PROBLEM TO BE SOLVED: To provide preventing means effective against streptococcal disease of fishes separating and identifying novel Lactococcus garvieae, and resulting from the bacterium thereof.SOLUTION: The invention provides an inactivated vaccine formulation against streptococcal infection of fishes resulting from Lactococcus garvieae, containing an inactivated bacterial cell of Lactococcus garvieae with a serotype of non-KG-type and non-KG+ type. Administration of the inactivated vaccine formulation to fishes has the potential to effectively prevent its generation, spread, and epidemic against streptococcal infection of the fishes resulting from the bacterium of Lactococcus garvieae with a serotype of non-KG-type and non-KG+ type, i.e., a novel type of Streptococcus which cannot be prevented using conventional inactivated vaccine against Lactococcus garvieae.
