These primitive bivalves are found in most marine and brackish water systems of the Northern hemisphere although this particular genus (the European oysters) are naturally found from Norway to France, Denmark, Germany, Netherlands, Belgium, Great Britain, and Ireland. They are commonly found in the Adriatic and Black Sea.

HABITS:

Oysters non-selectively settle on hard substrates and form beds in area of flowing water. All too often they settle in areas with inadequate food, but cannot relocate once attached. They are sessile filter-feeders.

SPAWNING:

Oysters are sequential hermaphrodites and are considered semi-broadcast spawners. When water temperatures are high enough, male release sperm into the water column. The gametes then enter the female where she retains the fertilized eggs in her pallial cavity until hatching. With some species, as long as the water temperature remains above a minimum spawning will continues. Year round spawning occurs in some of the tropical areas. Free-swimming larvae hatch hours to weeks after fertilization before they metamorphose and settle on a hard surface. Gametogenesis occurs around 10C in some species and spawning comences at 14 to 16C.

GROWTH:

Growth of the oyster is directly linked to the abundance of phytoplankton and zooplankton in the water, temperature, and salinity. Generally in culture situations, the oldest oysters are removed from the bed to allow fast growth of younger individuals. They are primarily grown in natural beds and culture racks.

USES:

These organisms serve two purposes in the commercial industry. First of all they are sold on the half shell in the raw oyster market, smoked and canned, or sold fresh for other purposes. Although this genera is not preferred, they can be used to produce pearls.

CULTURE:

The flat oyster (O. edulis) is the most popular culture specie of the genus, and is actively cultured in both Europe and Maine. Young oysters of spat are grown on mesh nursery trays until they obtain a length of 10-25mm. Grow-out is performed in off-bottom trays or mats suspended from rafts. This practice is costly, but oysters are a profitable species thus justifying the expense.

REFERENCES:

Avault, J.W. 1996. Fundamentals of Aquaculture. AVA Publising Company Inc., Baton Rouge, Lousiana.

Barnes, R.S.K, P. Calow, and P.J.W. Olive. 1988. The Invertebrates a new synthesis. Blqackwell Science Ltd. Cambridge, MA.

Bardach, J.E, J. H. Ryther, and W.O. McLarney. 1972. Aquaculture The farming and husbandry of freshwater and marine organisms. John Wiley and Sons, New York.