Japan invented the round cultured pearl and led the world's pearl trade for most of the 20th century. Its farms grow mostly Akoya pearls in the small Pinctada fucata oyster, along sheltered coastal bays in the south and west of the country. Japan also once produced well-regarded freshwater pearls in Lake Biwa and Lake Kasumigaura. Both lakes later faced serious water quality problems.
The Akoya oyster
The Akoya pearl oyster, usually classified as Pinctada fucata (often written Pinctada fucata martensii for the Japanese form), is one of the smallest commercial pearl oysters. Its shell rarely grows much wider than about 7 to 8 cm. That limits the size of bead it can carry, so most Akoya pearls fall between about 6 and 8 mm, with pearls over 9 mm rare and expensive.
Akoya oysters prefer temperate, sheltered water, and they are sensitive to cold snaps, red tides and disease. Their nacre is often fine and compact, which helps explain the sharp, mirror-like luster that made Akoya pearls the classic white strand. The page on what pearls are made of covers how layer structure affects luster.
Ago Bay and the birth of the industry
Ago Bay, on the Shima Peninsula in Mie Prefecture, is where commercial pearl culture began. Its many inlets and islands give calm water. Kokichi Mikimoto, a native of nearby Toba, started experimenting there in the late 1880s and produced semi-round cultured pearls in 1893. The technique for round pearls, credited to Tatsuhei Mise and Tokichi Nishikawa, made Japanese farms the main source of round pearls by the 1920s. The full story is on the cultured pearls page.
Ago Bay is within Ise-Shima National Park, and rafts holding oyster baskets have long been a familiar sight there. Farming later spread to other parts of Mie Prefecture and well beyond.
Toba and Mikimoto Pearl Island
Mikimoto Pearl Island sits in Toba Bay, a short distance from the town of Toba. It was the site of some of Mikimoto's early work and is now a visitor attraction with a pearl museum. It is also known for its demonstrations by ama, the female free divers who traditionally gathered shellfish and seaweed along this coast. In the early days of pearl culture, ama collected wild oysters and helped tend the farms. Their diving tradition in the Shima and Toba area goes back many centuries.
Other Akoya regions
As the industry grew, farms opened in many prefectures. Ehime Prefecture on Shikoku, especially the Uwajima area facing the Bungo Channel, became one of the largest producers. Nagasaki Prefecture in Kyushu, including Tsushima and the Omura Bay area, has also been a leading source. Kumamoto and Mie remained important, and Mie still carries the historic name. The relative share of each prefecture has changed over time.
The Japanese farming cycle
Akoya farming follows the seasons:
- Hatcheries or wild collection supply young oysters (spat), which grow for one to two years before they are large enough to nucleate.
- Technicians nucleate the oysters, mostly in spring and early summer, inserting a shell bead and a small piece of donor mantle tissue.
- The oysters hang in nets from rafts through the warm months, when nacre grows fastest.
- Harvest traditionally comes in winter, roughly December to February, when cold water slows growth and gives smoother, brighter surfaces.
Many Japanese Akoya pearls grow for less than a year to about two years after nucleation. Short growing times can mean thin nacre. The pearl grading page explains why nacre thickness matters.
After harvest, Japanese processors have long used a standard sequence of steps on Akoya pearls. These include cleaning, a mild bleaching to even out color, polishing and sometimes a light pink tint. Japan also became a processing and wholesale center for pearls grown elsewhere, with Kobe the best-known pearl trading city. These treatments are normal in the trade and should be disclosed. The gemstone treatments page covers disclosure more broadly.
Lake Biwa freshwater pearls
Lake Biwa, Japan's largest freshwater lake, lies in Shiga Prefecture near Kyoto. Pearl farming began there in the early 20th century and expanded over the following decades using the native mussel Hyriopsis schlegeli. Biwa farmers grafted mantle tissue without a bead, producing solid nacre pearls in many shapes, often elongated stick or irregular forms. They had a smooth surface and strong luster.
Biwa pearls became so well known that "Biwa" turned into a loose trade name for any freshwater pearl with a similar look, including Chinese pearls. Strictly, the term should mean pearls actually grown in Lake Biwa. Pollution and declining water quality hit the lake's mussel farms hard from the 1970s and 1980s onward. Production fell sharply, and true Biwa pearls are now uncommon.
Lake Kasumigaura
Lake Kasumigaura, in Ibaraki Prefecture northeast of Tokyo, supported a smaller freshwater pearl industry in the later 20th century. Farmers there used hybrid mussels that crossed the Japanese Biwa mussel with a Chinese species, and bead-nucleated them. That produced large, round to baroque pearls with rich colors, often sold as Kasumiga pearls. Water quality problems and a limited number of farms kept output small.
Decline and pressure on the industry
Japanese Akoya production peaked in the mid-20th century and has since fallen a long way. Several pressures added up:
- Mass oyster deaths in the 1990s, linked to disease and water conditions, killed a large share of Japan's farmed Akoya stock in several regions.
- Red tides and rising coastal water temperatures repeatedly damaged farms.
- Competition from Chinese Akoya and freshwater pearls pushed prices down.
- Many pearl farmers are elderly, and fewer young people have joined the trade.
Farms responded by breeding hardier oysters, including crosses with Chinese Akoya stock, and by stressing quality over volume. Japan kept its reputation for fine Akoya pearls and remained a major center for processing, sorting and trading pearls from many countries. The page on Chinese pearl farming shows how production shifted.
How Japanese Akoya compares
| Feature | Japanese Akoya | South Sea and Tahitian |
|---|---|---|
| Oyster | Pinctada fucata | Pinctada maxima, Pinctada margaritifera |
| Typical size | 6 to 8 mm | 9 mm and up |
| Common colors | White, cream, silver, with rose or silver overtones | White, gold, gray, black, peacock |
| Hallmark | Sharp luster and round shape | Large size and thick nacre |
For the larger pearls, see South Sea pearl farming and Tahitian pearl farming.
Frequently asked questions
Are all Akoya pearls from Japan?
No. China and, to a lesser degree, Vietnam also farm Akoya oysters. Japan is the best-known source and has the longest history with them.
Why are Akoya pearls usually small?
The Akoya oyster is small, so it can only carry a modest bead. Pearls above about 9 mm are rare for that reason.
What are Biwa pearls?
True Biwa pearls are freshwater pearls grown in Lake Biwa, Japan, usually without a bead. Production fell sharply because of pollution, and the name is now often used loosely for any similar-looking freshwater pearl.