Unveiling the threat: Aeromonas schubertii, an emerging bacterial pathogen inducing white nodule lesions in snakehead fish (Channa striata) at nursery farm in Thailand

Aeromonas schubertii has emerged as a significant bacterial pathogen that causes high mortality and characteristic white nodule lesions in striped snakehead fish (Channa striata) in nursery farms in Thailand. This study investigated a disease outbreak in July 2020 that resulted in elevated mortality and granulomatous lesions in the liver, kidneys, and spleen of the affected fish. Six bacterial isolates were recovered from diseased specimens and subjected to biochemical testing, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and molecular characterization using 16S rRNA and gyrB gene sequencing. The predominant isolate was conclusively identified as A. schubertii. An experimental infection trial in C. striata using the CUVETASC03 strain successfully fulfilled Koch’s postulates, with the bacterium inducing a peak mortality rate of 86% at the highest inoculum and an estimated median lethal dose (LD₅₀) of 3.9 × 10⁵ CFU/fish. Infected fish exhibited progressive white nodule formation in their internal organs, with a marked increase observed at 7, 14, and 21 days post-injection. Histopathological analysis confirmed the presence of granulomatous lesions in the liver, kidney, and spleen. These findings provide critical insights into the pathogenicity and tissue tropism of A. schubertii in striped snakeheads and highlight its emergence as a significant threat to the sustainability and productivity of snakehead aquaculture. This study underscores the importance of rapid diagnosis, ongoing epidemiological surveillance, and proactive disease management strategies to mitigate the impact of A. schubertii infection in aquaculture settings.