Aquaculture - Shellfish
Oysters

Two kinds of oysters are cultured in Massachusetts, the Eastern, or American oyster, Crassostrea virginica, and the European oyster, Ostrea edulis. Oysters, like other epifauna, live on the sediment surface. The larvae metamorphisize and search out hard clean surfaces (cultch), which may include live oysters, to which they cement themselves. Recently-set oysters are known as spat. Setting oysters, depending upon conditions, may result in heavy local concentrations in the form of bars or reefs, where competition for space is fierce. Once attached, an oyster never moves again, unless dislodged by external forces.

Oyster shells, or valves, differ in size and weight, with the right valve (the top valve) forming flat and the left (bottom valve) being heavier and cupped. The valves are joined by a ligament and the shell shape can vary widely. The size and shape of an oyster's shell is significant in aquaculture; the raw market demands a full, shapely, aesthetically-appealing shell. Shell growth largely depends upon water temperatures and culturing times will vary according to the size to be attained. For example, in Massachusetts, it can take two - four years to attain market size while in Florida, where oysters are grown year round, eighteen months is usually sufficient.

American oysters are divided into separate male and female individuals and spawn by spewing millions of eggs and sperm into surrounding waters, where external fertilization takes place. European oysters are hermaphroditic; each individual possesses male and female germ cells, and fertilization occurs inside the inhalant chamber of the oyster. The larvae then incubate in the chamber for up to ten days prior to being ejected into the surrounding waters. Immediately before setting, both types of oysters develop eye spots and a foot and begin to search out cultch to attach to. Satisfactory cultch includes any clean, hard surface (usually empty bivalve shells).

The color, texture, and quantity of the meat in the shell is very important to the raw oyster market and those qualities will vary with age, water quality, and time of harvest. Oysters will accumulate and/or metabolize almost every element contained in the water around them. The quality of the meat drops during the spawning season. After spawning, oysters build up glycogen, which provides the appearance of a "fattening" or "fat" oyster, the most desirable kind.

Oysters are subject to a variety of natural predators, an environmental hazard that may be substantially reduced by cultivation and predator-control methods. Depending upon salinity, Atlantic oyster drills, thick-lipped oyster drills, rock shells, knobbed whelks, channeled whelks, and starfish all prey on oysters.

Oysters are also subject to a variety of diseases and parasites, the most recently notorious being MSX, discussed infra. More recently, Juvenile Oyster Disease (JOD) has been blamed for some oyster mortalities in the Northeast and mid-Atlantic aquaculture facilities. The severity of impacts by disease and parasites on oyster populations is thought to be related to water quality; higher salinity, high temperatures, and nutrient loading appear to make oysters more susceptible to disease.

Oysters provide a welcome habitat for commensal and competing organisms. Several live in or on the shell; the boring sponge, the boring clam, and the mud worm are examples. Barnacles, tunicates, and mussels (as well as other oysters) will attach themselves to the outside of the shell, as will as several species of algae. One algal species, Codium fragile, produces aveoliated branches filled with gas that may actually lift the oyster and carry it off with the tide.

*Information found at the Massachusetts White Paper


White Paper Strategic Plan Industry Permit Assitance Technical Assistance Marketing Aquaculture Education Legislative Projects Grants Program Shellfish & Finfish	Aquaculture - Shellfish Oysters Quahogs \| Oysters \| Soft Shell Clams \| Mussels \| Scallops\| Crayfish Two kinds of oysters are cultured in Massachusetts, the Eastern, or American oyster, Crassostrea virginica, and the European oyster, Ostrea edulis. Oysters, like other epifauna, live on the sediment surface. The larvae metamorphisize and search out hard clean surfaces (cultch), which may include live oysters, to which they cement themselves. Recently-set oysters are known as spat. Setting oysters, depending upon conditions, may result in heavy local concentrations in the form of bars or reefs, where competition for space is fierce. Once attached, an oyster never moves again, unless dislodged by external forces. Oyster shells, or valves, differ in size and weight, with the right valve (the top valve) forming flat and the left (bottom valve) being heavier and cupped. The valves are joined by a ligament and the shell shape can vary widely. The size and shape of an oyster's shell is significant in aquaculture; the raw market demands a full, shapely, aesthetically-appealing shell. Shell growth largely depends upon water temperatures and culturing times will vary according to the size to be attained. For example, in Massachusetts, it can take two - four years to attain market size while in Florida, where oysters are grown year round, eighteen months is usually sufficient. American oysters are divided into separate male and female individuals and spawn by spewing millions of eggs and sperm into surrounding waters, where external fertilization takes place. European oysters are hermaphroditic; each individual possesses male and female germ cells, and fertilization occurs inside the inhalant chamber of the oyster. The larvae then incubate in the chamber for up to ten days prior to being ejected into the surrounding waters. Immediately before setting, both types of oysters develop eye spots and a foot and begin to search out cultch to attach to. Satisfactory cultch includes any clean, hard surface (usually empty bivalve shells). The color, texture, and quantity of the meat in the shell is very important to the raw oyster market and those qualities will vary with age, water quality, and time of harvest. Oysters will accumulate and/or metabolize almost every element contained in the water around them. The quality of the meat drops during the spawning season. After spawning, oysters build up glycogen, which provides the appearance of a "fattening" or "fat" oyster, the most desirable kind. Oysters are subject to a variety of natural predators, an environmental hazard that may be substantially reduced by cultivation and predator-control methods. Depending upon salinity, Atlantic oyster drills, thick-lipped oyster drills, rock shells, knobbed whelks, channeled whelks, and starfish all prey on oysters. Oysters are also subject to a variety of diseases and parasites, the most recently notorious being MSX, discussed infra. More recently, Juvenile Oyster Disease (JOD) has been blamed for some oyster mortalities in the Northeast and mid-Atlantic aquaculture facilities. The severity of impacts by disease and parasites on oyster populations is thought to be related to water quality; higher salinity, high temperatures, and nutrient loading appear to make oysters more susceptible to disease. Oysters provide a welcome habitat for commensal and competing organisms. Several live in or on the shell; the boring sponge, the boring clam, and the mud worm are examples. Barnacles, tunicates, and mussels (as well as other oysters) will attach themselves to the outside of the shell, as will as several species of algae. One algal species, Codium fragile, produces aveoliated branches filled with gas that may actually lift the oyster and carry it off with the tide. Information found at the Massachusetts White Paper*