Product Code Database
Oyster is the common name for a number of different families of Seawater bivalve that live in marine or Brackish water habitats. In some species, the valves are highly Calcification, and many are somewhat irregular in shape. Many, but not all oysters, are in the superfamily Ostreoidea.
Some species of oyster are commonly consumed and are regarded as a delicacy in some localities. Some types of are harvested for the pearl produced within the mantle. Others, such as the translucent windowpane oysters, are harvested for their shells.
are not closely related to true oysters, being members of a distinct family, the feathered oysters (Pteriidae). Both and can be extracted from pearl oysters, though other molluscs, such as the freshwater , 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.
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.
In the Philippines, a local thorny oyster species known as Tikod amo is a favorite seafood source in the southern part of the country. Because of its good flavor, it commands high prices.
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 develop in about six hours and exist suspended in the water column as veliger for two to three weeks before settling on a bed and reaching sexual maturity within a year.
Oysters are filter feeders, taking in 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 (the time periods of mildly shifting tides), they exhibit much longer closing periods than during the spring tide (the time period of more drasticly shifting tides).
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 . 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 10-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.
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. 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. In Europe, France remained the industry leader.
The France 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 , 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.
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. 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; water pollution 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 Britain, the native species ( European flat oyster) has five years to mature and is protected by the people during their May-to-August spawning season. The current market is dominated by the larger Pacific oyster and Rock oyster species which are farmed year-round.
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 , and even since then motor boats can be used only on certain days of the week. These regulations prompted the development of specialized (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.
The Pacific oyster has been grown in the outflow of mariculture ponds. When fish or 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 oysters. The resulting triploid oyster cannot propagate, which prevents introduced oysters from spreading into unwanted habitats.
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. Near the mouth of the Great Wicomico River in the Chesapeake Bay, five-year-old 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 annually. The 2009 harvest was less than . 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. 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 conserving the biolife within the oyster reefs.
In October 2017, it was reported that underwater noise pollution can affect oysters as they close their shells when exposed to low Audio frequency of sounds in experimental conditions. Oysters rely on hearing waves and currents to regulate their , and perception of weather events—such as rain—may induce spawning. , , 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 Pacific oyster
The Billion Oyster Project out of New York has a goal of engaging one million people to return a billion Oysters to the New York Harbor. The nonprofit partners with 60+ restaurants to recycle discarded oyster shells to rebuild Oyster reefs.
$5 Million was awarded to Restore America's Estuaries by the NOAA's Office of Habitat Conservation to rebuild oyster reefs in Louisiana, Florida, Alabama, and Texas to expand oyster recycling efforts and create new Oyster Recycling programs. Along the Gulf, many communities support nonprofits that recycle oyster shells.
The Shells for Shorelines Initiative similarly collects donated oyster shells from restaurants in Southern California. The shells are repurposed as part of a restoration project to restore native Ostrea lurida (Ostrea Larida) reefs, the only native oyster to the West Coast, Canada, and Alaska.
Historically, Oyster shell waste was repurposed to form tabby concrete in construction. The origins of the material is debated, but likely was developed on the Iberian Peninsula or North Africa, where it was then introduced to the Americas via colonization Tabby concrete is composed of burnt oyster shells for a source of lime and broken oyster shells as aggregate, and was a popular construction choice on the Atlantic coast until the mid 19th century. The Kingsley Plantation on Fort George Island, build by African slaves, is one of the most notable examples of tabby concrete, but it is commonly found on plantations, factories, military forts, and historical landmarks in the South.
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.
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 Black pepper, dry white wine and lemon juice or sherry vinegar. Raw oysters have complex flavors that vary among varieties and regions: salty, briny, buttery, metallic or fruity. The texture is soft and fleshy. 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, Rappahannock River and James River from Virginia, Chesapeake Bay from Maryland and Cape May from New Jersey. In Connecticut they are frequently fished in Niantic whose municipal symbol is a scallop shell in reference to its strong seafood culture. Variations in water salinity, alkalinity, and mineral and nutritional content influence their flavor.
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 . Their high zinc content aids the production of testosterone.
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 , 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.
Oyster-shucking has become a competitive sport; 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:
Cooked oysters that do not open are generally assumed to be previously dead 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 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.
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, and 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.
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.
|
|
