Spearmint (l-Carvone) Oil and Wintergreen (Methyl Salicylate) Oil Emulsion Is an Effective Immersion Anesthetic of Fishes

This study evaluates the effects of a spearmint (l-carvone) and wintergreen oil (methyl salicylate) emulsion (CMSE) on age 1 landlocked Atlantic salmon Salmo salar sebago (hereafter salmon). Salmon were immersed in either 257 mu l/L CMSE or 75 mg/L tricaine methanesulfonate (MS-222) to induce anesthesia (stage 4), useful for emersion and noninvasive husbandry procedures, and then salmon were recovered in fresh water. Induction was quicker in the CMSE group; however, recovery was quicker in the MS-222 group. A second experiment was conducted in which salmon were immersed in 257 mu l/L CMSE for 8.5 min, or 75 mg/L MS-222 for 8.5 min in order to compare electrocardiographs during deeper anesthesia (stage 5) between salmon continuously immersed in CMSE to those continuously immersed in MS-222. Because salmon remained sedated longer after CMSE exposure than after MS-222 exposure, a third group of salmon was immersed in 257 mu l/L CMSE for just 2.5 min before undergoing the 6-min electrocardiograph procedure. Anesthesia induction rates, recovery rates, and electrocardiographs of salmon anesthetized with CMSE were comparable to salmon anesthetized with MS-222. Salmon anesthetized with CMSE and then transferred immediately to fresh water had more stable heart rates than salmon anesthetized with either MS-222 or CMSE continuously. Salmon bathed continuously in CMSE showed clinical signs of increasing anesthetic depth including decreasing heart rate, decreasing respiration rate and electrocardiograph abnormalities. The CMSE, with its mint and wintergreen concentrations less than in household products such as chewing gum, toothpaste, and mouthwash, is a potent, rapid-acting immersion fish anesthetic comparable to MS-222 for stages 4 and 5 anesthesia.