Aeromonas spp. harmful bacteria are associated to the tilapia pathogen parasite Gyrodactylus cichlidarum double trouble?

Tilapia are fishes widely grown worldwide, and the main factors limiting their culture are climate change related factors and disease outbreaks, particularly bacterial and parasitic. Coinfections involving monogenean parasites and pathogenic bacteria are frequently reported and often result in increased fish mortality. In this study, we characterized the bacterial communities associated with farmed tilapia and the monogenean parasite Gyrodactylus cichlidarum. We found that bacterial communities associated with G. cichlidarum were significantly different from those collected from fish or the environment and enriched in members of the genus Aeromonas, which were further confirmed as belonging to the pathogenic species Aeromonas hydrophyla, Aeromonas jandaei, and Aeromonas veronii. This data is in line with the fact that gyrodactylids breach their fish host s primary line of defense (mucus covered skin) with their attachment hooks and through feeding, facilitating bacterial infections, frequently involving known pathogens like Aeromonas sp. If these harmful bacteria are intrinsically and widely associated with this parasite, G. cichlidarum is in effect both itself a pathogen and a vector for a secondary pathogen, a potential double trouble worthy of further investigation.