Etomidate: Effective Dosages for a New Fish Anesthetic

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Abstract
[Anesthetics are widely used in fisheris science and managemewnt to immobilize fish for handling.] Etomidate (r-(+)-ethyl-1-(1-phenylethyl)-1H-imidazole-5-carboxylate) is a potent and safe anesthetic for fish. The minimum effective dose for 4 spp. of aquarium fish [Pterophyllum scalare, Danio rerio, Gymnocorymbus ternetzi and Xiphophorus maculatus] ranged from 2.0-4.0 mg/l, and the maximum safe dose ranged from 7.0-20.0 mg/l. In general, the lower the dose, the longer the time for anesthesia, but the faster the recovery time. At 4.0 mg/l, fish typically entered anesthesia without 90 s and recovered within 40 min. Etomidate is more effective in alkaline water and higher water temperature but is not affected by total hardness. Test species varied in their ability to survive extended or repeated exposures to the drug. Etomidate has advantages over other commonly used fish anesthetics and should be evaluated further.