Many species of pathogenic bacteria have been reported from marine fishes in Japan : Aeromonas salmonicida (atypical), clamydia like organisms (epitheliocystis organisms), Edwardsiella tarda, Flexibacter maritimus, Lactococcus garvieae (syn. Enterococcus seriolicida), Mycobacterium sp., Nocardia seriolae (syn. N. kampachi), Photobacterium damsela subsp. piscicida (syn. Pasteurella piscicida), Pseudomonas anguilliseptica, Pseudomonas putida, Renibacterium salmoninarum (in maricultured salmonids), Staphylococcus epidermidis, Streptococcus equisimilis, Streptococcus iniae, Vibrio alginolyticus, Listonella anguillarum (syn. Vibrio anguillarum), Vibrio ichthyoenteri, Vibrio ordalii, Vibrio trachuri and some other minor or unknown species. These bacteria usually give damages to some limited fish species, however, most of them have been found to be distributed in other cultured and wild fish species which will be possible hosts or carriers of pathogens. Drug resistance, deterioration of water around farms, and spread of pathogens by transporting seedling fish are the major problems for the control of disease in Japanese mariculture.