Each species has different quality signs to examine. The shells of live clams, oysters or mussels should be plump and covered in their own liquor. There should be no strong odor. Purchase raw shellfish carefully. Clams, oysters and mussels in the shell are alive and the shells should close tightly when tapped.
Shucked oysters are plump, have a mild odor and a natural creamy color with clear liquid or nectar.
If the shell gapes open, then the shellfish are probably dead and not edible. They are usually shucked at sea, shortly after their capture. Fresh scallop meat must have a firm texture and a distinctly sweet odor. The meat is free of excess liquid when packaged. The meat of a large scallop is white, orange or pink.