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For sea bass (Dicentrarchus labrax) breeding, the first cause of mass mortality events is vibriosis caused by Vibrio harveyi. Previous work has highlighted the occurrence of V. harveyi in the water of the tanks of Aquanord Ichtus (Gravelines) but also its persistence in biofilms on the walls of the tanks.

The current work has highlighted the presence of different potential virulence genes in strains collected within the aquaculture structure. However, the mere presence of V. harveyi as well as the presence of potential virulence genes in the isolated strains are not sufficient conditions to explain the development of vibriosis. This thesis suggests the development of a transcriptomic approach to study the expression of potential virulence genes. Firstly, the expression of these genes will be studied in planktonic V. harveyi and secondly in biofilms in order to identify the virulence mechanisms involved in the development of vibriosis. A third part will study the influence of environmental parameters (biotic and abiotic ones) on the expression of these virulence genes. The identification of virulence mechanisms, as well as the environmental parameters that modulate them, will allow the development of antivirulence strategies, which are stainable alternatives to the antibiotics conventionally used in aquaculture.