Physiological stress responses, egg survival and sperm motility for rainbow trout broodstock anesthetized with clove oil, tricaine methanesulfonate or carbon dioxide

Egg survival, sperm motility and physiological stress responses (plasma cortisol, glucose and chloride) of rainbow trout (Oncorhynchus mykiss) broodstock were compared among three anesthetics: tricaine methanesulfonate (MS-222), clove oil in the form of AQUI-S(R) (a proprietary mix of 50% isoeugenol and other ingredients) and carbon dioxide gas. Concentrations of 60 mg/l tricaine, 20 mg/l isoeugenol (40 mg/l AQUI-S) and 220-275 mg/l carbon dioxide were based on preliminary tests and chosen to standardize induction time among anesthetics. Plasma glucose, chloride and cortisol concentrations indicated that none of the anesthetics used after crowding and netting completely eliminated the stress response. The return to prestress cortisol levels differed among the three anesthetics. Fish anesthetized with AQUI-S had significantly lower cortisol concentrations at 1 or 7 h postimmersion than the other anesthetics and controls, but were elevated at 24 h. Plasma cortisol in tricaine- and CO2-treated fish returned to prestress levels within 7 and 24 h, respectively, whereas cortisol levels in control fish remained elevated at 24 It. Sperm motility and duration of motility were assessed for a practical range of concentrations: tricaine, 15-100 mg/l; AQUI-S, 10-100 mg/l; CO2, 50-173 mg/l. The percentage of motile sperm was unaffected by anesthetic treatment, averages ranging from 68% to 87%. However, duration of motility decreased as anesthetic concentration increased, averages ranging from 55 to 36 s for tricaine and from 56 to 37 s for AQUI-S. Duration of sperm motility was low (31-43 s) for all levels Of CO2 tested. Fish recovery time was significantly longer for fish anesthetized by AQUI-S (370 s) than the either CO2 or tricaine (192 and 199 s, respectively). Gender had no effect on recovery time. Egg survival to the eyed stage and to hatch was not significantly different among anesthetic treatments and controls. No delayed mortality was observed for any of the fish handled and bled for the test. Results indicated that tricaine, AQUI-S and CO2 were all suitable for broodfish anesthesia, but the longer recovery time and lower cost for AQUI-S may make it more useful than the alternatives. None of the anesthetics wholly suppressed die stress responses during a typical spawning process, but did help reduce the duration of the stress responses and eased handling without compromising egg viability. (C) 2002 Elsevier Science B.V. All rights reserved.