SUMMARY The muscle of trawl‐caught haddock, lemon sole, and plaice contained little adenosine 5′‐triphosphate (ATP) and much inosine 5′‐monophosphate (IMP) at death. ATP, adenosine 5′‐diphosphate (ADP), and adenosine 5′‐monophosphate (AMP) changed rapidly after the fish died. IMP was lost from the muscle more slowly, with liberation of inosine, which was, in turn, degraded to hypoxanthine. A little adenine was formed by an alternative pathway of ATP degradation in lemon sole. A relatively high initial level of guanine was found in plaice muscle. Traces of xanthine were detectable in spoiling muscle from the three species. Implications of the findings arc discussed in relation to quality testing and flavor changes in iced fish.