Oyster
Oyster Temporal range:
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Pacific oyster from the Marennes-Oléron basin in France | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Mollusca |
Class: | Bivalvia |
Subclass: | Pteriomorphia |
Groups included | |
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Cladistically included but traditionally excluded taxa | |
All other members of: |
Oyster is the
Some types of oysters are commonly consumed (cooked or raw), and in some locales, they are regarded as a
Etymology
The word oyster comes from
Types
True oysters
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.
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.
In nature, pearl oysters produce pearls by covering a minute invasive object with nacre. 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.[6]
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 oystersin the genus Spondylus
- Pilgrim oyster, another term for a scallop, in reference to the scallop shell of St. James
- Saddle oysters, members of the Anomiidaefamily also known as jingle shells
- Dimydarian oysters, members of the family Dimyidae
- Windowpane oysters
-
Pacific oyster, opened
In the Philippines, a local thorny oyster species known as Tikod amo is a favorite seafood source in the southern part of the country.[7] Because of its good flavor, it commands high prices.
Anatomy
Oysters breathe primarily via
While some oysters have two sexes (
Once her millions of eggs are fertilized, the female discharges them into the water. The
Feeding
Oysters are
Habitat and behaviour
A group of oysters is commonly called a bed or oyster reef.
As a
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
Oysters 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. 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.[10]
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.[citation needed][inconsistent] Willapa Bay in Washington produces more oysters than any other estuary in the US.[11][full citation needed] 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.[12] In Europe, France remained the industry leader.
Common oyster predators include crabs, seabirds, starfish, and humans. Some oysters contain crabs, known as oyster crabs.[13]
Nutrient cycling
Ecosystem services
As an
Human history
The
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.[39] 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.[40] This scarcity increased prices, converting them from their original role as working-class food to their current status as an expensive delicacy.
In Britain, the native species (
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
In some areas, a
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.
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.[41] 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.[42]
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+1⁄4 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
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.[44] 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.[45] Near the mouth of the
- using waste oyster shells to elevate the reef floor 25–45 cm (9.8–17.7 in) to keep the spat free of bottom sediments
- building larger reefs, ranging up to 8.1 ha (20 acres) in size
- disease-resistant broodstock[46]
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.[47] 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.[48] 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.[49] Additionally Oyster reef restoration has shown to increase the population of oyster beds within the oceans while also conserving the biolife within the oyster reefs.
Human impact
The accidental or intentional
In October 2017, it was reported that
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.[53]
As food
Jonathan Swift is quoted as having said, "He was a bold man that first ate an oyster".[54] 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.[55] In recent years[citation needed], 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,
Care should be taken when consuming oysters. They may be eaten raw, with no dressing or with
-
Chargrilled oysters.
-
Deep fried oyster in Japan.[58]
-
Six steamed Eastern oysters on the half shell
-
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 460 kilojoules (110 kilocalories).[59] They are rich in protein (approximately 9 g in 100 g of Pacific oysters).[60] Two oysters (28 grams or 1 ounce) provide the Reference Daily Intake of zinc and vitamin B12.[61]
Traditionally, oysters are considered to be an aphrodisiac, partially because they resemble female sex organs.[62] A team of American and Italian researchers analyzed bivalves and found they were rich in amino acids that trigger increased levels of sex hormones.[63] Their high zinc content aids the production of testosterone.[39]
Shucking oysters
Opening oysters, referred to as "oyster-shucking", requires skill. The preferred method is to use a special knife (called an
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 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.[39]
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.
Oyster-shucking has become a competitive sport; competitions are staged around the world.[64] The Guinness World Oyster Opening Championship was held annually in September at the Galway International Oyster Festival, in Galway, Ireland until 2010.[65] Since 2011, "Guinness" has been dropped from the title.[66]
Food safety and storage
This section needs additional citations for verification. (January 2020) |
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.[67]
Cooked oysters that do not open are generally assumed to be previously dead and therefore unsafe.[68] There is only one criterion: the oyster must be capable of tightly closing its shell.[citation needed] Open oysters should be tapped on the shell; a live oyster will close up and is safe to eat.[citation needed] 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
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.[72] 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.[citation needed] 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
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 parasite (Perkinsus marinus). 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.[73] 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.[74]
- Multinucleated sphere X (MSX) is caused by the protozoan Crassostrea gigas, Pacific oyster variety, was introduced to Delaware Bay.[74]
- Denman Island disease causes visible yellow/green pustules on the body and adductor muscles of oysters. This disease mainly affects Pacific oysters (Mikrocytos mackini.
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
- Angels on horseback (classic recipe)
- Auckland oyster
- European flat oyster
- Bluff oyster
- Eastern oyster
- List of delicacies
- List of smoked foods
- Ostrea angasi (Australian southern mud or native flat oyster)
- Oyster omelette
- Oyster pirate
- Oyster sauce
- Oysters Kirkpatrick (classic recipe and minor English literary character)
- Red tide
- Rolled oyster
- San Leandro Oyster Beds
- Sydney rock oyster
- Tabby concrete
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External links
- molluSCAN-eye - Online biomonitoring project hosted by the University of Bordeaux and the CNRS A website devoted to the online study of molluscan bivalve behavior around the world, including oysters
- World of Boats (EISCA) Collection ~ Fal Oyster Boat, Sunny South
- Oysters grown on trestles in Ireland Archived 17 May 2008 at the Wayback Machine
- Oyster farming in the Rivers Crouch, Roach and Blackwater of Eastern Essex Archived 3 July 2009 at the Wayback Machine
- New International Encyclopedia. 1905. .