- India recognized the Pearls about thousands of years ago and has a long and glorious history of appreciating Pearls.
- Pearls were mentioned in the Rig-Veda, which is the oddest of the Vedas about 3,000 years ago.
- About 2,500 years ago, the Artha-Veda mentions an amulet made of Pearls and used as a talisman in India.
- The Indian epic book, the Ramayana, describes a necklace which was made with 27 Pearls.
- Ancient Hindu text provides evidences that the god Krishna discovered the first Pearl.
- Hyderabad is known as the Pearl City from the time of royal kings of Nizam.
- A Pearl is a Gem produced within the mentle of a living shelled mollusk.
- It is a mineral and is composed of calcium carbonate.
- Pearls were the first Gem discovered by human beings thousands of years ago.
- Pearls are the only organic Gem and it requires no processing.
- The ideal Pearl is perfectly round and smooth.
- According to Indian system of gemology of nine Maharatanas, the Pearl is only next to diamond.
- Pearl farming does not require artificial feeds, complicated farm structures or constant attention.
- Pearls are viewed as symbol of purity, love or source of wisdom & power.
- Hindu believes that Pearl brings happiness, to Chinese it brings wealth and to Egyptians it brings love.
- It is a Gem having deep lustre with wide ranges of colors and is perfectly round in shape.
- It is a composition of 85% of calcium carbonate 12% organic matrix and water.
- Pearl has 3.5 to 4.5 hardness with a specific gravity of 2.7.
- Any shell mollusk can produce a Pearl of some sort, but those molluscs who gave a Pearl lining or Pearl nacre in the interior of the shell surface can produce lustrous Pearls.
- The molluscs, the univalved gastropods and the two valved bivalves, with a nacreous layer can produce Pearls.
- Pearl is Produce by oysters in marine & mussels in the freshwater environment.
- Pearls are classified into three types:-
- Natural Pearls
- Cultural Pearls
- Artificial or Imitation Pearls
Indian Pearl Mussels:-
There are two genera of mussel fauna which is found in large scale in water bodies of India i.e.:-
- Lamellidens(9 species & 2 sub species)
- Parreysia(35 species & 6 sub species)
- Lamellidens are found in Ponds, Tanks, lakes and reservoirs because they like stagnant or slow flow of water.
- Parreysia are found in flowing water bodies like rivers, streams, canals.
- Natural Pearl is small in size & irregular in shape.
- The surface of a natural Pearlsare rough.
- The nucleus of natural Pearl is small with thick crystalline nacre.
- When a foreign particle such as piece of sand or parasite enters into any species of molluscs that cannot be expelled than the natural Pearls are formed.
- A mollusc secretes nacre to coat the foreign particle to avoid irritation due to it.
- As a result of which many layer by layer around the irritant of natural Pearl is formed.
- There are very less natural Pearls left due to the over-exploitation of the natural stocks.
- It is also a natural Pearl, the only difference being the human intervention in surgical implantation of live nucleus of desired shape into the body of mollusk where it cannot be expelled.
- Cultured Pearls are generally larger and are of a more consistent size and color than that of natural Pearl.
- Cultured Pearls are produced in both marine and freshwater environment with desired size, shape, color &lustre.
- Pearl Culture is done in many Asian countries including India.
- There are various steps and methods involved in Pearl Culture.
Pearl Culture:-Basic steps involved in freshwater Pearl culture operation of a mussel are:-
- Preparation of pond
- Collection of Mussels
- Pre-operative care
- Post-operative care
- Pond culture of Mussel
- Harvest of Pearl from mussel
- Pond is made for the molluscs for freshwater Pearl farming and it should be 2.5 to 3.5m deep.
- There should be clayey soil base.
- There should not be any aquatic macrophytes and algal blooms such as euglena µcystis inside the pond.
- Alkaline water is suitable for pond.
- V.C tubing (2”dia) with platforms (18x9in) as raft is provided for hanging Pearl mussels.
- Density of the pond can be between 50,000/ha to 60,000/ha.
- Nylon bag of 10cmx30cm(1cmmesh) are implanted in the pond and only two mussel per bag should be placed.
- This nylon bag is tied to the P.V.C tubing.
- The pond should be regularly fertilized with organic & inorganic manures periodically.
Collection of Mussel:-
- In India the common species used in freshwater environment in Pearl culture operations are L.marginalis, L.corrianus, and P.corrugata.
- These mussels are found where there is stagnant or slow flow of water like ponds, tanks, lakes and reservoirs.
- Choose mussels of size 8-10cm in shell length & weight of 50g.
- These mussels are kept in cemented tank and there should be 1 mussel/liter of water.
- The duration of pre-operative care is 2 to 3 days.
- This process of stocking ensures proper relaxation of the adductor muscles for preparation in surgery.
- The mussel on which grafting has to be operated upon is known as “grafting mussel” and the donor mussel is known as “surgical mussel”.
- Pallial mantle ribbon of 0.5cm wide and 70cm long is separated from the surgical mussel and are kept on a plain glass slit.
- The ribbon is than cut into pieces of size 2mmx2mm.
- A small nucleus of 2mm dia is also separated during the surgery.
- Then using a shell opener, the grafting mussel is carefully opened.
- The gills and the foot are gently pushed by means of a specialized needle until the inner side of the mantle is visible.
- Than the ribbon pieces are inserted gently inside the mantle of the grafting mussel and then similarly the prepared nucleus is inserted and is placed just adjacent to the piece of ribbon.
- Similarly more implantation can be done upon the same grafting mussel.
- The nuclear material can also be prepared from dead shell of the mussel L.marginalis.
- The live ribbon pieces should be kept moist till implantation and should be cleaned gently.
- The outer part of the ribbon piece should be inserted facing the inner side of the grafting mussel.
- Immediately after grafting operation the grafting mussels are kept in a cemented tank inside a nylon bag of 10cmx30cm (1cmmesh)
- The nylon bag should contain only 2 mussels and suspended at a depth of 0.2m in the tank for 10 days.
- Then daily examine the mussels and remove the dead mussels and the one that rejected the nucleus and ribbon tissue.
- Pond water treatment should be done with antibiotic at desired rate to ensure the survival and healing of wound of the grafted mussel.
- After post-operative care the grafted mussel are than placed in the pond in nylon bag as designed during preparation of pond.
- The mussels are suspended in a nylon bag at a depth of 1.0m on the P.V.C tubing platform.
- Ponds are fertilized with organic and inorganic manures periodically.
- There should be constant supply of supplementary food in the Pond.
- Micro-algae, rotifers, protozoa, detritus and planktonic are the food required by the mussel in their pond.
- The insertion of food in the mussel is dependent on the adductor muscles, gills, mantle and ciliary tract.
- Proper culture of natural feed of mussel should be done.
- Proper transparency, alkalinity and temperature have to be maintained until the harvest of the mussels takes place.
- The duration of pond culture of mussels varies from six month to eighteen months, depending on the grafting technique, size, number of nucleigrafted, health of mussel and condition of pond’s environment.
- At the end of the duration of pond culture harvesting is done and the Pearls are extracted from the mussels.
- The mussels should not be killed in order to extract the Pearls by cutting the shell valves or by crushing to prevent the depletion of mussels stocks from the natural environment.
- The technique developed by our organization and other developed Asian countries allows us to extract Pearls out of the mussels without killing them and moreover this same grafted mussel can be used again for mantle implantation and Pearl culture in second venture. These mussels can produce Pearls more quickly in their second usage which is both profitable and time saving and the Pearls are of more good quality in their second usage and also the cost of purchasing new fresh mussels for Pearl farming in second venture is minimized.
- During extraction in this method the mussels are open slightly and through surgical stick and fine forceps, the Pearls form inside the mussel is carefully removed without cutting or damaging the intestine or any other tissues of the mussels.
- A regular, round 3-5mm dia unattached Pearls are therefore obtained from the mussel.
- The success rate in this procedure of grafting is about 75%, which is really huge as compared to the traditional methods used earlier in our country.
- Mollusca are the largest phylum of invertebrate animals.
- Mollusca are the second largest living animal species after the antropods.
- Mollusk is originated from the latin word ‘molluscus’ which is derived from the word ‘mollis’ meaning soft.
- They can live in marine, terrestrial and freshwater.
- They are diverse in nature due to its size, structure and behavior.
- Freshwater mussels are mollusks which come under Bivalvia class.
- Freshwater mussels comprises of around 14% of total molluscan species.
- Freshwater mussels are found in pond, stream and rivers.
- Some of the uses of mussels are:-
- Formation of Pearls:-
- Pharmaceutical:-Chemicals found in bivalves are used in treatment of antithrombotic, extravasations agent, arthritis, ischemic heart disease and hyperlipidemia.
- As human food:-North east part of India have their diet of molluscs as their food and are sold in the markets of Odisha, West Bengal, Meghalaya, Jharkhand, Mizoram and Manipur.
- As a bio filters:-They remove and filter a variety of compound materials from water like sediments, bacteria, organic matter and phytoplankton which is beneficiary for the ecosystem of water in the rivers and pond.
- Biological indicators:-They are good indicators of water quality.
- Button industry:-In the early 19’s the shell of Pearls were used to make button unless the plastic button were introduced.
- Decorative:-Many companies make decorative items from the shell of mollusks.
Aquaculture in India:-
- Pond fish culture has already become a fulltime profession for livelihood of many people in our Country.
- Aquaculture in India has already gained a huge popularity due to the profit through it and capability of providing job opportunity.
- Today aquaculture has more than 6% of annual growth rate in our Country and it is increasing year by year.
- India’s average productivity in aquaculture is up to 2.9 tonnes/ha/year and therefore India ranks at second position when it comes to freshwater aquaculture production in the world.
- Fisheries contribute 4.5% of the agricultural GDP with 95% coming from freshwater culture.
Artificial Pearls:-Artificial Pearls are fake or imitate. These Pearls are made artificially by humans from a Pearl like material and with shining coating. The imitation Pearls are checked by rubbing them against teeth, if smooth feeling is observed than majority of Pearls are fake and it can also be check by pressing a pin on the surface of Pearl, if scratch occurs than it is fake.
Biology of mollusk:-In freshwater mollusk, the outer shell consists of two valves made of calcium and they are joined by a socket at the back. The both shell are bilaterally symmetrical and same but outer parts are asymmetrical on the four ends. The four ends are named as, Dorsal side, Ventral side, Anterior side and posterior side. Some of the properties of mussels found in India are:-
The longitudinal and concentric lines on the upper surface of the mollusks show the age of growth.Mollusk outer shell contains 94% calcium carbonate and 6% organic matrix and have three layers i.e. periostacum (made of organic matrix), prismatic calcite and inner nacreous layer (made of calcium).
- marginalist (i) Shell is thin, oblongovate and smooth. (ii) Posterior end is broad and angular curved. (iii) Dorsal end is just slightly curved. (iv) Anterior end is narrow curved and short as compared to posterior end. (v) Ventral margin is contracted. (vi) Two cardinal teeth and single lateral tooth on right valve end &one cardinal and two lateral teeth on left valve (vii) Blackish brown top layer and Light brown border.
- collrianus (i) Shell is elliptical & elongate. (ii) Posterior end is broad and angular. (iii)Dorsal end is straight and long. (iv) Anterior end is narrow and curved. (v) Ventral margin is contracted. (vi) Two cardinal teeth on each valves. (vii) Brown color with no Demarcation.
- corrugata (i) Shell is thick, solid & ovate (ii) Posterior end is broad and angular. (iii)Dorsal end is slightly curved. (iv) Anterior end is rounded. (v) Ventral margin is contracted.(vi) Both valves has two pseudo-cardinal and two lateral teeth. (vii) Greenish brown to deep brown color.
Mantle:- It is a skin like structure that covers the soft body of the mussel. The two mantle are joined at the posterior end to form two tube like openings called siphons. Lower siphon acts as inhalant of water and food to the body and the upper siphon act as the exhalent to waste excretory materials. These two siphons also help in respiration process of mussel.Mantle is divided into 3 divisions:-
The mantle helps inrepairing the damage to the shell.Mantle cavity: – It is the space between mantle and shell. It is filled by a fluid that helps in formation of outer shell.
- Outer epithelium consists of macrovilli consisting of compactly arranged cytoplasm and liquid amorphous material.
- In the middle there is a connective tissue with fibroblast cells and polygonal cells and cytoplasm.
- Inner epithelium consists of ciliated cells with central nucleus.
Internal organs:-Mouth is situated below the anterior adductor mussel and a pipe called oesophagus connects mouth to stomach which is near the mouth and inside the digestive gland. Gonads are present below the digestive gland (liver).The long intestine takes few turn and passes through the heart. The rectum comes from the pericardium and opens through the anus. The foot is below the internal organs of mussel. Gills are present between the exhalent siphon and inhalant siphon and a symmetric line of cilia is present in the gills.Digestion of food is due to the movement of cilia present on the gills. A food particle goes through ciliated groves towards labial palps due to the rhythmic upward and downward movement of cilia and through groves food reach to mouth and then to the stomach.The circulatory system of the mollusk is not so complicated and it consists of a heart inside the pericardium. The heart has a median ventricle and two lateral auricles. Through the ventricle, anterior and posterior, aorta arise which supplies oxygenated blood to different parts of the body. The oxygenated blood reaches to the anterior and posterior parts of the animals through the ventricle via gills and mantle through auricles. The deoxygenated blood for purification are carried by vena cava directly through the mantle and gills to kidney.The freshwater mussels are filter feeders in nature and they swallow their food after filtration by gills. The blood of the freshwater mussel is colorless and contains leukocytes.Respiration is done through a pair of gills or ctenidia. The septae divisions of ctendia into hollow tube allow the exchange of gases through them.The pair of nephridiasituated below pericardium is a tube like structure with two distinct regions which is responsible for excretion and removing the waste product by the lower and upper pair of nephridia respectively.The nervous system of the mussels is not so active and it consists of a pair of cerebral, visceral and pedal ganglia.Mussels are bisexual and have indirect reproduction with parasitic glochidal larval stages. The paired gonads are situated in the two sides of intestines. The gonads are red in females and of white color in males. The gonads become enlarge during breeding season. The coelomic epithelium living of tubules is responsible for giving rise to spermatozoa in males and ova in females. The sperms are released through genital aperture and are released from the body through exhalent siphon into the water.The sperms are large, rounded, rich in yolk, have a lot of granular cytoplasm and a nucleus. The sperm released into the water by males enters the branchial cavity of females where fertilization takes place. The development of the fertilized ovum takes place in the gills lamellae. Then this larva escapes through exhalent siphon of female mussel into the water again and through alternate expansion and contraction it swims actively in water and finds a suitable fish host for sixty to seventy days for taking nourishment from the host and this period is known as parasitic life of mussel. The juvenile mussel detaches after parasitic life from the host and swims in water for further growth on their own. The sexual maturity is attained within two years by the mussels and they can breed throughout the year and their peak time is monsoon season.
Stages of reproduction are:-
- Fertilized sperm produced in males
- release of mature egg in water by males
- enters female and ovum fertilization takes place
- release of ovum larva in water by female
- larva get attach to a host fish
- After sixty days it detaches from fish and develops of their own.