Oysters and Man: Oysters have been farmed for thousands of years – mounds of discarded oyster, scallop, and mussel shells have been found during archaeological digs of ancient Rome. The Romans imported North Sea oysters and were the first to create artificial oyster beds to satisfy the demand.

Breeding: The oyster has both male and female reproductive organs and undergoes a constant cycle of sex change. It may spawn (breed) as either a male or a female, depending on the salt content and temperature of the water. The eggs, which look like a milky white cloud, are normally released on an ebbing tide. An oyster sheds an average of 1 million eggs, on which small fish feed. The fertilized eggs float 7-18 days before settling, if they survive being eaten by prey.

In spite of its minute size, each larva has a tiny shell complete with muscles and a foot. Once its swimming stage is over, the larva extends its foot, settles on any solid object it can find, and cements itself in place. At this stage, it is known as an oyster spat. Once they are anchored in place, oyster spat begin to grow their shells, which are protection for their vulnerable bodies.

Food and Feeding: The oyster feeds by filtering tiny food particles from the water. By beating the tiny hairs, or cilia, of its gills, it forces water through its partly opened shell at the rate of 2-4 gallons an hour. Any food particles sucked in stick to mucus strings that are attached to the cilia. The food is then forced into the mouth. Inside its stomach, the oyster has a rod shaped mass of digestive enzymes, rotated by the current of water, which pulls in the food.

The Oyster Family: The name oyster has been given to a variety of bivalve mollusks, not all of which are considered true oysters. The true oyster is the European flat oyster Ostrea edulis, which is made up of two different sized shells that are irregular in shape. In the same family are Crassostrea virginica, found on the east coast of the United States, the Portuguese oyster, C. angulata, and the Japanese oyster C. gigas – all of which are edible.

Key Facts:
Length: European flat oyster, up to 3 in. at 5 years. Other species differ in size

Breeding:
Sexual maturity: Matures first as a male, then becomes a female and continues to change sex throughout its lifetime
Spawn: Year round, depending on water temperature and salt content
No. of eggs: From 1 to several million, according to species

Lifestyle:
Habit: Adult oysters live in clusters, attached to rocks or any clean solid object
Diet: Small edible particles filtered from sea water

Related Species: Other bivalves, including tropical pearl, thorny, and exotic oysters.

Distribution: Oysters are found along the coastlines of the United States, Europe, Mexico, Canada, Hawaii, and Australia. Pearls are most common in those from Japan, Australia, and Venezuela.

Conservation: Over fishing and marine pollution have led to the destruction of many natural oyster beds. Today oysters are a luxury food raised mainly on commercial farms throughout the world.

Inside the Oyster: The oyster is a mollusk with two hard shells, or valves, attached by a hinge and held together with a strong, triangular muscle. The flattened right and rounded left shells act as armor for the oyster’s soft body flesh. They vary slightly in shape according to species. The oyster adds fresh layers to its shell each year – just like the rings of a tree – providing easy way of estimating its age.

Once the two halves of its shell are pried apart more than ½ in., the muscle that holds them together opens, and the anatomy of the oyster can be studied in detail. Pearls are produced by the oyster, which coats any foreign object that gets inside, such as a piece of grit, with secretions called nacre. This covering builds up over the years to produce a highly valued jewel.

Did You Know:
During the eighteenth and nineteenth centuries, oysters were so plentiful and cheap that they were regarded as a poor man’s food.
It takes from 5 months to 7 years for an oyster to produce a cultured pearl.
The Chinese are credited with starting the cultured pearl trade in the fourteenth century. They introduced tiny metal buddhas into oysters, around which the pearls developed.

To return to animal menu click here