Etomidate as an Anesthetic for Fish: Its Toxicity and Efficacy

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Abstract
Etomidate was tested as an anesthetic on channel catfish Ictalurus punctatus, golden shiners Notemigonus crysoleucas, and bluegills Lepomis macrochirus. The 24‐hour median lethal concentration (LC50) at various temperatures was lowest for bluegills (0.61–0.68 mg/liter) and highest for golden shiners (1.87–2.73 mg/liter). Generally, etomidate was more toxic, and induction of anesthesia and recovery from anesthesia were slower, at 17 C than at 22 and 27 C. Water hardness and pH had no or only slight effect on the toxicity and efficacy of etomidate. All channel catfish in 8 mg/liter and all golden shiners in 10 mg/liter were anesthetized within 2 minutes at 22 ± 1 C (±range) and all survived if removed from the etomidate immediately after opercular movement stopped. Both channel catfish and golden shiners were anesthetized within 15 minutes by 3 mg/liter, and all of the fish survived at this concentration for 30 minutes. Concentrations of 0.2 and 0.4 mg/liter sedated channel catfish, and 0.4 and 0.6 mg/liter sedated golden shiners. The safety index LC50/EC50 (median effective concentration) for anesthesia of channel catfish and golden shiners at 22 ± 1 C decreased from 6.2 to 5.0 and 7.6 to 4.0, respectively, as exposure length increased from 10 to 80 minutes. Received October 22, 1982 Accepted May 8, 1983