By Dr Forkan Ali

Pearls are a valuable natural resource. Since ancient times people have collected natural pearls from various parts of the Bay of Bengal. Industrial pearl culture by artificial means began first in China, and artificial pearl production later began in Japan, Australia, France, India and other countries.

Bangladeshi pink pearls, however, are world-famous, and the country's bright pink pearls are still in demand abroad. Australia and other countries buy them from Bangladesh. Yet pearl farming has not really developed through either government or private initiatives. In 1974-79 the Department of Fisheries started an experimental project to culture pearl-bearing mussels, and later efforts at artificial pearl culture were made at the Mymensingh fisheries research centre with the cooperation of the Fisheries Research Institute. Proper management and the right technology could not be developed. Various universities and research institutions in the country are researching the subject, and many individuals are now also taking up pearl farming.

Not every mussel yields a pearl. Pearls are found in five kinds of mussel in Bangladesh. Pink pearls are found in the "landsalides" and "farsia" types, at a rate of 1-3 per cent, while pearls are found in 7-10 per cent of the "lamelia" and "marjenalia" species, as the author names them. Pearls are also found in a local sea mussel called placuna placenta.

Bangladesh's rivers, canals, beels and ponds are full of pearl-bearing mussels, and the country has water and soil chemistry and a climate suited to pearl formation. Pearl-bearing mussels are found in almost every district, but quality pink pearls are found only in greater Dhaka, Sylhet, Mymensingh, Rajshahi, Bogura, Pabna, Faridpur, Cumilla and Tangail.

Pearls come in different sizes, colours and names. By shape they are known as long, triangular, round pearl, methi, gara, chumki, raitki, phoski, oval-round and chur or jhur. Immature pearls are called chur/jhur or powdered pearls. Pearls are usually white, pink, bright pink, black-gold, golden yellow, grey and dead (colourless).

Mussels live in both fresh and saline water. They move along the bottom and eat rotting organic matter from the lower layer, so they are known as detritus feeders. Because of competition for food, bottom-feeding fish such as mrigel, shrimp, mirror carp and black carp cannot be farmed with mussels. Mussels act as hosts to various parasites, and fish or shrimp in the pond's lower layer may fall ill from contact with them.

For natural mussel culture, the elongated, swollen or slightly thick mussels of the species the author names "lemilidens orginalis" are best. Mussels spawn in rivers, canals and beels in June-July. The eggs are sticky and cling to submerged bamboo, bamboo twigs or weeds, and within two months they become small mussels of 2-3 cm with shells. That is the time to collect them and stock them in ponds or beels. Releasing them inside an enclosure of nylon net or bamboo makes them easy to collect when it is time to operate for pearl culture. Chemical fertiliser, organic fertiliser and lime should then be applied to the pond or beel.

A one-bigha pond can hold at most 2,000 mussels alongside fish. After 3 years, or when the mussels are generally over 10 cm, they should be taken out and the pearls collected. A pond depth of 2 metres is good for fish and mussel culture, with loam or clay-loam soil. Dry the pond and apply 60 kg of lime a bigha, then 500-600 kg of rotted cow dung, and mix it into the bottom soil. Release the mussels and fish once the pond fills with monsoon water. Following fish-farming practice, 15 kg of urea and 15 kg of TSP a bigha can be applied, followed by 5 kg every month.

Pearls are usually found in six parts of the mussel's body. Chemical tests show a pearl is 92 per cent calcium, 6 per cent inorganic minerals and 2 per cent water. A pearl's size and colour depend on what kind of calcium particle has entered the mussel. If, while feeding or moving naturally, a particle from the shell or an outside object such as a grain of sand, dirt or an insect lands on the mussel's body, the mussel secretes a kind of saliva that covers it. Layer after layer builds up over it until it becomes a pearl. Pearls of different colours form depending on the chemistry of the soil and water.

The mussel's hard outer shell is made of calcium carbonate. Just beneath it is a thin membrane called the mantle, whose upper part is extremely sensitive. A small particle, bead or small dead pearl is inserted through a cut in this part of the membrane (the upper part of the foot where the ovary begins). This irritates the cells of the upper part, which secrete saliva to protect themselves from the foreign particle and cover it. The irritation grows, more saliva is released, and the particle hardens into a pearl.

After a foreign particle is inserted, 20-25 per cent of the mussels die and at least 10 per cent expel the particle from their bodies. In Japan, Australia, China, India, the Philippines and Burma, 70-80 per cent of mussels now produce pearls by this method. To carry out the operation comfortably and well, chairs, tables, trays, basins, buckets, dry cloth, sponges, antibiotic medicine and other materials are needed.

A shaded place indoors or outdoors on the pond bank is best for the operation. It is good to collect the mussels in a cement tank 5-10 days beforehand, so that the operated mussels can be reared under proper management for the required period.

The nucleus is implanted in two places in the mussel: the gonad and the mantle covering the body. Round pearls form from the gonad, and small seed pearls from the mantle.

Pearls grow fast inside the mussel for two to two and a half years, after which growth slows. After 30 to 36 months, when the mussels reach 10 cm or more, they should be taken out of the water. When the harvested mussels are opened and the flesh separated from the shell, press it with your fingers. Any hard object you feel should be separated from the flesh and kept in a container of clean water. Pearls can also be separated by keeping the harvested mussels for 10 minutes in a 5 per cent solution of potassium hydroxide in water; any pearls will settle at the bottom of the container. Mussel shells also sell at a good price.

A pearl's price depends on its shape, colour and size. Large shimmering pearls with a pink sheen sell for up to Tk 60,000 to 70,000, more than white pearls. Small and dull pearls are cheaper, and some can be bought for a taka each. A pearl 5 cm deep and 7.5 cm long is famous as the Pearl of Asia. A diver found it in the Persian Gulf near Bahrain in 1628, and it is now kept in the United Kingdom's treasury. Before the Second World War it was valued at 30,000 pounds sterling. Such large pearls are still surrounded by great mystery, which tempts us to research the subject.

Palmists attach great importance to pearls in astrology: golden pearls for wealth, white pearls for ideals, black pearls for depth of philosophy, and pink and red pearls for beauty. Astrologers advise grey pearls for health, strength and better thinking.

Pearls are very valuable and rank next only to diamonds as jewellery. By culturing pearls not only in freshwater mussels but also in sea mussels and oysters, the country could meet domestic needs and earn large amounts of foreign currency. A Japanese scientist named Mikimoto was the first to produce pearls artificially, and an island in Japan named Pearl Island is named after him. Programmes to culture the large white-pearl-bearing sea mussel called pakuna placenta, found in abundance around Maheshkhali, Sonadia, Saint Martin's and Kutubdia in Cox's Bazar, could be taken up. This neglected resource of mussels and pearls could enrich the country. If pearl culture technology is developed and extended alongside fish farming, Bangladesh too could become a pearl-exporting country like others, earning large amounts of foreign currency and creating jobs for unemployed young people.

The writer is a researcher and former principal.

Source: Jagonews24. First published in Bengali on The Agro News.