The Use of Tricaine Methanesulfonate, Clove Oil, Metomidate, and 2-Phenoxyethanol for Anesthesia Induction in Alewives

The efficacy of four anesthetic agents—tricaine methanesulfonate (MS-222), clove oil, metomidate, and 2-phenoxyethanol (2-PE)—was studied in adult, juvenile (133.3 ± 1.5 mm, 27.5 ± 8.9 g; mean ± SE), and larval Alewives Alosa pseudoharengus. In an initial trial, wild-caught adults were anesthetized to a state where they failed to respond to strong tactile stimuli when dosed with 87.5–112.5 mg/L MS-222, 25–40 mg/L clove oil, 0.5–5.0 mg/L metomidate, and 125–550 mg/L 2-PE. Optimal doses for anesthesia, defined as those providing the combined shortest induction and recovery times, were similar for larvae and juveniles: 75–100 mg/L MS-222, 40 mg/L clove oil, 5–7 mg/L metomidate, and 500 mg/L 2-PE. All juvenile fish survived 48 h postexposure to each optimal dose. In a longer (24 h) sedation experiment, juvenile Alewives were netted and exposed to low clove oil (2.5 and 5.0 mg/L) and metomidate (0.25 and 0.50 mg/L) doses, after which plasma cortisol was measured. Fish exposed to the clove oil treatments exhibited a cortisol stress response that was prolonged in the higher-dose treatment. No cortisol stress response was observed in the metomidate treatments. Overall, optimal acute anesthesia doses for Alewives were similar to those reported for other species, and metomidate may be useful for longer-term sedation