Oxidative stress in liver and white muscles of Nile tilapia, Oeochromis niloticus captured in Rosetta branch of Nile River at Kafr El-Zayat area, Al-Gharbiyah Governorate, Egypt was studied. The toxic effects of water in this area that, receive a lot of sewage and other industrial pollutants discharge, on the antioxidant system of Nile tilapia (62.4 ± 6.9 g) were investigated. Water samples were analyzed for physicochemical parameters including pH, turbidity, total dissolved solids, ammonia, nitrite and nitrate. The activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST), glutathione reductase (GR) and the level of lipid peroxidation (LPO) in liver and white muscles were assayed. The examined physicochemical parameters found to be in excess than the maximum standard limits in water samples of the examined areas. The increase was more detectable during autumn and winter than other seasons. The alterations in the physicochemical parameters of water are consistent with the alteration reported in the enzymes activity of SOD, GST, GR, and GPx, as well as LPO, concentration which increased significantly (P ≤ 0.05) as compared to the control. However, the increase was more detectable during autumn and winter than in summer and spring seasons. The physicochemical parameters considered as the most important principles in the identification of the nature, quality and type of the water and/or any aquatic system. Antioxidant enzymes and the oxidative stress biomarkers lipid peroxidation considered as the most important biomarkers used to identify polluted marine sites. This can be taken as a useful biomarker for environmental managers in investigating the exposure of fish to contaminated freshwaters. This study could be beneficial for ecotoxicological researches in freshwaters as it provides data about antioxidant system response for fish exposed to different water pollutants.
Key words: Superoxide dismutase, catalase, glutathione-S-transferase, glutathione reductase, glutathione peroxidase, lipid peroxidation
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