Largemouth bass (Micropterus nigricans) is considered an emerging aquaculture species in North America. However, the expansion of this species through intensive aquaculture poses challenges, including disease outbreaks caused by bacterial pathogens such as Edwardsiella piscicida (Ep) and Aeromonas veronii (Av). Although previous studies have investigated the effects of these pathogens individually, their natural coexistence within the same habitat requires a more comprehensive coinfection model. In this study, a seven-day coinfection challenge with virulent strains of Ep (R18-43) and Av (ARS-32-2018) was investigated in largemouth bass. Juvenile bass were subjected to a full dose and a half dose of each pathogen in both mono- and coinfection (Co) models. The Ep was administered via intracoelomic injection (full-dose: 5.45×105/fish; half-dose: 2.40×105/fish), and Av was introduced via immersion (full-dose: 1.65×108/mL; half-dose: 8.25×107/mL). The results showed that the cumulative percent mortality (CPM) of the half-dose, specifically Av, was significantly (p < 0.05) lower than the half-dose of coinfection and the full-dose of both the mono and coinfection groups (Figure 1A). The Kaplan-Meier survival analysis revealed that survival probabilities were significantly higher (p < 0.05) in half-dose mono-infections compared to half-dose coinfections or other full-dose infections (Figure 1B). Additionally, RNA-seq analysis of spleen tissues at different time points is underway. Conclusively, both mono- and coinfection of Ep and Av pose a dynamic risk to largemouth bass aquaculture, and understanding mortality trends will assist in providing optimized treatment options for producers.