Author(s): N. Felix, U. Bala Murugan, K. Rajaram

Abstract: The use of anaesthetics facilitates work with fish at the research level for weighing, sampling, disease diagnosis, cannulation and transport where the fish must be held immobile for extended periods of time. Many chemicals have proved effective in anesthetization of fish. In this study, we selected two anaesthetics, phenoxyethanol and clove oil to test the efficacy in anesthetization of cobia Rachycentron canadum .The efficacy of clove oil and phenoxyethanol as anesthetics was evaluated in the marine finfish cobia, Rachycentron canadum. Significant differences were found in the induction and recovery stages at different concentration levels of the anesthetics. Fishes exposed to 0.01-0.04 ml/L clove oil and 0.1-0.4 ml/L phenoxyethanol, had a 100% survival rate in the experimental period. The cobia exposed to the lowest concentration of 0.01 ml/Lclove oil and 0.2 ml/Lphenoxyethanol did not reach the stage 3 due to the insufficient concentration to obtain complete loss of reflexes and immobilization. The concentration at 0.02 ml.l-1 clove oil and 0.2 ml/Lphenoxyethanol showed the complete loss of equilibrium at 4 min.07 sec. and 2 min.56 sec. respectively. After transferring them into the recovery tanks normal locomotor activity was observed. Based on our results both 2-phenoxyethanol and clove oil can be recommended for cobia, Rachycentron canadum. Our results indicate that the induction time of the fish exposed to the two anaesthetic solutions generally decreased with increasing concentrations, but the recovery time was increased with increasing concentrations. The effective concentration which produced anaesthesia within 3 min and allowed recovery within 5 min for phenoxyethanol is 0.2 ml/Land clove oil is 0.03 ml/L.

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