Introduction

What is pearl? • A hard, lustrous spherical mass, typically white or bluish-grey, formed within the shell of a pearl oyster or other bivalve mollusc and highly prized as a gem. • Highly esteemed as gems • Derived from ‘pirula’ mean pear • Counted among 9 gems • Needs no cutting or polishing • Modern pearl culture initiation: Japan in 1893 (Kokichi Mikimoto: Father of Pearl culture industry) • In India: CMFRI, Tuticorin in 1973. In 1981, pearl oyster hatchery Pearl oysters remain attached to: I. Rocks II. Live or dead corals III. Other molluscs IV. Hard substratum

India: highest demand for pearls: produces better pearls Location of Pearl oysters fisheries: 1) Gulf of Mannar off Tuticorin coast ▪ Depth of 23 m ▪ Large beds on hard substrata ▪ Pearl beds are known as ‘paars’ 2) Gulf of Kutch: northwest coast of country ▪ Intertidal zone ▪ Sparsely distributed ▪ ‘khaddas’ Types of pearls 1. Natural pearls: ➢Formed within the oyster by accidental entry of solid or accidental wound ➢Rare due to their accidental origin

2. Cultured pearls: ➢Produced by human interference ➢Through pearl oyster culture

3. Artificial pearls: ➢Formed by plastic, glass, fish, scales with an artificial lustre

Pearl producing molluscs Mollusc with Mother of Pearl layer is capable of producing pearl Few species produces pearl as a jewel (3 species): Systemic position Pinctada fucata kingdom Animalia Phylum Mollusca Class Bivalvia Pinctada Order Pterioda margaritifera Family Pteriidae Genus Pinctada Species Fucata/ Pinctada margaritifera/ maxima maxima 1. Pinctada fucata: ➢ Akoya pearl oyster: Marine species ➢Indian pearl oyster ➢Formerly known as: Pinctada martensii and Pinctada vulgaris in Japan ➢Distribution: Indian subcontinent, Japan and Persian gulf ➢In India: Gulf of Kutch and Gulf of Mannar (Lingah or oriental pearl) ➢Intertidal area to a depth 12 fathoms ➢Size: 9cm; life span: 7 years 2. Pinctada margaritifera: ➢Black lip pearl oyster ➢Indo-pacific region within coral reefs ➢In India, intertidal region of Andaman-Nicobar Islands upto 40m ➢No teeth in hinge ➢Size: 17cm; life span: 15 years 3. Pinctada maxima ➢ 2 different color varieties: silver lipped oyster and pearl lipped oyster ➢Largest and best all over the world ➢Strong Mother of pearl layer ➢Australia, China, Philippines, Thailand, Myanmar, Indonesia, Andaman & Nicobar ➢Low tide level: 40 fathoms deep ➢Size: 28.2cm, weight:5.5kg and life span: 40 years Internal Anatomy Pinctada maxima

Pinctada fucata

Pinctada margarifera Formation of Pearl

1. Natural pearl formation: Location: Nucleus: organic or inorganic: parasites, larvae, eggs, decay plants, • Within the mantle sand grains, epithelium or self blood cells • Other soft tissues • Between the mantle shell valve opens Enters the oyster when the for feeding/respiration • Interior surface of the shell In response, invagination of outer epithelium of the mantle ➢Accidental and occurs rarely Formation of pearl sac (Obligatory):derived from internal/external ➢Large and spherical very layer of epithelium of mantle or gill plates hard to find

Epithelium of pearl sac secretes nacre surrounding the foreign body

1. Cultured pearl formation: Two things are required: outer epithelium of the mantle (pearl secreting cells) lobe and Core substance or nucleus

Careful surgery: the mantle piece is grafted + shell bead nucleus into the gonad

Oyster is then returned to sea

Outer epithelium: rearrange themselves in the shell bead nucleus Inner epithelium: disintegrate and absorbed by the pearl

Pearl sac derives nourishment from of the surrounding tissues And form nacre as concentric rings Nacerous matter: thin alternate layer of aragonite (0.29-0.60mm thick) and conchiolin (Mucopolysaccharide) Aragonite: calcium carbonate Pearl oyster farming

Selection of Environmental Supply of Rafting Rearing culture site condition oysters method containers

On- Mother Juvenile Raft bottom oyster rearing culture culture culture Selection of culture site: based on various aspects

Technological Economical Behavioral Tolerance/ Ecological Industrial Adaptation & &Domestic Environm ental

➢ Sheltered bays: ideal location: good protection to culture structures ➢Shallow coastal waters: calm waters for pearl culture Environmental Conditions a. TEMPRATURE: Temprate regions: water temperature play important role ➢ Japan, 20-25℃. Below 13℃ causes hibernation. Below 6℃ they will die. Above 28℃ they will cause exhaustion ➢ Thickness of pearl layer is affected by minute changes in water temperature during day and according to season ➢ Deposition of calcium stops at 13℃ ➢ Grow vigorously in winter temp (23-27℃) in Gulf of Kutch ➢ Low temp: begins spawning in Gulf of Mannar b. SALINITY: ➢ Tolerate wide range of Salinity from 24-50% for 2-3 days. ➢ Salinity for more days will lead to death ➢ Prefer high salinity: produce pearl with golden tint c. BOTTOM: ➢ Bottoms with gravel are suitable: sandy and muddy bottoms are avoided ➢ Oyster growth is affected by water temp and nutrition of the bottom ➢ Repeated culture on same ground: deterioration of pearl quality ➢ Chemical & physical state at the bottom: affected by organic subs discharge by oysters & fouling organisms ➢ Therefore, periodic removal is necessary d. DEPTH: ➢ Optimum death: 15m ➢ Greater depth: less nacre but pearl of high quality with pinkish tinge e. SILT LOAD: ➢ Prefer clear waters ➢ High turbidity: high silt: less efficiency f. WATER CURRENT: ➢ Strong winds and strong waves ➢ Sufficient waves and current are required for circulation of oxygen, fresh plankton and flush away waste material ➢ Strong water covers: formation of pearl is fast but quality is affected g. PRIMARY PRODUCTIVITY: ➢ Depends on chemical constitution of the sea water, amt of plankton ➢ Rich nutrients from river are responsible for high productivity ➢ Conchiolin: from nitrogen of plankton ➢ Directly absorbed: calcium and organic matter ➢ Trace metals: influences color of pearl Supply of Oyster

▪ Collected from natural beds or reared from naturally collected cultures ▪ Gulf of Mannar: off Tuticorin at 12-15km distance and 12-25m depth ▪ Oysters are collected by SCUBA diving ▪ Gulf of Kutch: intertidal flats: collected by hand ▪ In Japan, oyster spats: submerging bundles of cedar twigs near the water surface, during peak larval season ▪ Spat collectors: Hyzez films & old fish nets ▪ In India this method is not successful Rearing methods

1. Raft culture: ➢ Suitable for sheltered bays ➢ Ideal size: 6X5m floated with 4 bouys ➢ Constructed with logs of teak, bamboo length of 10cm ➢ Logs are lashed with coir ➢ Floats are attached to the raft ➢ Floats are sealed with empty diesel drums with mild steels barrels coated with anti corrosives ➢ Rafts are suitable for Indian sea ➢ LONG-LINE CULTURE METHOD: cylindrical floats are used ➢ Oyster cages are suspended in sea with ropes ➢ In another method, hole is drilled in hinge of oyster and hanged with string

2. On-bottom culture: ➢ Sea bottom with granite or coral stones ➢ In Tuticorin, breakwater is used for culturing mother oysters ➢ Mother oyster: slower growth than raft

Rearing containers

1. Culture of mother oysters: ➢ Box cages: 40 x 40 x 15 cm (size may vary according to mesh size) ➢ Frames of the cage: 6mm mild steel rods coated with anti corrosives or coal tar ➢ Ideally, frame nets are used: 60 x 40 cm frame size with 5 compartments and hinged at one end ➢ Oysters are arranged in compartments: 10mm space in between the compartments for opening of shell valve 2. Juvenile rearing: ➢ Net cages: fabric velon screen bags ➢ Sides are stretched with steel rod in the form of prism ➢ Mesh size depends on size of the screen ➢ The mouth of the bag is tied with synthetic string ➢ These bags are placed in old nylon fish net bags: protection from predators ➢ Periodic replacement of velon bag is done to clean the clogging by silt and foul smell. It is sun dried and reused ➢ Spat upto 2 cm are reared in these net cages ➢ Box cages (mother oyster rearing) can be used at net cages (Juvenile rearing) by adding a velon bag

Uses of Pearl

ORNAMENT ORNAMENTAL HANDICRAFT

MEDICINE Use of by products of pearl culture: total mass of oyster after pearl culture: seed pearls, shell and the flesh

CLASS ‘C’ PEARLS: • Nacreous layer is removed • Remaining part is dissolved in phosphoric acid • Pearl calcium table is formed • In Japan, they are used for pregnancies, weakness, tooth cavities, acidity and allergy SEED PEARLS AS MEDICINE Mother of pearl layer: SHELL CRAFT FISH FEED POULTRY FEED ADDUCTOR MUSCLE: human consumption

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