Though there are at least 10 different species of freshwater pearls oysters used in China for pearl jewelry , the most widely uses is the Hyriopsis cumingi. They are typically nucleated when they are 6 or 7 months old. They can be nucleated at various times of the year, but most farmers in colder regions nucleate during warmer times such as April and May, or August to October.
The nucleator removes a long piece of tissue from the outer edge of a donor mussel’s mantle and places it on a wet board. It is then cut into pieces 2-3mm square. He then spreads open the host mussel very slightly, wedges them open, and places the mussel on a special holder. The nucleator makes two rows of small incisions, about 20-25 in total, in the mantle tissue and carefully inserts the mantle pieces one at a time. The wedge is then removed and the mussel closes its shell. Then the mussel is returned to the water.