Abstract
Aquarium fish are increasingly being recognized as reservoirs of zoonotic pathogens, with Aeromonas species posing a notable risk because of their environmental resilience and opportunistic pathogenicity. This study presents the most comprehensive genome-based investigation to date of Aeromonas diversity in aquarium fish, aiming to characterize their taxonomic distribution, population structure, and genomic features. A total of 64 Aeromonas isolates were collected from various aquarium fish species. Wholegenome sequencing was conducted on all isolates to facilitate comparative genomic analyses. Key approaches included multilocus sequence typing (MLST), pairwise Digital DNA-DNA hybridization (dDDH), and the construction of a phylogenomic tree for species-level classification. Furthermore, a population structure analysis was performed to explore genomic diversity and evolutionary trends among the isolates. The results identified 14 distinct Aeromonas species, with A. veronii, A. caviae, and A. hydrophila being the most common. Importantly, several isolates exhibited taxonomic ambiguity, indicating the possible presence of new species or subspecies lineages. Furthermore, antimicrobial resistance gene profiles and virulence factor distributions varied significantly across clades, indicating genomic plasticity. This study highlights the underappreciated genomic complexity of Aeromonas populations in aquarium environments and raises concerns about the public health implications of pathogen reservoirs in ornamental fish.