In this presentation, we report how the French hatcheries invested since 1990 in polyploidization and selective breeding of the Pacific oyster Crassostrea gigas. After its massive introduction in 1971 to replace previous oyster species hit by a virus and two parasites, the production was hit again mid 80’s by two new pathogens: OsHV-1 herpes virus and Vibrio aesturianus. A collective initiative to increase genetic resistance to OsHV-1 virus by sib-selection was not supported as this innovation could compete with the production of wild spats. Commercial hatcheries invested then in breeding program with SYSAAF expertise initially based on mass selection of surviving candidates to OsHV-1. Research works, developed in partnership with Ifremer and INRAE research organizations, improved practices by the development and application of reproductive and genomic tools to ease family productions (reproductive extenders), to manage inbreeding (DNA-parentage assignment) and since the last ten years by sib and genomic selection of the diploid lines (high-through put phenotyping, genomic indexation). The hatchery production of nearly 3 billion of mostly triploid spats (>50% of the national production) is making the application of breeding technologies and genomic selection as a case study for low trophic and extensive productions.