US Patent 7740864 Vaccines for diseases of fish

Fish are immunized by a mass vaccination method, such as by immersion in water containing an attenuated strain of a pathogenic bacterium that does not effectively cause disease in fish when the non-attenuated pathogenic bacterium is exposed to the fish by immersion. An illustrative example of the method is for immunizing against coldwater disease caused by Flavobacterium psychrophilum, which may be attenuated by serial passage in media containing increasing amounts of an antibiotic, such as rifampicin.