Aeromonas veronii caused disease and mortality in channel catfish in Vietnam

Channel catfish (Ictalurus punctatus) are one of the most commercially important fish species cultured in Vietnam, and has been a major driver of Vietnam's rise to become a leading country for fisheries exports in the world. Since 2016, there have been several outbreaks of a contagious disease which in channel catfish has resulted in severe levels of economic loss. In this study, bacterial isolates from diseased fish were sampled and analyzed from 22 farms in four Northern Vietnam provinces experiencing outbreaks. Isolates were identified as Aeromonas veronii based on their bacteriological characteristics, 16S rRNA sequence analysis, and presence of Aeromonas veronii specific rpoB gene by PCR examinations. Subsequently, A. veronii isolates were tested for their virulence to fish via an experimental infection challenge, and their susceptibility to 21 antibiotics was also assessed. Results showed that A. veronii is pathogenic and has probably contributed to the mass mortality of this channel catfish species in Vietnam. Notably, A. veronii also exhibited resistance to four common antibiotics including amoxicillin, bicozamycin, lincomycin, and vancomycin. To our knowledge, this is the first report of outbreaks associated with A. veronii infection in channel catfish in a Southeast Asian country. This report could be used to alert aquaculture farmers and managers in this region to develop an appropriate biosecurity strategy for protecting catfish and other vulnerable species to A. veronii infection, and find alternative solutions to help mitigate occurences of the disease.