This study was conducted to evaluate the effect of dietary melatonin supplementation (10 mg/kg body wt. for 4 weeks) on some erythrocytic antioxidant enzymes and lipid peroxidation as well as some plasma biochemical parameters in common carp. The results showed that the activities of glutathione peroxidase and superoxide dismutase were increased significantly (P < 0.05) after melatonin supplementation, whereas alterations in catalase activity were not significant. Malondildehyde concentrations in erythrocyte hemolysate were decreased significantly as a result of melatonin treatment. Plasma biochemical analysis revealed a significant decrease of glucose, cholesterol, albumin and triglyceride, in addition to a significant increase in total protein, AST and ALP values when compared to the control group. However, alterations in creatinine, urea and LDH levels were not significant following melatonin supplementation compared to the control values. These results offer that pharmacological amounts of melatonin effectively improve erythrocytic oxidative status biomarkers and also alter some plasma biochemical parameters in the common carp that some of them may be undesirable. However, more investigations are required to elucidate the pharmacokinetic effects of melatonin and also possible undesirable effects of high doses of this compound.

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