If food-poisoning bacteria are present, they can multiply and cause illness. Enzymes also cause spoilage. Enzymes in living seafood help build tissue, contract and relax muscles, and digest food. After harvest, enzymes continue to work and start to digest or breakdown the flesh. This causes the flesh to soften and lowers the quality.
Enzymes also produce more food for bacteria which increases the rate of spoilage.
This commonly occurs in fatty fish such as salmon and mackerel. Temperature Control and Shelf Life High temperatures increase rates of bacterial growth, enzyme activity, and chemical reactions. Low temperatures slow bacterial growth and chemical activity. Your supplier cannot guarantee a shelf life for a seafood product without knowing the catch date and the temperature history. Ideally, time-temperature monitors should accompany seafood from the fishing vessel to the retail store, but this is rarely feasible.