Evaluation of isoeugenol for anesthesia in koi carp (Cyprinus carpio).

Objective: To evaluate isoeugenol as an anesthetic agent in koi carp.

Animals: 216 juvenile koi carp (Cyprinus carpio).

Procedures: Fish were randomly allocated to 9 groups of 24, and each group was randomly exposed to isoeugenol concentrations ranging from 0 to 500 mg/L. General activity, excitement, fin and gill color changes, opercular movement rate, loss of equilibrium, muscle tone, jaw tone, and handleability were assessed. Five fish from the control (0 mg/L), 200 mg/L, and 500 mg/L groups were randomly selected prior to anesthetic recovery and again 24 hours after recovery for euthanasia, gross necropsy, and histologic assessment of gills, internal viscera, and skeletal muscles.

Results: Mean +/- SD interval to achieve stage 2 anesthesia with isoeugenol ranged from 22.4 +/- 6.2 minutes at 20 mg/L to 0.25 +/- 0.4 minutes at 500 mg/L, whereas the mean interval to stage 3 anesthesia ranged from 28.1 +/- 3.9 minutes at 20 mg/L to 0.33 +/- 0.48 minutes at 500 mg/L. With the exception of the 500 mg/L group, opercular movements were maintained throughout. Death was observed only in the 500 mg/L group, in which 50% of the fish either failed to recover or died within 24 hours after anesthetic exposure. There were no pathological differences between fish exposed to isoeugenol at 0 or 500 mg/L.

Conclusions And Clinical Relevance: Isoeugenol appeared to have a wide margin of safety with predictable dose-related effects. Concentrations of 40 to 80 mg/L induced anesthesia within 4 to 11 minutes and were considerably less than the concentration associated with fish death.