The effects of prospective anaesthetic substances on cephalopods: Summary of original data and a brief review of studies over the last two decades

Abstract

Trials were performed with magnesium chloride, ethanol and eight more complex organic substances screened for their effect as immersion anaesthetics for small, medium and large octopus species commonly used as experimental animals in Japan: Amphioctopus fangsiao, Octopus vulgaris, and Enteroctopus dofleini, respectively. Four of the organics were synthetic compounds commonly used as fish anaesthetics (metomidate, MS-222, propoxate, and quinaldine sulphate) and four have been used on other invertebrates (chloretone, gallamine, phenoxetol, and nicotine sulphate). Urethane (no longer used because of its carcinogenic properties) was used as a reference anaesthetic because of its long history of success with octopuses. Best results for anaesthetic effect were obtained with magnesium chloride and ethanol (which mimicked the typical anaesthetic effects seen with urethane) although some resistance to full anaesthesia was observed with ethanol when water temperatures were 10°C or below in winter. No successful anaesthetic effects were obtained with the fish anaesthetics: in particular, metomidate was toxic even at low concentrations. Similarly (at the temperatures tested), chloretone, nicotine sulphate and phenoxetol were ineffective as anaesthetics and had toxic effects. Substances used to date as anaesthetics for cephalopods are briefly reviewed and it is concluded that future investigations to improve the provision of stable, safe and reliable anaesthesia for cephalopods would probably benefit from combinations of higher doses for shorter exposure times, and the co-administration of two or more substances. Empirical testing is still required for application to different species and to define appropriate concentrations, temperature and pH ranges.