The farmer must raise the oysters for about three years before they are mature enough to implant, keeping them healthy. Then they implant them with the graft and nucleus and harvest the pearls 18 months to three years later. As natural pearls are very rare and hundreds of oysters or clams would have to be opened to find one wild pearl, cultured pearls are more common.
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Jennifer Kennedy, M. Therefore, a large amount of water must be filtered daily in order for the pearl oyster to obtain sufficient food. This is the reason importance is placed on not crowding pearl oysters on the farm and for keeping the shells clean from organisms that compete for food. Pearl oysters are protandric hemaphrodites which means that most are first male, then female. The male phase usually occurs during the first 2 to 3 years of life, with the change to the female phase in later years.
Pearl oysters have been reported to live as long as 25 years. Pearl oysters reproduce by releasing millions of eggs or sperm into the water column where fertilisation occurs randomly. In less than 24 hours, the fertilised egg develops into a trocophore larva, a free-swimming organism.
The larvae remain suspended in the water column for 2 to 3 weeks before undergoing metamorphosis, changing into an attached juvenile "spat". Shortly before metamorphosis, the larva develops an enlarged foot and an eye-spot. The foot remains after metamorphosis and the young spat retains the ability to move about for several months even after it attaches itself to a hard substrate.
Pearl oysters can attach and reattach themselves using the byssus. Sometimes a natural pearl forms when an irritant, such as a fragment of shell becomes lodged inside the mollusk when it is feeding, or a parasite drills through the shell.
To protect itself, the mollusk forms a sac around any irritant or invader that managers to get caught up inside its body. This sac secretes nacre to cover the irritant and, over time, the growing pearls are completely covered with the beautiful iridescent substance we call nacre, or mother-of-pearl.
The nacre and sac materials are made by the mollusk's mantle, the layer of tissue cells that surround the body of the mollusk and lines the shell. The mantle tissue cells that make up the pearl sac are called epithelial ep-uh-THEE-lee-yuhl cells. One commonality all cultured pearls share is the nucleus. Every pearl produced commercially today except naturally forming keshi pearls and pearls from Bahrain will have been nucleated.
The nucleus used in all pearls farmed in saltwater today is a mother-of-pearl bead made from freshwater mussel shells found in North America. This bead is made from an oyster shell that has been cut, rounded, and polished. A nucleus is surgically implanted in the oyster's gonads or mantle lobe together with a small section of mantle tissue.
Implanting a bead alone will not stimulate pearl formation. The epithelial cells - mantle tissue- play a vital role in the pearl formation process. As the oyster recognises the nucleus as an irritant, it forms a sac around the irritant before coating it with smooth layers of nacre.
Pearl farms now produce all the cultured pearls used in the jewellery industry today, and, while they are real, genuine pearls formed inside a living oyster, they are produced with a little human intervention. Saltwater oysters are nucleated by opening the shell a mere 2 to 3 centimetres and making a minute incision in the gonad - the oyster's reproductive organ. The mother of pearl nucleus is inserted into this incision which is then followed with a very small piece of mantle tissue from a donor oyster.
The mantle tissue is placed between the mother of pearl bead and the gonad with the side containing epithelial cells facing the nucleus. These epithelial cells are the catalyst of the pearl-sac. The pearl sac grows around the nucleus and begins to deposit nacre. This nacre layering is the beauty of the pearl. Saltwater oysters will only produce 1 to 2 pearls per typical nucleation.
Akoya oysters can be nucleated with up to 5 beads but the use of only 2 is most common. The Akoya oyster dies at harvest. While all mollusks, including oysters, mussels, and clams can technically make pearls, only some saltwater clams and freshwater mussels are used to commercially grow cultured gem-grade pearls.
Mollusks make pearls as a protection against irritants that sneak into their soft tissue. They do so by exuding layer upon layer of shell material. For some animals, this material is nacre, or mother of pearl. Nacre is a type of rind that gives pearls their pearly sheen. This brick-and-mortar process dates to at least million years in the fossil record, but natural pearls are incredibly rare.
So, people today farm pearls to make more for the gem market. Since the farming process is so effective, cultured pearls are more widely available than their natural counterparts.
So, instead of rarity, their value comes from their symmetry and shine. Although pearl farming is thriving currently, it faces an uncertain future just like many other aquatic industries threatened by climate change.
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