Kumamoto oysters are a separate biological species from their close relative, the Pacific oyster. Kumamoto oysters were accidentally introduced along with Pacific oysters from Japan in the mid-20th century. They have unique characteristics, which make them valuable in live shellfish markets. Although they are good biological species, as we have shown in the papers listed below, particularly Banks et al. (1994), sperm from the Pacific oyster can successfully fertilize the eggs of the Kumamoto oyster. This has led to inadvertent hybridization in commercial shellfish hatcheries and degradation of the desirable qualities of Kumamoto stocks. We have been active for several decades in the recognition and prevention of such hybridization and in efforts to import new Kumamoto oyster stocks from their native range in Japan.
Gametic incompatibility and genetic divergence of Pacific and Kumamoto oysters, Crassostrea gigas and Crassostrea sikamea
Banks, M.A., D.J. McGoldrick and D. Hedgecock. 1994. Gametic incompatibility and genetic divergence of Pacific and Kumamoto oysters, Crassostrea gigas and Crassostrea sikamea. Marine Biology 121:127-135.
Hedgecock, D., G. Li, M. A. Banks, and Z. Kain. 1999. Occurrence of the Kumamoto oyster Crassostrea sikamea in the Ariake Sea, Japan. Marine Biology (Berlin). 133:65-68
The Kumamoto oyster Crassostrea sikamea is neither rare nor threatened by hybridization in the northern Ariake Sea, Japan
Camara, M. D., J. P. Davis, M. Sekino, D. Hedgecock, G. Li, C. J. Langdon, and S. Evans. 2008. The Kumamoto oyster Crassostrea sikamea is neither rare nor threatened by hybridization in the northern Ariake Sea, Japan. Journal of Shellfish Research 27:313-322.This paper gives the results of an expedition to Japan to find and return stocks of the Kumamoto oyster. The acknowledgements section thanks Sam King, a Pacific Hybreed investor, for a generous gift to the University of Southern California for travel costs for D. H. and subsequent analysis of calmodulin gene sequences.
The status of the Kumamoto oyster Crassostrea sikamea (Amemiya 1928) in U.S. commercial brood stocks
Hedgecock, D., M.A. Banks and D.J. McGoldrick. 1993. The status of the Kumamoto oyster Crassostrea sikamea (Amemiya 1928) in U.S. commercial brood stocks. Journal of Shellfish Research 12:215-221.