A practical evaluation of metomidate and MS-222 as anaesthetics for Atlantic halibut ( Hippoglossus hippoglossus L.)

Metomidate and MS-222 were tested as anaesthetics for Atlantic halibut ( Hippoglossus hippoglossus L.) at temperatures of 9.5±0.3°C and 10.5±0.3°C. An effective concentration of the drug was defined as one giving a sure state of anaesthesia for 75% of the fish after an exposure time of less than 5 min. The lowest effective concentration of metomidate was 10 mg l −1; with MS-222, concentrations of 250 mg l −1 were required. Doses should further be kept below 60 mg metomidate l −1 or 480 mg MS-222 l −1. There was interaction between anaesthetic and dose for both drugs with respect to the required exposure time, which focuses on the necessity of testing several doses when a new anaesthetic is to be used on a given species. It is concluded that metomidate gives a broader safe anaesthetic range with a lower effective dose than MS-222.