Comparative efficacy of four anaesthetic agents in the yellow seahorse, Hippocampus kuda (Bleeker, 1852)

In modern aquaculture, anaesthetics play an important role in reducing handling stress and mortality. In this investigation, the efficacy of four anaesthetic agents (MS-222, benzocaine, clove oil and 2-phenoxyethanol) was compared in captive-bred yellow seahorse, Hippocampus kuda (Bleeker, 1852). The lowest effective concentrations based on the efficacy criteria of complete anaesthetic induction within 180 s and recovery within 300 s were determined to be 125 mg L−1 (induction 115 ± 16 s and recovery time 246 ± 36 s) for MS-222, 175 mg L−1 (induction 175 ± 19 and recovery time 354 ± 55 s) for benzocaine, 50 mg L−1 (induction 115 ± 28 and recovery time 385 ± 37 s) for clove oil, 1000 μl L−1 (induction 176 ± 22 and recovery time 271 ± 37 s) for 2-phenoxyethanol. Induction and recovery times for adult H. kuda anaesthetised with anaesthetic agents were dose-dependent (P < 0.05). The onset of individual phases of anaesthesia and recovery times depended significantly on the concentration of the anaesthetic used (P < 0.05). An inverse exponential relationship was observed between concentrations of anaesthetic and induction time, whereas exponential relationships were observed between concentrations and recovery times for all anaesthetic agents evaluated. Amongst all tested anaesthetics, MS-222 and clove oil were proven to be most effective and the latter appears to meet many of the criteria of an ideal fish anaesthetic. The study has potential significance with regards to seahorse husbandry in terms of stress, survival and production efficiency.