FLAVOBACTERIUM COLUMNARE IS RECOGNIZED AS ONE OF THE MOST IMPORTANT ENDEMIC PATHOGENS OF FARMED FISH IN THE USA. OUTBREAKS OF COLUMNARIS HAVE OCCURRED IN ALL STATES WHERE FRESH WATER FISH ARE CULTURED FOR HUMAN CONSUMPTION, AS WELL AS IN ORNAMENTAL SPECIES AND WILD FISH. A LACK OF EFFICACIOUS VACCINES, MOUNTING ANTIMICROBIAL RESISTANCE, AND LIMITED TREATMENT OPTIONS HAVE LED TO FISH KILLS APPROACHING 90% MORTALITY IN SOME US EPIZOOTICS. DIRECT ECONOMIC LOSSES ARE COMPOUNDED BY THE COSTS OF DELAYED PRODUCTION AND GROWTH, CHEMOTHERAPEUTANTS AND ADDED LABOR. FURTHERMORE, WHEN ANTIBIOTIC THERAPY IS ATTEMPTED, TREATMENT FAILURE IS COMMON. A LACK OF HOST SPECIFICITY POSES AN ADDITIONAL RISK, SHOULD THE PATHOGEN BE RELEASED INTO NATURAL HABITATS. THESE FACTORS ILLUSTRATE THAT PREVENTION THROUGH VACCINATION OFFERS SIGNIFICANT ADVANTAGES OVER TREATMENT. IN THIS PROPOSAL, THREE ESTABLISHED AQUATIC ANIMAL HEALTH LABORATORIES WILL PARTNER TO INVESTIGATE THE ANTIGENIC DIVERSITY OF F. COLUMNARE GENETIC GROUPS IN THREE IMPORTANT AQUACULTURED FISH SPECIES IN THE USA (E.G., RAINBOW TROUT, CHANNEL CATFISH, NILE TILAPIA). THE OVERARCHING GOAL OF THIS STUDY IS TO IDENTIFY SHARED IMMUNOGENIC PROTEIN VACCINE ANTIGENS OF F. COLUMNARE TO PROVIDE PROTECTION AGAINST EACH GENETIC GROUP REPORTED IN THE US. THIS RESEARCH WILL LEAD TO AN IMPROVED UNDERSTANDING OF THE EPIZOOTIOLOGY AND ANTIGENIC DIVERSITY OF THE PATHOGEN, AND THE DEVELOPMENT OF EFFECTIVE SUBUNIT VACCINE(S) TO PREVENT COLUMNARIS DISEASE. ADDITIONAL BENEFITS INCLUDE AN INCREASED KNOWLEDGE OF IMMUNE RESPONSES IN TELEOST FISH AND PATHOGENESIS OF BACTERIAL FISH PATHOGENS, AS WELL AS ADVANCES IN FISH VACCINOLOGY, ALL EXTREMELY RELEVANT TO DISEASE CONTROL IN AQUACULTURE.