Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food,including various species of molluscs,crustaceans,and echinoderms.Although most kinds of shellfish are harvested from saltwater environments,some kinds are found only in freshwater.In addition a few species of land crabs such as Cardisoma guanhumi,are eaten,for example in the Caribbean.
Familiar marine molluscs enjoyed as a food source by humans include many species of clams,mussels,oysters,winkles,and scallops.Some crustaceans commonly eaten are shrimp,prawn,lobster,crayfish,and crabs.
Echinoderms are not as frequently harvested for food as molluscs and crustaceans,but sea urchin roe is quite popular in many parts of the world.
Most shellfish eat a diet composed primarily of phytoplankton and zooplankton.
Shellfish are among the most common food allergens.
The term shellfish is used both broadly and specifically.In common parlance,as in having "shellfish" for dinner,it can refer to anything from clams and oysters to lobster and shrimp.For regulatory purposes it is often narrowly defined as filter-feeding molluscs such as clams,mussels,and oyster to the exclusion of crustaceans and all else.
Although the term is primarily applied to marine species,edible freshwater invertebrates such as crayfish and river mussels are also sometimes grouped under the umbrella of "shellfish".
Although their shells may differ,all shellfish are invertebrates.As non-mammalian animals that spend their entire lives in water they are "fish" in the historic sense; however the denotion finfish (or fin fish) has been developed to distinguish fish as animals defined by having vertebrae from shellfish in modern terminology.
The word "shellfish" is both singular and plural; the rarely used "shellfishes" is sometimes employed to distinguish among various types of shellfish.
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.
