Columnaris disease, caused by the gram-negative and yellow-pigmented columnaris-causing bacteria (CCB; formerly under the umbrella of Flavobacterium columnare), is a significant ailment in global fish culture. In the southeastern United States, columnaris disease is responsible for significant losses in the catfish industry and control methods rely heavily on antibiotic applications. As of 2022, CCB represents four distinct species: F. columnare, F. covae, F. davisii, and F. oreochromis, and there are associations between bacterial species and virulence in different hosts. The development of an efficacious vaccine for the prevention and control of columnaris disease has been restricted, partially due to a lack of understanding of the broad genetic diversity of these bacteria. Our team is incorporating these new concepts into strain selection and the optimization of new vaccine candidates. There is a licensed, attenuated vaccine for columnaris disease in channel catfish, but it is no longer available to U.S. catfish producers. This is due to inconsistent vaccine efficacy reported when administered under production settings. One possible reason for the lack of efficacy is the sub-optimal host-pathogen dynamics. Vaccine development has been re-initiated with the newfound knowledge of the genetic diversity of CCB and affinity for different host species. This project aims to identify and modify CCB strains associated with catfish and other cultured fish species within the Southern region to create an efficacious live-attenuated vaccine for columnaris disease. The project team is currently confirming and characterizing strain attenuation to achieve viable vaccine candidates while investigating the protective immune response of the catfish. Safety testing and delivery optimization (immersion or oral administration routes) will be performed on the most promising candidates. Finally, the attenuated vaccine will be tested in channel catfish fingerlings under experimental pond conditions in Mississippi to evaluate efficacy under intensive production conditions. To date, at least one strain of CCB that causes mortality in channel catfish has been attenuated. Results from additional virulence experiments involving attenuated CCB strains from channel catfish and Nile tilapia will also be discussed. The long-term project goal is to produce a viable vaccine to protect catfish and other essential aquaculture species in the southern region against columnaris disease. Together, this project will provide industry stakeholders with new vaccine candidates for the prevention of columnaris disease thus reducing economic losses and the use of antibiotics within U.S. fish farms.