Anesthetic efficacy and biochemical effects of citronellal and linalool in common carp (Cyprinus carpio Linnaeus, 1758) juveniles

Present study reports the anesthetic and biochemical effects of citronellal and linalool in common carp (Cyprinus carpio) juveniles (about 110 g). The fish were anesthetized with citronellal (200, 300, 400, 500, 600, 800, 1000 and 1200 mg/L) and linalool (200, 400, 600, 800, 1200, 1600, 2000 and 2400 mg/L) and their behavioral responses to anesthesia were recorded to determine anesthesia stages. Then, required concentration of each anesthetic was calculated to induce deep anesthesia within 5 min. The fish were exposed to these concentrations, along with 43 mg/L eugenol (as a reference anesthetic) for 5 min prior to blood sampling. In addition, the fish were exposed to 10 and 20 mg/L of either citronellal, linalool or eugenol for 3 h to find long-term effects of the compounds on fish blood health characteristics. At the concentration of 200 mg/L, both citronellal and linalool failed to induce deep anesthesia. Citronellal induced deep anesthesia within 457-114 s at the concentrations of 300-1000 mg/L; recovery time was 113-204 s. Further increase in citronellal concentration has no significant effects on the induction and recovery time. Linalool at the concentrations 400-2000 mg/L induced deep anesthesia within 467-118 s with recovery time of 174-215 s. Further increase in linalool concentration has no significant effects on the induction and recovery time. Increase in citronellal or linalool concentrations significantly decreased induction time of anesthesia with strong relationship. Short-term anesthesia with citronellal and linalool caused significantly lower AST and LDH activity compared to eugenol; however, long-term exposure to linalool caused higher AST and LDH activity compared to citronellal and eugenol. Plasma total protein and globulin levels of the citronellal- and eugenol-anesthetized fish were similar and significantly higher than that of the linalool-anesthetized fish. The present study demonstrated that citronellal is suitable for general fish handling, but not rapid blood sampling and surgery. Citronellal anesthetic efficacy was higher than linalool in the present study, but lower than other anesthetics previously used for carp fingerling anesthesia. Biochemical data after short-term anesthesia show that fish anesthetized with citronellal and linalool may experience lower tissue problems compared to eugenol; however, linalool had adverse effects on plasma protein and globulin levels compared to citronellal and eugenol. Under long-term exposure, linalool may cause higher tissue problems compared to citronellal and eugenol. Citronellal is less efficacious than eugenol for carp anesthesia, however is beneficial in the case of fish health as it causes less tissue problems.