The French oyster production is mainly based on the pacific oyster, Crassos/rea gigas. However, for several years, C. gigas spat has suffered severe mortality outbreaks. A multifactorial etiology implicating environment, oyster physiology, genetics and pathogens is heavily suspected. A herpesvims and bacteria belonging to the Vihrio s\p/endidus polyphyletic group have been isolated From summer mortality outbreaks. Moreover, several strains belonging to the genus Vibrio have been identified as pathogen for different mollusk species. However, few tools are available for the identification of these Vibrios and for the characterization of the virulence of the pathogenic strains.