β-Cyclodextrin–Eugenol Co-Ground preparation improves the functional stability of anesthesia in Xenocypris davidi

Eugenol is a widely used fish anesthetic, but its poor aqueous solubility, volatility, and environmental instability limit practical applications. This study compared the pharmacodynamic profiles and temporal stability of three eugenol formulations—raw dispersion, ethanol-solubilized solution, and a β-cyclodextrin (β-CD)/eugenol co-ground preparation—using juvenile Xenocypris davidi at 20 mg L⁻¹. Raw eugenol exhibited the longest induction time and lost efficacy entirely by 24 h post-preparation. Both the ethanol and β-CD formulations significantly accelerated induction, with no significant difference between them. However, the β-CD co-ground preparation produced a significantly prolonged recovery time and maintained consistent anesthetic performance over 24 h, whereas the ethanol formulation showed increased induction variability and the raw formulation failed completely. These results indicate that ethanol-solubilized eugenol is suitable for brief procedures requiring rapid recovery, whereas the β-CD co-ground preparation exhibited greater functional stability under the tested conditions.