The anaesthetic effects of clove-oil-derived eugenol were studied in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). Acute lethality and the effects of multiple exposures to eugenol were measured. The estimated 8-96 h LC 50 for eugenol was found to be approximately 9 p.p.m. Times to induction and recovery from anaesthesia were measured and compared with MS-222 under similar conditions. Eugenol generally induced anaesthesia faster and at lower concentrations than MS-222. The recovery times for fish exposed to eugenol were six to 10 times longer than in those exposed to similar concentrations of MS-222. Clove oil eugenol was determined to be an acceptable anaesthetic with potential for use in aquaculture and aquatic research. Doses of 40-60 p.p.m. eugenol were found to induce rapid anaesthesia with a relatively short time for recovery in juvenile trout.

The anaesthetic effects of clove‐oil‐derived eugenol were studied in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). Acute lethality and the effects of multiple exposures to eugenol were measured. The estimated 8‐96 h LC50 for eugenol was found to be approximately 9 p.p.m. Times to induction and recovery from anaesthesia were measured and compared with MS‐222 under similar conditions. Eugenol generally induced anaesthesia faster and at lower concentrations than MS‐222. The recovery times for fish exposed to eugenol were six to 10 times longer than in those exposed to similar concentrations of MS‐222. Clove oil eugenol was determined to be an acceptable anaesthetic with potential for use in aquaculture and aquatic research. Doses of 40‐60 p.p.m. eugenol were found to induce rapid anaesthesia with a relatively short time for recovery in juvenile trout.

Clove oil has been demonstrated to be an e¡ective, inexpensive anaesthetic and euthanizing agent for a number of ¢sh species, including rainbow trout, used in aquaculture and ¢sheries research. However, the potential for clove oil to cause perturbations in important plasma hormone concentrations has not been investigated. The e¡ect of anaesthesia and euthanasia in trout with eugenol (the active ingredient in clove oil) on plasma cortisol, glucose, growth hormone (GH) and two thyroid hormones [tri-iodothyronine (T 3 ) and thyroxine (T 4 )] was compared with tricaine methanesulfonate (MS-222) anaesthesia, and stunning by cranial concussion in two experiments. E¡ects on blood chemistry were di¡erent when comparing the particular anaesthetic method being used. Stunning ¢sh signi¢cantly increased plasma cortisol and glucose levels (both Po0.05), while euthanizing ¢sh using either clove oil or MS-222 had no e¡ect on these hormone levels. In contrast, the levels of GH,T 3 and T 4 hormones were un-a¡ected regardless of whether ¢sh were euthanized by stunning, MS-222 or clove oil. Variation in e¡ects between hormones were observed using clove oil eugenol. In ¢sh sampled 10 min after anaesthetizing with 150 mg L À1 of eugenol, cortisol levels were sig-ni¢cantly decreased (Po0.03), while there were no di¡erences in either glucose or GH levels. Tri-iodothyronine and T 4 also showed signi¢cantly elevated levels (Po0.05) after 10-min exposure to eugenol. These results highlight the importance of investigat-ing the potential e¡ects of any new anaesthetic or euthanizing compounds on blood plasma parameters, prior to using them in a research setting, or when comparing results to other studies which have utilized alternative anaesthetic compounds.