What is an Oyster?

The name oyster is used for a number of different groups of mollusks which grow for the most part in marine or brackish water. The shell, usually highly calcified, surrounds a soft body and strong adductor muscles are used to hold the shell closed. Some of these groups are highly prized as food, both raw and cooked.


Physical characteristics

Oysters are filter-feeders that draw water in over their gills. Suspended food plankton and particles are trapped in the gills and transported to the mouth, where they are eaten. Feeding activity is greatest in oysters when water temperatures are above 50°F (10°C). Healthy oysters consume algae and other water-borne nutrients, each one filtering up to five litres of water per hour.

Oysters breathe much like fish, using both gills and mantle. The mantle is lined with many small, thin-walled blood vessels which extract oxygen from the water and expel carbon dioxide. A small, three-chambered heart, lying under the abductor muscle, pumps colorless blood, with its supply of oxygen, to all parts of the body. At the same time two kidneys located on the underside of the muscle purify the blood of any waste products they have collected.

There is no way of determining male oysters from females by examining their shells. While oysters have separate sexes, they may change sex one or more times during their life span. The gonads, organs responsible for producing both eggs and sperm, surround the digestive organs and are made up of sex cells, branching tubules and connective tissue.

Oysters usually mature by one year of age. They are protandric, which means that during their first year they spawn as males (releasing sperm into the water). As they grow larger over the next two or three years and develop greater energy reserves, they release eggs, as females. Bay oysters are usually prepared to spawn by the end of June. An increase in water temperature prompts a few initial oysters to spawn. This triggers a spawning 'chain reaction', which clouds the water with millions of eggs and sperm. A single female oyster can produce up to 100 million eggs annually. The eggs become fertilized in the water and develop into larvae, which eventually find suitable sites on which to settle, such as another oyster's shell. Attached oyster larvae are called 'spat'. Spat are oysters 25 mm or less in length.

Some oysters in the tropics grow on mangrove roots and are exposed at low tide making them easy to collect. Tourists are often astounded when they are told that "oysters grow on trees."

Reference: Wikipedia.com, the free online encyclopedia.

Now, what we are interested in is the Culinary Oyster (food), more about this on my next post.