Pathogenic characteristics of Aeromonas veronii isolated from the liver of a diseased guppy (Poecilia reticulata)

Despite the significant development on their diagnoses and control, aeromonad infection is still a problem in aquaculture. This study described the key bacteriological and pathogenic features of a presumptive Aeromonas sp. isolated from the liver of a diseased guppy (Poecilia reticulata). Molecular identification revealed that the isolate was an Aeromonas veronii (A. veronii PR). It was able to grow in a wide range of temperatures and salt concentrations, and was capable of auto-aggregation and biofilm formation, with temperature as an influencing factor. Some of the extracellular enzymes that may be involved in its virulence include caseinase, gelatinase and lipase. The infection rate was relatively progressive, and fish with prior infection showed marginal resistance to secondary infection. Handling stress differentially influenced the infection kinetics at the early stages; however, the final mortality rates did not significantly differ between the groups. A comparative infection trial revealed that zebrafish (Danio rerio) were more susceptible to A. veronii PR than guppy. The presented intrinsic and extrinsic factors influencing the pathogenicity of A. veronii PR lay the foundation for future research to better understand this pathogen in freshwater ornamental fish aquaculture. Significance and Impact of the Study: Aeromonad infections continue to affect the fish farming industry. Several new species of Aeromonads in freshwater ornamental fish have been identified in the last years. In this study, we have characterized an Aeromonas veronii isolate from a diseased guppy. The series of experiments identified the intrinsic and extrinsic factors contributing to the pathogenic characteristics of the isolate. It has been shown to be pathogenic to both guppy and zebrafish. The results offer foundational knowledge in the development of preventive and therapeutic measures to combat this pathogen in the ornamental fish industry.