Lake Kasumigaura Pearls

The Kasumigaura Pearl is a freshwater cultured pearl from Lake Kasumigaura in Japan. Lake Kasumigaura is the second-largest lake in Japan, located 60 km to the northeast of Tokyo. Pioneer Mr. Kazuhisa Yanase began cultivating these pearls, in the size of more than 10 mm, with a round nucleus (akoya rejects have been mentioned as nucleus). He executed implantation of the molluscs himself. After seven years he succeeded in harvesting beautiful pearls.

To date, there are only three main farmers cultivating pearls in Lake Kasumigaura. Yanase set up his own nursery for rearing the necessary mussels, where they were allowed to grow for three years. Then, it takes further three to four years after implantation until the pearls can be harvested. Freshwater pearl farming began in Kasumigaura Lake in 1962. The method used in pearl production in Lake Kasumigaura is a drilled mother-of-pearl bead is inserted into the mollusc along with a piece of mantle tissue. During the peak production period of Lake Biwa pearls in the 1970s, Biwa pearl farmers produced six tons of freshwater cultured pearls per year, since that time, pollution, a devastating freshwater red algae bloom (red tide), and over-harvesting have caused the virtual extinction of the Biwa Hyriopsis Schlegeli pearl mussel.

Picture: Lake Kasumigaura pearls from Kojima Pearl

Mr. Yanase discovered that it would be possible to establish pearl molluscs in Lake Kasumigaura. Tests revealed that conditions were so ideal that the pearls could reach bigger sizes. Mr. Yanase cultivated the Kasumigaura Pearls (also called Kasumi Pearls in the trade) in ponds to protect the shell against diseases. Each Kasumigaura mussel produces just only one pearl. The mussel covers the nucleus and the piece with a pearl sack, to protect them from each other. If you scratch the pearl sack the typical lustre appears immediately.

The Kasumigaura cultured pearls appear in many different colours from white, apricot to deep purple, the most rare colour (but still quite frequent) is neon green. Most efforts of cultivating Kasumigaura pearls ended due to environmental conditions during the 1980s, and for a decade there was no production. After a quiet period of almost 10 years, success was achieved in 1993 with a handful of pearls as the result. Because of the four-year cultivation period, double that of its South Sea cultured pearl counterparts, the first marketable pearls were not available for sale on the world markets until 1997. The Kasumigaura mussel is a hybrid between the Hyriopsis Cumingi and the Hyriopsis Schlegeli. This hybrid mussel has two unique qualities:

a) These mussels have a greater resistance to pollution.

b) These mussels are able to accept a round nucleus.


Picture: Lake Kasumigaura pearls from Kojima Pearl

While Kasumigaura cultured pearls are cultivated with a round nucleus, Chinese freshwater pearls are nucleated by creating a small incision in the fleshy mantle tissue, inserting a 3mm square piece of mantle tissue from a donor mussel. By inserting bead nuclei in the soft inner tissue rather than the mantle, which is closer to the outside of the shell, in-body nucleation produces pearls with deeper luster, and highly nuanced colors.

To the eye, there is apparently no colour difference with Kasumigaura and Chinese freshwater cultured pearls, there is no lustre difference, and the Chinese pearls are often (but not always) at a lower price. China has dominated the freshwater pearl industry since the 1970s, and the fierce competition has led to prices ranging from incredibly cheap to reasonable, along with constant innovation to create new and different varieties. The price difference between the Kasumigaura cultured pearls and Chinese freshwater cultured pearls is due to marketing of Japanese pearls and also the limited quantity of Kasumigaura cultured pearls reaching the market every year. It is important to note that the Chinese are not growing these pearls to be Kasumigaura cultured pearl lookalikes. The market for the Chinese pearls is based on their stand-alone appeal, not the resemblance to Kasumigaura cultured pearls as such. The Chinese growers grade them separately due to their surface texture, but as always, would rather they be smooth surfaced.

Pictures: Chinese Kasumigaura lookalikes from

As the general production of nucleated freshwaters continues to improve, there will be less of the textured surfaced pearls amongst their harvests. Pond slime is the name given to the phenomenon of the colour of the pearl not being so evenly distributed, it looks almost like an algae stain. Apparently, these marks are very stable and not easily bleached. As most Chinese growers would rather be selling beautiful evenly coloured pearls, they are usually fairly inexpensive, despite the fact that some pearl lovers actively seek these types of pearls.

Today, there is another new mussel in Chinese freshwater pearl culture. The transformation is leading to even higher quality freshwater cultured pearls in more saturated colours and larger sizes. A Chinese company called Grace Pearl mentioned a mussel that is not know native to China. The literal translation was pond butterfly mussel. The scientific name for pond butterfly mussel is Hyriopsis Schlegeli. In Japanese, it’s Ikecho; common name is Biwa pearly mussel. The first report of the Biwa pearly mussel having been imported to China from Japan appeared in a scientific journal in 1997. The Hongmen City Reservoir Development Company began raising Biwa pearly mussels in hatcheries and experimenting with their pearling potential in China. They found that the mussel had greater vitality and produced better pearls overall. The advantages for the Chinese cultured pearl industry were obvious. But researchers did not stop with the simple use of the Biwa mussel. They crossbred it with the triangle mussel; thereby creating a hybrid that is better than either pure species with respect to pearl culture. There is no scientific or common name for the hybrid. Loosely translated, the Chinese call it the leisure mussel.

Picture: Lake Kasumigaura pearls from Kojima Pearl.

Information from,,, Fuji Voll Pacific Pearls, Grace Pearl, Doug Fiske GIA.