Hatchery-reared fish endure a series of stressors during routine handling procedures such as harvesting, sorting, weighing, and loading for live transport. These common handling practices can lead to osmoregulatory dysfunction and reduced disease resistance significantly compromising fish survival. Sedating fish before handling minimizes risk of injury and the stress response, yet currently no sedative is available in the U.S. that allows immediate release for stock enhancement or sale for human consumption. AQUI-S®20E (10% eugenol) is currently permitted for restricted use under the FDA’s Investigational New Animal Drug (INAD) exemption while further research is conducted to validate its efficacy and safety for procedures requiring exposure times > 15 minutes.
We conducted light sedation trials with four economically important fish (Red Drum, Sciaenops ocellatus; Florida Bass, Micropterus salmoides; Florida Pompano, Trachinotus carolinus; and Northern Red Snapper, Lutjanus campechanus). The goal of this research is to ultimately remove light sedation restrictions of AQUI-S®20E by addressing the research gaps required by FDA regulators. Light sedation is characterized by a decrease in activity and reactivity to stimulus while maintaining equilibrium. Assessment criteria were modified based on species specific behavior differences. For example, Florida Pompano are highly active so capture success by hand was highly variable; however, reactivity to tapping the side of the tank was reliable for determining light sedation. At the other end of the spectrum, Red Drum are lethargic so capture success was assessed using a lifting device and reactivity was ranked based on response to poking them with an instrument. Three independent trials were conducted for each species. Two preliminary trials initially determined the target dose based on the maximum dose of AQUI-S®20E that would not result in significant (< 5%) loss of equilibrium during two hours of exposure at low biomass density. The third and final trial evaluated the target dose at two practical loading densities for transport for five hours. Test fish were exposed to either the intended dose of AQUI-S®20E or hatchery water and assessed for selected light sedation criteria at different times throughout the trials by blind study participants.
We determined 40 mg/L was effective for producing light sedation in Red Drum and Florida Pompano and 50 mg/L for Florida Bass and Northern Red Snapper under the conditions tested. Anecdotally, temperature appeared to impact the dose for producing light sedation. Generally, light sedation was maintained for ≥ 2 hours, at 2 to 4 hours response criteria diminished significantly, and after 5 hours it was not statistically significant (p > 0.05) from controls. Eugenol is depleted over time via metabolic uptake by the fish biomass, which corresponds directly to the reductions in light sedation criteria observed in these studies. FDA approval of a zero-withdrawal anesthetic would advance aquaculture development potential in the U.S. by removing a regulatory barrier to sustainable and ethical fish production.