Crabs, scallops, clams, or oysters become tough and dry when overcooked. To cook raw shellfish, shucked or in the shell follow these basic guidelines:
Shucked shellfish (clams and oysters without shells) become plump and opaque when cooked thoroughly and the edges of the oysters start to curl. The Food and Drug Administration (FDA) suggests broiling shucked oysters for 3 minutes, frying them in oil at 375 degrees F for 10 minutes, and baking them for 10 minutes at 450 degrees F.
Clams and oysters in the shell will open when cooked. The FDA suggests steaming oysters for 4 to 9 minutes or broiling them for 3 to 5 minutes after they open.
When cooked, scallops turn milky white or opaque and firm. Depending on size, scallops take 3 to 4 minutes to cook thoroughly.