Effectiveness of the anesthetic aqui-s® 20e in marine finfish and elasmobranchs

Immersion anesthetics are used in hatchery settings by veterinarians, field biologists, and laboratory researchers to aid in handling finfish for medical procedures, research purposes, and moderating perceived stress responses. The only Food and Drug Administration– (FDA) approved anesthetic for food fish, tricaine methanesulfonate, requires a 21-d withdrawal period prior to harvest. Ten percent eugenol (AQUI-S® 20E) has been gaining momentum for FDA approval because of its 0-d withdrawal time if fish are not of harvestable size within 72 h of exposure. We performed two trials to determine appropriate anesthetic doses for two cultured marine finfish: Atractoscion nobilis (white seabass, WSB) and Seriola lalandi (California yellowtail, YT). Fish were held in a treated water bath for 10 min or until opercular beat rate slowed to a rate of <2 beats/min. Based on these results, we conducted a field trial with wild Paralabrax maculatofasciatus (spotted bay bass), Paralabrax nebulifer (barred sand bass), Paralichthys californicus (California halibut), Triakis semifasciata (leopard shark), and Mustelus californicus (grey smooth-hound) at a single dosing regime, with animals held 5–10 min in anesthetic baths. Anesthetic dosing of 35–55 mg L⁻¹ provided relatively fast induction and good anesthetic maintenance in cultured and wild finfish. Anesthetic induction times were comparable among S. lalandi and A. nobilis at 35–mg L⁻¹ to 75–mg L⁻¹ doses, but recovery times were variable. Mortality rates of 20-90% were observed at higher doses (75 mg L⁻¹ and 100 mg L⁻¹, A. nobilis; 55 mg L⁻¹ and 75 mg L⁻¹, S. lalandi). The apparent increase in sensitivity of S. lalandi may have been associated with nutritional stress in the fish tested. There were no differences in time to anesthesia or recovery among wild finfish species tested at a single dose. Anesthetic induction, maintenance, and recovery were less predictable in the elasmobranch species tested and additional trials are needed to determine optimal dosing.