We eat 2 billion pounds of oysters every year – East Coast or West Coast. Briny or sweet. There are over 100 kinds of oysters and at the moment is the day to rejoice in them.
What is an Oyster?
Oyster is the common name for a number of different families of salt-water bivalve mollusks that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape.
Some types of oysters are commonly consumed (cooked or raw), and in some locales are regarded as a delicacy. Some types of pearl oysters are harvested for the pearl produced within the mantle. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects.
Different Types of Oyster?
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 European flat oyster, eastern oyster, Olympia oyster, Pacific oyster, and the Sydney rock oyster. Ostreidae evolved in the Early Triassic epoch: The genus Liostrea grew on the shells of living ammonoids.
Pearl oysters
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 mollusks, such as freshwater mussels, also yield pearls of commercial value.
Almost all shell-bearing mollusks can secrete pearls, yet most are not very valuable. Pearls can form in both saltwater and freshwater environments.
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Pearl farmers can culture a pearl by placing a nucleus, usually a piece of a 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.
Thorny oysters
Thorny oyster is a genus of bivalve mollusks, the only genus in the family Spondylidae. They are known in English as spiny oysters (though they are not, in fact, true oysters).
Anomiidae
Anomiidae is a family of saltwater clams, marine bivalve mollusks related to scallops, and oysters, and is known as anomiids. It contains seven genera.
The family is known by several common names, including jingle shells, mermaid’s toenails, and saddle oysters.
Dimyidae
Dimyidae is a family of extremely flattened, small (<1 cm), pleurothetic, relatively rare marine bivalve mollusks in the order Pectinida inhabiting the deeper regions of continental shelves from the Caribbean to Japan. They are sometimes called dimyarian oysters. Unlike other ostreoids, the dimyarian oysters attach themselves to a substrate via their right (rather than left) valves. They are related to scallops and other oysters.
Windowpane oyster
The windowpane oyster (Placuna placenta) is a bivalve marine mollusk in the family of Placunidae. They are edible but valued more for their shells (and the rather small pearls). The shells have been used for thousands of years as a glass substitute because of their durability and translucence.
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 protozoan 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. 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.
MSX
- Multinucleated sphere X (MSX) is caused by the protozoan Haplosporidium nelsoni, generally seen as a multinucleated Plasmodium. It is infectious and causes heavy mortality in the eastern oyster; survivors, however, develop resistance and can help propagate resistant populations. MSX is associated with high salinity and water temperatures. MSX was first noted in Delaware Bay in 1957 and is now found all up and down the East Coast of the United States. Evidence suggests it was brought to the US when Crassostrea Gigas, a Pacific oyster variety, was introduced to Delaware Bay.
- Denman Island disease causes visible yellow/green pustules on the body and adductor muscles of oysters. This disease mainly affects Pacific oysters (Crassostrea Gigas). The disease was first described in 1960 near Denman Island off the eastern aspect of Vancouver Island, British Columbia. It was found that the causative agent of these lesions is associated with amitochondriate protistan microcells, which were later identified as Mikrocytos mackini.
Some oysters also harbor bacterial species which can cause human disease; of importance is Vibrio vulnificus, 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.
