It's a must for at-risk people. The edges should be opaque and the center slightly translucent with flakes beginning to separate. Let the fish stand three to four minutes to finish cooking. For shrimp, lobster and scallops, check color. Shrimp and lobster turn red and the flesh becomes pearly opaque.
Scallops turn milky white or opaque and firm.
For clams, mussels and oysters, watch for the point at which their shells open. That means they're done. Throw out those that stay closed. When using the microwave, rotate the dish several times to ensure even cooking. Follow recommended standing times.