Effects of dietary 1,8-cineole supplementation on serum stress and antioxidant markers of common carp (Cyprinus carpio) acutely exposed to ambient ammonia

Abstract

In the present study, the effects of dietary cineole were investigated on common carp (Cyprinus carpio) responses to ammonia toxicity. The fish were fed with diets containing 0%, 0.1%, 0.5% and 1% cineole for 2 weeks followed by a 24-h ammonia challenge (0.5 mg/L unionized ammonia-N). Serum cortisol, glucose, lactate, T4, T3, catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), total antioxidant capacity (TAC) and malondialdehyde (MDA) were measured before and after the ammonia challenge. Results showed that ammonia challenge significantly increased serum cortisol, glucose, TAC and MDA and decreased serum thyroid hormones, lactate, CAT and SOD. Cineole, especially at 0.5%, significantly decreased serum cortisol, glucose and MDA, and increased serum lactate, thyroid hormones and antioxidant enzymes. Ammonia had no effects on GPx activity but cineole administration significantly increased the enzyme activity. There were interaction effects of dietary cineole and ammonia toxicity on serum T3, CAT, SOD and MDA: 0.5% and 1% cineole administration inhibited the ammonia-induced T3 suppression; 0.5% cineole mitigated the ammonia-induced CAT and SOD suppression; and 0.5% cineole mitigated the ammonia-induced MDA elevation. These results suggest that cineole is capable to counteract the ammonia-induced changes in these parameters. In conclusion, cineole administration is beneficial for common carp as it suppresses stress response, augments thyroid hormones levels and suppresses oxidative stress. Moreover, cineole mitigates adverse effects of ammonia toxicity on serum T3 and suppresses oxidative stress caused by ammonia toxicity. Administration of 0.5% cineole to common carp diet for 2 weeks is recommended to counteract the adverse effects of periodical ammonia exposure.