Other thawed fish should be used within one to two days. Thorough cooking destroys harmful bacteria and parasites. The United States Department of Agriculture recommends using a meat thermometer and checking to make sure that fish is cooked to an internal temperature of 145 F. A good rule of thumb to follow is to cook fish 10 minutes for every inch of thickness. Small, thin fillets will cook in just a few minutes. Fish is done when the flesh has just begun to turn from translucent to opaque or white and is firm but still moist.
Overcooked fish is tough and dry.
Once fish is cooked, keep it hot or chill it. Refrigerate leftovers within two hours of serving. Cooked fish keeps another day in the refrigerator before its quality deteriorates. Avoid freezing leftover cooked fish as quality is poor. Pesticides or other substances may contaminate some waters, and these toxins are concentrated in the fatty parts of the fish.