Revealing the pathogenicity of a highly virulent Aeromonas caviae isolate and its effects on immune responses in...

Despite the known threat of Aeromonas caviae to aquaculture, its effects on mandarin fish (Siniperca chuatsi) were unknown. This study decisively addresses this critical knowledge gap by successfully isolating and identifying a highly pathogenic strain of A. caviae from diseased mandarin fish during a natural outbreak. We systematically profiled its virulence, establishing a lethal dose 50 % (LD₅₀) of 1.25 × 10⁶ CFU/mL, which confirms its high pathogenicity. Further histopathological examinations revealed extensive tissue damage, including severe necrotic lesions in vital organs such as the liver, kidney, and spleen, directly correlating with the observed clinical morbidity and mortality. Moving beyond phenotypic observations, liver transcriptome analysis provided mechanistic insights, indicating that the infection disrupts critical biological processes in the host, most notably signal transduction, translation, and ribosomal function. To our knowledge, this comprehensive investigation represents the first confirmed case of mass A. caviae-induced mortality in farmed mandarin fish within China, thereby expanding the known host range of this bacterium. Collectively, our research not only delivers a thorough analysis of the host's immune response to this specific pathogen but also establishes a vital foundation for the future development of targeted diagnostic and effective disease management strategies to safeguard mandarin fish aquaculture.