Antioxidant, enzymatic and hematological responses of common carp (Cyprinus carpio) fed with myrcene- or menthol-supplemented diets and exposed to ambient ammonia

Ammonia toxicity is common and risk factor in aquaculture, deteriorating fish health. Phytochemicals might attenuate adverse effects of ammonia toxicity in fish. The present study aimed to investigate the effects of dietary myrcene and menthol administration on common carp (Cyprinus carpio) health in response to ammonia toxicity. The fish were fed with either myrcene- or menthol-supplemented diets for 30 days before exposure to 0.5 mg/L unionized ammonia for 24 h. The experimental diets contained 0, 0.1, 0.25, 0.5 and 1% of either myrcene or menthol. Growth performance was determined after the 30-d feeding trial and the fish were blood-sampled before and after the ammonia challenge. The results showed that myrcene at 0.5% significantly improved the fish growth performance compared to the control diet (29.3 vs. 41.2% weight gain); however, menthol had no significant effects on the fish growth performance. Ammonia exposure led to significant decrease in plasma catalase, glutathione peroxidase, blood RBC and hemoglobin and significant increase in plasma superoxide dismutase, malondialdehyde, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and lactate dehydrogenase, which are indicators of oxidative stress, tissue damage and anemia. Myrcene at 0.25–1% and menthol at 0.25% levels significantly improved most of the tested parameters. Moreover, myrcene at 0.5 and 1% significantly inhibited the adverse effects of ammonia exposure on the fish antioxidant responses, tissue health and anemia; however, menthol was less effective compared to myrcene and the most effective concentration was 0.25%, which mitigated the adverse effects of ammonia exposure. In conclusion, myrcene at 0.5% and menthol at 0.25% levels are effective in reducing the adverse effects of ammonia toxicity in common carp. Such effects seem to be related to the compounds antioxidant effects, which mitigated ammonia-induced tissue damage and anemia. © 2019