Most of aquatic animals are dependent on molecular oxygen. Yet all living forms are prone to oxygen toxicity. This oxygen toxicity has been attributed to reactive oxygen metabolites including the Superoxide radicals(O2), Hydrogen peroxide (H2O2) and hydroxyl radicals (OH-). These highly reactive substances can directly or indirectly cause
substantial damage to living cells. The enzyme superoxide dismutase is essential for the survival of all respiring and metabolically active cells. Only respiring and metabolically active cells can generate reactive oxygen metabolites and they are controled at physiological concentration by a repertoire of cellular antioxidant defenses such as Superoxide Dismutase (SOD), Catalase (CAT), Glutathione Peroxidase (GPx), Glucose-6-Phosphate dehydrogenase (G-6-PDH)
and Glutathione-S-transferase (GST)

Keywords: CAT; GPx; G-6-PDH; GST; OH; ROMs.