not evoke oxidative stress.
