Biofilm and Sediment are Major Reservoirs of Virulent Aeromonas hydrophila (vAh) in Catfish Production Ponds

Abstract The genus Aeromonas comprises more than 60 recognized species that include many important fish pathogens such as the causative agents of furunculosis and motile Aeromonas septicemia (MAS). Although MAS is typically considered a secondary infection, a new virulent A. hydrophila (vAh) strain has been causing devastating losses to the catfish industry in Alabama since 2009. The objective of this study was to characterize the spatiotemporal distribution of Aeromonas sp. and, specifically, vAh in a commercial catfish farm in western Alabama. We sampled biofilm, sediment, and water from three ponds during four consecutive months during the growing season. Total aerobic counts were between 8.8 × 105 and 1.5 × 106 CFU/mL but were significantly higher in biofilm and sediment than in water throughout the sampling period. Total Aeromonas counts in water samples significantly increased in all three ponds after the month of August and ranged from 7.8 × 103 to 4.9 × 104 CFU/mL. A similar trend was observed in biofilm and sediment samples for which total Aeromonas counts increased in samples taken in late summer to early fall. Over time, the concentration of Aeromonas in water samples decreased by one order of magnitude, while there was a significant increase in sediments as temperature dropped. The virulent vAh was detected in 35.4% of biofilm samples and 22.9% of sediment samples, suggesting that both environments serve as the major reservoir for this pathogen. Future monitoring efforts should focus on targeting sediment and biofilms since samples of these appear to naturally enrich for the presence of vAh and other Aeromonas species.