In China, fresh-water mussel-rearing to produce cultured pearls can be done in natural lakes, reservoirs or ponds. The study group was able to observe this type of aquaculture (Figure 66) at the Fish Culture Centre of the Qingpu district.
Three species of pearl-producing mussels are reared there in ponds: Hyriopsis cumingi (the best), Cristaria plicata and Anodonta woodiana. Several dozen small pieces of mantle, taken from mussels killed for the purpose, are first implanted between the mantle and the shell of each pearl mussel. An average of four mantles per pearl mussel is used and a skilled worker can prepare about 30 mussels per day.
The mussels are then placed in ponds, suspended individually by a vertical thread. Stocking density is 150–225 mussels per 100 m2 of water. Two summers later (water temperature 20–25°C), up to 40–50 cultured pearls per mussel are harvested, depending on the number of nuclei implanted.
The quality of the pearls produced in this way varies widely. Even though, in China they are used chiefly for medicinal purposes and their shape and quality are not as important as in Japan, the price can treble depending on whether they are classified in the fourth (Y 700/kg) or first (Y 2 000/kg) category.
Figure 66 Pearl mussel farming in ponds. Qingpu District Fish Culture Centre, Shanghai
One hundred pearl mussels produce an average of 0.5 kg of cultured pearls, i.e., a yield of 0.75–1.125 kg/100 m2 of pond. Income from this activity can be advantageous if the quality of the pearls is good, particularly when they are farmed in natural lakes or reservoirs where it is possible to intensify farming without much investment being necessary. This applies to the ‘Liberation’ People's Commune (district of Qingpu, Shanghai), which farms in this way in the Dianshan Hu and produces 500 kg of pearls/year.
