How-to Test Fish for Doneness
Overcooked fish loses its flavor and becomes tough. As a general guideline, fish is cooked 10 minutes for every inch of thickness. For fish fillets, check for doneness by inserting a fork at an angle into the thickest portion of the fish and gently parting the meat. When it is opaque and flakes into sections, it is cooked completely. Whole fish or steaks are done when the flesh is opaque and is easily removed from the bones. The juices in cooked fish are milky white.