Evaluating a new population of Kumamoto oysters (Crassostrea sikamea) for breeding on the U.S. Pacific coast

We describe the introduction, evaluation, and integration of Kumamoto oysters ( Crassostrea sikamea ) collected from the Ariake Sea, Japan, in 2006, to create a new genetically verified Kumamoto breeding population for the U.S. Pacific Coast. Progeny derived from collected G 0 broodstock were used to create a G 1 cohort that was reared under quarantine conditions with frequent disease testing. The G 2 cohort with no detectable diseases, was released from quarantine and evaluated at a subtidal farm test site. Yields, survival, individual average weights, individual weights, shell dimensions, and shell shape index [SSI; shell depth / (width + length)] of G 2 and G 3 Japanese cohorts were not significantly different from those of an established Pacific Coast population; however, individual weights and shell lengths of the Pacific Coast population were significantly greater. Desirable harvest traits of Japanese cohorts G 2 and G 3 , except survival and SSI, showed high heritability and medium-to-high, positive genetic correlations, suggesting that genetic gains can be achieved via selection. Subsequently, G 2 and G 3 Japanese cohorts were crossed with an established Pacific Coast population to create an integrated G 5 breeding population that was evaluated at intertidal and subtidal farm sites. The G 5 inbreeding coefficient was estimated to be zero and the absence of genetic evidence of parental hybridization with Pacific oysters ( Crassostrea gigas ) was used to verify the species purity of the G 5 population. Consequently, this G 5 population provides the U.S. Pacific Coast oyster industry with a valuable breeding population for future production of Kumamoto oysters. • Kumamoto broodstock oysters ( Crassostrea sikamea ) collected from southern Japan were introduced to the US Pacific Coast. • Phenotypic traits of the new Japanese Kumamoto population were comparable to those of existing Pacific Coast populations. • Phenotypic and quantitative genetic parameters were determined for an integrated Japanese and Pacific Coast population. • The integrated population was genetically verified to be free of hybridization with Pacific oysters. • This integrated population provides the US Pacific Coast oyster industry with a valuable future broodstock population.