Some of the more popular high-fat fish are herring, butterfish, mackerel, rainbow trout, king salmon, shad, and yellowtail. The more even distribution of fat in moderate and high-fat fish gives their flesh a darker color, firmer texture, and more distinctive color. Shellfish is a broad term for all aquatic animals that have a shell of some kind, whether crustaceans or mollusks. Crustaceans have elongated bodies and jointed, soft, crustlike shells. Crustaceans include crabs, crayfish, lobster, and shrimp.
Mollusks are invertebrates with soft bodies covered by a shell of one or more pieces.
They're divided into three groups. Gastropods all have a single shell and a single muscle. Gastropods include abalone, limpet, periwinkle, snail, and whelk. Bivalves are soft-bodied mollusks that have two shells hinged together by a strong muscle. Bivalves include clams, mussels, oysters, and scallops.