A major factor in selecting offspring is genetics. Broodstock can be obtained from the wild or reared as offspring from previous years. To produce broods of larvae in the hatchery, sexually mature adult oysters, known as broodstock, must be available. This cultch can be sprayed onto large open-water leases and the oysters grown out on the bottom. Remote setting typically uses large tanks filled with oyster shells as cultch. Single set culture uses a small cultch sized to encourage development of single oysters for the half-shell market most of this type of oyster seed is grown out in bags, racks, or rafts. There are two main oyster culture methods to choose from, either single set or remote setting. The hatcheries spawn the oysters and grow the larvae in tanks until they are ready to set. In some places, such as the Pacific Northwest, almost all the commercially grown oysters are from hatcheries. This demand has created a new form of oyster aquaculture utilizing hatchery-produced seed. Meeting the marketplace demand now requires the use of land-based hatchery technology to produce oyster seed in addition to natural recruitment in the wild.
Oyster Life Cycle, Figure: Wallace et al 2008 Now with better management in place, including an effort to restore public bottom with suitable substrate, harvesting wild oysters in the Chesapeake Bay is still viable, although not at the level it once was. The Chesapeake Bay once was one of the most prolific oyster grounds in the U.S., but oyster disease, unregulated harvest, and the decline in water quality led to the decimation of the oyster populations. However, pollution and overfishing have modified the way oysters are produced to meet the marketplace demand. In addition, clean oyster shells or other media are planted in areas to attract natural recruitment. This practice has gone on for centuries and is still practiced today in many areas such as the Gulf of Mexico and the Chesapeake Bay.
The most traditional form of husbandry, or aquaculture, is the practice of moving wild oysters as small juveniles from public bottom to leased areas for grow-out. This reef formation is based on water quality, current flows, and the availability of a suitable setting material, known as cultch. Oyster larvae exhibit a preference to settle on and around where other oysters are located, creating reefs. Once an oyster sets in a location, it cannot move, so finding an ideal location is vital. The larvae are microscopic and will swim for approximately two weeks until they develop a foot and begin to crawl, searching for a location to set. Fertilized eggs will float in the water column for ~24 hours and hatch into swimming larvae. When water temperatures change from cold to warm, this change triggers males to release sperm which in turn triggers females to release eggs. Oyster reproduction is cued by temperature changes. The gut is made up of diffuse tissue that is both digestive and reproductive. The food sorted by the gills and labial palps becomes part of a mucous strand that is reeled into the gut known as the crystalline style. The oysters’ gills “pump” water to obtain oxygen but also filter particles from the water for the oyster to eat. Oysters are bivalves that is, they have two shells made up of calcium carbonate secreted by their mantle tissue that protects their soft bodies from the environment and predators. Factoring in both the economic and ecologic value of oyster reefs increases the number into the billions. That is probably a low estimate of the overall value of the oyster because it does account for the ecological value of the fish species that use oyster reefs as a food source and nursery habitat, nor the coastal protection and water-quality services oyster reefs provide. In 2011 31 million pounds of oysters were harvestede with a dockside value of approximately $135 million ( National Marine Fisheries Service).
Oyster culture is one of the most prominent forms of marine aquaculture in the U.S.