Frequently Asked Questions About Pearl Farming

Pearl Farming FAQs /Frequently Asked Questions About Pearl Farming

Today, let us discuss about Frequently Asked Questions  About Pearl Farming.

  1. How to start pearl farming?

  • You need to collect live oysters
  • After that, go searching for a big body of saltwater. You can also make this on your own.
  • If you have chosen an ocean or a sea, take a rope and put it in the water till the bottom level. Now with the oysters in the nets, attach them to the rope. The oysters should be in the water in order to be alive and the nets are kept to protect them from being eaten.
  • Pry open the shell by taking an oyster out of the net. Then you need to place a small bead which is being made from the shell of another oyster into the reproductive organ.
  • Place a piece of mantle from another oyster with the bead. The mantle is the organ which prepares the shell.
  • Now you need to close the oyster and put it back in the water. After 2-3 years, a pearl will be formed.
  • The point to remember here is that there is only a slight chance of the oyster becoming a pearl. Even if the pearl is made, that might not be perfect. The pearl may have an oval shape and it may be in any colour. There is also a chance of few oysters rejecting the bead or become sick or even die.
  • Pearl farming can also be done in freshwater with some differences.
  • Instead of oysters, mussels are used in freshwater.
  • A part of the mantle is enough to be inserted into the mussel’s mantle.
  • There is a chance of making up to 40 pearls in a mussel at a time.
  • There is a very small chance the pearl will be round; in fact, most of the world’s round pearls are made in saltwater
  • Natural pearls are the ones which are much easier to make because all the work is done by the oyster or mussel by itself. In Fact, these types are difficult to find. Natural pearls usually formed by small worms, parasites, or fish going inside the mollusc. These are not formed from grains of sand. When irritation occurs to a mollusc, mollusc has an irritation, it produces nacre, or mother-of-pearl, to cover the irritation. The nacre is the one which makes the pearl lustrous and beautiful. The mollusc continues to make more and more nacre until it forms layers around the irritation.

Read: Pearl Farming Project Report.

  1. What are the advantages of pearl culture?

  • Pearl culture is very eco-friendly because of the filter feeder oysters, which help in the purification of water.
  • Shellfish farming provides habitat for fish and enhances diversity in the species.
  • Pearl farming decreases turbidity, increases penetration of light,
  • It also improves the quality of water by reducing anoxia and nitrification.
  • A single oyster can clear over 15 gallons of water a day. It retains the particles which are as small as 2 microns.
  • A small oyster farm clears 30 to 100 million gallons of water each day
  • It not only accumulates heavy metals from the water, but also removes pollutants which are harmful to water.
  • Pearl farming also encourages the promotion of tourism as the technology of pearl farming and the end product is a topic of interest for tourists.
  • Pearl industry promotes foreign exchange earnings for the country.
  • Pearl farming also provides tremendous employment opportunities for youngsters and play a vital role in socio-economic development.
  1. What are the Indian freshwater pearl mussels?

The  Indian freshwater mussel fauna comprises two major species and these are abundantly found in most of the freshwater bodies. The  Lamellidens is one of the genes which is represented by nine species and two subspecies, whereas the other one is Parreysia which is represented by 35 species and six subspecies. Even though a majority of other regional species also possess pearl nacre, indicating future prospects, only three species out of the 52 Indian species are being employed in pearl culture operations.

Read: Fish Farming FAQ.

  1. What are the basic steps involved in freshwater pearl farming?

Farming of the freshwater pearl involves six steps sequentially, a collection of mussels, pre-operative conditioning, surgery, post-operative care, pond culture and harvesting of pearls.

  • Collection of mussels

The mussels, which are healthy are collected from the freshwater bodies like pond, river, etc. The collection of these mussels is done manually and are kept in buckets or containers with water. The ideal mussel size used for pearl culture is over 8 cm in length.

  • Pre-operative conditioning

The mussels, which are collected will need to be kept for pre-operative conditioning for 2 to 3 days. This is done by keeping them in the crowded condition in captivity with aged tap water at a stocking density of 1 mussel/l. Pre-operative conditioning is done to in weakening the adductor muscles, which helps to handle mussels easily during surgery.

  • Mussel surgery

Considering the place of surgery,  the implantation is of three types

  1. Mantle cavity
  2. Mantle tissue
  3. Gonadal implantations.

The key materials required during the surgical implantations are beads or nuclei, which are generally made from the shell of mollusc or other calcareous materials.

  • Post-operative care

The mussels, which are implanted are kept in post-operative care unit in nylon bags for 10 days with antibiotic treatment and supply of natural food. The units are examined daily with a removal of dead mussels and the ones that reject the nucleus.

  • Pond culture
  1. After the post-operative step is carried, the mussels which are implanted are stocked in the ponds. The mussels are kept in nylon bags of 1 cm mesh-12 sq. cm. Bamboo or PVC pipes are used to handle the nylon bags containing the mussels. These Bamboo or PVC pipes are placed in ponds at 1 m depth. The mussels will be kept at a depth of up to 2.0m during hot the months of summer and this is done to avoid surface heat. The mussels are cultured at a stocking density of 20,000 -30,000/ha.
  2. The pearl culture implantation operations are carried throughout the year, except during hot summer months of May and June. This is to minimize postoperative mussel mortality and rejection rate of implanted graft and nuclei.
  3. Ponds which are at a depth of 2.5m with the base of clay soil and waters which are slightly alkaline are suitable for operations of pearl culture. A pond which is of rectangular shape and with proper inlets and outlets is ideal for rearing implanted pearl mussel.
  4. Ponds without aquatic macrophytes and algal blooms such as Microcystis sp. and Euglena sp. are suitable for pearl culture operations. These ponds are provided with P.V.C tubing with a diameter of 2″ and platforms which are of 16 x 8 m as rafts for hanging pearl mussel culture units. The implanted mussels at a density of 50,000 to 75,000/ha are placed in nylon bags (l.0 cm mesh, 12x 14 cm)  at the rate of 2 mussels per bag.
  5. The area of the pockets and mesh size in these simple culture units are enough for a mussel to open and close the valves of the shell for feeding and operation. These bags are tied to the P.V.C floating platform units or bamboo rafts which are being maintained in the culture environment.
  6. The hanging depth which is ideal for the pearl mussel culture units is 1.5 to 2.0 min the ponds for better survival and growth of mussels. In an alternate way, the mussels can be kept in plastic crates which are about 0.5 x 0.35 x 0.25 m at the rate of 20 to 25 mussels per crate. The physical and chemical parameters and the water level of the ponds should be observed and taken care of throughout the culture period of the mussels. The optimum temperature regime lies between 25°C to 30° c. The freshwater pearl culture pond environment is generally the same as employed for the aquaculture of the carps.
  7. The mussels in freshwater have the benthic invertebrates in the pond ecosystem and because of this, there would be free dispersal at the bottom of the pond which is ideal in terms of growth and survival.
  8. It has been observed that mussels when maintained in the bottom- set culture units have recorded a poor survival of 27%, whereas against the surface and column-set units, they recorded a survival rate of 66%. The reason for poor survival in bottom units is because of the decrease in the level of primary production and siltation aggravated by the restricted space in the units.

5. What is the food and feeding in Pearl farming?

As algae is the most predominant components of the first trophic level in the aquatic food chain, they are considered the most important ones in aquaculture systems. Few species of algae, which belong to Chlorophyta (green algae), Bacillariophyta (Diatoms) and Cyanophyta (blue, green algae) generally use as a feed by the mussels in freshwater. The algal species which are most commonly preferred by the freshwater mussel Lamellidens marginalis are diatoms green algae (Chlorella chlorococcum, Scenedesmus etc.) and blue green algae (Spirulina). Tanks of desired capacities and culture vessels need to be chosen on priority to algal culture. A medium which would be perfect should be prepared well in advance for the culture of different species.

The pond culture of mussels that are operated might be from six month or more depending  upon the size and number of nuclei implanted, the health of the mussels and the condition of the pond environment. The culture units need cleaning of accumulated silt and other fouling fauna periodically, finding entry into the units.

6. How are pearls harvested in pearl farming?

  • At the end of the culture period, the mussels are harvested. This harvesting is done either by crushing the mussels followed by sieving to extract, pearl or each individual mussel is taken out from the pearl sac of the live mussels without sacrificing. The latter method, though difficult, is desirable to prevent depleted stocks of mussels in the natural environment.
  • In mantle cavity insertion method, the culture period is generally about 6 to 12 months, depending on the size and number of nuclei implanted. In this method the mussel at the end of the culture period is sacrificed. The mussels are opened one by one and the half round or design, shell attached pearls are cut out of the shell valves. Two to five attached pearls are obtained with this method, depending on the number of nuclei inserted. As on the attached side of the pearl, nacre cannot be deposited, it is ground off and cemented with a piece of mother of pearl layer obtained from the shell interior. The success rate is about 60 – 70% of the mussels implanted.
  1. What is a mantle cavity insertion procedure in pearl farming?

  • In the mantle cavity insertion method, appropriate nuclei up to 1.0 cm in size are kept in the mantle cavity of pearl mussels (L. marginalis and L. corrianus)of the size 8 cms to 10 cm in shell length and the mussels which are implanted are reared for a span of one year in pond culture environment. Depending on the shape of the nucleus implanted, the products are generally shell- attached, half round or design pearls.
  • Mantle cavity insertion method is a simple technique. Before the surgery, the indigenous freshwater mussel species Lamellidens marginalis, L. corrianus and Parreysia corrugata of required shell length and net weight are collected. These are opened carefully by the means of speculum which is 1 cm wide, without the causingvajy kind of injury to the adductor mussels and soft parts of the mussel. A small piece of the mantle from the anterior side is removed carefully from the upper shell valve and a nucleus of size and shape which is desired I.e., upto 1 cm is inserted carefully into the mantle cavity and is further pushed deep to avoid rejection. The mussel is turned over now and the same kind of implantations are made in the opposite mantle cavity.
  • After the implantation is done, the mussels are kept in postoperative care units. These units generally consist of Ferro- cement tanks of approximately 250 litres filled with aged tap water and 55 nylon bags, each of 13 sq.cm arranged in two rows,suspended at a depth of 0.2 m. These units are monitored on a daily basis for the dead mussels and the ones that reject the nucleus and are then removed.
  • After postoperative care, these mussels are then stocked in the ponds. The mussels, which are implanted are kept in nylon bags which are of 1 cm mesh- 13 sq.cm at the rate of 2 mussels per bag suspended at a depth of 1.0 m in culture ponds. The mussels can be placed in deeper zones up to 2.0 m during hot summer months to avoid surface heat. The stocking density of implanted mussels can be 25000/0.4 ha.
  1. What is mantle tissue implantation in pearl farming?

The mantle tissue implantation method is the one in which placement of the donor mantle graft of 2 to 5 sq. mm in the space and inner epithelial layers of the left and right mantle lobes of the recipient mussels which are off 9 to 10 and in shell length preferably. A small nucleus which is below 2mm in diameter can be placed along with the graft depending on the size and development of the mantle tissue of the recipient mussels. The implanted mussels are sent for culture to the pond environment  for a span of one year. The products are removed irregular to oval graft pearl or nucleated, round cultured pearls.

The freshwater pearl mussel has an internal structure which is complicated  and virtually there would be no space left for the insertion of a foreign body. However, the mantle is the only structure that occupies the entire bulk, by having two folds on either side of the shell valves. Hence, in China and Japan this method of implantation is chosen for production of more pearls per mussels. This also reduces the stress on the animal.

  1. What is the preoperative condition surgical method in pearl farming?

  • The Lamellidens marginalis and L.corrianus which are the indigenous pearl mussel species will be collected from the freshwater bodies like ponds, lakes etc, and are subjected to pre-operative conditioning for 2 to 3 days. They are kept in Ferro cement tanks of capacity approximately 180-200 litres with aged tap water at a density of 1 muss per litre of water.
  • Pre-operative conditioning makes sure that there is proper relaxation of adductor muscles in surgery preparation. This step is significant which helps in the limited application of narcotizing procedures as followed in marine pearl culture operations. The mussels are divided into two groups before surgery.
  1. the mussels to be operated upon ‘the operation mussel’ or ‘recipient mussel’ and those to be sacrificed,
  2. and the ‘cell mussels’ or the ‘donor mussels’.
  • The live donor mussel is removed and the pallial mantle ribbon of 0.5mm in length and 7 cm in width is taken on a moist wooden board which is precleared.
  • The strip is• now cut into graft pieces of appropriate sizes such as 2-4 mm and is embedded individually or along with small nucleus which is 2m in diameter into the mantle tissue of the recipient mussel.
  • The recipient mussel is opened carefully using a shell opener which is 1.0 cm wide. By pushing aside the gills and the foot carefully, the inner side of the mantle is exposed. Some pockets are removed in the inner mantle with the help of a specialized needle.
  • The pieces of the live graft which are made in the previous step are inserted into these pockets with care. One graft piece is inserted into each pocket with the outer side of the graft facing the inner side of the operation mussel shell. This kind of grafting will be done on two sides of the mantle lobes.
  • It is observed that the  mantle graft epithelium which is being implanted will surround the nucleus in the form of a pearl sac in about 12-15 days and the microvillus of the pearl sac epithelium contains the cellular basis for crystallization of aragonite calcium carbonate, the first step in pearl formation which is being introduced in 1997 by Janaki Ram & Gayatri Misra 1997.
  • The number of implantations will vary across 2-8 which is again dependent on the size and thickness of mantle of the recipient mussel.
  • In operations, which are nucleated, a small nucleus which is less than 2 mm in diameter is inserted along with the live graft piece in close association into these mantle pockets.
  • As soon as the implantation is done, the mussels are kept in postoperative care units consisting of a series of Ferro- cement tanks with a capacity of 200 litres filled with aged tap water and 50 nylon bags each of size 12 sq.cm suspended at a depth of 0.2m.
  • The mussels, which are implanted are placed at the rate of 2 mussels per bag with the ventral side up position for a span of 10 days.
  • The units are monitored on a daily basis to check the dead mussels and the ones that rejected the nucleus and the graft are removed. Treatment of the water in post-operative care units with done broad-spectrum antibiotic.
  • Chloramphenicol at the rate of 1-2 ppm as a prophylactic measure is beneficial for the survival and wound healing of the implanted mussels. It is desirable to add green water which is enriched in algae into these units after 3 to 4 days of postoperative care.
  1. What is Gonadal Implantation surgery in pearl farming?

  • In this method of surgery, the donor mantle grafts of 2 sq.mm in size and a nucleus with a diameter of 3 to 6 mm are implanted into the gonad of the recipient mussels.
  • The mussels, which have gonads implanted in them are maintained in post-operative care units with supplements of antibiotic for a period of 7 to 10 days. This is done to reduce the rate of rejection of the implanted graft and nuclei before transferring them to the pond culture environment. The products are unattached, regular, round cultured pearls.
  1. How is post-operative conditioning done in pearl farming?

  • Before the common freshwater mussels, L.marginalis and L. corrianus and L.corrugata of 8.0cm or above in size and 50g or above in wet weight are implanted, they are collected from the natural environment.
  • Split bamboo or cane baskets or in open plastic buckets are used to transfer live mussels for shorter distances. Anyways, for transport, which takes more time, it is advisable to use moist pond soil in between layers of mussels.
  • These mussels are kept in Ferro- cement tanks with aged tap water for a period of 2 to 3 days at a stocking density of 1 mussel per litre of water. Gathering mussels in this way for shorter periods make sure that there is proper relaxation of the adductor muscles in preparation for surgery.
  • After pre-operative conditioning is done, the mussels are segregated into two groups. The larger i.e., which are 10 cm and above contain the donor while the rest forms the recipient stock. The donor mussel is cut open through the adductor mussels with a sharp knife which creates a ventral gap between the two. Valves are shelled without causing any kind of damages to the mantle on both the valves.
  • The• margin mantle just above and along the pallial line is then cut using a pair of scissors or a grafting knife. The pallial mantle which is cut out is lifted gently from the posterior end with a pair of forceps and shifted to a pre-cleaned moist wooden block making sure that the inner side of the cut-out mantle ribbon faces upward in direction.
  • The mantle strip is wiped gently and cleaned with a wet sponge. The moist mantle strip is trimmed according to its length. A graft scalpel is employed on both the sides in order to obtain a pallial mantle ribbon of width 2 to 3 mm.
  • The pallial ribbon which is trimmed will be turned upside down exposing the outer side of the pallial mantle. The ribbon is again wiped with a wet sponge in order to clean it.
  • By using the graft scalpel,  the ribbon is cut into small pieces of 2 to 3 sq mm. The live graft pieces are kept moist until the implantation is done. The mantle on another side of the sacrificed donor can also be processed in the above-mentioned method and can also be used for implantations.
  • Once the live graft pieces are ready, the recipient mussels are opened carefully with the shell opener, which is inserted through the posterior aspect of the ventral margin of the shell.
  • With the help of the regulator ring of the shell opener, the recipient mussel is opened to a width of 1.0 cm and is placed on the clamped recipient mussel and is carefully pushed up with a spatula due to which the operating gonad area is exposed.
  • By using a pair of forceps, elevation of gonads done by stretching the foot. A measured small incision is created with the help of a special knife placed at the other end of the graft needle, under the outer membrane of the gonad.
  • Ultimate care has to be taken to make sure that it is not cut deep into the gonadal tissue. This avoids damage or injury to the intestine.
  • A live graft piece is selected and is slowly and carefully inserted through the incision ensuring that the outer side of the graft is facing the entry point.
  • Nucleus implantation is a sensitive procedure which is done after graft insertion. Here, the nucleus is picked up with the moistened nuclear of an appropriate size and is pushed through the same incision cut for the graft, until it comes in contact with the implanted graft.
  • As soon as the nucleus is released, the nucleus cup is withdrawn. Care must be taken to make sure that the nucleus is in close contact with the outer epithelium of the implanted graft.
  • Smoothening of the margins of the incision is done with the nucleus needle cup to reduce the gap at the incision site. The middle area of the gonad is the possible site for single implantation.

Postoperative care:

  • Postoperative care is the significant step in operation of fresh pearl culture.
  • This is required for the recovery of implanted mussels. As soon as the surgery is completed, the restricted movement of mussel is essential for the retention of the implanted graft and nucleus.
  • Thus, after completing the implantation, the mussels are kept in postoperative care units. These units consist of rectangular Ferro- cement tanks with a capacity of 200 litres per tank which are filled with aged tap water and 50 nylon bags each of size 12 sq. cm. These are suspended at a depth of 0.5m in two rows.
  1. What are the procedures to prepare steel beads, Stelon nuclear material and shell bead nucleus in pearl farming?

  • The first type of nucleus which is called as stelon beads is made by the use of commercially available self-cure acrylic repair material which can be used both as powder and solvent. This will be most needed in dentistry. The second type of nuclear material called as shell bead is prepared from the pieces of dead shell from the freshwater mussel Lamellidens marginalis.
  • For the preparation of stelon nuclear material, a glass container is taken with the required amount of acrylic powder and slowly the solvent is added to it. In most cases, this is done by using a syringe which is then mixed thoroughly to prepare a dough. Immediately, nuclear material of desired shape and size is prepared and kept in the air to dry. After that, they are stored in dust free close containers. The nuclear material is boiled in water, air dried and cooled few hours prior to implantation.
  • For the shell bead nucleus is prepared, dead shells of Lamellidens marginalis are collected and are thoroughly washed in water in order to remove dirt and sand particles. If there are any dry flesh materials, they are scraped out. The shells will be dipped in 5000 ppm of chlorine solution which is made of 50 grams of bleaching powder containing 10% chlorine in 0.1 liters of water for twenty-four hours or forty-eight hours depending on the requirement.
  • The Complete lye- peeled shells are selected and are then continuously washed in tap water. They are then moved into an maintained at 60°C, for more than two hours. This can also be dried in the sun, for a longer duration to make sure that chlorine is completely removed from the treated shells.
  • The dried shells are then cut into small pieces by using a mortar and pestle and are then by using an electric grinder, they are finely powdered. The powdered shells are then processed through a sieve of 0.01 – 0.05 mm mesh size. The commercial glue Araldite hardener and resin that acts as a binder are mixed in a ratio of 1:1 to prepare a paste.
  • The sieved shell powder is added to this paste slowly to prepare dough which is of thick consistency. The ratio of the adding shell powder to the paste should be 5:1. Immediately, nuclei of desired shape and size are prepared and then, they are air dried till they become hard. Before implantation, the nuclei are boiled in water and cooled. The mussels can now be suspended in the ponds for pond culture.

Read: Prawn Cultivation.

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