Abstract

Isoeugenol (Aqui-S) is a bath anesthetic agent that has potential use in both recreational and commercial fisheries.¹ Juvenile koi carp (n=216) were divided into nine treatment groups. Groups were exposed to solutions of isoeugenol in water at concentrations from 0 mg/L to 500 mg/L. Fish were monitored for activity, opercular rate, initial loss of equilibrium (ILE), jaw tone, handle ability, and stage 3 anesthesia (STA). Once recovered in water without anesthetic, the fish were returned to their initial holding tanks and observed for 24 h.

Increasing concentrations of isoeugenol resulted in decreasing times to ILE and STA, all statistically different from the control and 20 mg/L groups. At a concentration of 40 mg/L, ILE occurred at 7.21±3.51 min, with STA at 11.0±4.20 min. At a concentration of 150 mg/L, ILE occurred at 1.67±0.56 min, with SFA at 2.46±0.66. Larger fish in each group showed a trend toward a faster time to STA, but this was only statistically significant at a concentration of 80 mg/L (p<0.001). Twelve fish in the group exposed to 500 mg/L died within 24 h, but no mortality was seen in other groups. Histopathologic analysis of control and 500 mg/L groups did not show lesions attributable to isoeugenol.

All fish were easily handled once at STA. All maintained opercular movement throughout anesthesia and recovery, except for those that died.

Isoeugenol is a safe and effective anesthetic for koi, causing rapid induction at concentrations between 60–200 mg/L. Future studies should evaluate isoeugenol for surgical procedures and anesthetic maintenance.

Literature Cited

1.  Stehly, G.R., and W.H. Gingerich WH. 1999. Evaluation of Aqui-S (efficacy and minimum toxic concentration) as a fish anaesthetic/sedative for public aquaculture in the United States. Aquaculture Research. 1999;30:365–372.