The aim of this study was to investigate the lipid peroxidation (thiobarbituric acid reactive substance content) and oxidative modified protein levels (stable 2.4-dinitrophenyl hydrazine derivates of the carbonyl groups), and antioxidant defense system (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase activity, and total antioxidative activity) in livers of males and females from a control group (healthy specimens) and a group of sea trout,