** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** LACTOCOCCOSIS IS AN EMERGING DISEASE OF SIGNIFICANT CONCERN FOR AMERICAN AQUACULTURE. THE DISEASE TYPICALLY PRESENTS AS A HEMORRHAGIC SEPTICEMIA WITH HIGH MORTALITY RATES. AT PRESENT, THERE ARE NO EFFICACIOUS VACCINES OR OTHER PROPHYLACTIC METHODS AVAILABLE FOR THIS DISEASE, AND TREATMENT WITH ANTIMICROBIALS OFTEN FAILS TO CONTROL OUTBREAKS. ADDITIONALLY, THE DYNAMICS OF DISEASE TRANSMISSION AND PATHOGENESIS REMAINS UNCLEAR. LACTOCOCCUS PETAURI POSES A PARTICULAR PROBLEM FOR CONTROL EFFORTS, AS IT IS BOTH HIGHLY PREVALENT IN THE AMERICAS, AND HAS DEMONSTRATED BOTH HIGH VIRULENCE AND HIGH TRANSMISSION EFFICIENCY IN RAINBOW TROUT COHABITATION STUDIES. FURTHER, L. PETAURI MAY PERSIST OUTSIDE THE HOST IN BOTH BIOFILM AND PLANKTONIC FORMS. THE CONTRIBUTION OF THESE CHARACTERISTICS TO PATHOGENESIS HAVE NOT BEEN ASSESSED COLLECTIVELY. WE AIM TO USE A MULTI-PRONGED APPROACH TO MEET THE NEEDS FOR NEW TOOLS AND MODELS TO MANAGE PISCINE LACTOCCOSIS. WE WILL INVESTIGATE THE POTENTIAL FOR HORIZONTAL TRANSMISSION OF L. PETAURI UNDER VARIED AQUACULTURE RELEVANT CONDITIONS USING IN-VIVO LABORATORY-CONTROLLED CHALLENGE MODELS. INFORMATION GARNERED FROM THESE EXPERIMENTAL STUDIES, IN COMBINATION WITH EXISTING KNOWLEDGE, WILL BE USED TO DEVELOP AN EPIDEMIOLOGICAL MODEL OF LACTOCOCCAL TRANSMISSION AND VACCINE EFFICACY. TOGETHER, THESE AIMS COMBINE TO HELP IDENTIFY RISK FACTORS ASSOCIATED WITH THE DISEASE AND TO PREVENT FUTURE LOSES TO THE AQUACULTURE INDUSTRY. THE PROPOSED PROJECT ENCOMPASSES TWO OF THE PROGRAM AREA PRIORITIES. SPECIFICALLY, THE PROJECT WILL ADDRESS: 1) CRITICAL DISEASE ISSUES IMPACTING COMMERCIAL AQUACULTURE SPECIES, AND 2) DEVELOPMENT OF CLIMATE RESILIENT TECHNOLOGIES, PRODUCTION SYSTEMS, AND/OR MANAGEMENT STRATEGIES FOR COMMERCIAL AQUACULTURE SPECIES.