Behavioral and physiological assessment of low concentrations of clove oil anaesthetic for handling and transporting largemouth bass (Micropterus salmoides)

Clove oil has become a popular fish anaesthetic for invasive fisheries research procedures, but few studies have examined the use of low concentrations of clove oil to achieve sedation for aquaculture procedures such as fish handling and transport. In this study, we used largemouth bass as a model species to examine the behavioral and physiological responses of fish to a gradation of clove oil concentrations (0 to 20 mg l(-1)) while exposed to truck transport. Concentrations of clove oil ranging from similar to5 to 9 mg l(-1) elicited a sedative effect resulting in loss of reactivity and reduced cardiac output while maintaining equilibrium. Fish sedated by 5 to 9 mg l(-1) clove oil achieved that level of anaesthetization rapidly and recovered behaviorally more quickly than at higher concentrations. During transportation, videography revealed that fish in deep sedation (stage 2 induction) experienced the least opportunity for physical damage from the tank or conspecifics and had reduced activity relative to other concentrations. Cardiovascular assessments indicated that when exposed to clove oil of any concentration, cardiac output and heart rate rose following an initial bradycardia. Fish exposed to low levels of clove oil recovered rapidly when returned to fresh water, but those exposed to higher concentrations (usually stage 4 or 5 induction) exhibited protracted cardiovascular recovery. Recovery occurred more rapidly for fish that were exposed to stage 2 anaesthesia than nonanaesthetized controls. Low levels of clove oil (5 to 9 mg l(-1)) yielded rapid induction and maintenance of stage 2 anaesthesia in subadult largemouth bass and was effective for mitigating the effects of fish transport stress. The results from this study could be useful for aquaculturists and other handling related husbandry practices that require sedation of fish. (C) 2004 Elsevier B.V. All rights reserved.