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European Flat Oyster

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Species group:

Other common names: Bélon oyster; Mud Oyster; Colchester Native Oyster; Edible Oyster

Scientific name: Ostrea edulis

The basics:
Ostrea edulis is Europe's native oyster and is a species of bivalve mollusc found either in marine or brackish waters. It is found along the western and southern coasts of Europe, ranging from Norway south to Morocco. It was the Romans, who pioneered oyster farming (mariculture) along with that of many other marine species during the 1st century BCE. They brought these techniques to Britain, where the estuarine conditions from Colchester down to the Thames estuary were found particularly suitable for large-scale production. Mariculture of oysters continued in Britain and France through the middle ages and reached a peak in the 1800s, where oysters were cheaper to buy than many mushrooms. However, over-fishing hand over-stocking led to disease and decline of the native oyster and it is only now that stocks and oyster beds are recovering again. Today, the European flat oyster is farmed in Britain, France, and in the states of California, Maine, and Washington in the United States.

Oysters are a surprisingly complex animal, with a heart, circulatory system and kidneys. Although the European oyster technically has two sexes, their reproductive organs contain both eggs and sperm. As a result it is technically possible for European oysters to self-fertilize. European flat oysters require five years to mature, which can make establishing new mariculture beds expensive due to the lag. However, they do command a premium and are considered superior in taste to other oyster species.
Oysters are essentially sedentary filter-feeders, so activity levels are low. At the microscopic level they present some fascinating behaviours and they are surprisingly social animals but you will not notice this. Unlike other shellfish, they can be reared completely indoors from spawning to maturity. However, housing is expensive and they are not really suitable for the hobbyist.

Appearance:
The two hinged shell halves of the oyster are the 'valves' and these are held together by a ligament on the convex side. The shell is then closed by a strong internal muscle. The shells protect the soft bodies of the oysters within from predation and from desiccation when they are exposed by the tide. The shell is essentially hemispherical in shape, with a convex long edge and a small rounded projection at the base. The animal grows outwards from the base and the growth is visible as a series of concentric, shelved, rings on the shells. The top shell is curved and the bottom shell is flat. Shells vary in colour from muddy brown to pearl. The inner surface is white or cream, being a prismatic calcitic layer.

Size:
6—9cm (when harvested)

Temperament:

Housing:
When farmed, oyster are typically grown in tidal bays with brackish water where plankton levels are high. Although they can be farmed, they are not suitable as pets as they require either strong water currents or need to be exposed by tidal flows twice a day. It is these tidal flows that bring them the microplankton and food particles they live on. There are three main methods of farming oysters. For both, oysters are cultivated to the size of a 'spat' before being grown on in the bay beds. Oysters can be allowed to spawn naturally, or they can be spawned indoors in 'hatcheries'. If harvested from the wild, oyster 'spat' is usually removed from seaweed, or they are removed from longlines of oyster shells introduced into oyster beds.

1. Natural Method: For this method the spat or seed oyster is distributed over existing oyster beds and are allowed to attach to the beds naturally before growing.

2. Caging Method: This method typically uses seed oysters. They are either placed in racks, bags, or cages or by gluing them in groups of threes into ropes. These are then lowered into the water and allowed to grow naturally. The advantage of this method is that the ropes or cages can be raised at low tide and only the mature oysters need be removed.

3. Artificial Housing: In this method, the spat or seed oyster are placed on an artificial substrate that's set within an artificial maturation tank. The tank is then fed with brackish water that has been specially enriched with medium that's designed to maximize the oyster's growth. This includes the carbonate minerals calcite and aragonite that help the shells develop faster than they would in the wild.

Being sedentary, oysters are prone to local environmental conditions. Algal blooms or toxins in the water can kill them. They are also susceptible to some viral diseases. In wild conditions natural predation is the largest problem, however.

Temperature:
0.00-0.00 °F

pH:
0.00-0.00

Alkalinity:
0.000-0.000 mg/L

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