Etomidate: Effective Dosages for a New Fish Anesthetic

Etomidate (r-(+)-ethyl-1-(1-phenylethyl)-1H-imidazole-5-carboxylate) is a potent and safe anesthetic for fish. The minimum effective dose for four species of aquarium fish ranged from 2.0 to 4.0 mg/liter, and the maximum safe dose ranged from 7.0 to 20.0 mg/liter. In general, the lower the dose, the longer the time for anesthesia, but the faster the recovery time. At 4.0 mg/liter, fish typically entered anesthesia within 90 seconds and recovered within 40 minutes. 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.