PEARL CULTURE

Pearl is mainly aragonite or a mixture of aragonite and calcite in minute crystalline form, which has been deposited in concentric layers produced within the soft tissue (specifically the mantle) of a living shelled mollusc or another animal, such as a conulariid.
TYPES, Environmental conditions, STEPS IN PEARL FARMING , Pearl Quality, Uses of Pearl.

1. PEARL CULTURE NAME- SANDEEP PATRE SUBJECT- ECONOMIC ZOOLOGY DEPARTMENT- SOS GEOLOGY & WRM

2. What is pearl ? Pearl is mainly aragonite or a mixture of aragonite and calcite in minute crystalline form, which has been deposited in concentric layers produced within the soft tissue (specifically the mantle) of a living shelled mollusc or another animal, such as a conulariid . The ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur. The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries. P earl has become a metaphor for something rare, fine, admirable and valuable.

3. TYPES (A) Natural pearls : Natural pearls may be formed within the oyster or mussels by either accidental entrance of a solid or accidental wound within the shell muscles or tissues. very rare because of their accidental origin . (B) Cultured pearls : Cultured pearls are produ­ced by human interference, when the pearls are pro­duced through the process of culture of pearl produc­ing oysters or mussels . (C) Artificial pearls: Such pearls are cheap imitations made of plastics, glass, fish scales, etc. with an artificial luster.

4. oyster diagram

5. FORMATION

6. A natural pearl is formed by the following way: (1) The outer epithelial layer of the mantle acci­dentally falls into the body of the pearl oyster. ( 2) It regenerates a sac consisting of a single layer of cells, thus forming the pearl sac. (3 ) Sometimes a foreign body accidently enters into the body of the oyster, when the shells remain open, and gets trapped between the shell and the mantle. The outer epithelium of the mantle invagina­tes and form the pearl sac. (4) Inside the pearl sac, as a result of secretion of nacre, a natural pearl grows. (5) The secretion of nacre continues till the end of life of the pearl oyster, thereby forming/producing a beautiful, natural pearl.

7. (b) Cultured pearl: The technique of the forma­tion of natural pearl is manipulated in the cultured pearl formation process . Here for the formation of pearl, the two pre-requisites are : (1) The outer epithelium of the mantle lobe and (2) A core substance or nucleus . (i) Formation of pearl sac : Here, a small piece of mantle from a donor oyster is grafted skillfully into the gonad of the recipient oyster along with a nucleus. The outer epithelium of the grafted mantle piece regenerates itself around the implanted nucleus and forms a pearl sac.

8. (ii) Secretion of pearl forming matters: Initia­lly , after the formation of pearl sac, its internal part is alkaline and the secretion contains organic substan­ces such as Keratin. The secretion is due to the prismatic layer containing calcites. The internal part of pearl sac later becomes acidic and subsequently neutral. The secretive matter ultimately becomes pearl forming material . (iii) Calcium absorption and formation of cal­cium carbonate : The main ingredient of pearl is calcium carbonate (calcite and aragonite). In pearl oysters the main source of calcium is food. However, the gill, mantle and fool can directly absorb calcium from water.

9. Calcium absorbed through food and from water slowly moves into the pallium through blood. The carrying of calcium in the body depends mainly upon the role played by alkaline phosphatase present in the epithelial cells of the connective tissue and mantle of the pearl sac. Alkaline phosphatase combines with the calcium ion (Ca+2) to form phosphate and other salts. The calcium ion in the presence of phosphatase gains energy and passes through the mantle to be absorbed by its epidermal cells. This is then carried to the connective tissue of the pearl sac. In the course of its passage the Ca+2 also unites with the cartila­ginous sulphate . It further induces the calcium ion to become active and is transported to the cytoplasm of nacreous layer and ultimately excreted by the epidermal cells. The excreted calcium then under the activity of carbonic acid releasing hydrase combines with the carbon dioxide (and ultimately forms calcium carbonate.

10. (iv) Factors influencing secretion of nacre: Morphological structure of the epidermal cells of pearl sac : Calcium carbonate crystallization: Amount of CO2: Temperature and pH: In the presence of common salt or calcium phosphate, calcium carbonate crystallises into calcite. Crystallisation of calcium carbonate in granpel form is favoured by the presence of urea, and salts of ammonia, magnesium and strontium.

11. Environmental conditions 1 Temperature The optimum temperature for oyster growth has been found to be between 20–25 °C. A temperature below 13 °C causes hybernation . Below 6 °C, the oysters die. 2 Salinity Pearl oysters tolerate a wide range of salinity from 24–50 ‰ for a short duration of 2–3 days. 3 Bottom Gravelly bottoms are suitable for pearl oyster farming, while sandy or muddy bottoms should be avoided. Oyster growth is affected by water temperature and nutritional condition of the ground. 4 Depth The optimum depth for farming pearl oysters is around 15 m. At greater depths, even if the rate of nacre deposition is slower, pearls of high quality with a pinkish colouration are obtained

12. 5 Silt load Pearl oysters generally prefer clear waters as high turbidity levels will affect their filtration efficiency. A decline in oyster condition was noted at Veppalodai farm due to the high silt content in the farm area throughout most of the year. 6 Water current In strong water currents the formation of the pearl layers is usually fast, but the quality of pearls produced is affected. 7 Primary productivity Rich nutrients discharged by rivers into the sea are responsible for high primary productivity.

13. Rearing methods 1 Raft culture Raft culture is considered to be one of the most suitable farming methods in sheltered bays. The size of the rafts can be altered according to the convenience of the situation. 2 On-bottom culture. Sea bottoms with a granite or coral stones composition can be used for on-bottom culture. it has been noted that the growth of the mother oyster is slower in on-bottom culture compared to the growth of oysters cultured in raft

14. STEPS IN PEARL FARMING :

15. Pearl Quality There are 7 features or“VALUE FACTORS ” 1 . SIZE A pearl’s ultimate size can depend on many variables Size and health of the mollusk Size of the nucleus Amount of time in the water adding layers of nacre Larger pearls usually more valuable 2 . SHAPE While round is perhaps the most familiar shape, pearls come in many different forms. Spherical, Symmetrical, Ovals, buttons, drops, baroque 3 . COLOR A pearl’s color is made up of Hue-the color’s first impression Tone-its lightness or darkness Saturation-its strength or intensity GIA recognizes 19 pearl hues

16. 4 . LUSTER “The true magic of a pearl lies in its luster” and how it reflects light Luster is the most important of all of the value factors to the beauty of a pearl. 4 categories: Excellent-reflections bright, sharp, distinct Good-bright reflections but not sharp Fair-weak and hazy Poor-dim, no reflections 5. SURFACE QUALITY Cultured pearls are organic so it isn’t surprising when they show surface characteristics. Abrasions, bump, chips, cracks, gaps, pit, scratches, spots or wrinkles Categories: Clean Lightly blemished Moderately blemished Heavily blemished

17. 6 . NACRE QUALITY Nacre is the very essence of the pearl itself A pearl’s appearance helps determine its quality and it has a LOT to do with whether the nacre is thick or thin (thin=“blinking”) Classifications: Acceptable Nucleus Visible Chalky Appearance 7 . MATCHING The matching value factor is relative (only applies to strands, or jewelry with more than one pearl) Classifications: Excellent Good Fair

18. Advantages of Pearl Aquaculture   Pearl farming is eco friendly. Being Filter feeder oysters purify the water. Shellfish farming provides habitat for fish and improves species diversity Reduces turbidity, Improves light penetration, Improves water quality reduces anoxia and nitrification A single oyster clears over 15 gallons of water a day, retaining particles as small as 2 micron A small oyster farm clears 30 to 100 million gallons of water each day It accumulates heavy metals from the water, and removes harmful pollutants as well

19. Uses of Pearl: ( 1) Used as an ornament and a symbol of grandeur. (2) Used in ornamental handicraft. (3) It is a very precious medicine for surgery, pediatrics, ENT, etc. as used by the Chinese. By-Products of Pearl: The by-products of pearl culture is referred to the total mass of the oysters after extraction of the cultured pearl. The by-products of pearl culture are, thus, the seed pearls, shell and the flesh.

20. In India pearl powder and pearl liquid are important ingredients as follows: (1)Pearl powder is a highly stimulant tonic and aphrodisiac. Its other medicinal values are — laxative, sedative, emetic and nutritive. (i) The tiny seed pearls (which are unsuitable as a gem) are used in the preparation of medi­cine. (ii) Pearl powders act as an antacid. It is also used in heart burn and bilious affections. (2) In case of class ‘C’ category of pearls (not used in jewellery ), the nacreous layer is removed from the nuclei and ground into a powder. It is then dissolved in phosphoric acid. The final product (pearl calcium tablet) is formed by additional chemical processes. The pearl calcium tablet, thus formed, is marketed in Japan for pregnancies, weak bodies, tooth cavities, stomach acids and allergies. (3) Large oyster shells, for their mother-of-pearl layer, are used in shell craft. (4) Small and broken shells are ground and used as ingredients in poultry-feed. (5) The adductor muscle portion of the flesh of oyster is used for human consumption. (6) After removal of the pearl, the entrails of the oyster are used for feeding fishes.

21. Pearl Production Countries : China, Japan, Australia, South seas, Vietnam, India, UAE, USA, Mexico, Fiji, Philippines, France, Myanmar, and Indonesia are some of the major pearl production countries.

22. R eferences https://www.agrifarming.in/pearl-farming-information#Pearl_Farming_Information http:// www.pearlindia.org/advantages.htm Pearl Oyster farming and pearl culture eprints.cmfri.org.in The Basic Methods of Pearl Farming:A Layman’s Manual pdf