oyesters The molluscs mantle protective membrane deposits layers of calcium carbonate CaCO 3 in the form of the mineral aragonite or a mixture of aragonite and calcite ID: 933734
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Pearl Culture
Pearl is the Gem produced by Pearl oyesters The mollusc's mantle (protective membrane) deposits layers of calcium carbonate (CaCO3) in the form of the mineral aragonite or a mixture of aragonite and calcite (polymorphs with the same chemical formula, but different crystal structures) held together by an organic horn-like compound called conchiolin.
Slide2Pinctada
fucata (Akoya pearl oyester)Native to Indo-pacific regionPinctada margaritifera (Black-Lip Pearl Oyster)
Slide3p
Slide4Steps in pearl culture
The preparatory stage :Mature oysters aged 2 to 3 years, at least 12 cm in length, are selected for implanting the graft.Oyesters with mature gonad is more suitable as gonad is the best place for implantation. Oysters are cleaned to rid them of the parasites which collect on their shells. The grafter or one of his technical assistants has to prise the oyster open with a dilator and hold it open with a wedge to be able to operate quickly. The opening must not be any larger than 1.5 cm, otherwise the adductor muscle might be damaged .Usually Menthol powder is used to open the shell.
Slide5Preparation of graft tissue
Preparation of graft tissue- Mantle from healthy donor is cut into pieces. Small strips of epithelium (the grafts) are prepared .This is used as graft tissue.
Slide6Steps in graft tissue preparation.
(A) mantle tissue when removed from an oyster (p.m.= pallial mantle and m.m.= marginal mantle) (B) trimming of the margins to remove marginal mantle and inner muscular tissue(C) further trimming to obtain ribbons of pallial mantle(D) cutting of the ribbon into small sections.
Slide7Preparation of nucleus
Spherical shell beads are used as nuclei to produce round pearls. These beads are prepared out of thick shells of other molluscs, usually freshwater mussels. Molluscan shell material is preferred due to phylogenic affinity, chemical composition, binding strength and heat resistance properties which are similar to those of the nacre. The shells are processed into spherical beads of different diameters, generally 2–7 mm for Pinctada fucata, through cutting, grinding, shaping and polishing using appropriate machines and tools. Dimensional accuracy, smooth finish and high polish are important factors. The beads should be cleaned and dried before use.
Slide8Implantation of the nucleus
The number of nuclei to be implanted in one oyster is usually decided before the operation. Single and double implantations are common while multiple implantations are usually carried out when large numbers of small pearls of about 2–3 mm are required. Large diameter nuclei, in the range of 6–7 mm, are generally used in single implantation, one nucleus in each oyster. Nuclei with diameters ranging from 4–6 mm are used for double implantation, a large and a small one in each oyster. Nuclei with diameters of 2–3 mm are generally used in multiple implantations, five or more nuclei in one oyster.
Slide9The best site for nucleus implantation is the gonad, particularly in its ventral portion. Single implantation is always done at this site.
In double implantation, the above site is used for the larger nucleus while a site in the dorsal region of the gonad, close to the hepato-pancreas, is used for the smaller nucleus. Skill and patience are the key factors for a successful operation.
Slide10Post-operation care
Freshly operated oysters should be reared undisturbed for a few days. If kept in the laboratory, they should be placed in plastic troughs or FRP tanks, where seawater is allowed to flow gently. If no flow-through system is available, the seawater has to be changed frequently to overcome the narcotizing effect of menthol. When normalcy is resumed, the oysters slowly re-open their valves and commence their pumping and filtering activity. If the sea is not calm, it is desirable to rear the operated oysters under laboratory conditions till the wound heals completely. The normal duration of wound healing is only a day or two. However, if the surgery is rough or the incision is large, the nucleus could slip out of the oyster, if cultured in rough waters.