Changes in the antioxidant systems of the liver tissues of sea bass (Dicentrarchus labrax) adapted to low salinity levels (0 parts per thousand) were investigated. Malondialdehyde levels, as a specific indicator of oxidant stress, were determined. The results indicated highly significant differences among the test and control groups (P < 0.05). Some histopathological destruction, liver weight and hepatosomatic index values were determined at high levels and, moreover, superoxide dismutase, glutathione peroxidase (GPX), glucose-6phosphate-dehydrogenase and malondialdehyde activities increased, while reducted glutathione levels decreased in comparison with the control group. An increase in the malondialdehyde level was determined to be an indicator of lipid peroxidation.