Just over a century ago, an enterprising villager in this little fishing town on Japan's Pacific coast robbed Mother Nature of one of her most charming secrets - how to grow a pearl.

Now, nature is striking back.A mysterious disease the past several years has almost made Japan's pearl oysters an endangered species. Unless a solution is found soon, Japan's venerable pearl industry fears it may be on the way out.

If the oysters die en masse again this year, "most of us will be forced to quit," said Toru Nishii, a pearl grower who has been in the business for more than 40 years. "I'm afraid the entire industry will go belly up."

The die-off is causing some shortages on the world market and prices are rising, people in the American gem trade report.

Devin Macnow, executive director of the Cultured Pearl Information Center, a trade group in New York, expects the shortage to push prices up by 10 percent to 15 percent this year.

Elizabeth Parker, an appraiser for Curt Parker Jewelers in St. Louis, offered a similar prediction but considers that modest given the situation. "I was very pleased with the prices" at a fine jewelry trade show in June, she said. "They were not as high as I expected."

Although the bigger and more expensive South Sea pearls from Australia and Tahiti are gaining ground, Japan's Akoya cultured pearls still dominate much of the world market - including nearly 65 percent of sales in the United States.

But just keeping the Akoyas on the market has become increasingly difficult.

In 1996, only 56.6 tons of pearls were harvested in Japan, down 22 percent from the amount harvested in 1993, the year before the first widespread oyster deaths were reported. Those deaths were caused by a "red tide," a deadly plankton called heterocapsa.

What is killing the oysters now is unknown.

The mortality rate surged to more than 50 percent last year, much higher than the average of 20 percent to 35 percent, according to fishery agency statistics. Of the deaths, about 92 million - or nearly 55 percent - were first- and second-year pearl-bearing oysters.

Some marine biologists suspect viruses, but their findings have been met with skepticism.

"We haven't been able to isolate any virus, at least at our lab here," said Dr. Toshihiko Matsusato, a pathologist at the National Research Institute of Aquaculture. "It could be even something totally un-known."

A government-led team recently speculated the culprit might be a shellfish parasite called perkinsus, which devastated oysters in the Mississippi River delta nearly 50 years ago.

Some pearl growers suspect artificial insemination and other scientific tinkering may have inadvertently spawned oysters that are more prone to disease.