Histamine in Fish

What is histamine and why is it found in fish?

Histamine is a toxic substance produced by certain bacteria when fish start to spoil or ferment into fish products. These bacteria naturally live on the skin, gills, and in the gut of freshly caught fish. The level of histamine in fish depends on the storage time and condition and the amount of histidine amino acid which are naturally higher in fishes like mackerel, sardine, tuna and anchovy. Without proper refrigeration and freezing, histamine can form at any point throughout the supply chain.