Oyster farming is an aquaculture (or mariculture) practice in which oysters are raised for human consumption. Oyster farming most likely developed in tandem with pearl farming, a similar practice in which oysters are farmed for the purpose of developing pearls. It has been practiced in one form or another since the Ancient Romans cultured oysters in Great Britain and transported them to Italy. The French oyster industry has relied on aquacultured oysters since the late 18th century.
Commonly farmed food oysters include the Eastern oyster Crassostrea virginica, the Pacific oyster Crassostrea gigas, Belon oyster Ostrea edulis, the Sydney rock oyster Saccostrea glomerata, and the Southern mud oyster Ostrea angasi.
Oysters naturally grow in estuarine bodies of brackish water. When farmed, the temperature and salinity of the water are controlled (or at least monitored) so as to induce spawning and fertilization, as well as to speed the rate of maturation - which can take several years.
Three methods of cultivation are commonly used. In each case oysters are cultivated to the size of "spat," the point at which they attach themselves to a substrate. The substrate is known as a "culch" or "cultch". The loose spat may be allowed to mature further to form "seed" oysters with small shells. In either case (spat or seed stage) they are then set out to mature. The maturation technique is where the cultivation method choice is made.
In one method the spat or seed oysters are distributed over existing oyster beds and left to mature naturally. Such oysters will then be collected using the methods for fishing wild oysters, such as dredging.
In the second method the spat or seed may be put in racks, bags, or cages which are held above the bottom. Oysters cultivated in this manner may be harvested by lifting the bags or rack to the surface and removing mature oysters, or simply retrieving the larger oysters when the enclosure is exposed at low tide. The latter method may avoid losses to some predators but is more expensive.
In the third method the spat or seed are placed in a culch within an artificial maturation tank. The maturation tank may be fed with water that has been especially prepared for the purpose of accelerating the growth rate of the oysters. In particular the temperature and salinity of the water may be altered somewhat from nearby ocean water. The carbonate minerals calcite and aragonite in the water may help oysters develop their shells faster and may also be included in the water processing prior to introduction to the tanks. This latter cultivation technique may be the least susceptable to predators and poaching but is the most expensive to build and to operate. The Pacific oyster C. gigas is the species most commonly used with this type of farming.
Diseases that can affect either farmed C. virginica or C. gigas oysters include Perkinsus marinus (Dermo) and Haplosporidium nelsoni (MSX). However, C. viginicus are much more susceptible to Dermo or MSX infections than are the C. gigas species of oyster. Pathogens of O. edulis oysters include Marteilia refringens and Bonamia ostrea. In the north Atlantic Ocean, oyster crabs may live in an endosymbiotic commensal relationship within a host oyster. Since oyster crabs are considered a food delicacy they may not be removed from young farmed oysters, as they can themselves be harvested for sale.
Nineteenth century shallow draft sailboats designed primarily for oystering include: