Flavobacterium psychrophilum and Flavobacterium columnare are the etiological agents of bacterial coldwater disease (BCWD) and columnaris disease, respectively. Trends such as intensification of farming practices, wide-spread development of antibiotic resistance, and climate change have increased the overlap of these two diseases, resulting in combined infections that may exacerbate losses while further complicating treatment strategies. Few studies have attempted to elucidate concurrent infections in salmonids, as such, the goal of our present research - as part of an overarching study on mitigation of F. psychrophilum and F. columnare through probiotic treatment - is to better understand the effects of dual infection by BCWD and columnaris disease on rainbow trout survival. In a preliminary experiment, 360 fingerling rainbow trout (1.8g) were challenged for one hour using an immersion bath containing a pre-determined “High”, “Mid”, and “Low” dose of either F. pyschrophilum (CSF-259-93), F. columnare (051-10-S5), or a 1:1 mixture of the two bacteria. The presence of pathogens will be determined by streaking of the spleen and kidney on TYES agar and subsequent identification of bacterial colonies. Provided the results of this prechallenge are positive, further investigations will include a comprehensive analysis of the presence of F. psychrophilum and F. columnare using real-time quantitative polymerase chain reaction (qPCR) as well as through ELISA to measure IgM antibodies post challenge. The outcomes of these studies are crucial for clarifying the virulence of bacterial co-infections compared to single-pathogen infections, providing valuable insights into effective treatment strategies for managing concurrent infections in rainbow trout aquaculture.