Efficacy of Aqui-S as an Anesthetic for Market-Sized Striped Bass

—Market-sized 2-year-old striped bass Morone saxatilis (average weight, 645 g) were evaluated in three different concentrations of Aqui-S at one of three different temperatures. Time to stage 4 of anesthesia, recovery time, and plasma cortisol level as an indicator of acute stress response, were determined. We found a significant difference in the time to stage 4 between 25 mg/L and 35 or 45 mg/L. This difference was present at all three temperatures tested. There were also significant differences in recovery time and blood cortisol level, but these differences were not consistent across all temperatures. There was a significant interaction between temperature and dose when analyzing cortisol levels. For the range of concentrations evaluated, we recommend an Aqui-S dose of 35 mg/L when anesthetizing market-sized striped bass. There are numerous situations in aquaculture (such as netting, crowding, and transport) that can cause primary stress responses in fish, including elevated plasma cortisol concentrations (Donaldson 1981). Repetitive stressors can lead to chronic stress and chronic elevation of plasma cortisol (Pickering 1992), which is considered undesirable because it has been associated with depressed growth (Pickering et al. 1991), reproduction (Campbell et al. 1992), and immune response (Pickering and Pottinger 1989). The use of an anesthetic during the handling or relocation of fish may not only protect the fish and the fish handler from physical trauma but also reduce the perception of the stressor and thus the magnitude of the stress response. A number of anesthetics have been tested for use with fish in the United States, though at present the only compound approved for use by the U.S. Food and Drug Administration (FDA) is Finquel (3-aminobenzoic acid ethyl ester methanesulfonate, also known as tricaine methanesulfonate or MS-222), which has a 21-d withdrawal period (Schnick et al. 1986) and is currently banned in Canada (Peake 1998). Carbon dioxide is generally recognized as safe by the FDA and has been used by aquaculturists (Anderson et al. 1997), but it typically has very long induction and recovery times (Gilderhus and Marking 1987), which can lead to increased and unnecessary stress for the animals. An efficacious fish anesthetic needs to be soluable in water and provide smooth, rapid induction and recovery from anesthesia (Brown 1993). Marking and Meyer (1985) described a number of characteristics of an efficacious anesthetic. These included (1) an induction time of less than 15 min, (2) nontoxicity to fish and humans, (3) no persistent effects on fish physiology, and (4) no withdrawal time. A relatively new compound, Aqui-S, is approved as an anesthetic for food fish in Australia, New Zealand, and Chile (Small and Chatakondi 2005). The product, reported to contain 50% isoeugenol (2-methoxy-4-propenylphenol) and Polysorbate 80 as an inert surfactant, was recently evaluated for its effects as an anesthetic on the coldwater Atlantic salmon Salmo salar by Iverson et al. (2003). Small (2004) recently reported the effects of isoeugenol on the warmwater channel catfish Ictalurus punctatus. The FDA currently has Aqui-S under consideration as a food fish anesthetic (FDA 2002) and will ultimately determine whether there are toxicity issues and whether the product can be used with a zero withdrawal time. The times to induction and recovery and the stress response as determined by postexposure plasma cortisol levels were used to evaluate Aqui-S as an anesthetic for the temperate striped bass Morone saxatilis.