Growth-related phenotypic and genetic diversity analysis of successive mass selected generations of Kumamoto oyster (Crassostrea sikamea)

The Kumamoto oyster, Crassostrea sikamea, is widely found in China, from Jiangsu to Guangxi, and has high aquaculture potential due to its beautiful shape and unique flavor. The individual size of C. sikamea in China is significantly smaller than that in the United States of America, the main reason should be the lack of artificial breeding. In 2012, a mass selective breeding program for C. sikamea was initiated to improve growth perfor-mance of our successive mass-selected C. sikamea generations, with the ultimate aim of improving the growth rate of C. sikamea. At harvest, each selective breeding generation showed superior growth performance compared to the corresponding control line. In the four generations of mass selection, the response to selection (SR), realized heritability (h2R) and genetic gain (GG) for shell height were 0.63-0.82, 0.38-0.51 and 5.54-9.50%, respectively. Meanwhile, the average SR, h2R and GG of the total weight of C. sikamea after mass selection for four successive generations were 0.61-0.90, 0.36-0.56 and 12.25-15.34%, respectively. The positive selection response for the fast growth of C. sikamea suggested that they have high levels of genetic variation, that can be used in future breeding programs to further improve their aquaculture traits. In addition, we also studied the genetic variability of successive mass-selected generations using microsatellite markers, and the results indicated that the selected line F4 exhibited significant lower genetic variation compared to F0 population. In future, we will use the F4 population to cross with other fast-growing breeding populations from other wild populations to retain the fast-growing traits while restoring its population genetic diversity.