Luyun Ni ¹ Pengcheng Li ¹ Qiaolin Zou ¹ Feiyang Li ¹ Yeyu Chen ¹ Haoting Chen ² Jiansheng Lai ¹ Jun Du ¹ Ya Liu ^1*

• ¹ Sichuan Academy of Agricultural Sciences, Chengdu, China
• ² Guangzhou Tencent Technology Co., LTD, Guangzhou, China

In August 2023, hybrid sturgeons (Acipenser baerii♀×Acipenser schrenckii♂) cultured in Sichuan, China, showed infectious disease symptoms, including ulcers, liver and spleen nodules, and high mortality rates. Pathogenic bacteria were isolated and phylogenetic analyses of the 16S rRNA gene confirmed that the isolated bacteria clustered within the Nocardia seriolae group. The TaqMan RT-PCR assay was performed to detect the presence of white sturgeon iridovirus (WSIV), with the outcome indicating a weakly positive signal. Histopathological examination revealed severe damage to various tissues of the diseased sturgeons, and a notable presence of bacteria was observed through acid-fast staining. Transmission electron microscopy analysis showed the presence of abundant bacteria and virus particles, indicating cellular invasion and subsequent damage. In summary, the disease in hybrid sturgeons was diagnosed as infection of N. seriolae and WSIV. To investigate the immune response of hybrid sturgeons to this infection, spleen transcriptomes were analyzed. Numerous immune-related genes and pathways, including the "Toll-like receptor", "B-cell receptor", and "T-cell receptor" signaling pathways, were altered in response to pathogenic threats. Significantly downregulated of key components of TCR and BCR signaling pathways, such as ZAP70, BTK, and CD79A, suggested a temporary inhibition of these pathways critical for cellular immunity postinfection. Gene set enrichment analysis revealed significant suppression of the apoptosis signaling pathway and activation of autophagy and mitophagy signaling pathways following infection. Specifically, in the death receptor-mediated apoptosis signaling pathway, downregulation of TNFα, TRAIL, CASP6, and CASP8 was observed, while several genes in the autophagy and mitophagy pathways showed upregulated expression post-infection. To our knowledge, this is the first report of N. seriolae infection in cultured sturgeons. These findings could provide a theoretical basis for diagnosing and preventing this disease, as well as enhance the understanding of host-pathogen interactions in fish.