Also known as the American or Virginia oyster, the eastern oyster is a bivalve with two rough, whitish shells. It forms reefs in brackish and salty waters throughout the Chesapeake Bay.
Eastern oysters grow to three to five inches in length, but can reach a length of eight inches. Two rough shells enclose its soft body and vary in color from white to gray to tan. The right or top shell is flat, while the left or bottom shell is cupped, with a purple muscle scar on the inside.
Oysters live in brackish and salty waters from 8 to 35 feet deep. They are often concentrated on oyster bars, beds or rocks, which are located in waterways with firm bottom areas. Oysters attach to one another, forming dense reefs that provide habitat for many fish and invertebrates.
Found in the middle and lower Chesapeake Bay and its rivers. Their range extends along eastern North America from the Gulf of St. Lawrence to the Gulf of Mexico.
Filter feeders, oysters feed on plankton by opening their shells and pumping water through their gills. This action traps particles of food.
Oysters are prone to infection by parasites that cause the aquatic diseases MSX and Dermo.
Spawning occurs in early summer when water temperatures rise. Adults release eggs and sperm into the water. Females can produce about 100 million eggs each year. After spawning, oysters are thin because they have used up their stored food reserves. Adults grow larger and stronger as the weather cools. In less than 24 hours, fertilized eggs develop into free-swimming larvae.
Over the next two to three weeks, oyster larvae grow a "foot," which is used to crawl over and explore a surface before settling. Once larvae find a suitable surface to settle on, they secrete a cement-like substance, which fixes the left valve into place. Settled juvenile oysters are called "spat." Many oysters change sex over the course of their lifetime. Most oysters less than one year old are male, while most older oysters are female.