The ability of clove oil and MS-222 to minimize handling stress in rainbow trout (Oncorhynchus mykiss Walbaum)

The effects of 60-mg L−1 clove oil and 60-mg L−1 tricaine methanesulphonate (MS-222) on the blood chemistry of rainbow trout were compared after exposure to handling stress via caudal puncture blood sampling. Fish sampled by caudal puncture and subsequently exposed to anaesthetics showed a typical handling stress response over a 48-h period. There were no significant differences between the responses of fish exposed to equal concentrations of clove oil and MS-222, with the following exceptions: the blood glucose at full anaesthesia, and lactate at full recovery increased significantly in the clove oil-exposed fish. In a subsequent experiment, the stress response observed in fish sampled by caudal puncture and exposed to clove oil and MS-222 was compared with a non-anaesthetized control group. The increases in plasma cortisol levels were significantly lower at recovery in fish treated with either anaesthetic compared with the control fish. Fish exposed to MS-222 had significantly higher cortisol levels at 1 h. These findings show that few differences exist between the anaesthetic effects of clove oil and MS-222 on the physiological response of fish to stress. However, clove oil is more effective at reducing the short-term stress response induced by handling and blood sampling, and is recommended as an alternative fish anaesthetic.