Cytophaga, Flavobacterium, Flexibacter and Chryseobacterium infections in cultured marine fish

Many cases of fin or tail rot, skin ulcer, and jaw erosion were reported over the years in cultured marine fish. The aetiological role of various bacteria belonging to the Flavobacterium-Cytophaga group was frequently suspected, but only 3 bacterial species pathogenic for marine fish were fully described until now. Flexibacter maritimus was first identified in Japan in the late seventies from several fish species reared in sea water. Subsequently, the disease was recognized in very different geographic areas such as France, Scotland, Spain, Malta, Tasmania and California. The pathogenicity of the bacterium was demonstrated experimentally, phenotypic and genomic characteristics as well as virulence mechanisms were investigated, and treatment methods were proposed. Significant losses due to Flexibacter maritimus may occur locally. In Norway, Flexibacter ovolyticus was isolated from the adherent bacterial epiflora of Atlantic halibut eggs and was shown to be an opportunistic pathogen for halibut eggs and larvae. Chryseobacterium scophthalmum (first described under the epithet Flavobacterium scophthalmum) was isolated 10 years ago in Scotland from turbot suffering from gill hyperplasia and haemorrhagic septicaemia. A large collection of strains was studied, and investigations of the disease included experimental infection, histopathology and immunization trials. Until now, Flexibacter ovolyticus and Chryseobacterium scophthalmum have not been recognized in fish species or regions other than those from which they were initially isolated.