They swim near the surface of the sea and are found in shoals, e.g. herring, mackerel. This checklist summarises the main points to look for when choosing fish. Spoilage is mainly caused by the actions of enzymes and bacteria. Enzymes are present in the gut of the living fish and help convert its food to tissue and energy. When the fish dies, these enzymes carry on working and help the bacteria in the digestive system to penetrate the belly wall and start breaking down the flesh itself.
Bacteria exist on the skin and in the fish intestine.
While the fish is alive, the normal defence mechanisms of the body prevent the bacteria from invading the flesh. Once the fish dies, the bacteria invade the flesh and start to break it down, the higher the temperature the faster the deterioration. Fish, once caught, has a shelf life of I0 to 12 days if kept properly on ice . In a refrigerator the storage temperature should be between 0 C and 5 C. Fresh fish Fresh fish should be used as soon as possible, but it can be stored overnight. Rinse, pat dry, cover with cling film and store towards the bottom of the refrigerator.