Induction of anaesthesia in the commercial scallop, Pecten fumatus Reeve

Anaesthetic properties of a range of chemical compounds were tested on mature commercial scallops ( Pecten fumatus) as a means of reducing stress and subsequent unplanned spawning caused by routine handling and assessment of breeding condition. Of 14 compounds tested, only chloral hydrate, magnesium chloride and magnesium sulphate successfully induced anaesthesia within 1 h. Magnesium sulphate induced high post-anaesthesia mortality and was not investigated further. Doses of 4 g chloral hydrate/1 (0.024 M) or 30 g magnesium chloride/1 (0.31 M) were selected as most suitable on the basis of time to, and recovery from, anaesthesia. Neither anaesthetic caused mortality nor increased spawning activity and magnesium chloride actually reduced the incidence of unplanned spawning. With the use of chloral hydrate, time to anaesthesia was found to decrease significantly with increasing water temperature in the range 12–24 °C, but to be independent of temperature in the case of magnesium chloride.