If your fish is cooked in foil, in a sauce, or with vegetables or other added ingredients you will generally need to add 5 minutes to the original cooking time specified by the 10-Minute Rule. Frozen fish can be cooked directly without thawing. To estimate the proper cooking time simply double the amount of time specified by the 10-Minute Rule. In most situations you should be able to achieve this temperature using the 10-Minute Rule. When in doubt you can always cook your seafood for a minute or two longer, but avoid overcooking since it can quickly become dry and tasteless.
Most shellfish are smaller and more delicate than fish and usually cook faster.
The 10-Minute Rule may not be appropriate since it could result in overcooking. For live clams, oysters and mussels use current FDA's recommendations that suggest boiling for 4 to 6 minutes after the water returns to a boil or steaming for 6 to 8 minutes. Shucked meats will cook faster. Shellfish like scallops and shrimp also cook rapidly. The amount of time needed depends on size, product form, and cooking method.