An oyster's left, or bottom, shell is cupped and has a purple muscle scar on the inside. (Fisheries and Oceans Canada/World Register of Marine Species)
The eastern oyster is a bivalve with rough, whitish shells. It forms reefs in brackish and salty waters throughout the Chesapeake Bay.
Varies in color from white to grayish or tan
Right (top) shell is flat
Left (bottom) shell is cupped. It has a purple muscle scar on the inside.
Usually grows 3-4 inches
Lives in brackish and salty waters from 8-35 feet deep
Concentrated in areas with shell, hard sand or firm mud bottoms. These areas are called oyster bars, beds or rocks.
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
Feeds by opening its shells and pumping water through its gills to filter out plankton and other particles
Prone to infection by the parasites that cause the aquatic diseases MSX and Dermo
Humans harvest oysters for food
Reproduction and Life Cycle:
Spawns in early summer when water temperatures rise
Adults release eggs and sperm into the water. Females can produce about 100 million eggs per year.
After spawning, oysters are thin and watery because they have used up their stored food reserves. They grow larger and stronger as the weather cools.
In less than 24 hours, the fertilized eggs develop into free-swimming larvae. During the next 2-3 weeks, oyster larvae grow a foot, which is used to crawl over and “explore” a surface before settling.
Larvae eventually find a suitable hard surface to settle on. They secrete a cement-like substance, which fixes the left valve into place. Attached juvenile oysters are called spat.
Many oysters change sex over their lives. Most oysters less than one year old are male, and most older oysters are female.
Also known as the American or Virginia oyster
The cavity within an oyster’s shell is always filled with water. This allows oysters to survive for a long time without having to open their shells to feed. During cooler months, oysters can live out of the water for extended periods of time.
Historically, oysters were only eaten during months whose names contain an “R.” This was because oysters would spoil without refrigeration during warm months. Also, oyster quality is poor during summer because the oysters have just finished spawning.