Abundance and spatial patterns over time of Vibrionaceae and Vibrio harveyi in water and biofilm from a seabass aquaculture facility

One of the major threats to the seabass (Dicentrarchus labrax) aquaculture sector is the development of vibriosis, a disease caused mainly by bacteria from the family Vibrionaceae, especially Vibrio harveyi. Given the relationship between abundance in the surrounding environment and prevalence in fish, monitoring the presence of V. harveyi in rearing water and biofilms over time may help better understand the dynamics of the pathogen and factors that increase the risk of vibriosis outbreaks. In this study, the dynamics and spatial patterns of cultivable Vibrionaceae and V. harveyi in water and biofilms from rearing tanks and in the cold- and hot-water inlets supplying the farm were monitored for 7 months, from April to October 2018. Several potential seabass pathogens were isolated: Photobacterium damselae, Vibrio alginolyticus, V. harveyi, Vibrio owensii and Vibrio rotiferianus. Nevertheless, V. harveyi remained the most problematic pathogen: its constant presence throughout the sampling campaign represents a risk for vibriosis outbreaks. More precisely, the potential pathogen has been found in rearing tanks and water inlets supplying the farm, from biofilm and water samples. Besides, the positive correlation between water temperature and the abundance of V. harveyi suggests that increasing water temperature may increase the risk for vibriosis outbreaks in fish farms. Overall, obtaining qualitative data regarding the relative diversity of viable culturable Vibrionaceae and quantitative data on the abundance of V. harveyi over time in a seabass aquaculture facility is the essential first step for designing new solutions to manage vibriosis.