The Pinctada fucata/martensii/radiata/imbricata species complex (Akoya Pearl Oyster)

The Pinctada fucata/martensii/radiata/imbricata species complex

Naming Problems
  • Ever since Shohei Shirahi's book "Pearls and Pearl Oysters of the World" (1994) came out, many species that were once believed to be different have been confirmed as actually belonging to one species. Such is the case for the Pinctada imbricata species, that now encompasses species that were once considered unique to one area.
  • Under this name we now have the former species of "Akoya" pearl oysters: P. fucata, P. martensii, P.radiata, P.anomioides, P.vulgaris, and several others. Shirahi mentions that the problem was caused by having small samples of shells, and when larger samples are used you can really see the species continuum.
  • Furthermore, Southgate's book ("The Pearl Oyster") calls the Akoya pearl oyster the Pinctada fucata/martensii/radiata/imbricata species complex and -just like Shirahi- considers this "group" as the most widely distributed and cosmopolitan pearl oyster species in the world, being distributed from the Mediterranean Sea, Persian Gulf, Red Sea, South Africa's Cape, India, Vietnam, China, Indonesia, Japan, Korea, Palau, Hawaii, Australia, the Gulf of Mexico and the Caribbean Sea and all the way down to Brazil.
Ecology and Habitat
  • P. imbricata is a Cosmopolitan species. In Japan it is found locally along the South-eastern Pacific coast of Japan and extends north to the southern coast of Korea. The area includes the warm Kuroshio Stream.
  • Because of volatile water temperatures, P. imbricata adapts well to seasonal changes in water temperature and current. Mohar, a variety of P. martensii , have also been found in the Persian Gulf, along the coast of the great bight that curves from the peninsula of Oman to Qatar.
  • These oysters are found at depths of between 8-20 fathoms (48-120 feet). They are found attached to corals or rocks. Mohar oysters produce some of the finest natural Oriental pearls.

P. imbricata in Pearls
The Japanese have used this species for pearl culture for over a century under the local name of "akoya-gai". Although several pearl-oyster species are present on the coast of Japan, P. imbricata is the only one of importance. Due to the proximity of its habitat to Korea, the species is used by Japanese companies in Korean pearl farms as well.
In Japan they are distinguished by their coloration: brown and white exterior with an interior lip that is yellow and brown. In contrast, the Ceylon oyster shell has a pink inner lip.
This mollusk fell from pearl prominence during the Japanese pearl oyster die-off of the mid 1990's. To recoup the industry, Japanese farmers imported akoya oysters from China. Today, both Japan and China use this animal as the primary akoya pearl producer.

First Use of the Pinctada in Perliculture
  • Mass production of pearls began in 1890 in Japan. The pearl culturing Industry was centrally located in Ago Bay. The proprietor of the 1,000 acres of sea bottom was the famous Kokichi Mikimoto, who began with about a million oysters and produced a harvest of 30,000-50,000 pearls annually. At that time, 1907, Mikimoto was only producing cultured blister pearls, which were hemispherical in shape. These pearls were cultured on the shell of the oyster and were deficient in luster and fragile. They could not be used in necklaces.
  • Dr. Tatsuei Nishikawa of the Tokyo Imperial University first discovered the technology to produce spherical "akoya" pearls. In a letter he wrote in 1907, he stated: "It is a great pleasure for me to tell you that I am studying pearl formation and pearl-oyster culture work this summer (1907). Fortunately, I have found the cause of Japanese pearl formation, i.e. the reason why and how the pearl is produced in the tissue of the oyster. I made a practical application of this theory with great prospects for producing the natural and true pearls at will." (Kunz, George Frederick. The Book of the Pearl. New York: 1908. pp 292-3).
  • The information referenced by Nishikawa in this letter describes the technology that changed the science of pearl culturing from shell nucleation to tissue nucleation. After receiving his patent in 1916, round Japanese akoya entered the pearl market for the first time.
  • It is common misconception that Mikimoto invented this process. Mikimoto acquired Nishikawa's research through marriage to Nishikawa's daughter. Using Nishikawa's process, Mikimoto became famous for inventing round "Akoya" pearls.
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A Japanese Akoya oyster shell with 3 Akoya pearls.

It is also important to note that in recent years it has been uncovered that the "discovery" made by Nishikawa was most likely gleaned from a British expatriate living in Australia named William Saville-Kent who died shortly after discovering the secret of culturing spherical pearls.

Common SynonymsMargaritifera martensii
P. fucata
P. pica
P. japonica
P. imbricata
P. vulgaris
Popular NamesLingah
Akoya gai
White Butterfly
Primary SourceJapan, China, Persian Gulf
Other geographical locationsSouthern coast of Korea
Persian Gulf: peninsula of Oman to Qatar
P. martensii in pearlsKnown as the "Akoya pearl oyster"
Origin of the "Mikimoto Akoya"

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