Routine Measures of Stress Are Reduced in Mature Channel Catfish during and after AQUI-S Anesthesia and Recovery

—Mature channel catfish Ictalurus punctatus were exposed to water containing three different concentrations (20, 40, and 60 mg/L) of AQUI-S (50% isoeugenol) during routine handling procedures at a commercial catfish facility. Anesthetic efficacy, recovery time, and the effects of AQUI-S on routine measures of stress were compared with similar measures in a group of fish sampled prior to anesthesia (preanesthesia [PA] group) and a group anesthetized with 100 mg tricaine methanesulfonate (TMS)/L. On average, all the fish lost equilibrium at 8.0, 3.9, and 3.7 min when anesthetized in 20, 40, and 60 mg AQUI-S/L, respectively. Fish anesthetized with TMS lost equilibrium at 4.5 min. Recovery time in freshwater was 2.1, 2.8, and 5.3 min for fish anesthetized in 20, 40, and 60 mg/L AQUI-S, respectively. Recovery time after TMS anesthesia was 1.7 min. Short-term (24-h) survival was 100% for all treatments, and long-term (21-d) survival ranged from 87.5% for TMS-anesthetized fish to 98.8% for fish anesthetized in 40 mg/L AQUIS. All anesthetic treatments significantly reduced (P , 0.05) plasma cortisol levels relative to PA fish, and circulating cortisol was lower (P , 0.05) in all AQUI-S2anesthetized fish than in TMSanesthetized fish. Plasma glucose concentrations were significantly lower (P , 0.05) in fish anesthetized with 40 mg/L AQUI-S than in PA and TMS-treated fish after both anesthetization and recovery. Plasma lactate and chloride concentrations were not reduced (P . 0.05) in any treatment compared with the levels in PA fish. Fish anesthetized with 40 mg/L AQUI-S had lower (P , 0.05) plasma lactate levels after recovery than TMS-anesthetized fish, and plasma chloride levels were significantly lower (P , 0.05) immediately following AQUI-S anesthesia at all concentrations than in fish anesthetized with TMS. Anesthesia did not affect (P . 0.05) postrecovery plasma chloride concentrations. Overall, AQUI-S exhibited efficacy as an anesthetic for mature channel catfish and demonstrated stress-reducing properties during handling procedures. Selective breeding programs for channel catfish Ictalurus punctatus and its hybrid with the blue catfish I. furcatus inherently involve acute handling stressors. During selection, fish are often seined from ponds, moved to raceways, and graded. Hybridization involves additional levels of stress, such as broodfish preparation, hormonal induction of spawning, and artificial hand stripping. Numerous researchers have demonstrated that stress has the capacity to inhibit reproductive performance and viability of fish eggs (de Montalembert et al. 1978; Stacey et al. 1984; Campbell et al. 1994; Schreck et al. 2001). The challenges for the producer are keeping fish healthy and obtaining quality gametes. For this reason, chemical anesthetics may be used to ease handling and reduce fish stress. In addition to preventing physical injury, certain * Corresponding author: [email protected] Received June 21, 2004; accepted September 17, 2004 anesthetics are thought to reduce the perception of stress. Some anesthetics, such as metomidate hydrochloride (dl-1-[1-phenylethyl]-5-[metoxycarbonyl] imidazole hydrochloride), are thought to block activation of the hypothalamo-pituitaryinterrenal (HPI) axis associated with handling stress in fish (Olsen et al. 1995; Small 2003). Metomidate is the methyl derivative of etomidate, which has been demonstrated to affect the mitochondrial cytochrome P450-dependent enzymes that catalyze the synthesis of cortisol (Vanden Bossche et al. 1984; Wagner et al. 1984). Failure to suppress activation of the HPI axis during stress results in a release of cortisol, which in turn causes various secondary stress responses, including increases in circulating levels of glucose and lactate (Rotllant et al. 2001; Skjervold et al. 2001). Currently, tricaine methanesulfonate (TMS; MS-222) is the only anesthetic approved by the U.S. Food and Drug Administration (FDA) for use with food fish in the United States. However, even when fish D ow nl oa de d by [ So ut he rn I lli no is U ni ve rs ity ] at 1 4: 47 3 0 O ct ob er 2 01 2 73 AQUI-S REDUCES CATFISH STRESS INDICES are deeply anesthetized with TMS, handling procedures or simply the exposure to TMS can increase plasma cortisol concentrations (Thomas and Robertson 1991; Small 2003). A relatively new fish anesthetic, AQUI-S, has approval for use with food fish in Australia, Chile, and New Zealand with no withholding period and has been shown to reduce the stress response of juvenile channel catfish to crowding and acute oxygen depletion (Small 2004). AQUI-S is currently in the process of evaluation for approval as a food fish anesthetic by the FDA. The purpose of this study was to determine whether anesthesia with AQUI-S during simulated broodfish selection procedures at a commercial catfish production facility reduces routine measures of stress (cortisol, glucose, lactate, and chloride) in mature channel catfish. This research provides necessary data for assessing the potential use of AQUI-S as an anesthetic to reduce channel catfish stress response to commercial handling procedures, such as those that might occur during broodfish selection and preparation.