Bacterial diseases are amongst the major limitations in aqauculture. The frequent use of antibiotics in order to control diseases has lead to the development and spread of antibiotic resistance. Therefore, there is an urgent need for alternative disease control methods. Bacterial pathogens rely on the production of virulence factors, i.e. compounds that enable them to colonize and damage the host. The production of these virulence factors is controlled by several regulatory mechanisms, amongst which sensing of host hormones. In this project, we will aim at interfering with catecholamine and steroid hormone sensing in order to control disease caused by various aquaculture pathogens. We will first determine the impact of hormone sensing on the virulence of Aeromonas hydrophila, Vibrio anguillarum and Vibrio campbellii, both in vitro (in synthetic growth media) and in vivo (in animal models). Further, we will isolate hormone-degrading bacteria from various sources, preferentially the intestinal tract of healthy aquatic animals, using the hormones as the sole carbon source. Finally, the ability to neutralise hormone-induced virulence of promising isolates will be evaluated in the appropriate in vivo models.