Identification and characterization of Vibrio anguillarum (GA strain) isolated from Obscure Pufferfish Takifugu obscurus.

Objective: Aquaculture has faced significant challenges due to the emergence of various pathogens affecting fish species. One such species, the Obscure Pufferfish Takifugu obscurus, has experienced high mortality rates due to an outbreak of disease on a fishery farm in Shanghai.

Methods: The pathogen responsible for this outbreak was isolated and identified as Vibrio anguillarum (GA strain) using a combination of morphological, biochemical, and whole-genome single-nucleotide polymorphism-based phylogenetic analyses. Pathogenicity tests confirmed that the GA strain could cause disease in healthy Obscure Pufferfish, inducing overt hemorrhagic symptoms. Histopathological analysis was performed to assess whether tissue damage had occurred. Whole-genome sequencing revealed that the GA strain possessed 235 virulence genes and two drug resistance-related genes: cyclic AMP receptor protein (CRP) and regulator of secondary metabolites A (rsmA). Testing via PCR further confirmed the presence of 10 common virulence genes.

Results: Antibiotic susceptibility testing showed that the GA strain was highly sensitive to antibiotics such as tetracycline, doxycycline, minocycline, and compound sulfamethoxazole and was resistant to cefradine, cefazolin, penicillin, and vancomycin.

Conclusions: To the best of our knowledge, this is the first study to report V. anguillarum as the pathogen responsible for this disease in Obscure Pufferfish. The isolate exhibited strong virulence and multidrug resistance. The findings lay the foundation for further disease control in Obscure Pufferfish and the investigation of the epidemiological mechanisms of V. anguillarum.