Some types of pearl oysters are harvested for the pearl produced within the mantle. True oysters are members canned oysters in water the family Ostreidae. Almost all shell-bearing mollusks can secrete pearls, yet most are not very valuable.
Pearls can form in both saltwater and freshwater environments. The largest pearl-bearing oyster is the marine Pinctada maxima, which is roughly the size of a dinner plate. Not all individual oysters produce pearls naturally. In nature, pearl oysters produce pearls by covering a minute invasive object with nacre. Over the years, the irritating object is covered with enough layers of nacre to become a pearl. The many different types, colours and shapes of pearls depend on the natural pigment of the nacre, and the shape of the original irritant.
Pearl farmers can culture a pearl by placing a nucleus, usually a piece of polished mussel shell, inside the oyster. In three to seven years, the oyster can produce a perfect pearl. Since the beginning of the 20th century, when several researchers discovered how to produce artificial pearls, the cultured pearl market has far outgrown the natural pearl market. Pilgrim oyster, another term for a scallop, in reference to the scallop shell of St.
In the Philippines, a local thorny oyster species known as Tikod amo is a favorite seafood source in the southern part of the country. Because of its good flavor, it commands high prices. In addition to their gills, oysters can exchange gases across their mantles, which are lined with many small, thin-walled blood vessels. Because of this, it is technically possible for an oyster to fertilize its own eggs. The gonads surround the digestive organs, and are made up of sex cells, branching tubules, and connective tissue.
Once her millions of eggs are fertilized, the female discharges them into the water. The larvae develop in about six hours and exist suspended in the water column as veliger larvae for two to three weeks before settling on a bed and reaching sexual maturity within a year. Oysters are filter feeders, drawing water in over their gills through the beating of cilia. A group of oysters is commonly called a bed or oyster reef.
As a keystone species, oysters provide habitat for many marine species. Crassostrea and Saccostrea live mainly in the intertidal zone, while Ostrea is subtidal. An oyster reef can increase the surface area of a flat bottom 50-fold. An oyster’s mature shape often depends on the type of bottom to which it is originally attached, but it always orients itself with its outer, flared shell tilted upward. One valve is cupped and the other is flat. Oysters usually reach maturity in one year. As they grow over the next two or three years and develop greater energy reserves, they spawn as females by releasing eggs.
They regularly shut their valves to enter a resting state, even when they are permanently submersed. Their behaviour follows very strict circatidal and circadian rhythms according to the relative moon and sun positions. Some tropical oysters, such as the mangrove oyster in the family Ostreidae, grow best on mangrove roots. Low tide can expose them, making them easy to collect.