Shellfish is a culinary and fisheries term for those aquatic invertebrate animals that are used as food: various species of molluscs, crustaceans, and echinoderms. Although the word is primarily used as a term for marine species, freshwater edible invertebrates (such as crayfish and river mussels etc) are also sometimes grouped with the marine species under the umbrella concept of "shellfish".
Almost all shellfish have a hard exterior or exoskeleton, known as a shell, hence the first part of the word. The second word fragment "fish", is here used in the archaic sense, to mean an animal that lives its whole life in water. However, these invertebrate animals are not "fish" in the modern sense of the word, and therefore the term finfish or fin fish is sometimes used to distinguish ordinary (vertebrate) fish from shellfish.
The word "shellfish" is used as singular and plural, but the less common plural "shellfishes" is sometimes used when referring to various "types of shellfish".
Molluscs commonly used as food include many species of clams, mussels, oysters, winkles, and scallops. Some crustaceans commonly eaten are various species of shrimp, prawn, lobster, crayfish, and crabs. Echinoderms are not as frequently eaten as molluscs and crustaceans, but the roe of sea urchins is quite popular in many parts of the world, and in Asia, sea cucumbers (echinoderms which have no shell) are gathered as a food item.
Other edible mollusks such as shell-less cephalopods (squid octopus and cuttlefish) and terrestrial snails which do have a shell such as escargot, are sometimes considered to be "shellfish" and sometimes not.
On occasion, the word is used to refer only to edible marine molluscs, and then shrimp, crab, or lobster are not included in the category.
Shellfish are among the most common food allergens.
Archaeological finds has shown that humans have been making use of shellfish as a food item for thousands of years. In the present, shellfish dishes are a feature of almost all the cuisines of the world, providing an important source of protein in many cuisines around the world, especially in the countries with coastal areas.
In the Japanese cuisine, chefs often use shellfish and their roe in different dishes. Sushi (vinegared rice, topped with other ingredients, including shellfish, fish, meat and vegetables), feature both raw and cooked shellfish. Sashimi primarily consis of very fresh raw seafood, sliced into thin pieces and served with only a dipping sauce (soy sauce with wasabi paste (a type of Japanese horseradish or hot mustard, a spice with extremely strong hot flavor), and thinly-sliced ginger root), and a simple garnish such as shiso (a kitchen herb, member of the mint family) and shredded daikon radish.
Lobster in particular is a great delicacy in the United States, where families in the Northeast region make them into the centerpiece of a clam bake, usually for special occasions. Lobsters are eaten on much of the East Coast; the American lobster ranges from Newfoundland down to about the Carolinas, but is most often associated with Maine. A typical meal involves boiling the lobster with some slight seasoning and then serving with drawn butter, baked potato, and corn on the cob.
Clamming is done both commercially and recreationally along the Northeast coastline of the US. Various type of clams are incorporated into the cuisine of New England. Notable is the soft-shelled clam, which is eaten fried or steamed, where they are called "steamers." Many types of clams can be used for clam chowder, but quahogs, a hard shelled clam also know as a chowder clam, are often used because the long cooking time softens its tougher meat.
The Chesapeake Bay and Maryland region has generally been associated more with crabs, but in recent years the area has been trying to reduce its catch of blue crabs as wild populations have been depleted. This has not, however, stemmed the demand: Maryland style crabcakes are still a well known treat in crabhouses all over the bay, though the catch now comes from points farther south.
In the Southeast, and particularly the gulf states, shrimping is an important industry. Copious amounts of shrimp are harvested each year in the Gulf of Mexico and the Atlantic Ocean to satisfy a national demand for shrimp. Locally, prawns and shrimp are often deep fried; in the Cajun and Creole kitchens of Louisiana, shrimp and prawns are a common addition to traditional recipes like jambalaya and certain stews. Crawdads are a well known and much eaten delicacy here, often boiled in huge pots and heavily spiced.
In many major cities with active fishing ports, raw oyster bars are also a feature of shellfish consumption. When served freshly shucked (opened) and iced, one may find a liquid inside the shell, called the liqueur. This is a primary feature of the raw bar, and should be sampled, if not enjoyed. Some believe that oysters have the properties of an aphrodisiac. "Rocky mountain oysters" is a euphemism for bull testicles, as their appearance and preparation is similar.
Inter-tidal herbivorous shellfish such as mussels and clams can help people reach a healthy balance of omega-3 and omega-6 fats in their diets, instead of the current Western diets. For this reason the eating of shellfish is often encouraged by dietitians.