Raw shrimp turn pink and firm. Depending on the size, it takes from 3 to 5 minutes to boil or steam one pound of medium size shrimp in the shell.
Shucked shellfish (clams, mussels 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 boiling shucked oysters for 3 minutes, frying them in oil at 375°F for 10 minutes, and baking them for 10 minutes at 450°F.
Clams, mussels and oysters in the shell will open when cooked. The FDA suggests steaming oysters for 4 to 9 minutes or boiling them for 3 to 5 minutes after they open.
Scallops turn milky white or opaque and firm. Depending on size, scallops take 3 to 4 minutes to cook thoroughly.
Boiled lobster turns bright red. Allow 5 to 6 minutes per starting to time the lobster when the water comes back to a full boil.
National Fisheries Institute; www.nfi.org