These enzymes work rapidly at warm temperatures. Fish are also subject to bacterial degradation after death. Natural barriers that protect fish while they are alive break down when they die. Bacteria from the environment and the gut can grow and multiply in fish tissue. This activity diminishes fish quality and eventually causes spoilage.
Bacteria also grow rapidly at warm temperatures.
Finally, the highly unsaturated fat in fish is also affected by oxygen in the air. Oxygen reacts with this fat to produce the odors and flavors associated with rancidity. Fat oxidation can be a serious problem if the fish is to be frozen or stored for very long. This is one reason why fattier fish like bluefish do not remain in good condition during frozen storage as long as leaner fish like flounder. Many fish are wasted because of mishandling.