Preparation and Characterization of Eugenol and 1,8-Cineole Nanoemulsions for Enhancing Anesthetic Activity in Guppy Fish (Poecilia reticulata)

This study aimed to prepare and characterize nanoemulsions containing eugenol and 1,8-cineole using the emulsification method and to investigate their anesthetic effects on guppy fish. The optimized formulation comprised a 5–10% mixture of eugenol and 1,8-cineole in a 1:2 ratio, stabilized with 15–20% Tween 80. The selected formulations displayed mean particle sizes below 15 nm, a low polydispersity index (PDI) (<0.5), and a zeta potential that was more negative than −40 millivolts (mV), indicating stable emulsions. Their pH ranged from 6.50 to 6.63, indicating slight acidity. The formulations exhibited non-Newtonian rheology, as well as thinning under shear stress. Three formulations (F2, F6, and F12) remained stable after both accelerated and long-term stability testing. All nanoemulsions were able to induce guppy fish to the third stage of anesthesia. The nanoemulsions with concentrations of 50 mg/L and 100 mg/L eugenol effectively induced sedation and anesthesia in both sexes and reduced the induction and recovery times compared with the ethanol solution. In conclusion, this study highlights nanoemulsions as a promising drug delivery system for alternative anesthetics in aquaculture.