PoCD9.1 and PoCD9.3 expression in response to pathogen challenge. Vibrio anguillarum and Edwardsiella piscicida were cultured in LB broth at 28 °C to an optical density of 0.8 at 600 nm. Then, the cells were washed with PBS and resuspended in PBS to a concentration of 5 × 106 CFU. ISKNV was resuspended in PBS to a concentration of 1 × 106 copies/mL. Flounders were injected intraperitoneally with 50 μL of V. anguillarum (A), E. piscicida (B), ISKNV (C), or PBS. After infection, the head kidney, spleen, and liver from three fish were taken aseptically at 6, 12, 24, 48, and 72 h post-infection (hpi) for bacterial infection and at 1, 3, 5, and 7 days post-infection (dpi) for viral infection. PoCD9.1 and PoCD9.3 expression in the three tissues was determined by RT-qPCR at various time points. In each case, the expression level at 0 h was set as 1. Values are shown as the mean ± SEM (N = 3). N represents the number of times the experiment was performed. *, P < 0.05; **, P < 0.01.