Sportfish viruses are a persistent and costly problem for natural resource agencies. New approaches are needed to mitigate the spread of these viruses in hatchery and wild sportfish populations. For any infectious disease, knowledge of pathogen transmission is critical to controlling spread and is a critical tool in disease management. Regarding sportfish viruses, a gap in our knowledge of viral transmission is the role of ectoparasites as vectors of viral disease. Because no information on this critical transmission pathway is available for sport fisheries in the southeastern US, the goal of this project is to understand the interaction of gill lice and viral infections in sportfish in the Southeastern United States, which will give fisheries managers new knowledge/understanding with which to prevent and mitigate viral infections in sport fishes. This will be accomplished by detecting viral infections in rainbow trout and largemouth bass using conventional (cell culture and polymerase chain reaction) and emerging (quantitative polymerase chain reaction) methods, screening gill lice infecting these fish for viral infections, quantifying viral load in fish and gill lice using quantitative polymerase chain reaction, and using histopathology to assess the pathological effects of gill lice and viral infections. These will field test the theory that high intensity/prevalence of gill lice infections is correlated with high intensity/prevalence of sportfish viral infections. This project produces knowledge/understanding that improves disease biosecurity and mitigation strategies; thereby reduces the spread of sportfish viral infections. By detecting viruses using conventional and emerging methods, the project will assess sensitivity of viral detection methods and optimize viral diagnostics protocols. If gill lice represent viral vectors, this project will assess gill lice as a potential non-lethal sampling method for sportfish viruses. These results will contribute to developing more robust risk assessment models for the potential impact of viral infections on wild and cultured sportfish. The results of this project will be incorporated into fish health workshops for agency staff, presentations at regional and national meetings, and peer-reviewed manuscripts in national and international journals. This project benefits the majority of Southeastern Association of Fish and Wildlife Agency states: Tennessee, Alabama, Georgia, South Carolina, North Carolina, West Virginia, Kentucky, Missouri, and Arkansas. There are no subrecipient activities associated with this project.