page_title: Oyster
section_title: Cultivation
hierarchical_section_title: Oyster / Human history / Cultivation
caption_attribution_description: Working on oysters at Belon, Brittany, France
context_page_description: Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not all oysters are in the superfamily Ostreoidea.
  Some types of oysters are commonly consumed cooked or raw, and in some locales are regarded as a delicacy. Some types of pearl oysters are harvested for the pearl produced within the mantle. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects.
context_section_description: Oysters have been cultured since at least the days of the Roman Empire. The Pacific oyster (Magallana gigas) is presently the most widely grown bivalve around the world. Two methods are commonly used, release and bagging. In both cases, oysters are cultivated onshore to the size of spat, when they can attach themselves to a substrate. They may be allowed to mature further to form "seed oysters". In either case, they are then placed in the water to mature. The release technique involves distributing the spat throughout existing oyster beds, allowing them to mature naturally to be collected like wild oysters. Bagging has the cultivator putting spat in racks or bags and keeping them above the bottom. Harvesting involves simply lifting the bags or rack to the surface and removing the mature oysters. The latter method prevents losses to some predators, but is more expensive.
  The Pacific oyster has been grown in the outflow of mariculture ponds. When fish or prawns are grown in ponds, it takes typically 10 kg (22 lb) of feed to produce 1 kg (2 ¹⁄₄ lb) of product (dry-dry basis). The other 9 kg (20 lb) goes into the pond and after mineralization, provides food for phytoplankton, which in turn feeds the oyster.
  To prevent spawning, sterile oysters are now cultured by crossbreeding tetraploid and diploid oysters. The resulting triploid oyster cannot propagate, which prevents introduced oysters from spreading into unwanted habitats.
caption: Oyster culture in Riec-sur-Belon, France
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