Clove Oil Used at Lower Concentrations is Less Effective than MS‐222 at Reducing Cortisol Stress Responses in Anesthetized Rainbow Trout

Abstract

AbstractAnesthetics are widely used for surgical, field sampling, and experimental procedures in fisheries sciences. Given the high cost and the U.S. Food and Drug Administration's (FDA) mandatory withdrawal time of the only FDA‐approved fisheries anesthetic, tricaine methanesulfonate (MS‐222), clove oil has emerged as an alternative anesthetic that is generally regarded as safe. However, studies regarding the effectiveness of clove oil in retarding the stress response of fish are contradictory. This study evaluated the effectiveness of MS‐222 (60 mg/L), clove oil (30 mg/L) emulsified in ethanol, and clove oil (30 mg/L) mechanically emulsified in water in reducing the stress response of rainbow trout Oncorhynchus mykiss during a 15‐min confinement. Clove oil emulsified in ethanol (mean, 56.3 ng cortisol/mL) was not as effective in reducing the cortisol response as MS‐222 (mean, 33.4 ng/mL). Furthermore, clove oil emulsified in ethanol and clove oil mechanically emulsified in water (means, 49.0 and 56.2 ng/mL, respectively) produced a greater cortisol response in undisturbed fish. Our results suggest that clove oil is less effective than MS‐222 in reducing cortisol responses in rainbow trout subjected to handling and confinement. Our results also indicate that clove oil can induce stress and possibly lead to greater release mortality of field‐handled fish.