Efficacy of Eugenol to Lightly Sedate Freshwater Salmonids for an Extended Time Period

Abstract

Lightly sedating fish for purposes such as sorting or loading onto a distribution truck makes fish crowding, netting, and handling easier and minimizes the risk of injury to fish and handler. We conducted three experiments to evaluate the effectiveness of eugenol (AQUI-S 20E, 10% eugenol) to lightly sedate fingerling Rainbow Trout Oncorhynchus mykiss, Cutthroat Trout O. clarkii, and Chinook Salmon O. tshawytscha for 5 h in static conditions. Thirty fish were introduced to each tank that contained either freshwater (control, n = 5) or freshwater treated with eugenol (treated, 3 mg/L, n = 10) and assessed the fish in terms of various sedation criteria at 0, 5, 15, 30, 45, and 60 min and then hourly for four more hours. Fish were considered lightly sedated if three fish per tank could be captured readily by hand and were dispersed throughout the water column. Results from all studies showed that light sedation criteria were met in at least 80% of the treated tanks at all time points except 0 min. After completion of the 5-h assessment period, water exchanges were conducted, normal water flow was restored to the tanks, and fish were monitored for an additional 48 h to evaluate their recovery from light sedation and determine any adverse effects. All fish recovered within 20–30 min and no posttreatment mortality was observed. Our results indicate 3 mg/L eugenol (30 mg/L AQUI-S 20E) is effective for lightly sedating juvenile salmonids for up to 5 h under the conditions tested.