Histopathological analysis and the immune related gene expression profiles of mandarin fish (Siniperca chuatsi) infected with Aeromonas hydrophila.

Hemorrhagic septicemia of mandarin fish (Siniperca chuatsi) was mainly caused by Aeromonas hydrophila which was an opportunistic pathogen. In recent years, the disease has caused tremendous economic loss with high morbidity and mass mortality in the mandarin fish breeding industry. Histopathological analysis and the immune related gene expression profiles of mandarin fish (S. chuatsi) infected with A. hydrophila were investigated in this study. Transmission electron microscopy (TEM) images showed that the cells of A. hydrophila densely covered with a mass of fimbriae. Histopathological analysis revealed that inflammation, vacuolization and extensive necrosis existed in the gill, liver, spleen and head kidney of the diseased fish. Quantitative real-time PCR was performed to measure mRNA expression levels for six immune related genes in mandarin fish after A. hydrophila infection. The transcriptional analysis of these immune related genes demonstrated that the expression levels of major histocompatibility complex class II (MHC II), T cell receptor α (TCRα), tumor necrosis factor α (TNFα), CC chemokine 3, interleukin 8 (IL-8) and Hepcidin were strongly up-regulated in spleen and head kidney of mandarin fish post-infection. These results will contribute to further study on the pathogenesis and host defensive system in A. hydrophila infection.