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Oyster is the
common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...
for a number of different families of
salt-water Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approx ...
bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
s that live in
marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...
or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not all oysters are in the superfamily Ostreoidea. Some types of oysters are commonly consumed (cooked or raw), and in some locales are regarded as a delicacy. Some types of pearl oysters are harvested for the pearl produced within the
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects.


Etymology

The word ''oyster'' comes from Old French , and first appeared in English during the 14th century. The French derived from the Latin , the feminine form of , which is the latinisation of the Ancient Greek () 'oyster'. Compare () 'bone'.


Types


True oysters

True oysters are members of the family Ostreidae. This family includes the edible oysters, which mainly belong to the genera '' Ostrea'', '' Crassostrea'', '' Ostreola'', ''
Magallana ''Magallana'' is a genus of true oysters (family Ostreidae) containing some of the most important oysters used for food. Species in this genus have been moved from ''Crassostrea'' after it was found to be paraphyletic. Species Extant species ...
'', and '' Saccostrea''. Examples include the European flat oyster, eastern oyster,
Olympia oyster ''Ostrea lurida'', common name the Olympia oyster, after Olympia, Washington in the Puget Sound area, is a species of edible oyster, a marine bivalve mollusk in the family Ostreidae. This species occurs on the northern Pacific coast of North A ...
, Pacific oyster, and the
Sydney rock oyster ''Saccostrea glomerata'', is an oyster species belonging to the family Ostreidae.MolluscaBase eds. (2022). MolluscaBase. Saccostrea Dollfus & Dautzenberg, 1920. Accessed through: World Register of Marine Species at: https://www.marinespecies.org/ ...
. Ostreidae evolved in the Early Triassic epoch: The genus ''
Liostrea ''Liostrea'' is a genus of extinct oysters, marine bivalve mollusks in the family Gryphaeidae. These fossils range from the early Triassic Period to the Cenomanian Epoch of the late Cretaceous Period and were widely distributed geographically. ...
'' grew on the shells of living ammonoids.


Pearl oysters

Almost all shell-bearing mollusks can secrete pearls, yet most are not very valuable. Pearls can form in both saltwater and freshwater environments. Pearl oysters are not closely related to true oysters, being members of a distinct family, the feathered oysters (
Pteriidae Pteriidae, also called the feather oysters, is a family of medium-sized to large saltwater clams. They are pearl oysters, marine bivalve molluscs in the order Pteriida. Some of the species in this family are important economically as the sou ...
). Both
cultured pearl Cultured pearls are formed within a cultured pearl sac with human intervention in the interior of productive living molluscs in a variety of conditions depending upon the mollusc and the goals. Just as the same as natural pearls, cultured pearls ...
s and
natural pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle (mollusc), mantle) of a living animal shell, shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pea ...
s can be extracted from pearl oysters, though other molluscs, such as the freshwater
mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...
s, also yield pearls of commercial value. The largest pearl-bearing oyster is the marine ''Pinctada maxima'', which is roughly the size of a dinner plate. Not all individual oysters produce pearls naturally. In nature, pearl oysters produce pearls by covering a minute invasive object with
nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is f ...
. Over the years, the irritating object is covered with enough layers of nacre to become a pearl. The many different types, colours and shapes of pearls depend on the natural pigment of the nacre, and the shape of the original irritant. Pearl farmers can culture a pearl by placing a nucleus, usually a piece of polished mussel shell, inside the oyster. In three to seven years, the oyster can produce a perfect pearl. Since the beginning of the 20th century, when several researchers discovered how to produce artificial pearls, the cultured pearl market has far outgrown the natural pearl market.


Other types

A number of bivalve molluscs (other than true oysters and pearl oysters) also have common names that include the word "oyster", usually because they either taste like or look somewhat like true oysters, or because they yield noticeable pearls. Examples include: * Thorny oysters in the genus ''Spondylus'' *Pilgrim oyster, another term for a
scallop Scallop () is a common name that encompasses various species of marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families ...
, in reference to the scallop shell of St. James * Saddle oysters, members of the Anomiidae family also known as jingle shells * Dimydarian oysters, members of the family Dimyidae * Windowpane oysters File:Crassostrea_gigas_p1040847.jpg, Pacific oyster File:Ostrea edulis Marennes p1050142.jpg, Pacific oyster, opened In the Philippines, a local thorny oyster species known as
Tikod amo Tikod amo is the Kamayo language name for an edible oyster species, a species of marine bivalve mollusk that is found in the coastal waters of Lianga Bay in Barobo Surigao del Sur in the Philippines. The scientific identity of this species is n ...
is a favorite seafood source in the southern part of the country. Because of its good flavor, it commands high prices.


Anatomy

Oysters breathe primarily via gills. In addition to their gills, oysters can exchange gases across their mantles, which are lined with many small, thin-walled
blood vessels The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
. A small, three-chambered heart, lying under the
adductor muscle A adductor muscle is any muscle that causes adduction. It may refer to: Humans * Adductor muscles of the hip, the most common reference in humans, but may also refer to ** Adductor brevis muscle, a muscle in the thigh situated immediately behind ...
, pumps colorless blood to all parts of the body. At the same time, two kidneys, located on the underside of the muscle, remove waste products from the blood. Their nervous system includes two pairs of nerve cords and three pairs of
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympatheti ...
. There is no evidence that oysters have a brain. While some oysters have two sexes (European oyster and Olympia oyster), their reproductive organs contain both eggs and sperm. Because of this, it is technically possible for an oyster to fertilize its own eggs. The gonads surround the digestive organs, and are made up of sex cells, branching tubules, and connective tissue. Once her millions of eggs are fertilized, the female discharges them into the water. The
larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...
develop in about six hours and exist suspended in the water column as veliger larvae for two to three weeks before settling on a bed and reaching sexual maturity within a year.


Feeding

Oysters are
filter feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...
s, drawing water in over their gills through the beating of
cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...
. Suspended plankton and non-food particles are trapped in the mucus of a gill, and from there are transported to the mouth, where they are eaten, digested, and expelled as
feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...
or
pseudofeces Pseudofeces or pseudofaeces are a specialized method of expulsion that filter-feeding bivalve mollusks (and filter-feeding gastropod mollusks) use in order to get rid of suspended particles such as particles of grit which cannot be used as food, ...
that fall to the bottom and remain out of the water column. Oysters feed most actively at temperatures ranging from the high 60s to the high 70s (). Under ideal laboratory conditions, an oyster can filter up to of water per day. Under average conditions, mature oysters filter . Chesapeake Bay's once-flourishing oyster population historically filtered excess nutrients from the estuary's entire water volume every three to four days. As of 2008 it was estimated that a complete cycle would take nearly a year.


Habitat and behaviour

A group of oysters is commonly called a bed or oyster reef. As a
keystone species A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaini ...
, oysters provide habitat for many marine species. ''Crassostrea'' and ''Saccostrea'' live mainly in the
intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
, while ''Ostrea'' is subtidal. The hard surfaces of oyster shells and the nooks between the shells provide places where a host of small animals can live. Hundreds of animals, such as sea anemones, barnacles, and hooked mussels, inhabit oyster reefs. Many of these animals are prey to larger animals, including fish, such as
striped bass The striped bass (''Morone saxatilis''), also called the Atlantic striped bass, striper, linesider, rock, or rockfish, is an anadromous perciform fish of the family Moronidae found primarily along the Atlantic coast of North America. It has al ...
, black drum and croakers. An oyster reef can increase the surface area of a flat bottom 50-fold. An oyster's mature shape often depends on the type of bottom to which it is originally attached, but it always orients itself with its outer, flared shell tilted upward. One valve is cupped and the other is flat. Oysters usually reach maturity in one year. They are
protandric Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...
; during their first year, they spawn as males by releasing
sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
into the water. As they grow over the next two or three years and develop greater energy reserves, they spawn as females by releasing eggs.
Bay oyster A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a narr ...
s usually spawn from the end of June until mid-August. An increase in water temperature prompts a few oysters to spawn. This triggers spawning in the rest, clouding the water with millions of eggs and sperm. A single female oyster can produce up to 100 million eggs annually. The eggs become fertilized in the water and develop into larvae, which eventually find suitable sites, such as another oyster's shell, on which to settle. Attached oyster larvae are called spat. Spat are oysters less than long. Many species of bivalves, oysters included, seem to be stimulated to settle near adult conspecifics. Oysters filter large amounts of water to feed and breathe (exchange and with water) but they are not permanently open. They regularly shut their valves to enter a resting state, even when they are permanently submersed. Their behaviour follows very strict circatidal and circadian rhythms according to the relative moon and sun positions. During neap tides, they exhibit much longer closing periods than during the spring tide. Some tropical oysters, such as the mangrove oyster in the family Ostreidae, grow best on mangrove roots. Low tide can expose them, making them easy to collect. The largest oyster-producing body of water in the United States is the Chesapeake Bay, although these beds have decreased in number due to overfishing and pollution.
Willapa Bay Willapa Bay () is a bay located on the southwest Pacific coast of Washington state in the United States. The Long Beach Peninsula separates Willapa Bay from the greater expanse of the Pacific Ocean. With over of surface area Willapa Bay is the ...
in Washington produces more oysters than any other estuary in the US. Other large oyster farming areas in the US include the bays and estuaries along the coast of the Gulf of Mexico from Apalachicola, Florida, in the east to
Galveston, Texas Galveston ( ) is a coastal resort city and port off the Southeast Texas coast on Galveston Island and Pelican Island in the U.S. state of Texas. The community of , with a population of 47,743 in 2010, is the county seat of surrounding Galvesto ...
, in the west. Large beds of edible oysters are also found in Japan and Australia. In 2005, China accounted for 80% of the global oyster harvest. In Europe, France remained the industry leader. Common oyster predators include
crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
s, seabirds,
starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...
, and humans. Some oysters contain crabs, known as oyster crabs.


Nutrient cycling

Bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
, including oysters, are effective filter feeders and can have large effects on the water columns in which they occur. As filter feeders, oysters remove plankton and organic particles from the water column. Multiple studies have shown individual oysters are capable of filtering up to of water per day, and thus oyster reefs can significantly improve water quality and clarity. Oysters consume nitrogen-containing compounds (
nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
s and ammonia), phosphates, plankton, detritus, bacteria, and dissolved organic matter, removing them from the water. What is not used for animal growth is then expelled as solid waste pellets, which eventually decompose into the atmosphere as nitrogen. In Maryland, the
Chesapeake Bay Program The Chesapeake Bay Program is the regional partnership that directs and conducts the restoration of the Chesapeake Bay in the United States. As a partnership, the Chesapeake Bay Program brings together members of various state, federal, academic a ...
had implemented a plan to use oysters to reduce the amount of nitrogen compounds entering the Chesapeake Bay by per year by 2010. Several studies have shown that oysters and mussels have the capacity to dramatically alter nitrogen levels in estuaries. In the U.S., Delaware is the only East Coast state without aquaculture, but making aquaculture a state-controlled industry of leasing water by the acre for commercial harvesting of shellfish is being considered. Supporters of Delaware's legislation to allow oyster aquaculture cite revenue, job creation, and nutrient cycling benefits. It is estimated that can produce nearly 750,000 oysters, which could filter between of water daily. Also see nutrient pollution for an extended explanation of nutrient remediation.


Ecosystem services

As an
ecosystem engineer An ecosystem engineer is any species that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on species richness and landscape-level heterogeneity of an area. As a result, ecosystem enginee ...
, oysters provide supporting ecosystem services, along with provisioning, regulating and cultural services. Oysters influence
nutrient cycling A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cycli ...
,
water filtration A water filter removes impurities by lowering contamination of water using a fine physical barrier, a chemical process, or a biological process. Filters cleanse water to different extents, for purposes such as: providing agricultural irrigation ...
, habitat structure, biodiversity, and food web dynamics. Assimilation of nitrogen and phosphorus into shellfish tissues provides an opportunity to remove these nutrients from the water column. In California's Tomales Bay, native oyster presence is associated with higher species diversity of benthic invertebrates. The ecological and economic importance of oyster reefs has become more acknowledged, restoration efforts have increased.


Human history

Midden A midden (also kitchen midden or shell heap) is an old dump for domestic waste which may consist of animal bone, human excrement, botanical material, mollusc shells, potsherds, lithics (especially debitage), and other artifacts and ecofact ...
s testify to the prehistoric importance of oysters as food, with some middens in New South Wales, Australia, dated at ten thousand years. They have been cultivated in Japan from at least 2000 BC. In the United Kingdom, the town of Whitstable is noted for oyster farming from beds on the Kentish Flats that have been used since Roman times. The borough of Colchester holds an annual Oyster Feast each October, at which "Colchester Natives" (the native oyster, '' Ostrea edulis'') are consumed. The United Kingdom hosts several other annual oyster festivals; for example,
Woburn Oyster Festival Woburn may refer to: Places Caribbean * Woburn, Village, Grenada, Caribbean (W.I) * Woburn, Marine Protected Area, Grenada, Caribbean (W.I) Canada * Woburn, Toronto, Ontario, Canada ** Woburn Collegiate Institute * Woburn, Quebec, Canada Eng ...
is held in September. In fact, in Victorian England, it was quite common for people to go to the pub and enjoy their favorite beer with some oysters. They quickly realized that the "rich, sweet, malty stouts" were great with the "briny, creamy oyster." Then Brewers found that oyster shells naturally clarify a beer and they started putting crushed oyster shells into their brews. The first known brewery to start this was in 1938 at the Hammerton Brewery in London. That is where the
oyster stout Stout is a dark, top-fermented beer with a number of variations, including dry stout, oatmeal stout, milk stout, and imperial stout. The first known use of the word ''stout'' for beer, in a document dated 1677 found in the Egerton Manuscript ...
was first started. The
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
seaside resort of
Cancale Cancale (; ; Gallo: ''Cauncall'') is a commune in the Ille-et-Vilaine department in Brittany in northwestern France. It is known as the birthplace of Saint Jeanne Jugan. Population Inhabitants of Cancale are called ''Cancalais'' in French. T ...
in Brittany is noted for its oysters, which also date from Roman times.
Sergius Orata Caius Sergius Orata ( fl. c. 95 BC) was an Ancient Roman who was a successful merchant, inventor and hydraulic engineer. He is credited with inventing the cultivation of oysters and refinement to the hypocaust method of heating a building to prov ...
of the Roman Republic is considered the first major merchant and cultivator of oysters. Using his considerable knowledge of hydraulics, he built a sophisticated cultivation system, including channels and locks, to control the
tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...
. He was so famous for this, the Romans used to say he could breed oysters on the roof of his house. In the early 19th century, oysters were cheap and mainly eaten by the working class. Throughout the 19th century, oyster beds in
New York Harbor New York Harbor is at the mouth of the Hudson River where it empties into New York Bay near the East River tidal estuary, and then into the Atlantic Ocean on the east coast of the United States. It is one of the largest natural harbors in t ...
became the largest source of oysters worldwide. On any day in the late 19th century, six million oysters could be found on barges tied up along the city's waterfront. They were naturally quite popular in New York City, and helped initiate the city's restaurant trade. New York's oystermen became skilled cultivators of their beds, which provided employment for hundreds of workers and nutritious food for thousands. Eventually, rising demand exhausted many of the beds. To increase production, they introduced foreign species, which brought disease;
effluent Effluent is wastewater from sewers or industrial outfalls that flows directly into surface waters either untreated or after being treated at a facility. The term has slightly different meanings in certain contexts, and may contain various pollut ...
and increasing sedimentation from erosion destroyed most of the beds by the early 20th century. Oysters' popularity has put ever-increasing demands on wild oyster stocks. This scarcity increased prices, converting them from their original role as working-class food to their current status as an expensive delicacy. In the United Kingdom, the native variety (''Ostrea edulis'') requires five years to mature and is protected by an Act of Parliament during the May-to-August spawning season. The current market is dominated by the larger Pacific oyster and
rock oyster Rock oysters are true oysters of the genus ''Saccostrea'', belonging to the subfamily Saccostreinae of the family Ostreidae . MolluscaBase eds. (2022). MolluscaBase. Saccostrea Dollfus & Dautzenberg, 1920. Accessed through: World Register of Ma ...
varieties which are farmed year-round.


Fishing from the wild

Oysters are harvested by simply gathering them from their beds. In very shallow waters, they can be gathered by hand or with small rakes. In somewhat deeper water, long-handled rakes or oyster tongs are used to reach the beds.
Patent tong A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...
s can be lowered on a line to reach beds that are too deep to reach directly. In all cases, the task is the same: the oysterman scrapes oysters into a pile, and then scoops them up with the rake or tongs. In some areas, a scallop dredge is used. This is a toothed bar attached to a chain bag. The dredge is towed through an oyster bed by a boat, picking up the oysters in its path. While dredges collect oysters more quickly, they heavily damage the beds, and their use is highly restricted. Until 1965, Maryland limited dredging to sailboats, and even since then motor boats can be used only on certain days of the week. These regulations prompted the development of specialized sailboats (the bugeye and later the skipjack) for dredging. Similar laws were enacted in Connecticut before World War I and lasted until 1969. The laws restricted the harvesting of oysters in state-owned beds to vessels under sail. These laws prompted the construction of the oyster sloop-style vessel to last well into the 20th century. ''Hope'' is believed to be the last-built Connecticut oyster sloop, completed in 1948. Oysters can also be collected by
divers Diver or divers may refer to: *Diving (sport), the sport of performing acrobatics while jumping or falling into water *Practitioner of underwater diving, including: **scuba diving, **freediving, **surface-supplied diving, **saturation diving, a ...
. In any case, when the oysters are collected, they are sorted to eliminate dead animals, bycatch (unwanted catch), and debris. Then they are taken to market, where they are either canned or sold live.


Cultivation

Oysters have been cultured since at least the days of the Roman Empire. The Pacific oyster (''Magallana gigas'') is presently the most widely grown bivalve around the world. Two methods are commonly used, release and bagging. In both cases, oysters are cultivated onshore to the size of spat, when they can attach themselves to a substrate. They may be allowed to mature further to form "seed oysters". In either case, they are then placed in the water to mature. The release technique involves distributing the spat throughout existing oyster beds, allowing them to mature naturally to be collected like wild oysters. Bagging has the cultivator putting spat in racks or bags and keeping them above the bottom. Harvesting involves simply lifting the bags or rack to the surface and removing the mature oysters. The latter method prevents losses to some predators, but is more expensive. The Pacific oyster has been grown in the outflow of
mariculture Mariculture or marine farming is a specialized branch of aquaculture (which includes freshwater aquaculture) involving the cultivation of marine organisms for food and other animal products, in enclosed sections of the open ocean ( offshore mari ...
ponds. When fish or prawns are grown in ponds, it takes typically of feed to produce of product ( dry-dry basis). The other goes into the pond and after mineralization, provides food for phytoplankton, which in turn feeds the oyster. To prevent spawning, sterile oysters are now cultured by crossbreeding tetraploid and
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
oysters. The resulting triploid oyster cannot propagate, which prevents introduced oysters from spreading into unwanted habitats.


Restoration and recovery

In many areas, non-native oysters have been introduced in attempts to prop up failing harvests of native varieties. For example, the eastern oyster (''Crassostrea virginica'') was introduced to California waters in 1875, while the Pacific oyster was introduced there in 1929. Proposals for further such introductions remain controversial. The Pacific oyster prospered in
Pendrell Sound Pendrell Sound is a sound located in the Discovery Islands in British Columbia, Canada. The sound branches off from Waddington Channel and deeply incises East Redonda Island. The northern limit of Pendrell Sound delineates part of the northern lim ...
, where the surface water is typically warm enough for spawning in the summer. Over the following years, spat spread out sporadically and populated adjacent areas. Eventually, possibly following adaptation to the local conditions, the Pacific oyster spread up and down the coast and now is the basis of the North American west coast oyster industry. Pendrell Sound is now a reserve that supplies spat for cultivation. Near the mouth of the Great Wicomico River in the Chesapeake Bay, five-year-old artificial reefs now harbor more than 180 million native ''
Crassostrea virginica The eastern oyster (''Crassostrea virginica'')—also called the Atlantic oyster, American oyster, or East Coast oyster—is a species of true oyster native to eastern North and South America. Other names in local or culinary use include the Wel ...
''. That is far lower than in the late 1880s, when the bay's population was in the billions, and watermen harvested about annually. The 2009 harvest was less than . Researchers claim the keys to the project were: * using waste oyster shells to elevate the reef floor to keep the spat free of bottom sediments * building larger reefs, ranging up to in size * disease-resistant broodstock The "oyster-tecture" movement promotes the use of oyster reefs for water purification and wave attenuation. An oyster-tecture project has been implemented at Withers Estuary, Withers Swash, South Carolina, by Neil Chambers-led volunteers, at a site where pollution was affecting beach tourism. Currently, for the installation cost of $3000, roughly 4.8 million liters of water are being filtered daily. In New Jersey, however, the Department of Environmental Protection refused to allow oysters as a filtering system in Sandy Hook Bay and the Raritan Bay, citing worries that commercial shellfish growers would be at risk and that members of the public might disregard warnings and consume tainted oysters. New Jersey Baykeepers responded by changing their strategy for utilizing oysters to clean up the waterway, by collaborating with Naval Weapons Station Earle. The Navy station is under 24/7 security and therefore eliminates any poaching and associated human health risk. Oyster-tecture projects have been proposed to protect coastal cities, such as New York, from the threat of rising sea levels due to climate change. Additionally Oyster reef restoration has shown to increase the population of oyster beds within the oceans while also conservating the biolife within the oyster reefs.


Human impact

The accidental or intentional introduction of species by humans has the potential to negatively impact native oyster populations. For example, non-native species in Tomales Bay have resulted in the loss of half of California's
Olympia oyster ''Ostrea lurida'', common name the Olympia oyster, after Olympia, Washington in the Puget Sound area, is a species of edible oyster, a marine bivalve mollusk in the family Ostreidae. This species occurs on the northern Pacific coast of North A ...
s. In October 2017, it was reported that underwater noise pollution can affect oysters as they close their shells when exposed to low
frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of sounds in experimental conditions. Oysters rely on hearing waves and currents to regulate their
circadian rhythm A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogeno ...
s, and perception of weather events—such as rain—may induce spawning.
Cargo ship A cargo ship or freighter is a merchant ship that carries cargo, goods, and materials from one port to another. Thousands of cargo carriers ply the world's seas and oceans each year, handling the bulk of international trade. Cargo ships are usu ...
s, pile drivers, and explosions conducted underwater produce low frequencies that may be detected by oysters. Environmental stressors as a result of global change are also negatively impacting oysters around the world, with many impacts affecting molecular, physiological, and behavioral processes in species including ''Magallana gigas.''


As food

Jonathan Swift is quoted as having said, "He was a bold man that first ate an oyster". Evidence of oyster consumption goes back into prehistory, evidenced by oyster middens found worldwide. Oysters were an important food source in all coastal areas where they could be found, and oyster
fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, both ...
were an important industry where they were plentiful. Overfishing and pressure from diseases and pollution have sharply reduced supplies, but they remain a popular treat celebrated in oyster festivals in many cities and towns. It was once assumed that oysters were only safe to eat in months with the letter 'r' in their English and French names. This myth is based in truth, in that in the Northern Hemisphere, oysters are much more likely to spoil in the warmer months of May, June, July, and August. In recent years, pathogens such as '' Vibrio parahaemolyticus'' have caused outbreaks in several harvesting areas of the eastern United States during the summer months, lending further credence to this belief.


Dishes

Oysters can be eaten on the half shell, raw,
smoked Smoking is the process of flavoring, browning, cooking, or preserving food by exposing it to smoke from burning or smoldering material, most often wood. Meat, fish, and ''lapsang souchong'' tea are often smoked. In Europe, alder is the tradi ...
, boiled,
baked Baking is a method of preparing food that uses dry heat, typically in an oven, but can also be done in hot ashes, or on hot stones. The most common baked item is bread but many other types of foods can be baked. Heat is gradually transferre ...
, fried,
roasted Roasting is a cooking method that uses dry heat where hot air covers the food, cooking it evenly on all sides with temperatures of at least from an open flame, oven, or other heat source. Roasting can enhance the flavor through caramelization ...
,
stew A stew is a combination of solid food ingredients that have been cooked in liquid and served in the resultant gravy. A stew needs to have raw ingredients added to the gravy. Ingredients in a stew can include any combination of vegetables and ...
ed, canned, pickled, steamed, or broiled, or used in a variety of drinks. Eating can be as simple as opening the shell and eating the contents, including juice. Butter and salt are often added. Poached oysters can be served on toast with a cream roux. In the case of Oysters Rockefeller, preparation can be very elaborate. They are sometimes served on edible seaweed, such as brown algae. Care should be taken when consuming oysters. They may be eaten raw, with no dressing or with lemon juice, vinegar (most commonly shallot vinegar), or cocktail sauce. Upscale restaurants pair raw oysters with mignonette sauce, which consists primarily of fresh chopped shallot, mixed
pepper Pepper or peppers may refer to: Food and spice * Piperaceae or the pepper family, a large family of flowering plant ** Black pepper * ''Capsicum'' or pepper, a genus of flowering plants in the nightshade family Solanaceae ** Bell pepper ** Chili ...
corn, dry white wine and lemon juice or sherry vinegar. Like fine wine, raw oysters have complex flavors that vary greatly among varieties and regions: salty, briny, buttery, metallic or fruity. The texture is soft and fleshy, but crisp on the palate. North American varieties include Kumamoto and Yaquina Bay from Oregon,
Duxbury Duxbury (alternative older spelling: "Duxborough") is a historic seaside town in Plymouth County, Massachusetts, United States. A suburb located on the South Shore approximately to the southeast of Boston, the population was 16,090 at the 20 ...
and Wellfleet from Massachusetts, Malpeque from Prince Edward Island, Canada, Blue Point from Long Island, New York, Pemaquid from Maine, Rappahannock River from Virginia,
Chesapeake Chesapeake often refers to: *Chesapeake people, a Native American tribe also known as the Chesepian * The Chesapeake, a.k.a. Chesapeake Bay *Delmarva Peninsula, also known as the Chesapeake Peninsula Chesapeake may also refer to: Populated plac ...
from Maryland and Cape May from New Jersey. Variations in water salinity, alkalinity, and mineral and nutritional content influence their flavor. File:Chargrilled oysters.jpg, Chargrilled oysters. File:FriedOyster.JPG, Fried oyster with egg and
flour Flour is a powder made by grinding raw grains, roots, beans, nuts, or seeds. Flours are used to make many different foods. Cereal flour, particularly wheat flour, is the main ingredient of bread, which is a staple food for many culture ...
is a common dish in Malaysia and Singapore. File:Deep fried oysters by Kossy@FINEDAYS in Akabane.jpg, in Japan. File:Six steamed oysters on the half shell.jpg, Six steamed Eastern oysters on the half shell File:"Fine de Claire" raw oysters.jpg, Raw "Fine de Claire" oysters served at Mercado de San Miguel in Madrid.


Nutrition

Oysters are an excellent source of zinc, iron, calcium, and selenium, as well as vitamin A and vitamin B12. Oysters are low in food energy; one dozen raw oysters provides only . They are rich in protein (approximately 9 g in 100 g of Pacific oysters). Two oysters () provide the
Reference Daily Intake The Reference Daily Intake (RDI) used in nutrition labeling on food and dietary supplement products in the U.S. and Canada is the daily intake level of a nutrient that is considered to be sufficient to meet the requirements of 97–98% of health ...
of zinc and vitamin B12. Traditionally, oysters are considered to be an aphrodisiac, partially because they resemble female sex organs. A team of American and Italian researchers analyzed bivalves and found they were rich in amino acids that trigger increased levels of sex hormones. Their high zinc content aids the production of testosterone.


Shucking oysters

Opening oysters, referred to as "oyster-shucking", requires skill. The preferred method is to use a special knife (called an
oyster knife A kitchen knife is any knife that is intended to be used in food preparation. While much of this work can be accomplished with a few general-purpose knives – notably a large chef's knife, a tough cleaver, a small paring knife and some sort o ...
, a variant of a shucking knife), with a short and thick blade about long. While different methods are used to open an oyster (which sometimes depend on the type), the following is one commonly accepted oyster-shucking method. *Insert the blade, with moderate force and vibration if necessary, at the hinge between the two valves. *Twist the blade until there is a slight pop. *Slide the blade upward to cut the adductor muscle which holds the shell closed. Inexperienced shuckers can apply too much force, which can result in injury if the blade slips. Heavy gloves, sometimes sold as
oyster glove An oyster glove is a special glove worn to protect the hand holding an oyster when opening it with an oyster knife. The oyster glove is worn only on the hand holding the oyster. These gloves traditionally are made with a heavy leather palm but are ...
s, are recommended; apart from the knife, the shell itself can be razor-sharp. Professional shuckers require fewer than three seconds to open the shell. If the oyster has a particularly soft shell, the knife can be inserted instead in the "sidedoor", about halfway along one side where the oyster lips widen with a slight indentation. Opening or "shucking" oysters has become a competitive sport. Oyster-shucking competitions are staged around the world. The Guinness World Oyster Opening Championship was held annually in September at the Galway International Oyster Festival, in Galway, Ireland until 2010. Since 2011, "Guinness" has been dropped from the title.Comparison of archived title of the game: * * *


Food safety and storage

Unlike most shellfish, oysters can have a fairly long shelf life of up to four weeks. However, their taste becomes less pleasant as they age. Fresh oysters must be alive just before consumption or cooking. Oysters that do not open are generally assumed to be dead before cooking and therefore unsafe. There is only one criterion: the oyster must be capable of tightly closing its shell. Open oysters should be tapped on the shell; a live oyster will close up and is safe to eat. Oysters which are open and unresponsive are dead and must be discarded. Some dead oysters, or oyster shells which are full of sand, may be closed. These make a distinctive noise when tapped, and are known as "clackers". Oysters can contain harmful bacteria. Oysters are filter feeders, so will naturally concentrate anything present in the surrounding water. Oysters from the Gulf Coast of the United States, for example, contain high bacterial loads of human pathogens in the warm months, most notably ''
Vibrio vulnificus ''Vibrio vulnificus'' is a species of Gram-negative, motile, curved rod-shaped (bacillus), pathogenic bacteria of the genus ''Vibrio''. Present in marine environments such as estuaries, brackish ponds, or coastal areas, ''V. vulnificus'' is relat ...
'' and '' Vibrio parahaemolyticus''. In these cases, the main danger is for immunocompromised individuals, who are unable to fight off infection and can succumb to sepsis, leading to death. ''Vibrio vulnificus'' is the most deadly seafood-borne pathogen.


Depuration

Depuration Depuration of seafood is the process by which marine or freshwater animals are placed into a clean water environment for a period of time to allow purging of biological contaminants (such as ''Escherichia coli'') and physical impurities (such as s ...
of oysters is a common industry practice and widely researched in the scientific community but is not commonly known by end consumers. The main objective of seafood depuration is to remove fecal contamination in seafood before being sold to end consumers. Oyster depuration is useful since they are generally eaten raw and in many countries, the requirement to process is government-regulated or mandatory. The United Nations Food and Agriculture Organization (FAO) formally recognizes depuration and has published detailed documents on the process, whereas the
Codex Alimentarius The Codex Alimentarius () is a collection of internationally recognized standards, codes of practice, guidelines, and other recommendations published by the Food and Agriculture Organization of the United Nations relating to food, food production ...
, encourages the application of seafood depuration. Oyster depuration begins after the harvest of oysters from farmed locations. The oysters are transported and placed into tanks pumped with clean water for periods of 48 to 72 hours. The holding temperatures and salinity vary according to species. The seawater that the oysters were originally farmed in does not remain in the oyster, since the water used for depuration must be fully sterilized, plus the depuration facility would not necessarily be located near the farming location. Depuration of oysters can remove moderate levels of contamination of most bacterial indicators and pathogens. Well-known contaminants include '' Vibrio parahaemolyticus'', a temperature-sensitive bacterium found in seawater animals, and ''Escherichia coli'', a bacterium found in coastal waters near highly populated cities having sewage systems discharging waste nearby, or in the presence of agricultural discharges. Depuration expands beyond oysters into many shellfish and other related products, especially in seafood that is known to come from potentially polluted areas; depurated seafood is effectively a product cleansed from inside-out to make it safe for human consumption.


Cultural aspects


Religious

As shellfish, consumption of oyster is forbidden by
Jewish dietary law (also or , ) is a set of dietary laws dealing with the foods that Jewish people are permitted to eat and how those foods must be prepared according to Jewish law. Food that may be consumed is deemed kosher ( in English, yi, כּשר), from ...
. Similarly, in
Islam Islam (; ar, ۘالِإسلَام, , ) is an Abrahamic religions, Abrahamic Monotheism#Islam, monotheistic religion centred primarily around the Quran, a religious text considered by Muslims to be the direct word of God in Islam, God (or ...
, Jaʽafari Shia and Hanafi
Sunni Sunni Islam () is the largest branch of Islam, followed by 85–90% of the world's Muslims. Its name comes from the word '' Sunnah'', referring to the tradition of Muhammad. The differences between Sunni and Shia Muslims arose from a disagr ...
dietary jurisprudence prohibit consuming bivalves, including oysters, as it is ''makruh'' (highly prohibited).


Diseases

Oysters are subject to various diseases which can reduce harvests and severely deplete local populations. Disease control focuses on containing infections and breeding resistant strains, and is the subject of much ongoing research. *"Dermo" is caused by a
protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
n parasite (''
Perkinsus marinus ''Perkinsus marinus'' is a species of alveolates belonging to the phylum Perkinsozoa.Joseph, S., et al. (2010)The alveolate ''Perkinsus marinus'': biological insights from EST gene discovery.''BMC Genomics'' 11(1), 228. It is similar to a dinofl ...
''). It is a prevalent pathogen, causes massive mortality, and poses a significant economic threat to the oyster industry. The disease is not a direct threat to humans consuming infected oysters. Dermo first appeared in the Gulf of Mexico in the 1950s, and until 1978 was believed to be caused by a fungus. While it is most serious in warmer waters, it has gradually spread up the east coast of the United States. * Multinucleated sphere X (MSX) is caused by the protozoan ''
Haplosporidium nelsoni ''Haplosporidium nelsoni'' is a pathogen of oysters that originally caused oyster populations to experience high mortality rates in the 1950s, and still is quite prevalent today. The disease caused by ''H. nelsoni'' is also known as MSX (multinuc ...
'', generally seen as a multinucleated '' Plasmodium''. It is infectious and causes heavy mortality in the eastern oyster; survivors, however, develop resistance and can help propagate resistant populations. MSX is associated with high salinity and water temperatures. MSX was first noted in Delaware Bay in 1957, and is now found all up and down the East Coast of the United States. Evidence suggests it was brought to the US when ''
Crassostrea gigas The Pacific oyster, Japanese oyster, or Miyagi oyster (''Magallana gigas''), is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand. Etymology The genus ''Maga ...
'', Pacific oyster variety, was introduced to Delaware Bay. *Denman Island disease causes visible yellow/green pustules on the body and adductor muscles of oysters. This disease mainly affects Pacific oysters (''
Crassostrea gigas The Pacific oyster, Japanese oyster, or Miyagi oyster (''Magallana gigas''), is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand. Etymology The genus ''Maga ...
''). The disease was first described in 1960 near
Denman Island Denman Island, or Sla-dai-aich (Taystayic), its Indigenous name, is one of the Northern Gulf Islands and part of the Comox Valley Regional District of British Columbia, Canada. It is a member of the Islands Trust group of islands and is home ...
off the eastern aspect of Vancouver Island, British Columbia. It was found that the causative agent of these lesions are associated with amitochondriate protistan microcells, which were later identified as '' Mikrocytos mackini.'' Some oysters also harbor bacterial species which can cause human disease; of importance is ''
Vibrio vulnificus ''Vibrio vulnificus'' is a species of Gram-negative, motile, curved rod-shaped (bacillus), pathogenic bacteria of the genus ''Vibrio''. Present in marine environments such as estuaries, brackish ponds, or coastal areas, ''V. vulnificus'' is relat ...
'', which causes
gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydra ...
, which is usually self-limiting, and cellulitis. Cellulitis can be severe and rapidly spreading, requiring antibiotics, medical care, and in some severe cases amputation. It is usually acquired when the contents of the oyster come in contact with a cut skin lesion, as when shucking an oyster.


See also


References


External links


MolluSCAN eye
, a website devoted to the online study of molluscan bivalve behavior around the world, including oysters. Daily update.
World of Boats (EISCA) Collection ~ Fal Oyster Boat, Sunny South


* {{Authority control Ostreida Dishes involving the consumption of live animals Symbols of Mississippi Smoked food Mollusc common names Aphrodisiac foods