Crayfish are freshwater crustaceans resembling small lobsters (to which they are related). In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mudbugs, or yabbies. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some species are found in brooks and streams, where freshwater is running, while others thrive in swamps, ditches, and paddy fields. Most crayfish cannot tolerate polluted water, although some species, such as Procambarus clarkii, are hardier. Crayfish feed on animals and plants, either living or decomposing, and detritus.
Crayfish are eaten worldwide. Like other edible crustaceans, only a small portion of the body of a crayfish is eaten. Only the tail portion is served in most prepared dishes, such as soups, bisques, and étouffées. At crawfish boils or other meals where the entire body of the crayfish is presented, other portions, such as the claw meat, may be eaten.
Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of mollusks, crustaceans, and echinoderms.
Although most kinds of shellfish are harvested from saltwater environments, some are found in freshwater. Shellfish are among the most common food allergens.