Pollution problems in Japan's Biwa lake have lead to ever increasing demand for Chinese cultured pearls.

Pearl farming in China dates to the mid 60's.  Until recently most of the pearls were of a low quality.  Recently, pearl production and quality have advanced significantly.

The typical freshwater mollusk is nucleated with 30 to 40 small pieces of tissue.  The mollusk secretes layers of nacre around the tissue.  In three to five years the pearls are harvested. The pearls average 7 to 8 mm.  Most of the pearls are of a inferior shape.  Approximately 3% are round, 5% are nearly round, and 15% are oblong.  The remainder are judged to be of a poor shape or highly blemished and marked for use in industries other than jewelry.  Common uses are wine, medicine and cosmetics.  

Most mollusk are grown in lakes, ponds, and rivers.  The water should be well circulated, peaceful, and full of bacteria.  The mussels are suspended at a depth of 2 to 2.5 mm. below the surface.  The ideal temperature is between 18 and 25 degrees Celsius.  

After implantation, it takes from five to seven days for the mollusk to cover the irritant with tissue. At ten days the mollusk begins producing nacre.  The nacre forms concentric circles around the irritant.  The nacre is allowed to thicken for a minimum of two years. The longer the mollusk stays in the water the thicker the nacre and the larger the pearl.  

Pearl farmers typically implant the mollusk in March, April, May, September and October.  

Due to the slow nacre growth in the winter months the mollusk are usually harvested between October and February.