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.