To analyze the effect of the Cyprinus carpio Slc15a2 gene on the immune response mechanism during Aeromonas hydrophila infestation, this experiment prepared rat-derived Slc15a2-1 and Slc15a2-2 polyclonal antibodies, and changes in protein expression of Slc15a2-1 and Slc15a2-2 in C. carpio sera following A. hydrophila infection was detected by enzyme linked immunosorbent assay (ELISA). The results showed that ① compared with the blank control the maximum protein expression levels of the two copies after infection were increased by 4.81 and 2.48 times, respectively. The protein expression of Slc15a2-2 was consistently higher from 0 h to 48 h compared to that of Slc15a2-1. ② Overall, there was a similar expression trend between the two copies of Slc15a2, with both increasing, then decreasing, then increasing and then decreasing again. However, Slc15a2-1 reached its first expression peak at 3 h, while Slc15a2-2 reached its first expression peak at 6 h. ③ Slc15a2-1 and Slc15a2-2 protein expression showed complementary expression trends during the four periods from 6 h to 24 h. That is, the expression of one copy decreased significantly and the expression of the other copy increased significantly during the same period, but the overall expression level remained high. The results indicate that the two polyclonal antibodies prepared in this experiment have high affinity and specificity, and the overall similar expression trend between the two copies after infection with A. hydrophila suggests that they may have similar gene functions. Slc15a2-2 had significantly higher expression between 0 h and 48 h than Slc15a2-1, possibly as the major gene in the copy. The two copies showed complementary expression from 6 h to 24 h, and the co-expression was maintained at a high level, enabling an effective response in the face of pathogen attack. This study may provide some basis for insight into the regulatory immune response mechanism of C. carpio Slc15a2 gene.