[jshepherd]

The Japanese had originally used the Pinctada martensii. The Chinese started using the Pinctada chemnitzii and cross bred the two. But since the early nineties the Japanese have also used the chemnitzii martensii cross. The only operation I have heard to use exclusively the chemnitzii in China was the Nan'ao island farm (now defunct). The Chinese and the Japanese now use the same oyster.
As for the nucleation process... where do you suppose the Chinese learned to nucleate? From the Japanese, of course. The same Japanese that started Akoya farms in China to take advantage of lower wages and land prices. The Chinese have since largely taken it back, but to this day nearly all equipment is still Japanese - at least in the larger operations. Many of the factories are still coop factories run by the Japanese, producing Japanese Akoya pearls, even though the pearls are harvested, and for the most part, processed in China.