Efficacy of AQUI-S 20E as a Sedative for Handling and Cortisol Suppression in Pallid Sturgeon

Challenges and regulations associated with handling fish during fisheries management activities have increased efforts to achieve U.S. Food and Drug Administration approval for an immediate-release sedative for fish. The objectives of this study were to (1) identify the target concentration of AQUI-S 20E for sedation of Pallid Sturgeon Scaphirhynchus albus to a handleable state followed by rapid recovery, and (2) to compare sedation and recovery times and cortisol stress response in sturgeon treated with the identified target concentration to those treated with MS-222. Juvenile Pallid Sturgeon from two size-classes were exposed to five concentrations of AQUI-S 20E: 70, 153, 364, 598, and 779 mg/L of water. The target concentrations of AQUI-S 20E for optimal sedation (<3 min) and recovery times (<5 min) identified for Pallid Sturgeon were 476 mg/L for small and 537 mg/L for large size-classes. Cortisol secretion in relation to presedation plasma cortisol levels was suppressed at the AQUI-S 20E target concentration of 500 mg/L but was not for MS-222. These data suggest an AQUI-S 20E concentration of 500 mg/L is efficacious while blocking the cortisol stress response for sedation to a handleable state in Pallid Sturgeon. Both wild and hatchery-reared fish undergo stressors through practices common to fisheries management, such as capture, handling, transportation, tissue collection, tagging procedures, surgical operations, and artificial spawning. These stressors can be especially detrimental to biologically sensitive species such as Pallid Sturgeon Scaphirhynchus albus (Barton et al. 2000) and may lead to immune suppression, decreased survivorship, and reduced growth rates, among others. Activities involving handling and transportation of fish can be better facilitated through the immobilizing actions of aquatic sedatives, which also have the potential to reduce associated fish stress and tissue injuries (Iversen et al. 2003; Di Marco et al. 2011). An ideal aquatic sedative induces rapid sedation to a handleable state (<3 min) and recovery (<5 min) and also minimizes hyperactivity and stress responses from treated fish (Marking and Meyer 1985). Additional variables to be considered when selecting an ideal aquatic sedative are its regulation status, commercial availability, delivery method, cost efficiency, environmental impact, and consumer safety (Akbulut et al. *Corresponding author: [email protected] Received February 6, 2013; accepted July 24, 2013 2012). Currently, one of the most widely used chemical sedatives for aquatic species is tricaine methanesulfonate (MS-222; Marking and Meyer 1985; Popovic 2012), and it is the only U.S. Food and Drug Administration (FDA) approved chemical sedative for use with fish having the potential for human consumption. However, MS-222 has a mandatory 21-d withdrawal period for human consumption. Withdrawal periods make the use of sedatives often impossible for fisheries managers who often need to immediately release the fish with which they are working. In addition to inducing rapid sedation and recovery, an ideal chemical sedative would suppress handling stress by blocking activation of the hypothalamic-pituitary-interrenal (HPI) axis, thus reducing the release of plasma cortisol, which is a blood indicator of physiological stress response in fish (Barton 2002; Small 2003, 2004; Webb et al. 2007). Following sedation, MS222 has been shown to increase plasma cortisol levels in a variety of fish species, including Brown Trout Salmo trutta (Pickering et al. 1982), Channel Catfish Ictalurus punctatus (Small 2003), Striped Bass Morone saxatilis (Davis et al. 1982), Red Drum 1172 D ow nl oa de d by [ So ut he rn I lli no is U ni ve rs ity ], [ B ri an C . S m al l] a t 0 9: 27 0 8 Ja nu ar y 20 14 SEDATIVE AQUI-S 20E FOR PALLID STURGEON 1173 Sciaenops ocellatus (Thomas and Robertson 1991), and Fathead Minnow Pimephales promelas (Palić et al. 2006). These findings suggest that MS-222 activates the HPI axis and the pathway by which cortisol is released (Barton 2002). Moreover, because of increased risk of mortality, MS-222 is not recommended for use in certain species, including Pallid Sturgeon (Wanner 2006). Making its Jurassic debut approximately 70 million years ago, the Pallid Sturgeon is a phylogenetically ancient bony fish species (Gardiner 1984; Krieger and Fuerst 2002) indigenous to the North American Mississippi and Missouri river systems. Anthropogenic activities spanning the past 100 years, including overfishing, pollution, impoundment, damming, and channelization of rivers, have dramatically altered their native habitats (Duffy et al. 1995; Mayden and Kuhajda 2002). Consequently, Pallid Sturgeon populations and catch rates declined, and the species was listed as federally endangered in 1990 (55 Federal Register 36641 36647). In response to this decline, recovery efforts were implemented through health-risk assessments, habitat and wild populations monitoring, supplemental stocking, and artificial propagation of wild and hatchery-reared fish (Webb et al. 2005). As previously mentioned, such activities can prove stressful to any fish but are particularly concerning for imperiled species. Given the limited available chemical sedative options, it is pertinent to evaluate a chemical sedative for use in Pallid Sturgeon and to identify the concentration that induces both rapid sedation and recovery, as well as suppresses the physiological stress reaction. Identification of an ideal chemical sedative for Pallid Sturgeon could serve as a potential model for use among other sturgeon species. Because sturgeon populations are in critical decline throughout the Northern Hemisphere, many species are artificially propagated in hatcheries with the goal of increasing wild stocks (Webb et al. 2005). Additionally, as wild stocks continue to decrease, sturgeon are becoming more prevalent in culture conditions where they are reared for their prized meat and caviar (Wei et al. 2004; Di Marco et al. 2011). As such, commercial sturgeon operations would also benefit from an immediate-release chemical sedative alternative. Both isoeugenol and eugenol, active ingredients found in clove oil, have been observed to sedate and suppress stressrelated cortisol levels in some fish species (Iversen et al. 2003; Small and Chatakondi 2005; Roubach et al. 2005; Palić et al. 2006). A relatively new aquatic chemical sedative composed of 10% eugenol (active ingredient), AQUI-S 20E (AQUI-S New Zealand, Ltd.) has been authorized by the U.S. FDA as an immediate-release sedative for field use under U.S. Fish and Wildlife Service (USFWS) Investigational New Animal Drug (INAD) 11–741. Under this INAD, hatchery use requires a 72-h withdrawal period before treated fish can be harvested or released. With this authorization comes the need to establish specific guidelines for use. The objectives of this study were to (1) identify the target concentration of AQUI-S 20E for sedation of Pallid Sturgeon to a handleable state followed by rapid recovery, and (2) to compare sedation and recovery times and stress response in sturgeon treated with the identified target concentration to those treated with MS-222. Plasma cortisol was measured to evaluate stress response because it is the primary glucocorticoid indicative of stress in sturgeon (Sangalang 1971; Webb et al. 2007).