Biotic and abiotic heterogeneity in aquaculture tanks : a survey to understand the “Killer Queen” Vibrio harveyi

International audience

إنجليزي. Vibrio harveyi is a serious pathogen for farmed sea bass (Dicentrarchus labrax) and is responsible forvibriosis. This disease leads to mass mortality events, resulting in substantial economic losses for fishfarms. Previous work highlighted the persistence of V. harveyi in the tanks in planktonic form but alsoin biofilms, lessening its sensitivity to biocides. Antibiotics and vaccinations currently used to fightvibriosis are time- and money-consuming, and less and less accepted by consumers seeking naturalproducts. Thus, it is important to develop effective prophylactic diagnosis and control measures toprevent outbreaks. It is relevant to investigate spatially and temporally the occurrence of V. harveyi inrearing tanks for this purpose. Here, it deals with the monitoring of bacterial populations encounteredin a 4-meters deep tank, during a 7-months sampling campaign. From May to November 2022, bothrearing water and biofilms formed on immersed pieces of concrete will be sampled from three equallydistributed depths. Physicochemical parameters (temperature, pH, O2 concentration, etc.) will bemeasured simultaneously. DNA will be extracted from water and biofilms to sequence the variable V4-V5 region of the 16S rRNA gene. Generated data will provide a global vision of the biotic environmentof the rearing tank. Moreover, V. harveyi will be specifically quantified in samples by qPCR. Itsabundance will be covered through time and space in rearing tanks and studied according to the bioticand abiotic environments. Vibriosis outbreaks occur mainly in the summer. Therefore, the abundanceof V. harveyi may fluctuate depending on the temperature of the rearing water, but also on thedifferent coexisting bacterial populations and sampling depths. After identifying the biotic and abioticparameters favouring the growth of V. harveyi, its virulence genes will be investigated, giving a moreproper understanding of the ins and outs of sea bass vibriosis.