CCR9 and infection: Furthermore, cxcr1, cxcr3-2, ccr3, and ccr5 mRNAs were notably up-regulated at 6 h or 12 h and maintained until 120 h post-infection, whereas cxcr3-1, cxcr4, ccr4, ccr7, and ccr9 mRNAs were notably down-regulated after E. ictaluri infection, therefore it is necessary to further verify the bioactivity of these chemokine receptors of yellow catfish in the following study.