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

To evaluate isoeugenol as an anesthetic agent in koi carp.

216 juvenile koi carp (Cyprinus carpio).

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.

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.

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.