Pearls - oldest of gems Used - ornamental, have medicinal value, in cosmetics and tooth pastes The species of pearl oysters found in India are Pinctada maxima, P. fucata and P. margaritifera Pinctada maxima P. fucataP. margaritifera

Biology: Pinctada fucata - commonly used for pearl production attaches to hard substratum by means of byssus threads Stenohaline ; survives short term salinity fluctuations Filter feeder, mainly on phytoplankton, occasionally on bivalve eggs and copepods Life span years, maximum size 10cm Annual growth rate - 50mm Environmental factors such as depth, transparency, temperature, salinity, currents, calcium content of water, food and foulers influence growth rates Sexes are separate

hermaphroditism and change of sexes from one spawning season to another are not uncommon Attains maturity at a size of 25-30mm Two peak spawning seasons- 1.during July to August; 2. from November to December Eggs and sperms are shed in water, fertilization is external Hatching takes place in about 4 hours Spat settle when 0.3mm in size Spat availability in the wild fluctuates, hence hatchery produced spat are used for culture.

Development of pearl: Natural pearl is formed when a foreign material enters the body of pearl oysters Epithelial layer of mantle forms a sac around the foreign body which secretes nacre over the nucleus (foreign body) layer after layer resulting in pearl formation Shape of the pearl depends on the shape of the nucleus/foreign body Nucleus/nuclei can be implanted along with a piece of mantle tissue as graft into the gonads oysters which results in formation of cultured pearls

Culture methods: Cages are stocked with seed oyster and suspended from the rafts or long lines in protected bays Allowed to grow for four months when they become ready to receive nucleus Oysters from cages are brought to the laboratory for implantation of nucleus

They are kept in glass troughs containing filtered seawater A few menthol crystals are sprinkled into the troughs to anesthetize the oysters After one hour the oysters are ready to receive the nucleus Graft tissues are prepared by sacrificing a few oysters Pieces of mantle are cut, cleaned and trimmed to 3x2mm pieces They are smeared with weak eosin solution to avoid deterioration Nuclei are made from chank shells of shells of freshwater mussels Nuclei range in size from 2-8mm

The anaesthetized oysters are mounted on a stand An incision is made at the base of the foot and a canal is cut through the gonad A graft tissue is first implanted into the gonad through the canal followed by insertion of nucleus using special instruments made for the purpose Depending on the size of the oyster and the nuclei, 1-8 nuclei can be inserted into the same oyster After implantation, oysters are returned to the farming sites in frame nets which have compartments for individual oysters

The frame nets are suspended from the rafts/long-lines for development of the pearl The outer epithelium of the graft tissue grows over the nucleus and forms pearl sac in about a week The pearl will form in about 3 months 3-20 months are required to produce pearls of 3-8mm respectively Six months are required to coat nacre 0.2mm thick.

The oysters are harvested after the formation of required size of pearls They are sacrificed to recover pearls The harvested pearls are bleached in hydrogen peroxide to remove any blemishes