This sought-after two-shelled mollusc is now farmed to ensure quality and supply.
NATIVE OYSTERS, which are Northern European in origin, have lacy, slightly ridged, silvery-grey round shells.
AMERICAN OYSTERS are longer, thinner and larger than natives and often have small barnacles on their shell.
ROCK OR PACIFIC OYSTERS, which look similar to American oysters, are now widely cultivated in Europe.
Pearl oysters are also edible, but they aren't considered to be true 'oysters'.
IN THE KITCHEN
Oysters are sold live and in their shells, which should be firmly shut or shut tight when touched, and the whole oyster should feel heavy for its size. The old saying that they should be eaten only when there is an 'R' in the month isn't really applicable now as they are farmed, but natives at least are best during the autumn and winter months.
Oysters should be opened just before being served. The most common way of serving them is raw on the half-shell.
DID YOU KNOW?
Oysters have a reputation as an aphrodisiac, which may be due to their being a rich source of zinc, a mineral needed in reproduction.