The effects of fish anaesthetics (MS222, metomidate and AQUI-S) on heart ventricle, the cardiac vagus and branchial vessels from Chinook salmon (Oncorhynchus tshawytscha)

The acute effects of 3 fish anaesthetics (MS222, metomidate and AQUI-S) were investigated on 3 parts of the cardiovascular system of Chinook salmon (Oncorhynchus tshawytscha). All 3 anaesthetics reduced the contractile force of paced strips of ventricular myocardium. MS222 reduced the contractility by almost 75%, and was more potent than metomidate and AQUI-S, which reduced the contractility by about 25%. MS222 blocked vagal nerve transmission to the heart at the normally applied anaesthetic concentration (NAAC) for Chinook salmon, whereas metomidate and AQUI-S required 100 times their NAACs to have the same effect. Using myography, MS222 and AQUI-S caused a maximal 30–40% dilation of EBAs at 10% NAAC, whereas the equivalent effect with metomidate was only seen at 100% NAAC. MS222 again caused the greatest dilation of the ABAs. AQUI-S dilated the ABAs at up to 50% NAAC, but this was reversed so that there was no dilation at 100% NAAC. Metomidate did not affect the ABAs. These data from in vitro and in situ experiments, which generally show inhibitory effects, are used to suggest possible cardiovascular outcomes in anaesthetised Chinook salmon.