Fish is done when it looks opaque and just begins to flake easily with a fork. Undercooked fish looks translucent and overcooked fish looks dry and falls apart.
Keeping it Safe
Never refreeze fish or seafood, whether fresh or frozen, once it's been thawed. Store in the refrigerator, tightly wrapped or in an airtight container, for no more than 2 days.
Prepare using other firm white fish fillets, such as halibut or tilapia.