A volatile compound found in seafoods that has a characteristic herring-like aroma — the classic ‘fishy‘ smell. Trimethylamine is associated with the onset of microbial spoilage in ice-stored fish: spoilage bacteria reduce trimethylamine oxide (TMAO), the osmoregulant of marine fish, to trimethylamine. Hence, analysis of trimethylamine content — often as total volatile basic nitrogen (TVB-N) — is used to evaluate fish quality and freshness, with regulatory limits marking the boundary between acceptable and spoiled. Rapid chilling suppresses the bacterial reduction, keeping TMA low and fish sweet-smelling.