This is the first report to characterize the macrophage-expressed gene 1 protein in C. tritonis, and these results suggest that macrophage-expressed gene 1 protein Ct-Mpeg1 is an important immune molecule of C. tritonis that is involved in the bacterial infection resistance of Vibrio, and this study may provide crucial basic data for the understanding of the innate immunity system of C. tritonis. Here, MPEG1 is linked to bacterial infectious disease.