Combine a common freshwater mussel with an ingenious implantation technique and presto, a profitable industry is born. Its product: lovely, lustrious pearls for use in makeup and medicine.
Pearls, especially those with a good lustre, have been among man’s favorite gems since ancient times. Wearing pearls makes a person look radiant and more attractive. Is it any wonder then that men and women, young and old alike admire and cherish the pearl.
With the advance of scientific technology and the rising standard of living, pearls are now used in make-up and medicine. Demand has never been higher that it is today. The result is that pearls have become even more precious, with the price rising remarkably.
Freshwater mussels are found in abundance in the fish ponds of Taiwan. Previously, these mussels were of no commercial value and were, in fact, considered a nuisance by the fish farmers. Since recently, however, a new use has been found for these mussels in the culture of freshwater pearls. Smooth, bright and clear pears can be harvested after 2-3 years of cultivation using the fresh water mussels.
From Pest to Profit
The type of mussel used to culture pearls in Taiwan s found living in the soft mud at the bottom of most freshwater ponds. It is the benthic freshwater bivalve. Anodanta woodlana commonly called river clam or freshwater mussel.
In actual fact, freshwater mussels are really a nuisance to fish farmers when they invade their fish ponds. The adults compete with cultured fish for oxygen and freshwater plankton which comprises their food. Mussel larvae enter the bodies of the fish and attach themselves to the gills, causing young and weaker fish to die. So, as can be seen, freshwater clams are actually a scourge to fish farms.
Because the epithelium of the mantle margin of freshwater mussels secretes a substance called nacre, the utilization of technology to implant pieces of the epithelium in these clams can result in the production of pearls. Farmers have thus been able to take a pest and use it to create a profit-making industry.
Pearls are made up of about 90% calcium carbonate, 4-7% conchiolin and 0.4-0.8% water. There are five characteristics to consider in determining a pearls value: texture, shape, color, size and lustre. If food technique is used during implantation, the resulting pearl will have good texture and shape. If the mussel is active, the implanted epithelial pieces are of good quality, and the mussel farm is well managed, the pearl will have superior color, size and lustre.
The mussels from which the epithelial implants will be taken are collected and put in buckets of clear water to flush them. For cutting the epithelial pieces from the mussels, a sharp razor blade is used. First, the adductor muscle is cut so that the shell may be easily opened. A pair of scissors is then used to cut strips of epithelial lining between the inhalant siphon and the adductor muscle. The epithelial strips are placed on a hard wooden board and the connective tissue is cleaned off the back of the strips. They are then cut into 3.0-4.0 mm long pieces. The thickness of the strips should be between 0.5-1.0 mm
Healthy mussels are selected and put into a vise assembly that will force the valves open 1.0-1.5cm apart, are made in the epithelium of the marginal zone. The previously cut epithelial pieces are then inserted into the holes, about 0.5 cm deep, making sure they are firmly in place. When one is familiar with the technique, one can use one’s left hand to make the holes and the right hand to insert the pieces.
There are basically two methods of culturing pearls. One is the scattering method and the other the net-suspension method. The scattering method consists simply of distributing the mussels in the pond. The net-suspension method uses stainless steel wire mesh baskets to suspend the mussels in the water. The net-suspension method has three advantages:
- the mussels can be inspected easily during the culture period,
- harvesting is easy, and
- fish can be raised in the same pond, thereby conserving space and increasing productivity.
The stainless steel basket can be kept in the water for 2-3 years before deteriorating. The baskets are 40×60 cm in diameter. A piece of netting is used to divide the inside of the basket into two levels, from which the clams are suspended. The net has a mesh size of 2-3 cm. Netting is also used to wrap the steel basket.
The baskets are then suspended in ponds from racks made from type of bamboo called gwet. The racks can be of the fixed or floating type. The fixed racks are used in small ponds where it is easy to control the water level. Floating racks are used in large reservoirs.
In order to stimulate more rapid secretion of nacre, the mussels should be suspended 20-30 cm below the water surface. About 6 months before harvest, they are lowered to 80-100 cm below the surface. Although during these last six months, the nacre will be secreted more slowly, the pearl will become denser and its color and lustre will improve.
For more information, contact
#103 J. Abad Santos cor. Lopez Jaena Sts.,
Little Baguio, San Juan, Metro Manila
Tel: (02) 727-6205
Bureau of Fisheries and Aquatic Resources
Philippine Coconut Authority (PCA) Building,
Elliptical Road Diliman, Quezon City
Tel No. : +63(2)929.9597; 929.8074
Email : [email protected]
D.A. Compound, Elliptical Rd.,
Tel. Nos. (632) 929-6065 to 67 / 920-3991 / 928-1134
photo from purepearls.com