Menthol and 1,8-cineole as new anaesthetics in common carp, Cyprinus carpio (Linnaeus, 1758)

This study describes anaesthetic efficacy of menthol and 1,8-cineole in common carp, Cyprinus carpio, in comparison with eugenol. Common carp fingerlings were exposed to eugenol: 5, 10, 15, 25, 35, 50, 75, 100, 150 and 200 ppm; menthol: 5, 10, 15, 25, 50, 100, 200, 300, 400, 500 and 600 ppm; 1,8-cineole: 100, 150, 200, 300, 400, 500, 600, 700 and 800 ppm. Induction time and recovery time were recorded. Results showed that menthol and 1,8-cineole anesthetized the fish at higher concentrations compared to eugenol. The fish exposed to menthol showed common fish behavioural responses to anaesthesia, similar to eugenol. But, 1,8-cineole-exposed fish showed tail-up swimming, which was not observed before. Also, 1,8-cineole failed to completely cease muscle tone. Exposure to 200 ppm eugenol and 600 ppm menthol resulted in 40% and 20% mortality, respectively. Induction time was exponentially dependent on anesthetic concentrations. Recovery time was linearly correlated to eugenol and menthol, but not 1,8-cineole concentrations. Recovery time was exponentially dependent on induction time in the fish anesthetized with eugenol and menthol, but not 1,8-cineole. Menthol and 1,8-cineole are recommended for carp anaesthesia. Menthol is capable to anesthetize common carp within 1-3 min at 118-512 ppm. Common carp anesthetized with 108-133 ppm menthol recovers within 5 min. 1,8-cineole failed to anesthetize common carp within less than 150 s at 300-800 ppm concentrations. However, it anesthetizes carp within 3 min at 595 ppm concentration. Also, 1,8-cineole is not recommended for fish surgery. Both menthol and 1,8-cineole were less efficacious than eugenol.