USE OF AQUI-S20E, TRICAINE-S, AND AQUACALM TO SEDATE RAINBOW TROUT TO HANDLEABLE

Fish sedatives are used to achieve various stages of sedation to facilitate fisheries research and management, such as "light sedation" for transportation, "loss of equilibrium" for routine handling, and "deep sedation" for surgical procedures. Only Tricaine-S (MS222;) is approved by the U.S. Food and Drug Administration (FDA) as a fish sedative/anesthetic and available in the U.S. However, efforts are under way to gain FDA approval of AQUI-S20E (10% eugenol) and there is interest in gaining such an approval for Aquacalm (metomidate hydrochloride). For comparison purposes, we sedated small fingerling Rainbow Trout Oncorhynchus mykiss with AQUI-S20E, Aquacalm, or Tricaine-S to assess time to handleable and recovery.

Thirty Rainbow Trout (9.8 cm) were individually sedated to handleable under static conditions with either 25 mg/L eugenol, 80 mg/l MS222, or 6 mg/L metomidate. A fish was deemed handleable when it lost equilibrium and the ability to swim, could easily be caught by hand, and did not struggle while being weighed or measured. When a fish became handleable, it was removed from the sedative solution and transferred to a recovery tank of fresh, flowing water. Fish were considered recovered when they regained equilibrium, resumed normal swimming behavior, and could avoid a net handle placed in their path.

Regardless of sedative used, mean times for fish to become sedated were < 2 min and individual times ranged from 0.8 to 3.1 min. Mean recovery times for fish sedated with eugenol, MS222 and metomidate were 2.1, 1.2, and 5.0 min, respectively. Mean elapsed time for fish to become sedated and recover was longest for metomidate (6.4 min) and shortest for MS222 (2.5 min). Based on these results, doses of all sedatives effectively sedated fish to handleable in times that would be considered reasonable by most users.