Seafood is any form of sea life regarded as food by humans. Seafood prominently includes fish and shellfish. Shellfish include various species of molluscs, crustaceans, and echinoderms. Historically, sea mammals such as whales and dolphins have been consumed as food, though that happens to a lesser extent in modern times. Edible sea plants, such as some seaweeds and microalgae, are widely eaten as seafood around the world, especially in Asia (see the category of sea vegetables). In North America, although not generally in the United Kingdom, the term "seafood" is extended to fresh water organisms eaten by humans, so all edible aquatic life may be referred to as seafood. For the sake of completeness, this article includes all edible aquatic life.
The harvesting of wild seafood is usually known as fishing or hunting, and the cultivation and farming of seafood is known as aquaculture, or fish farming in the case of fish. Seafood is often distinguished from meat, although it is still animal and is excluded in a strict vegetarian diet. Seafood is an important source of protein in many diets around the world, especially in coastal areas.
Types of seafood
Fish:
Fish are aquatic vertebrates which lack limbs with digits, use gills to breathe, and have heads protected by hard bone or cartilage skulls. See: Fish (food).
Marine pelagic
Pelagic fish live and feed near the surface or in the water column of the sea, but not on the bottom of the sea. The main seafood groups can be divided into larger predator fish (sharks, tuna, marlin, swordfish, mackerel, salmon) and smaller forage fish (herring, sardines, sprats, anchovies, menhaden). The smaller forage fish feed on plankton, and can accumulate toxins to a degree. The larger predator fish feed on the forage fish, and accumulate toxins to a much higher degree than the forage fish.
Marine demersal
Demersal fish live and feed on or near the bottom of the sea. Some seafood groups are cod, flatfish, grouper and stingrays. Demersal fish feed mainly on crustaceans they find on the sea floor, and are more sedentary than the pelagic fish. Pelagic fish usually have the red flesh characteristic of the powerful swimming muscles they need, while demersal fish usually have white flesh.
Diadromous
Diadromous fish are fishes which migrate between the sea and fresh water. Some seafood groups are salmon, shad, eels and lampreys.
Freshwater
Freshwater fish live in rivers, lakes and ponds. Some seafood groups are carp, tilapia, catfish and trout. Generally, freshwater fish lend themselves to fish farming more readily than the ocean fish, and the larger part of the tonnage reported here refers to farmed fish.
Molluscs:
Molluscs (from the Latin molluscus, meaning soft ) are invertebrates with soft bodies that are not segmented like crustaceans. Bivalves and gastropods are protected by a calcareous shell which grows as the mollusc grows. Cephalopods are not protected by a shell.
Bivalves
Bivalves, sometimes referred to as clams, have a protective shell in two hinged parts. A valve is the name used for the protective shell of a bivalve, so bivalve literally means two shells. Important seafood bivalves include oysters, scallops, mussels and cockles. Most of these are filter feeders which bury themselves in sediment on the seabed where they are safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some, such as scallops, can swim. Bivalves have long been a part of the diet of coastal communities. Oysters were cultured in ponds by the Romans and mariculture has more recently become an important source of bivalves for food.
Gastropods
Aquatic gastropods, also known as sea snails, are univalves which means they have a protective shell that is in a single piece. Gastropod literally means stomach-foot, because they appear to crawl on their stomachs. Common seafood groups are abalone, conch, limpets, whelks and periwinkles.
Cephalopods
Cephalopods are not protected with a shell. Cephalopod literally means head-foots, because they have limbs which appear to issue from their head. They have excellent vision and high intelligence. Cephalopods propel themselves with a water jet and lay down "smoke screens" with ink. Examples are octopus, squid and cuttlefish. They are eaten in many cultures. Depending on the species, the arms and sometimes other body parts are prepared in various ways. Octopus must be boiled properly to rid it of slime, smell, and residual ink. Squid are popular in Japan. In Mediterranean countries and in Britain squid are often referred to as calamari. Cuttlefish is less eaten than squid, though it is popular in Italy and dried, shredded cuttlefish is a snack food in East Asia.
Crustaceans:
Crustaceans (from Latin crusta, meaning crust ) are invertebrates with segmented bodies protected by hard crusts (shells or exoskeletons), usually made of chitin and structured somewhat like a knight's armour. The shells do not grow, and must periodically be shed or moulted. Usually two legs or limbs issue from each segment. Most commercial crustaceans are decapods, that is they have ten legs, and have compound eyes set on stalks. Their shell turns pink or red when cooked.
Shrimps
Shrimp and prawns, are small, slender, stalk-eyed ten-legged crustaceans with long spiny rostrums. They are widespread, and can be found near the seafloor of most coasts and estuaries, as well as in rivers and lakes. They play important roles in the food chain. There are numerous species, and usually there is a species adapted to any particular habitat. Any small crustacean which resembles a shrimp tends to be called one.
Crabs
Crabs are stalk-eyed ten-legged crustaceans, usually walk sideways, and have grasping claws as their front pair of limbs. They have small abdomens, short antennae, and a short carapace that is wide and flat.
Lobsters
Clawed lobsters and spiny lobsters are stalk-eyed ten-legged crustaceans with long abdomens. The clawed lobster has large asymmetrical claws for its front pair of limbs, one for crushing and one for cutting. The spiny lobster lacks the large claws, but has a long, spiny antennae and a spiny carapace. Lobsters are larger than most shrimp or crabs.
Krill
Krill are like baby shrimps, except they have external gills and more than ten legs (swimming plus feeding and grooming legs). They are found in oceans around the world where they filter feed in huge pelagic swarms. Like shrimp, they are an important part of the marine food chain, converting phytoplankton into a form larger animals can consume. Each year, larger animal eat half the estimated biomass of krill (about 600 million tonnes). Humans consume krill in Japan and Russia, but most of the krill harvest is used to make fish feed and for extracting oil. Krill oil contains omega-3 fatty acids, similarly to fish oil.
Other aquatic animals:
Aquatic mammals
Sea mammals form a diverse group of 128 species that rely on the ocean for their existence. Whale meat is still harvested from legal, non-commercial hunts. About one thousand long-finned pilot whales are still killed annually. Japan has resumed hunting for whales, which they call "research whaling". In modern Japan, two cuts of whale meat are usually distinguished: the belly meat and the more valued tail or fluke meat. Fluke meat can sell for $200 per kilogram, three times the price of belly meat. Fin whales are particularly desired because they are thought to yield the best quality fluke meat. In Taiji in Japan and the Faroe Islands, dolphins are traditionally considered food, and are killed in harpoon or drive hunts. Ringed seals are still an important food source for the people of Nunavut and are also hunted and eaten in Alaska. The meat of sea mammals can be high in mercury, and may pose health dangers to humans when consumed. The FAO record only the reported numbers of aquatic mammals harvested, and not the tonnage. In 2010, they reported 2500 whales, 12,000 dolphins and 182,000 seals.
Aquatic reptiles
Sea turtles have long been valued as food in many parts of the world. Fifth century BC Chinese texts describe sea turtles as exotic delicacies. Sea turtles are caught worldwide, although in many countries it is illegal to hunt most species. Many coastal communities around the world depend on sea turtles as a source of protein, often gathering sea turtle eggs, and keeping captured sea turtles alive on their backs until needed for consumption. Most species of sea turtle are now endangered, and some are critically endangered. The FAO reports 1,418,975 crocodiles were harvested in 2010, but they do not record the tonnage.
Echinoderms
Echinoderms are headless invertebrates, found on the seafloor in all oceans and at all depths. They are not found in fresh water. They usually have a five-pointed radial symmetry, and move, breathe and perceive with their retractable tube feet. They are covered with a calcareous and spiky test or skin. The name echinoderm comes from the Greek ekhinos meaning hedgehog, and dermatos meaning skin. Echinoderms used for seafood include sea cucumbers, sea urchins, and occasionally starfish. Wild sea cucumbers are caught by divers and in China they are farmed commercially in artificial ponds. The gonads of both male and female sea urchins, usually called sea urchin roe or corals, are delicacies in many parts of the world.
Jellyfish
Jellyfish are soft and gelatinous, with a body shaped like an umbrella or bell which pulsates for locomotion. They have long, trailing tentacles with stings for capturing prey. They are found free-swimming in the water column in all oceans, and are occasionally found in freshwater. Jellyfish must be dried within hours to prevent spoiling. In Japan they are regarded as a delicacy. Traditional processing methods are carried out by a jellyfish master. This involve a 20 to 40 day multi-phase procedure which starts with removing the gonads and mucous membranes. The umbrella and oral arms are then treated with a mixture of table salt and alum, and compressed. Processing reduces liquefaction, odor, the growth of spoilage organisms, and makes the jellyfish drier and more acidic, producing a crisp and crunchy texture. Only scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for food; about 12 of the approximately 85 species. Most of the harvest takes place in southeast Asia.
Aquatic plants and microphytes:
Seaweed
Seaweed is a loose colloquial term which lacks a formal definition. Broadly, the term is applied to the larger, macroscopic forms of algae, as opposed to microalga. Examples of seaweed groups are the multicellular red, brown and green algae. Edible seaweeds usually contain high amounts of fibre and, in contrast to terrestrial plants, contain a complete protein. Seaweeds are used extensively as food in coastal cuisines around the world. Seaweed has been a part of diets in China, Japan, and Korea since prehistoric times. Seaweed is also consumed in many traditional European societies, in Iceland and western Norway, the Atlantic coast of France, northern and western Ireland, Wales and some coastal parts of South West England, as well as Nova Scotia and Newfoundland.
Microphytes
Microphytes are microscopic organisms, and can be algal, bacterial or fungal. Microalgae are another type of aquatic plant, and includes species that can be consumed by humans and animals. Some species of aquatic bacteria can also be used as seafood, such as spirulina, a type of cyanobacteria.
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