If you don't cook much seafood, you may wonder how to tell when it’s done. All kinds of seafood give you clear indications of doneness, you just have to know what you’re looking for.
Whole fish: The easiest way to check is to pull on the dorsal fin (on the back of the fish). If it comes out easily, it’s done; if not, it needs more cooking.
Fish fillet or steak: Done when it flakes easily with a fork. Salmon and tuna are darkish pink at the center when medium. White fish should be glistening and wet-looking only at the innermost core.
Scallops: Turn opaque when done, but the center should be barely opaque. Scallops become rubbery when overcooked.
Shrimp: Takes only a couple of minutes to cook and turns pink when done.
Mussels, clams, and oysters: Give you a clear indication that they’re cooked — their shells open when they’re done, no matter how you cook them, like a built-in kitchen timer. If the shell is still closed after cooking, discard it.
Unless the recipe instructs you to do otherwise, remove all cooked fish from the heat or the poaching liquid immediately.