The genotoxicity of the anaesthetic MS222 (tricaine) was analysed in fish under both in vivo and in vitro conditions. Based on results of the single cell gel/ Comet assay, MS222 had no direct genotoxic effect on the experimental fish, indicating that MS222 does not induce primary DNA damage. These results suggest that the use of this important anaesthetic in aquaculture can be considered to be safe in terms of genotoxicity.Keywords Anaesthetic tricaine (ethyl meta-aminobenzoate) AE DNA damage AE Methanesulfonate salt AE MS222 AE Single cell gel (SCG)/Comet assay AE