Oxidative stress and antioxidant enzymes in liver and white muscle of Nile tilapia juveniles in chronic ammonia exposure

Oxidative stress and antioxidant enzyme activities in liver and white muscle of Nile tilapia (Oreochromis niloticus) juveniles (10+/-1.2g) in chronic exposure to sublethal total ammonia nitrogen (TAN) were studied. The fish were exposed to the TAN concentrations, 5 mg L(-1) (low) or 10 mg L(-1) (high) for consecutive 70 days at 26+/-0.5 degrees C temperature. At the end of experimental period, lipid peroxidation and protein carbonylation levels and the activities of xanthine oxidase (XO), aldehyde oxidase (AO), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), glutathione reductase (GR), gamma-glutamyl cysteinyl synthetase (gamma-GCS), and gamma-glutamyl transpeptidase (gamma-GT) in liver and white muscle were assayed. The levels of oxidative stress biomarkers and the activities of the enzymes assayed were significantly increased in liver and white muscle of fish exposed to both low and high TAN levels. The changes in these parameters were intensified at high TAN level. The significance of these alterations in enzyme activities is discussed.