Effectiveness of the Anesthetic Aqui-S® 20e in Marine Finfish and Elasmobranchs

Abstract

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.

Efficacy of two different doses of 10% eugenol in adult California yellowtail ( Seriola dorsalis )

“…This was likely due to the differences in total anaesthetic bath time (based on opercular rate), with those in the higher eugenol treatment dose and control groups having truncated total anaesthetic times when compared with the lower treatment dose. Longer induction times were associated with the lower dose as has been seen in other anaesthetic trials using 10% eugenol (Christiansen et al, 2013;Fenn et al, 2013;Silbernagel & Yochem, 2016). In a non-research setting without a capped time of 10 min in the anaesthetic bath, this disadvantage of a longer induction time would be less deleterious as procedures could continue beyond 10 min.…”

“…Fish anaesthetized with this dose generally maintained an appropriate and steady opercular rate throughout the entire 10-min holding period (11/12 fish). The 15 mg/L eugenol dose is slightly lower than what has been found as the ideal anaesthetic dose in pallid sturgeon (~50 mg/L eugenol: Fenn et al, 2013) and other trials with juvenile yellowtail (25-55 mg/L eugenol; Silbernagel & Yochem, 2016). The differences in reported ideal anaesthetic doses may be due to species' differing size or sensitivity to eugenol utilized in research (Hoseini et al, 2015;Roubach, Gomes, Leão Fonseca, & Val, 2005), and this highlights the need for species-specific eugenol anaesthetic trials.…”

“…The anaesthetic trials consisted of two treatments of 15 and 25 mg/L doses of eugenol with 12 fish per treatment group, and 12 control fish anaesthetized with 75 mg/L MS‐222 (Tricaine‐S; Western Chemical) buffered 1:1 by weight with sodium bicarbonate. The treatment doses were chosen based on previous work with 10% eugenol in California yellowtail (Silbernagel & Yochem, ). Investigators performing observations were blinded to treatment and control doses administered.…”

“…Ten per cent eugenol has been efficacious in cultured marine and freshwater juvenile finfish as well as wild marine finfish and elasmobranchs (Bowker, Wandelear, & Bowman, 2015Bowker, Wandelear, & Silbernagel, 2017;Christiansen, Gee, & Mesa, 2013;Fenn et al, 2013;Silbernagel & Yochem, 2016). Proper immersion dosing has been investigated in three species of juvenile marine fish (Christiansen et al, 2013;Silbernagel & Yochem, 2016), but data on appropriate doses for adult marine finfish are lacking.…”

“…Western Chemical) buffered 1:1 by weight with sodium bicarbonate. The treatment doses were chosen based on previous work with 10% eugenol in California yellowtail (Silbernagel & Yochem, 2016). Investigators performing observations were blinded to treatment and control doses administered.…”