Temporal and Spatial Dynamics of Vibrio Harveyi: An Environmental Parameter Correlated Investigation in a 4-Metre-Deep Aquaculture Tank

Nowadays, European sea bass (Dicentrarchus labrax) aquaculture knows a significant expansion. Nevertheless, the aquaculture industry is plagued by several microbial diseases, including vibriosis. The spatial and temporal dynamics of pathogenic Vibrio harveyi were studied on a European seabass farm in northern France over seven months in 2022. Cylindrical concrete specimens were suspended in a water column and water was pumped from different depths (top: 0.3 m deep, middle: 2.15 m deep, and bottom: 4 m deep), providing insights into biofilm and planktonic V. harveyi dynamics. The abundances of V. harveyi, in biofilm and free-living forms, were positively correlated. Water parameters were monitored, revealing seasonal fluctuations in temperature, pH, and salinity, with no significant differences observed across the water column. Fish mortality peaks were recorded in July and August, coinciding with elevated temperatures and emphasizing the impact of environmental factors on aquaculture health. Quantification of V. harveyi by quantitative PCR revealed no significant differences between water top, middle and bottom layers. Vibrio harveyi exhibited seasonality, with peak abundances observed in August, correlating with temperature increases. Principal component analysis identified temperature as a primary driver, but also additional parameters such as salinity and pH. vibriosis outbreaks occurred during the sampling period, providing valuable insights on conditions before, during, and after the outbreak. This study underscores the importance of understanding V. harveyi behaviour in aquaculture systems, particularly in the context of global warming, for effective disease management and sustainable practices.