Nanoemulsion boosts anesthetic activity and reduces the side effects of Nectandra grandiflora Nees essential oil in fish

Nectandra grandiflora essential oil has become an alternative to synthetic anesthetics and sedation in fish. However, essential oil volatility, light sensitivity, and low water-solubility may limit its use in the fish farm. To overcome these drawbacks, we developed a new nanoemulsion product that may be applied as an anesthetic. We evaluated the anesthetic property and safety of free essential oil (FEO) and its nanoemulsion (NEN) for Nile tilapia (Oreochromis niloticus). Formulations were made using the spontaneous emulsification process, and stability was tested for NEN and FEO at 4, 25, and 40 degrees C for 90 days. The NEN contained 95% of FEO, the major compounds remained stable up to 60 days, and the NEN protected the active substances at all temperatures. Fish behavior was observed during a bath with FEO and NEN 3-300 mg/L concentrations for 30 min. The difference between sedated and anesthetized fish was detected by their swimming behavior and response to stimuli on the caudal peduncle. Behavior score, survival, or adverse effects were accessed with 10 and 30 mg/L concentrations of FEO and NEN during 24 h exposure and 72 h recovery. Only 100 mg/L of NEN induced anesthesia without side effects. Long-term exposure tests confirmed the 30 mg/L NEN safety, with a 100% survival rate for fish exposed to NEN and a 25.5% survival rate for fish exposed to surfactants. Therefore, this poorly water-soluble essential oil was converted into a novel sedative and anesthetic for fish through nanoemulsion. Thus, nanoemulsion protects the essential oil and improves the pharmacological activity, with the suggested use of 30 mg/L during 24 h, for sedation, and 100 mg/L, for anesthesia.