The Eastern oyster is relatively large, growing up to 10 cm. in length. It is normally somewhat pear-shaped in outline, but members of this species vary greatly in size and shape. The shell is dirty gray externally and white internally, except for the muscle scar, which is deep purple.
Other Physical Features: ectothermic ; bilateral symmetry
Although it is only distantly related to the true pearl oyster (which, in fact, is not an oyster), it can and occasionally does produce pearls. The Eastern oyster can exist in water of extreme variations in turbidity and salinity.
Oyster health is highly contingent upon water quality. Chemical contamination is widespread and detrimental. Extensive efforts are being made in British Columbia to purify water to benefit all aquatic organisms. Toxicity in shellfish can be passed on to consumers, resulting in a condition termed PSP in humans, which is potentially fatal.
A major problem caused by the oyster is fouling, or attachment, often to boats.
Oyster cultch or oyster spat is fairly valuable to jewelry trade, though it is rather abundant, due to the large numbers of existing oysters and their relatively high rate of reproductive success. Certain lime or cement coatings are enhaced by use of the cultch. Some Eastern oysters produce pearls as well. Oyster meat is also smoked and canned as a food.
After spawning in early spring, the oyster loses a great deal of weight. This event usually coincides with the spring bloom of phytoplankton, their primary food source. Feeding is dependent upon water temperature; more food is consumed at higher temperatures than at lower.
Gulf of St. Lawrence to the Gulf of Mexico and the West Indies. It was introduced to San Francisco Bay but did not survive.
Biogeographic Regions: nearctic (Native ); neotropical (Native ); atlantic ocean (Native )
Although water temperature affects growth rate, it appears to be irrelevant in site selection. Oysters inhabit areas of fairly constant turbidity and salinity. The oyster is eurytherma,l or able to withstand a wide range of temperatures including freezing temperatures.
Aquatic Biomes: reef ; coastal
Reproductive organs can be readily observed only during the breeding season. There is no reproductive activity during the winter. Sexual maturity is a function of size rather than age. The first spawning usually occurs when the oyster is 2 years of age. Fertilization occurs when huge numbers of sperm sperm and eggs are expelled from the male or female and meet in the water.
Crassostrea virginica en anglès:eastern oyster,[1] és una espècie d'ostra nativa de la banda oriental del Golf de Mèxic i també cultivada en aqüicultura. a Puget Sound, Estat de Washington, on rep el nom de Totten Inlet Virginica.,.[2][3][4][5]
Crassostrea virginica en anglès:eastern oyster, és una espècie d'ostra nativa de la banda oriental del Golf de Mèxic i també cultivada en aqüicultura. a Puget Sound, Estat de Washington, on rep el nom de Totten Inlet Virginica.,.
Die Amerikanische Auster (Crassostrea virginica) ist die zweitwichtigste Austernart mit einem Weltmarktanteil von 5,1 Prozent (2003). Sie heißt auf Französisch Huître (creuse) américaine und auf Englisch American (cupped) oyster.
Amerikanische Austern sind meist oval geformt. Die Schale ist hart aber nicht sehr kantig, dabei ist die untere Schale relativ flach. Die Farbe ist meist grau, gelegentlich auch bräunlich. Die Auster ist mittelgroß und kann bis zu 38 cm lang und 1,3 kg schwer werden, die kommerzielle Größe beträgt 8–18 cm.
Diese Austernart findet sich an der Ostküste Nordamerikas, von der Mündung des Sankt-Lorenz-Stroms in Kanada bis zum Golf von Mexiko und weiter bis Panama. Ein wichtiger Herkunftsort ist die Chesapeake Bay (USA).
Die Amerikanische Auster lebt in Küstengewässern in Tiefen von 0,5 bis 75 Metern. Sie benötigt harten Untergrund, zur Not setzt sie sich auch auf älteren Austern fest. Sie bevorzugt Buchten und Mündungen von Flüssen, wo der Salzgehalt des Wassers zwischen 5 ‰ und 30 ‰ beträgt.
Die Amerikanische Auster wird selten in Aquakultur gezüchtet, als einzige Austernart wird sie vorzugsweise (70 %) mit Schürfnetzen vom Meeresboden abgefischt. In manchen Regionen Nordamerikas leidet die Zucht der Amerikanischen Auster sehr unter Angriffen der auch als Austernbohrer bezeichneten Schnecke Urosalpinx cinerea, die eine ganze Population vernichten kann. In diesen Gegenden werden die jungen Austern in geschützten Becken groß gezogen und erst im Alter von zwei Jahren im Meer ausgesetzt. Die Schalen sind dann dick genug, um dem Austernbohrer zu widerstehen.
Weltgrößter Produzent sind die USA mit 184.000 Tonnen pro Jahr, das sind 77 Prozent der Weltproduktion. Hier werden viele Austern in Chesapeake Bay abgefischt. Es folgen Mexiko (10 %) und Kanada (3 %). Die Auster leidet unter Überfischung und Gewässerverschmutzung und ist derzeit im Rückgang begriffen.
Amerikanische Austern werden oft als „Fleischaustern“ verarbeitet und in Dosen gefüllt. In den USA werden sie auch roh verzehrt („geschlürft“), wobei sie zuvor nicht selten mit Ketchup und anderen würzigen Saucen „verfeinert“ werden. Bekannte Handelsbezeichnungen sind „Bluepoint“ (Connecticut), „Wellfleet“ und „Cotuit“ (Massachusetts), „Patuxent“ (Maryland), „Apalachicola“ und „Indian River“ (Florida), „Breton Sound“ und „Black Bay“ (Louisiana) sowie „Malpeque“ (Prince Edward Inseln, Kanada). Die Austernart wird außerhalb Nordamerikas nicht nachgefragt.
Die Amerikanische Auster (Crassostrea virginica) ist die zweitwichtigste Austernart mit einem Weltmarktanteil von 5,1 Prozent (2003). Sie heißt auf Französisch Huître (creuse) américaine und auf Englisch American (cupped) oyster.
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 Wellfleet oyster,[3] Virginia oyster, Malpeque oyster, Blue Point oyster, Chesapeake Bay oyster, and Apalachicola oyster. C. virginica ranges from northern New Brunswick south through parts of the West Indies[4] to Venezuela.[5][6]: 7 It is farmed in all of the Maritime provinces of Canada and all Eastern Seaboard and Gulf states of the United States, as well as Puget Sound, Washington, where it is known as the Totten Inlet Virginica.[7] It was introduced to the Hawaiian Islands in the nineteenth century and is common in Pearl Harbor.[8]
The eastern oyster is an important commercial species. Its distribution has been affected by habitat change; less than 1% of the population present when the first European colonists arrived is thought to remain in the Chesapeake Bay and its tributaries.[9] As of 2014, the global conservation status of Crassostrea virginica, as assessed by NatureServe, is "vulnerable," as the oyster's populations are threatened by overharvest and water pollution.[1] Other threats to the eastern oyster include global warming, diseases and parasites and competition with invasive species.[10]
Like all oysters, Crassostrea virginica is a bivalve mollusk with a hard calcium carbonaceous shell that protects it from predation.
This particular type of oyster is important to its ecosystem. Like all oysters, C. virginica is a filter feeder. It sucks in water and filters out the plankton and detritus to swallow, then spits the water back out, thus cleaning the water around it. One oyster can filter up to 50 gallons of water in 24 hours.[11] Eastern oysters also provide a key structural element within their ecosystem, making them a foundation species in many environments, and they serve as ecosystem engineers in western Atlantic estuaries.[12][13] Like coral reefs, oyster beds, also known as oyster reefs, provide key habitat for a variety of different species by creating hard substrate for attachment and habitation.[14] Oyster beds have an estimated 50 times the surface area of an equally sized flat bottom. The beds also attract a high concentration of larger predators looking for food.[15]
The eastern oyster, like all members of the family Ostreidae, can make small pearls to surround particles that enter the shell. These pearls, however, are insignificant in size and of no monetary value; the pearl oyster, from which commercial pearls are harvested, is of a different family.
Unlike most bivalves, whose shells are aragonite, adult eastern oysters have calcite shells. The larvae, however, retain the aragonite shell of their ancestors. The specific gravity of the two types of shell is similar, so neither would confer a weight advantage over the other for a freely swimming larva.[16] The transition to the thicker calcite shell in the adult of this species is thought to be an adaptation for defense against predators because the oysters are immobilized in exposed locations.[16]
Side
Outside
Inside
Cluster of oysters
Oysters growing on a post
The life cycle of C. virginica consists of spawn, floating fertilized egg, trochophore, swimming straight-hinge veliger, swimming late veliger, swimming and crawling pediveliger, early spat, later spat, and adult oysters.[17] Spawning of C. virginica is controlled by water temperatures and varies from north to south; northern oysters spawn at temperatures between 60 and 68 °F (15.5 and 20 °C), whereas southern oysters spawn at temperatures above 68 °F (20 °C). Spawning can occur throughout the warm months.[18]
Eastern oysters can reach sexual maturity at four months old in southern waters.[19] The eastern oyster's reproductive cycle begins during late summer and autumn months with the storage of glycogen energy reserves.[20] This glycogen is then used to support gametogenesis during the next winter and early spring when food intake is at a minimum.[20] The gametes begin to mature in late spring and then, from June to August, they are spawned into the water column, where fertilization occurs.[20] Each female produces from 75 to 150 million eggs, but only one in a thousand survives.[21] Fertilized eggs develop in about six hours into planktonic, free-swimming, trochophore larvae, also known as the early umbo stage, which have cilia and a small shell.[17] The trochophore larvae depend on their internal yolk supply for energy.[22] They then develop within 12 to 24 hours into a fully shelled veliger larvae, also known as the late umbo stage, which has a hinged side and a velum.[17] During this time, the shelled veliger larvae use their ciliated vela to capture food and swim.[22] The larvae remain planktonic for about 2 to 3 weeks, depending on food and temperature conditions, and towards the end of this period, they develop into pediveliger larvae, also known as eyed larvae, which have an umbo, an eyespot, and a foot.[17] During this time. the pediveliger larvae settle to the bottom, where they seek a hard substrate.[17] Ideally, the pediveliger larvae try to locate an adult oyster shell to which they attach, often as part of an existing oyster reef, but other hard surfaces will suffice. Upon settling, a larva cements its left valve to the substrate and metamorphoses into an oyster spat by discarding its velum, reabsorbing its foot, and enlarging its gills.[22] During the first year of life, C. virginica oysters are protandric. Most spat are male, but once they reach sexual maturity, some males change to females after the first or second spawning.[18] Some females may change back to males again.[18]
Before Columbus and the rise of industrial oyster operations, oysters abounded in the bay. Oysters first arrived in the Chesapeake 5,000 years ago, and shortly after, local Indians began eating them. Archaeologists found evidence the local Native Americans returned to the same place to collect oysters for 3,000 years. John Smith, on a voyage up the Chesapeake, stated oysters "lay as thick as stones."[23] In fact, the word Chesapeake derives from an Algonquian word meaning 'Great Shellfish Bay'.[24] Because of the abundance of oysters filtering the waters of the Chesapeake, the water was much clearer than it is now. Visibility would sometimes reach 20 feet. When the English began settling the area, they evidently had a localized impact of the oyster population. One archaeological site measured oyster sizes near Maryland's old capital St. Mary's city from 1640 to 1710. In 1640, when the city was still small, oysters measured 80 mm, and in the city's maximum population in 1690, they measured to 40 mm. When the capital moved to Annapolis, the population moved with it, and by 1710, the oysters were back up to 80 mm.[25] However, the effect of overharvesting would remain local until after the Civil War, when a combination of new technologies led to the removal of nearly all the bay oysters.
During the industrial revolution, several new technologies were introduced to the Chesapeake Bay area which allowed for more intensive oyster harvesting. First was the invention of canning. This allowed oysters to be preserved much longer, and created demand for oysters across the world. Secondly, the invention of the dredge enabled oyster harvesters to reach untouched depths of the Chesapeake. And finally, the proliferation of steam-powered ships and railroads made transportation more reliable, enabling merchants to sell oysters far and wide. Estimates for the harvest in 1839 give a figure of 700,000 bushels. After the Civil War, dredges were legalized, and harvesting exploded to 5 million bushels that year. By 1875, 17 million bushels were taken from the bay. The harvesting would reach its peak in the 1880s, with 20 million bushels being harvested from the bay each year.[25] Not only were they being taken for food, but also oyster reefs, where oysters had built hills of their dead shells over thousands of generations, were being dredged out. Surplus oyster shells had many uses then. They were ground into mortar, used as filler in roads, and as a source of lime in agricultural fertilizer. By the 1920s, harvests would be down to just 3–5 million bushels per year because of overharvesting.
Overharvesting eventually depleted the remaining oyster population in the bay to just 1% of its historical level, where it stands today. Oyster harvests began to decline in the 1890s. They were being taken much faster than they could reproduce. Also, many of the shells and reefs were being taken and not being replaced. Oyster spat need a hard surface on which to attach, and these were vanishing because of the destruction of oyster reefs. By the 1920s, harvests were down to 3–5 million bushels per year,[25] stabilized for a time by returning oyster shells back to the bay. But in the 1950s, the weakened oyster population had to deal with the diseases "dermo" and MSX. These decimated the remaining oyster population. The parasites which carried the disease are alien to eastern waters, and they were thought to have been brought to the Chesapeake by Asian oysters. Currently, oyster harvests average less than 200,000 bushels a year.
The eastern oyster used to be of great commercial value. Due to the steep decline in the number of oysters in various traditionally harvested areas, primarily because of overfishing and diseases,[26] the annual catch has declined significantly. In Maryland, the 2006–2007 catch was 165,059 bushels (about 7600 m³) of oysters.[27] Other regions of the East Coast of the United States have successful oyster farms, including most notably Cotuit , Martha's Vineyard and Wellfleet, Massachusetts, on Cape Cod.
Harvestable size of a C. virginica oyster is 75 mm (3.0 in), which can take from 12 to 36 months, depending on temperature, salinity of the water, and food supply.[18] Salinity is a very important climatological variable that affects spatfall. Oysters do best where salinities range from 10 to 30 ppt; the range of 15 to 18 ppt is considered optimal.[18] Typically, when salinity levels are less than 6 ppt, larvae will not settle and metamorphose into spat.[28] In 2010, 665 miles of coastline were affected by the Deepwater Horizon oil spill.[29] To keep the oil at bay and to spare the oystermen, the authorities of Louisiana made an unprecedented decision to maximize the fresh water flow through the region's canals to three times usual levels.[21] At the mouth of the canals, salinity fell to almost zero, which was probably why most of the oysters died.[21] Sujata Gupta ventured into the marshlands and Gulf of Mexico with Brad Robin, a man from a line of generations of oystermen in southeastern Louisiana. Robin and his crew threw a net over the side to haul in a catch.[21] There were dozens of palm-sized oysters, but 75% of them were "boxes" or empty shells.[21] However, as they traveled further towards the Gulf of Mexico, where the water was less salinity-stressed by the flush, only 20% of the haul came back as boxes, a promising sign the oysters are trying to come back.[21] Gupta reported, "Now since there are so many empty shells scattered on the sea floor, the larvae have more to latch onto, improving their odds".[21] However, salinity levels are not the only concern. Eastern oysters are filter feeders, so they are greatly affected by their surroundings since they are sessile organisms. This means if the water around them was contaminated with oil and the dispersant used to get rid of the oil, then these chemicals were collected by the oysters as they filtered the water.[30] This is cause for great concern that the oysters are being killed by the toxins in the dispersant, as well.[30] An added dilemma is oysters are in their weakest state after spawning season, which may have caused some of them to close their shells, resulting in death by suffocation within just a few days due to warm temperatures in the Gulf if the shells remain closed.[30] The toxins in the oil and dispersants can also kill the larvae.[30] To highlight the recovery of the state's oyster industry, the shell of C. virginica cut into cabochons was made Louisiana's official state gem in 2011.[31][32]
"Dermo" (Perkinsus marinus) is a marine disease of oysters, caused by a protozoan parasite. It is a prevalent pathogen of oysters, causing massive mortality in oyster populations, and poses a significant economic threat to the oyster industry.
Multinucleated sphere X (MSX) (Haplosporidium nelsoni), another protozoan, was first described along the mid-Atlantic coast in 1957.[33] Mortalities can reach 90% to 95% of the oyster population within 2 to 3 years of being seeded.[34] MSX slows the feeding rates of infected oysters, leading to a reduction in the amount of stored carbohydrates, which in turn inhibits normal gametogenesis during spawning, resulting in reduced fecundity.
The eastern oyster is the state shellfish of Connecticut,[35] its shell is the state shell of Virginia and Mississippi, and its shell in cabochon form is the state gem of Louisiana.[31]
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 Wellfleet oyster, Virginia oyster, Malpeque oyster, Blue Point oyster, Chesapeake Bay oyster, and Apalachicola oyster. C. virginica ranges from northern New Brunswick south through parts of the West Indies to Venezuela.: 7 It is farmed in all of the Maritime provinces of Canada and all Eastern Seaboard and Gulf states of the United States, as well as Puget Sound, Washington, where it is known as the Totten Inlet Virginica. It was introduced to the Hawaiian Islands in the nineteenth century and is common in Pearl Harbor.
The eastern oyster is an important commercial species. Its distribution has been affected by habitat change; less than 1% of the population present when the first European colonists arrived is thought to remain in the Chesapeake Bay and its tributaries. As of 2014, the global conservation status of Crassostrea virginica, as assessed by NatureServe, is "vulnerable," as the oyster's populations are threatened by overharvest and water pollution. Other threats to the eastern oyster include global warming, diseases and parasites and competition with invasive species.
El ostión de Virginia (Crassostrea virginica) pertenece a la clase Bivalvia de moluscos. Viven exclusivamente en medio acuático, con una forma corporal de simetría bilateral, comprimida lateralmente y una concha de dos valvas (bivalva) que, en general, es bastante grande para admitir al animal completo.
El sistema circulatorio está formado por un corazón con dos aurículas. El sistema nervioso carece de particularidad alguna (ganglionar). La respiración es branquial. La cabeza es reducida hasta la parte branquial, faltando la región faríngea y la rádula. En general se alimentan filtrando agua. Los bivalvos son animales predominantemente de sexos separados, rara vez hermafroditas. La fecundación tiene lugar de manera libre en el agua o bien en la cavidad del manto.[1]
C. virginica es un molusco que pertenece a la clase Bivalvia; orden Ostreoidea; familia Ostreidae.[2] Sus características son: concha de tamaño grande, hasta 150 mm de largo, de forma irregular, muy variable, desde orbicular hasta francamente alargada; moderadamente gruesa; superficie rugosa con escamas; márgenes de las valvas rectos y ondulados. Umbo largo y curvado; valva derecha más pequeña y aplanada que la izquierda. Concha cementada al sustrato por un biso calcificado. Valva izquierda un poco mayor que la derecha, la impresión muscular subcentral, púrpura obscuro. Interior liso y carente de sifones.[1]
Este organismo se puede encontrar desde el golfo de San Lorenzo, el golfo de México, hasta Las Antillas.[3]
Es un molusco comestible. Esta especie se puede encontrar aguas someras. También es un molusco muy abundante en su lugar nativo y puede encontrarse en cualquier superficie dura, esto puede llevar a una sobrepoblación. Son tolerantes a bajas salinidades.[4]
El ostión de Virginia (Crassostrea virginica) pertenece a la clase Bivalvia de moluscos. Viven exclusivamente en medio acuático, con una forma corporal de simetría bilateral, comprimida lateralmente y una concha de dos valvas (bivalva) que, en general, es bastante grande para admitir al animal completo.
El sistema circulatorio está formado por un corazón con dos aurículas. El sistema nervioso carece de particularidad alguna (ganglionar). La respiración es branquial. La cabeza es reducida hasta la parte branquial, faltando la región faríngea y la rádula. En general se alimentan filtrando agua. Los bivalvos son animales predominantemente de sexos separados, rara vez hermafroditas. La fecundación tiene lugar de manera libre en el agua o bien en la cavidad del manto.
Crassostrea virginica (Gmelin, 1791) est le nom scientifique de l'huître américaine, aussi appelée huître de Virginie, ou encore huître creuse de Virginie ; elle est parfois commercialisée sous le nom de son lieu de provenance comme Malpèque, Caraquet, Blue Point, Pine Island, Pugwash.
C'est une espèce indigène américaine, présente sur la façade atlantique ; sa culture est possible.
L'huître américaine est présente sur toute la côte est de l'Amérique du Nord, du Golfe du Mexique jusqu'au Golfe du Saint-Laurent. Pour la croissance et la reproduction, l'huître américaine tolère une échelle de température allant de −2 °C à 32 °C. Elle peut facilement hiberner sous la glace, cessant de s'alimenter en dessous de 4 °C. Par conséquent, au Canada, la période de croissance s'étend de mai à novembre et il faut de 4 à 7 ans pour obtenir une huître de taille commerciale[1]. La plupart des zones de peuplement naturel n'ont pas une marée très forte, les huîtres sont recouvertes d'eau en permanence et vivent en haut de la zone infratidale.
On pêche actuellement environ 109 000 tonnes de Crassostrea virginica par an aux États-Unis, et environ 2 400 tonnes au Canada[2].
Plusieurs études suggèrent que le peuplement actuel de Crassostrea virginica n'est plus qu'une fraction du peuplement initial, à l'arrivée des colons au XVIIe siècle, en particulier dans la Baie de Chesapeake[3], en Virginie.
Au Canada, l'élevage de l'huître américaine est pratiqué principalement à l'Île-du-Prince-Édouard, au Nouveau-Brunswick et en Nouvelle-Écosse. Aux États-Unis, l'huître américaine est cultivée depuis 1810 au New Jersey, et les fermes actuelles sont surtout situées au Massachusetts (Cotuit et Wellfleet). La production canadienne est proche de 7 000 tonnes[4],[5], et la production américaine approche 4 000 tonnes[2].
Il faut noter que la capture du naissain dans le milieu naturel est la règle. Les élevages se font le plus souvent en poches flottantes, dans des baies peu profondes. Au Canada, les poches sont déplacées avant l'hiver de manière que les huîtres hivernent sous la glace.
Crassostrea virginica (Gmelin, 1791) est le nom scientifique de l'huître américaine, aussi appelée huître de Virginie, ou encore huître creuse de Virginie ; elle est parfois commercialisée sous le nom de son lieu de provenance comme Malpèque, Caraquet, Blue Point, Pine Island, Pugwash.
C'est une espèce indigène américaine, présente sur la façade atlantique ; sa culture est possible.
Ameríkuostran (fræðiheiti: Crassostrea virginica), einnig kölluð austurostra eða virginíuostra, er tegund ostru af diskaætt. Hún er eingöngu veidd á austurströnd Norður-Ameríku, frá Lawrence-flóa í Kanada niður að Júkatanskaga í Mexíkóflóa. Þegar ostruveiðar hófust fyrst voru þær ekki eingöngu veiddar til átu, heldur einnig til vegagerðar. Ameríkuostran er ríkisskelfiskur bandarísku fylkjanna Connecticut, Virginíu og Missisippi. Ameríkuostrur eru meðal þekktustu, verðmætustu og mikilvægustu nytjalindýra.
Ameríkuostran er af fylkingu samloka, sem þýðir að hún hefur tvö lok eða skeljar. Þykka, lægri lokið festir sig við hart undirlag og er mótað öðruvísi en efra lokið, sem almennt er minna og flatara. Lömin sem tengir lokin og heldur ostrunni fast lokaðri er teygjanlegur púði sem haldið er saman af þykkum, sterkum vöðvum. Ameríkuostrur geta verið uppistaðan af harða botninum við strendur.
Erfitt er að meta stofnstærð Ameríkuostrunnar. Líklegt er að svæði geti haft mismunandi tegundir eða undirhópa ostra með takmarkaða stofnblöndun. Ameríkuostran er mikið ræktuð og eru menn því ekki hræddir við stofnhrun þó svo unnið sé að endurreisn á sumum villtum svæðum.
Ameríkuostrur geta orðið allt að 20 ára. Þær lifa margar saman í einskonar klösum; smærri ostrur geta verið um 1500 talsins á hvern fermetra, stærri ostrur sem löglega má veiða geta verið allt að 336 saman í klasa á fermetra. Þær finnast við strendur og rif. Ráðist er á ostrurnar á ýmsum stigum lífsferils þeirra meðal annars af kuðungum, krossfiskum, fiskum, kröbbum, flatormum, tjaldinum og moldarormum.
Ameríkuostrur sía strendur og spila því mikilvægan þátt í að fjarlægja bakteríur, málma og eiturefni úr sjónum. Þær hafa mest saltþol allra ostrutegunda. Kjörselta ameríkuostrunnar til vaxtar er 10-28 ppm. Þær geta lifað við allt að 35 ppm.
Ameríkuostran hrygnir frá júní og fram í nóvember og nær hámarki á sumrin í júní og júlí þegar hiti er mestur. Norðurostran hrygnir við 15°-20°C en suðurostran hrygnir við 20°C og yfir.
Hrygnur geta framleitt um og yfir 100 milljón egg á ári. Kynþroska ostrur losa egg og sæði út í vatnið. Á um 24 tímum umbreytist eggið í frjálsa lirfu eða svif. Að hrygningu lokinni er ostran mjó sökum þess að hún hefur klárað allan forða sinn. Við kulda stækka kynþroska ostrur betur.
Á um tveggja til þriggja vikna tímabili vex ostrulirfunni augu og einhverskonar löpp sem hún notar til þess að finna sér samastað. Þegar hún hefur fundið ákjósanlegan stað, helst einhvern með hart og hrjúft yfirborð, sprautar hún út efni sem virkar líkt og steypa og festir sig. Margar ostrur breyta um kyn á lífsferli sínum, flestar ostrur undir eins árs aldri eru karlkyns og flestar yfir eins árs aldri eru kvenkyns.
Ytri skel ameríkuostrunnar er gráhvít; sú innri er hvít með dökkfjólublárri eða rauðbrúnni vöðvarák. Hún verður 8 til 13 sentímetrar að lengd, en getur þó orðið allt að 20 sentímetrar. Hún er samsett af tveimur hrjúfum skeljum. Innvols ostrunnar er mjúkt og hefur að geyma kjöt hennar. Neðri skel ostrunnar er kúpt og inní henni er kjötið eða vöðvinn, með áðurnefndri fjólublárri rák. Efri skelin er slétt eða flöt.
Við fæðuöflun slaka vöðvar ostrunnar á sem veldur því að skelin opnast og dregur í sig vatn fullt af svifi í gegnum tálkn. Skelin lokast svo og er ostran full af sjó, sem gerir henni kleift að lifa í langan tíma á yfirborði við kaldar og þurrar aðstæður. Hún nærist því á svifi.
Bandaríkin eru langmesta veiðiþjóðin. Frá því mælingar hófust árið 1950 og fram að lokum 5. áratugs 20. aldar var afli BNA á norðvesturströnd, líkt og sjá má á mynd 1, um og yfir 225.000 tonn en í lok 1950 hrundi stofninn um 100.000 tonn. Ástæður hrunsins má rekja til sýkingar af völdum svokallaðs MSX-sjúkdóms. Stofninn hélt sér nokkuð stöðugum frá 1960-70 í um og yfir 100.000 tonnum. Hann náði svo miklu flugi 1970 og var afli í kringum 150.000-175.000 tonn til 1983 þegar hann féll aftur og enn harðar niður í 50.000 tonn. Stofninn hefur síðan þá verið í mikilli lægð og náði afli lágmarki árið 2004 í 8.878 tonnum. Hann hefur þó verið að taka við sér á 21. öldinni og var kominn í 48.656 tonn árið 2015. Einnig stunda Kanada á norðvesturströndinni veiðar. Þær eru þó mjög litlar og hefur aflinn alltaf verið undir 10.000 tonnum og hefur verið mjög stöðugur á 21. öld í um 5.000 tonnum.
Á miðvesturströndinni er hins vegar annað uppi á könnunni. Þar, líkt og sést á mynd 2, hefur afli aukist jafnt og þétt frá upphafi mælinga. Árið 1950 er aflinn um 75.000 tonn og hefur verið nokkuð stöðugur síðustu ár í um og yfir 150.000 tonnum. Mexíkó veiðir einnig ostru á miðvesturströndinni. Þeirra afli er talsvert minni en Bandaríkjamanna. Frá upphafi veiða þeirra árið 1953 var aflinn 10.000 tonn og hefur hann verið stöðugur en vaxið þétt og náðu þeir 50.044 tonnum árið 2015.
Heildarafli ameríkuostrunnar er um 10.000 tonn af kjöti á ári. Ameríkuostran telur um 70% af öllum ostruafla á jörðinni og er tegundin því bersýnilega mikilvæg. Afli hefur minnkað mikið frá því fyrir 40 árum síðan og spilar ofveiði þar mikið inn í. Eftirspurn eftir ostrum hefur einnig minnkað mjög og má álykta að það sé annars vegar vegna aukinnar meðvitundar um hættur þess að borða hráar ostrur og hins vegar breyttar matarvenjur manna.
Stofninn frá 1950-1980 var ríflegur fyrir norðan en hefur ekki verið góður síðustu 40 ár. Á sumum svæðum virðist staða hans vera stöðug eða vaxandi, líkt og á miðvesturströnd Ameríku. Veiðistjórnendur hafa tekið að sér endurreisnaraðgerðir á mörgum svæðum. Vegna þess að ostrur eru neyddar hráar er verið að auka við reglugerðir til verndar neytendanna. Ostrur eru mikið ræktaðar og er því auðvelt að endurreisa stofninn.
Stofninn stendur nokkuð stöðugur og virðist vera að styrkjast. Veiðum er stjórnað og samkvæmt töflu 1 benda kannanir eindregið til þess að nýliðun sé nægjanleg til að viðhalda sjálfbærni stofnsins.
Margar hættur eru á stofnhruni þrátt fyrir mikla ræktun á tegundinni; Ameríkuostran hefur orðið fyrir miklum sýkingum, olíuleka og mörgu fleiru. Helstu sýkingar og í kjölfarið stofnhrun eru eftirfarandi; MSX-sjúkdómurinn herjaði á stofninn á 7. og 8. áratugnum og varð hann fyrir niðurbroti á 9. áratugnum sökum Perkinsósis.
Ostrur eru berskjaldaðar fyrir sýkingu frá sníkjudýrum sem herja á samlokur. Ameríkuostran getur orðið fyrir sjúkdómum á borð við MSX-sjúkdómnum, SSO-sjúkdómnum, Perkinsósis og Dvergkornadreyri.
Sjúkdómar þessir geta verið lífshættulegir fyrir menn, einkenni koma oftast fram innan 24 til 48 klukkustunda frá átu og eru dæmi um einkenni; skyndilegur kuldahrollur, hiti, ógleði, uppköst, niðurgangur, lost og húðskemmdir.
Árin 1959-60 varð stór MSX faraldur í Chesapeak flóa sem olli því að höggvið var stórt skarð í hluta stofnsins. Margir einkaræktendur töpuðu stórfenglega á þessum faraldi. MSX-sníkjudýrið er það skæðasta sem verkar á ostrur. Vísindamenn hafa lengi vel átt mjög erfitt með að skilja og greina sjúkdóminn. Eitt hafa vísindamenn þó fundið út þ.e að sjúkdómurinn kemur einungis upp við seltu ofan 15 ppm.
Ameríkuostran er mest seld á innanlandsmarkaði vestanhafs. Hún er seld til heildsala, hótela, veitingastaða, sjávarmarkaða og hinna og þessa stofnana. Frakkland og Evrópa er einnig ágætur markaður og er Ameríkuostran mikið seld á dýra og fína veitingastaði þangað.
Ameríkuostran (fræðiheiti: Crassostrea virginica), einnig kölluð austurostra eða virginíuostra, er tegund ostru af diskaætt. Hún er eingöngu veidd á austurströnd Norður-Ameríku, frá Lawrence-flóa í Kanada niður að Júkatanskaga í Mexíkóflóa. Þegar ostruveiðar hófust fyrst voru þær ekki eingöngu veiddar til átu, heldur einnig til vegagerðar. Ameríkuostran er ríkisskelfiskur bandarísku fylkjanna Connecticut, Virginíu og Missisippi. Ameríkuostrur eru meðal þekktustu, verðmætustu og mikilvægustu nytjalindýra.
Crassostrea virginica is een tweekleppigensoort uit de familie van de Ostreidae.[1] De wetenschappelijke naam van de soort is voor het eerst geldig gepubliceerd in 1791 door Gmelin.
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Multimedia w Wikimedia Commons Ostryżyca amerykańska (Crassostrea virginica) – gatunek osiadłego małża nitkoskrzelnego z rodziny ostrygowatych (Ostreidae), wraz z ostrygą jadalną i ostryżycą japońską zaliczany do najcenniejszych mięczaków jadalnych. W tłumaczeniu z języka angielskiego określana jest nazwami ostryga atlantycka lub ostryga wirginijska. Jej muszla osiąga przeciętnie 8–18 cm, maksymalnie do 25 cm[4].
Występuje w północno-zachodniej części Oceanu Atlantyckiego, wzdłuż wybrzeży Ameryki Północnej po Zatokę Meksykańską. Przed 1939 sprowadzono ją na Wyspy Brytyjskie. Spotykana jest też w Morzu Adriatyckim[4]. Jest hodowana i poławiana na dużą skalę, przede wszystkim w Atlantyku[2]. W 1999 roku złowiono 132 207 t tego gatunku. Największy udział w połowach miały Stany Zjednoczone i Meksyk. W wyniku przełowienia i zanieczyszczenia wód liczebność populacji tej ostryżycy spada[4].
Ostryżyca amerykańska (Crassostrea virginica) – gatunek osiadłego małża nitkoskrzelnego z rodziny ostrygowatych (Ostreidae), wraz z ostrygą jadalną i ostryżycą japońską zaliczany do najcenniejszych mięczaków jadalnych. W tłumaczeniu z języka angielskiego określana jest nazwami ostryga atlantycka lub ostryga wirginijska. Jej muszla osiąga przeciętnie 8–18 cm, maksymalnie do 25 cm.
Występuje w północno-zachodniej części Oceanu Atlantyckiego, wzdłuż wybrzeży Ameryki Północnej po Zatokę Meksykańską. Przed 1939 sprowadzono ją na Wyspy Brytyjskie. Spotykana jest też w Morzu Adriatyckim. Jest hodowana i poławiana na dużą skalę, przede wszystkim w Atlantyku. W 1999 roku złowiono 132 207 t tego gatunku. Największy udział w połowach miały Stany Zjednoczone i Meksyk. W wyniku przełowienia i zanieczyszczenia wód liczebność populacji tej ostryżycy spada.
Crassostrea virginica ou ostra-americana, é uma ostra comestível da costa ocidental do oceano Atlântico, comum na costa brasileira, onde também é conhecida pelos nomes de gueriri, leriaçu e ostra-da-virgínia. A concha alongada, irregular, com a valva inferior côncava e a superior alta, atinge um comprimento de 20 cm. [1]
Crassostrea virginica ou ostra-americana, é uma ostra comestível da costa ocidental do oceano Atlântico, comum na costa brasileira, onde também é conhecida pelos nomes de gueriri, leriaçu e ostra-da-virgínia. A concha alongada, irregular, com a valva inferior côncava e a superior alta, atinge um comprimento de 20 cm.
Hàu Mỹ (Danh pháp khoa học: Crassostrea virginica) là một loài hàu trong họ Ostreidae phân bố ở Mỹ. Đây là một loại hàu có giá trị kinh tế và được nuôi nhiều ở Mỹ.
Hàng triệu con hàu đang được nuôi tại các vùng biển ở New York và các thành phố khác nhằm làm sạch môi trường nước bị ô nhiễm. Con hàu và các loài thủy sản có vỏ khác có thể làm sạch các chất độc và bụi bẩn. Việc khôi phục số lượng loài hàu tại sông Hudson gần Yonkers, bắc New York vì loài hàu giúp cải thiện môi trường sống thủy sinh, có tác dụng thu hút các loài thủy sản và sinh vật biển khác vào khu vực chúng sống. Các con hàu này chỉ nên sử dụng để làm sạch ô nhiễm, không nên ăn hay thu hoạch để bán. Một mẫu (0,4 ha mặt nước nuôi trồng) với 1 triệu con hàu cần khoản chi phí ít nhất là 50.000 USD. Mỗi con hàu có khả năng lọc khoảng 189,26 lít nước bẩn mỗi ngày[1].
Hiện nay Mỹ nhập khẩu hầu hết các sản phẩm hàu nuôi, khai thác, hun khói và các loại khác cùng tăng trưởng từ 16 - 123%, riêng sản phẩm hàu hun khói được Mỹ nhập khẩu nhiều nhất và chiếm đến 46,3% tổng giá trị, trong khi sản phẩm hàu khai thác chỉ chiếm chưa đến 2% thị phần. Xuất khẩu hàu của Mỹ cũng tăng trưởng nhẹ 1% về khối lượng và 6% về giá trị so với cùng kỳ năm trước, mặt hàng hàu tươi sống chiếm tỷ trọng cao nhất trên 70% tổng xuất khẩu mặt hàng này của Mỹ với khối lượng 1.820 tấn và giá trị 13,3 triệu USD, trong khi sản phẩm hàu đông lạnh và các loại khác của Mỹ lại xuất chủ yếu sang Hồng Kông[2].
Trước đây Trung Quốc đã từng nhập khẩu khoảng 4.140 con Hàu các loại từ bang Washington Mỹ, nay Trung Quốc dừng nhập khẩu Hàu biển từ Mỹ do nhiễm khuẩn, việc nuôi dưỡng và sản xuất Hàu ở khu vực eo biển Hood bị nhiễm vi khuẩn Vibrio parahaemolyticus do ô nhiễm. Đồng thời một số lượng nhỏ loại thực phẩm này đã được phía Mỹ tiến hành xuất khẩu sang các nước như Trung Quốc, Thái lan và Indonexia. Trung Quốc đã nhập khẩu khoảng 4.140 con Hàu nhiễm bệnh. Hiện nay trên thị trường hải sản tươi sống tại thành phố Bắc Kinh không còn phát hiện thấy việc kinh doanh Hàu nhiễm bệnh có nguồn gốc từ Mỹ[3].
Loại hàu mang tên Cape Neddick/Blue Point Oysters được khách hàng ưa thích dùng ăn sống vừa bị thu hồi tại Mỹ do nghi nhiễm vi khuẩn Vibrio parahaemolyticus. Loại khuẩn này dễ gây bệnh cho những người có hệ miễn dịch yếu, triệu chứng nhiễm khuẩn bao gồm tiêu chảy, buồn nôn, nôn, sốt và ớn lạnh. Thông thường các triệu chứng xảy ra trong vòng 24 giờ, kéo dài ba ngày.
Hàu Mỹ (Danh pháp khoa học: Crassostrea virginica) là một loài hàu trong họ Ostreidae phân bố ở Mỹ. Đây là một loại hàu có giá trị kinh tế và được nuôi nhiều ở Mỹ.
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