Chemokines are small secreted cytokine peptides (8-14 kD), which were initially found to have the ability to recruit a wide range of immune cells to sites of infection and disease in mammals. In this study, we cloned the cDNA is 910 bp, contains an open reading frame of 408 nucleotides encoding 135 amino acid residues. Four conserve cysteine residues at 35, 37, 60, and 77, and the first two cysteines are separated with leucine acid, which is exactly consistent with the features of CXC. Amino acid sequence analysis revealed that the CXCL9 protein of and at 78.5% and 71.0%, respectively. RT-PCR demonstrated that mRNA was expressed highest in the liver and spleen, and high in the skin and gills of healthy mRNA expression was upregulated in the liver after being infected with for 6 h, while in the head kidney and spleen, the peak value of CXCL9 expression was 24 h or 48 h after infection. After being infected with mRNA expression in the liver was upregulated at 6 h, and its expression in the head kidney was upregulated at 24 h. The expression model is different in the spleen, as expression 10-fold after 6 h, then decreased gradually, before upregulating approximately 20-fold at 48 h. These results indicate that genes play an important role in the immune response, and can be a biomarker of bacterial disease in .