Oyster

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Oysters
Crassostrea gigas p1040848.jpg
Pacific oyster from the Marennes-Oléron basin in France
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Pteriomorphia
Groups included
Cladistically included but traditionally excluded taxa

All other members of:

Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine 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.

In biology, a common name of a taxon or organism is a name that is based on the normal language of everyday life; this kind of name is often contrasted with the scientific name for the same organism, which is Latinized. A common name is sometimes frequently used, but that is by no means always the case.

Seawater Water from a sea or ocean

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%. This means that every kilogram of seawater has approximately 35 grams (1.2 oz) of dissolved salts. Average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F). The coldest seawater ever recorded was in 2010, in a stream under an Antarctic glacier, and measured −2.6 °C (27.3 °F). Seawater pH is typically limited to a range between 7.5 and 8.4. However, there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units.

Brackish water Water with salinity between freshwater and seawater

Brackish water is water having more salinity than freshwater, but not as much as seawater. It may result from mixing seawater with fresh water together, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak". Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment.

Contents

Some kinds of oysters are commonly consumed cooked or raw and are regarded as a delicacy. Some kinds of pearl oysters are harvested for the pearl produced within the mantle. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects.

Delicacy food item that is considered highly desirable in certain cultures

A delicacy is usually a rare or expensive food item that is considered highly desirable, sophisticated or peculiarly distinctive, within a given culture. Irrespective of local preferences, such a label is typically pervasive throughout a region. Often this is because of unusual flavors or characteristics or because it is rare or expensive compared to standard staple foods.

Pearl hard object produced within the soft tissue of a living shelled mollusc

A pearl is a hard glistening object produced within the soft tissue of a living shelled mollusk or another animal, such as a conulariid. Just like the shell of a mollusk, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur. The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries. Because of this, pearl has become a metaphor for something rare, fine, admirable and valuable.

Mantle (mollusc) part of the anatomy of molluscs

The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.

Etymology

First attested in English during the 14th century, [1] the word "oyster" comes from Old French oistre, in turn from Latin ostrea, the feminine form of ostreum, [2] which is the latinisation of the Greek ὄστρεον (ostreon), "oyster". [3] Compare ὀστέον (osteon), "bone". [4]

Old French was the language spoken in Northern France from the 8th century to the 14th century. In the 14th century, these dialects came to be collectively known as the langue d'oïl, contrasting with the langue d'oc or Occitan language in the south of France. The mid-14th century is taken as the transitional period to Middle French, the language of the French Renaissance, specifically based on the dialect of the Île-de-France region.

Latin Indo-European language of the Italic family

Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets and ultimately from the Phoenician alphabet.

Greek language language spoken in Greece, Cyprus and Southern Albania

Greek is an independent branch of the Indo-European family of languages, native to Greece, Cyprus and other parts of the Eastern Mediterranean and the Black Sea. It has the longest documented history of any living Indo-European language, spanning more than 3000 years of written records. Its writing system has been the Greek alphabet for the major part of its history; other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic, and many other writing systems.

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 , and Saccostrea . Examples include the Belon oyster, eastern oyster, Olympia oyster, Pacific oyster, and the Sydney rock oyster.

Ostreidae family of molluscs

The Ostreidae, the true oysters, include most species of molluscs commonly consumed as oysters. Pearl oysters are not true oysters, and belong to the order Pterioida.

<i>Ostrea</i> genus of molluscs

Ostrea is a genus of edible oysters, marine bivalve mollusks in the family Ostreidae, the oysters.

<i>Crassostrea</i> genus of molluscs

Crassostrea is a genus of true oysters containing some of the most important oysters used for food. Some species in the genus have been moved to the genus Magallana.

Pearl oysters

Removing a pearl from a pearl oyster Pearl Oysters.jpg
Removing a pearl from a pearl oyster

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). Both cultured pearls and natural pearls can be extracted from pearl oysters, though other molluscs, such as the freshwater mussels, also yield pearls of commercial value.

Pteriidae family of molluscs

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 Pterioida.

Cultured pearl

A cultured pearl is a pearl created by an oyster farmer under controlled conditions. Cultured pearls can be farmed using two very different groups of bivalve mollusk: the freshwater river mussels, and the saltwater pearl oysters.

Mussel Common name for members of several families of bivalve molluscs

Look at bottom

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 fact, in a harvest of two and a half tons of oysters, only three to four oysters produce what commercial buyers consider to be absolute perfect pearls.[ citation needed ]

The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of mass. Its original use as a measurement of volume has continued in the capacity of cargo ships and in terms such as the freight ton. It can also be used as a measure of energy, for truck classification, or as a colloquial term.

In nature, pearl oysters produce pearls by covering a minute invasive object with nacre. [5] 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. These pearls are not as valuable as natural pearls, but look exactly the same. In fact, 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 of oysters

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:

In the Philippines, a local thorny oyster species known as Tikod Amo is a favorite seafood source in the southern part of the country. [6] Because of its good flavor, it commands high prices.

Anatomy

Oysters are filter feeders, drawing water in over their gills through the beating of cilia. Suspended plankton and 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 or pseudofeces. Oysters feed most actively at temperatures above 10 °C (50 °F). An oyster can filter up to 5 L (1.3 US gal) of water per hour. The Chesapeake Bay's once-flourishing oyster population historically filtered excess nutrients from the estuary's entire water volume every three to four days. Today, that would take nearly a year. [7] Excess sediment, nutrients, and algae can result in the eutrophication of a body of water. Oyster filtration can mitigate these pollutants.

In addition to their gills, oysters can also exchange gases across their mantles, which are lined with many small, thin-walled blood vessels. A small, three-chambered heart, lying under the adductor muscle, 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.

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 the female is fertilized, she discharges millions of eggs into the water. The larvae 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 maturing to sexual adulthood within a year.

Habitat and behaviour

Oyster reef at about mid-tide off fishing pier at Hunting Island State Park, South Carolina Oyster reef Hunting Island SC.jpg
Oyster reef at about mid-tide off fishing pier at Hunting Island State Park, South Carolina

A group of oysters is commonly called a bed or oyster reef.

Rocks in intertidal zone covered by oysters, at Bangchuidao Scenic Area, Dalian, Liaoning Province, China Oyster Dalian.JPG
Rocks in intertidal zone covered by oysters, at Bangchuidao Scenic Area, Dalian, Liaoning Province, China

As a keystone species, oysters provide habitat for many marine species. Crassostrea and Saccostrea live mainly in the intertidal zone, 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, 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; during their first year, they spawn as males by releasing sperm 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 oysters 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 25 mm (1 in) long. Many species of bivalves, oysters included, seem to be stimulated to settle near adult conspecifics.

Pacific oyster Crassostrea gigas equipped with activity electrodes to follow their daily behaviour Electric oyster MolluSCAN eye project.jpg
Pacific oyster Crassostrea gigas equipped with activity electrodes to follow their daily behaviour

Oysters are considered to filter large amounts of water to feed and breathe (exchange O2 and CO2 with water) but they are not permanently open. They regularly shut their valves to enter a resting state, even when they are permanently submersed. In fact 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. [8]

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. In Trinidad in the West Indies, tourists are often astounded when they are told, in the Caribbean, "oysters grow on the trees here".

The largest oyster-producing body of water in the United States is Chesapeake Bay, although these beds have decreased in number due to overfishing and pollution. Willapa Bay in Washington produces more oysters than any other estuary in the US. [9] 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 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. [10] Within Europe, France remained the industry leader.

Common oyster predators include crabs, seabirds, starfish, and humans. Some oysters contain crabs, known as oyster crabs.

Nutrient cycling

Bivalves, including oysters, are effective filter feeders and can have large effects on the water columns in which they occur. [11] As filter feeders, oysters remove plankton and organic particles from the water column. [12] Multiple studies have shown individual oysters are capable of filtering up to 50 gallons of water per day, and thus oyster reefs can significantly improve water quality and clarity. [13] [14] [15] [16] Oysters consume nitrogen-containing compounds (nitrates and ammonia), phosphates, plankton, detritus, bacteria, and dissolved organic matter, removing them from the water. [17] What is not used for animal growth is then expelled as solid waste pellets, which eventually decompose into the atmosphere as nitrogen. [5] In Maryland, the Chesapeake Bay Program plans to use oysters to reduce the amount of nitrogen compounds entering the Chesapeake Bay by 8,600 t (19,000,000 lb) per year by 2010. [18] Several studies have shown that oysters and mussels have the capacity to dramatically alter nitrogen levels in estuaries. [19] [20] [21] 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. [22] Supporters of Delaware's legislation to allow oyster aquaculture cite revenue, job creation, and nutrient cycling benefits. It is estimated that one acre can produce nearly 750,000 oysters, which could filter between 57,000 to 150,000 m3 (15,000,000 to 40,000,000 US gal) of water daily. [22] Also see nutrient pollution for an extended explanation of nutrient remediation.

Ecosystem services

As an ecosystem engineer oysters provide "supporting" ecosystem services, along with "provisioning", "regulating" and "cultural" services. Oysters influence nutrient cycling, water filtration, habitat structure, biodiversity, and food web dynamics. [23] Oyster feeding and nutrient cycling activities could "rebalance" shallow, coastal ecosystems if restoration of historic populations could be achieved. [24] Furthermore, assimilation of nitrogen and phosphorus into shellfish tissues provides an opportunity to remove these nutrients from the environment, but this benefit has only recently been recognized. [24] [25] [26] In California's Tomales Bay, native oyster presence is associated with higher species diversity of benthic invertebrates [27] but other ecosystem services have not been studied. [28] As the ecological and economic importance of oyster reefs has become more widely acknowledged, creation of oyster reef habitat through restoration efforts has become more important- often with the goal of restoring multiple ecosystem services associated with natural oyster reefs. [29]

Human history

Still-Life with Oysters by Alexander Adriaenssen Alexander Adriaenssen - Still-Life with Oysters - WGA0035.jpg
Still-Life with Oysters by Alexander Adriaenssen
The Whaleback Shell Midden in Maine contains the shells from oysters harvested for food dating from 2200-1000 years ago Whaleback Shell Midden gully - 20070722 07986.JPG
The Whaleback Shell Midden in Maine contains the shells from oysters harvested for food dating from 2200-1000 years ago

Middens testify to the prehistoric importance of oysters as food, with some middens in New South Wales, Australia dated at ten thousand years. [30] They have been cultivated in Japan from at least 2000 BC. [30] 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 is held in September. Many breweries produce oyster stout, a beer intended to be drunk with oysters that sometimes includes oysters in the brewing process.

The French seaside resort of Cancale in Brittany is noted for its oysters, which also date from Roman times. Sergius Orata 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. He was so famous for this, the Romans used to say he could breed oysters on the roof of his house. [31]

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 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. [32] 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 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. [33] 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 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 tongs 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.

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.

Cultivating oysters

Oyster culture in Riec-sur-Belon, France Oyster culture in Belon, France 03.jpg
Oyster culture in Riec-sur-Belon, France

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. [34] 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. [35]

The Pacific oyster has been grown in the outflow of mariculture ponds. When fish or prawns are grown in ponds, it takes typically 10 kg (22 lb) of feed to produce 1 kg (2.2 lb) of product (dry-dry basis). The other 9 kg (20 lb) 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 oysters. The resulting triploid oyster cannot propagate, which prevents introduced oysters from spreading into unwanted habitats. [36]

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. [37] Proposals for further such introductions remain controversial.

The Pacific oyster prospered in Pendrell Sound, 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. [38] 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 . That is far lower than in the late 1880s, when the bay's population was in the billions, and watermen harvested about 910,000 m3 (25,000,000 imp bsh) annually. The 2009 harvest was less than 7,300 m3 (200,000 imp bsh). Researchers claim the keys to the project were:

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. [40] 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. [41] 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. [42]

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 oysters. [43]

In October 2017, it was reported that underwater noise pollution can affect oysters as they close their shells when exposed to low frequencies of sounds in experimental conditions. Oysters rely on hearing waves and currents to regulate their circadian rhythms, and perception of weather events—such as rain—may induce spawning. Cargo ships, pile drivers, and explosions conducted underwater produce low frequencies that may be detected by oysters. [44]

As food

Chargrilled oysters Chargrilled oysters.jpg
Chargrilled oysters
Raw oysters presented on a plate Oysters p1040741.jpg
Raw oysters presented on a plate
Dishes with Oysters, Fruit, and Wine, a 1620s painting by Osias Beert, now in the National Gallery of Art in Washington, DC. Osias Beert the Elder - Dishes with Oysters, Fruit, and Wine - Google Art Project.jpg
Dishes with Oysters, Fruit, and Wine, a 1620s painting by Osias Beert, now in the National Gallery of Art in Washington, DC.

Jonathan Swift is quoted as having said, "He was a bold man that first ate an oyster", [46] but 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 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. [47] 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.

Consumption of oyster is forbidden by Jewish dietary law, for religious reasons.

Depuration

Depuration 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, [48] whereas the Codex Alimentarius, encourages the application of seafood depuration. [49]

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. [50] 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. [51] 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.

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 contains 110 kilocalories (460 kJ). [52] They are rich in protein (approximately 9 g in 100 g of Pacific oysters). [53]

Traditionally, oysters are considered to be an aphrodisiac, partially because they resemble female sex organs. [54] A team of American and Italian researchers analyzed bivalves and found they were rich in amino acids that trigger increased levels of sex hormones. [55] Their high zinc content aids the production of testosterone. [32]

Dietary supplements may contain calcium carbonate from oyster shells, though no evidence shows this offers any benefits beyond what calcium may offer.[ citation needed ]

Selection, preparation 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. Oysters should be refrigerated out of water, not frozen, and in 100% humidity. Oysters stored in water under refrigeration will open, consume available oxygen, and die.

Freshly opened pearl oysters Fresh Oysters.jpg
Freshly opened pearl oysters
Freshly shucked European flat oyster European Flat Oyster.jpg
Freshly shucked European flat oyster

Traditionally, oysters that do not open have been assumed to be dead before cooking and therefore unsafe. [56] However, according to at least one marine biologist, Nick Ruello, this advice may have arisen from an old, poorly researched cookbook's advice regarding mussels, which has now become an assumed truism for all shellfish. Ruello found 11.5% of all mussels failed to open during cooking, but when forced open, 100% were "both adequately cooked and safe to eat." [57]

Giant oyster in southern Angola Ostra gigante em Angola.jpg
Giant oyster in southern Angola
Fried oyster with egg and flour is a common dish in Malaysia and Singapore. FriedOyster.JPG
Fried oyster with egg and flour is a common dish in Malaysia and Singapore.

Oysters can be eaten on the half shell, raw, smoked, boiled, baked, fried, roasted, stewed, 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. 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. Purists insist on eating them raw, with no dressing save perhaps 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 peppercorn, 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 even fruity. The texture is soft and fleshy, but crisp on the palate. North American varieties include Kumamoto and Yaquina Bay from Oregon, Duxbury and Wellfleet from Massachusetts, Malpeque from Prince Edward Island, Canada, Blue Point from Long Island, New York, Pemaquid from Maine, and Cape May oysters from New Jersey. Variations in water salinity, alkalinity, and mineral and nutritional content influence their flavor profile.

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 and Vibrio parahaemolyticus . In these cases, the main danger is for immunocompromised individuals, who are unable to fight off infection and can succumb to septicemia, leading to death. Vibrio vulnificus is the most deadly seafood-borne pathogen.[ citation needed ]

Opening oysters

Special knives for opening live oysters, such as this one, have short and stout blades. Couteau a huitre - cote.jpg
Special knives for opening live oysters, such as this one, have short and stout blades.

Fresh oysters must be alive just before consumption or cooking.[ citation needed ] 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".

Opening oysters, referred to as "oyster-shucking", requires skill. The preferred method is to use a special knife (called an oyster knife, a variant of a shucking knife), with a short and thick blade about 5 cm (2.0 in) 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.

Inexperienced shuckers can apply too much force, which can result in injury if the blade slips. Heavy gloves, sometimes sold as oyster gloves, are recommended; apart from the knife, the shell itself can be razor-sharp. Professional shuckers require fewer than three seconds to open the shell. [32]

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 is held in September at the Galway Oyster Festival. The annual Clarenbridge Oyster Festival "Oyster Opening Competition" is also held in Galway, Ireland.

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.

Some oysters also harbor bacterial species which can cause human disease; of importance is Vibrio vulnificus , which causes gastroenteritis, 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

Related Research Articles

Shellfish culinary and fisheries term for exoskeleton-bearing aquatic invertebrates

Shellfish is a food source 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 in freshwater. In addition, a few species of land crabs are eaten, for example Cardisoma guanhumi in the Caribbean.

Bivalvia class of molluscs

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. Bivalves as a group have no head and they lack some usual molluscan organs like the radula and the odontophore. They include the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. The shipworms bore into wood, clay, or stone and live inside these substances.

Filter feeder 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

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 feeding are clams, krill, sponges, baleen whales, and many fish. Some birds, such as flamingos and certain species of duck, are also filter feeders. Filter feeders can play an important role in clarifying water, and are therefore considered ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.

Eastern oyster species of mollusc

The eastern oyster —also called Wellfleet oyster, Atlantic oyster, Virginia oyster, or American oyster—is a species of true oyster native to the eastern seaboard and Gulf of Mexico coast of North America. It is also farmed in Puget Sound, Washington, where it is known as the Totten Inlet Virginica. Eastern oysters are and have been very popular commercially. Today, less than 1% of the original 17th-century population is thought to remain in the Chesapeake Bay and its tributaries, although population estimates from any era are uncertain. The eastern oyster is the state shellfish of Connecticut, its shell is the state shell of Virginia and Mississippi, and its shell in cabochon form is the state gem of Louisiana.

Fish hatchery place for artificial breeding, hatching and rearing through the early life stages of fish

A fish hatchery is a place for artificial breeding, hatching, and rearing through the early life stages of animals—finfish and shellfish in particular. Hatcheries produce larval and juvenile fish, shellfish, and crustaceans, primarily to support the aquaculture industry where they are transferred to on-growing systems, such as fish farms, to reach harvest size. Some species that are commonly raised in hatcheries include Pacific oysters, shrimp, Indian prawns, salmon, tilapia and scallops. The value of global aquaculture production is estimated to be US$98.4 billion in 2008 with China significantly dominating the market; however, the value of aquaculture hatchery and nursery production has yet to be estimated. Additional hatchery production for small-scale domestic uses, which is particularly prevalent in South-East Asia or for conservation programmes, has also yet to be quantified.

Pacific oyster species of mollusc

The Pacific oyster, Japanese oyster, or Miyagi oyster, previously and currently also known as Crassostrea gigas, considered by part of the scientific community to be the proper denomination as an accepted alternative in WoRMS, is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand.

Oyster farming commercial growing of oysters

Oyster farming is an aquaculture practice in which oysters are raised for human consumption. Oyster farming was practiced by the ancient Romans as early as the 1st century BC on the Italian peninsula and later in Britain for export to Rome. The French oyster industry has relied on aquacultured oysters since the late 18th century.

<i>Ostrea angasi</i> species of mollusc

The southern mud oyster, Australian flat oyster, native flat oyster, or angasi oyster, is endemic to southern Australia, ranging from Western Australia to southeast New South Wales and around Tasmania. Ostrea angasi superficially resembles Ostrea edulis and both species may be referred to with the name “flat oyster”. However, the two species do not occur naturally in the same geographic distribution.

<i>Ostrea edulis</i> species of mollusc

Ostrea edulis, commonly known as the European flat oyster, is a species of oyster native to Europe. In the British Isles, regional names include Colchester native oyster, mud oyster, or edible oyster. In France, Ostrea edulis are known as huîtres plates except for those that come from the Belon River estuary in Brittany, France, which are known as 'Belons'.

Integrated multi-trophic aquaculture Aquaculture which provides the byproducts, including waste, from one aquatic species as inputs for another

Integrated multi-trophic aquaculture (IMTA) provides the byproducts, including waste, from one aquatic species as inputs for another. Farmers combine fed aquaculture with inorganic extractive and organic extractive aquaculture to create balanced systems for environment remediation (biomitigation), economic stability and social acceptability.

Pseudofeces or pseudofaeces are a specialized method of expulsion that filter-feeding bivalve mollusks use in order to get rid of suspended particles such as particles of grit which cannot be used as food, and which have been rejected by the animal. The rejected particles are wrapped in mucus, and are then expelled without having passed through the digestive tract. Thus, although they may closely resemble the mollusk's real feces, they are not actually feces, hence the name pseudofeces, meaning false feces.

<i>Ostrea lurida</i> species of mollusc

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 America. Over the years the role of this edible species of oyster has been partly displaced by the cultivation of non-native edible oyster species.

Aquaculture in New Zealand

Aquaculture started to take off in New Zealand in the 1980s. It is dominated by mussels, oysters and salmon. In 2007, aquaculture generated about NZ$360 million in sales on an area of 7,700 hectares. $240 million was earned in exports.

Scallop aquaculture

Scallop aquaculture is the commercial activity of cultivating (farming) scallops until they reach a marketable size and can be sold as a consumer product. Wild juvenile scallops, or spat, were collected for growing in Japan as early as 1934. The first attempts to fully cultivate scallops in farm environments were not recorded until the 1950s and 1960s. Traditionally, fishing for wild scallops has been the preferred practice, since farming can be expensive. However worldwide declines in wild scallop populations have resulted in the growth of aquaculture. Globally the scallop aquaculture industry is now well established, with a reported annual production totalling over 1,200,000 metric tonnes from about 12 species. China and Japan account for about 90% of the reported production.

Oyster reef restoration

Oyster reef restoration refers to the process of rebuilding or restoring of oyster reefs all over the globe. Over time, oysters have been negatively affected by environmental change, such as harmful fishing techniques, over harvesting, water pollution, and other factors. The results of these factors have been disease and ultimately, a large decline in the global population of oysters and the prevalence and sustainability of oyster reefs. Apart from the ecological importance of oyster reefs, oyster farming is an important industry, particularly in coastal areas. Both artificial materials and natural components have been used to rebuild the reefs in an attempt to regenerate the oyster population thus fostering the reformation of reefs.

The Suminoe oyster, is a species of true oyster which inhabits intertidal hard grounds and substrate, as well as muddy creeks of warm estuaries throughout the western Pacific. It is large and flat in appearance and almost identical in gross morphology to Crassostrea virginica.

Oyster reef

The term oyster reef refers to dense aggregations of oysters that form large colonial communities. Because oyster larvae need to settle on hard substrates, new oyster reefs may form on stone or other hard marine debris. Eventually the oyster reef will propagate by spat settling on the shells of older or nonliving oysters. The dense aggregations of oysters are often referred to as an oyster reef, oyster bed, oyster bank, oyster bottom, or oyster bar interchangeably. These terms are not well defined and often regionally restricted.

Thousands of years prior to European settlement of the Pacific Northwest of the United States the native oyster species Ostrea lurida had been established as a valuable dietary resource for indigenous people living on the coastal waters. European settlers who began to colonize the area had an acquired taste for shellfish and especially oysters a delicacy that were considered a symbol of wealth. In the early history of the Northwest people satisfied their hunger for shellfish by harvesting naturally occurring oyster beds. At first some people believed the populations of the native oyster were sufficient to supply both tribal and commercial harvest. A marketable industry was created on the export of oysters and soon exploitation of harvesting had depleted the natural oyster beds in California and Oregon. As a result Washington State became the main supplier to areas along the coast which had failed to establish any conservation practices. Noticing the economic value and decline of natural availability, farmers began efforts to cultivate oysters to try and satisfy demand. Over the years the oyster industry of the Pacific Northwest has gone from extremely lucrative to completely nonexistent, but still the industry has been able to adapt and survive.

Vibrio tubiashii is a Gram-negative, rod-shaped (0.5 um-1.5 um) marine bacterium that uses a single polar flagellum for motility. It has been implicated in several diseases of marine organisms.

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