Aquatic animal health surveillance is notably based on the observation of any increased shellfish mortality by shellfish farmers and its immediate mandatory notification to the local competent authority. According to current EU regulation, increased mortality is defined using a participatory approach: case reporting is based on individual farmer perception, which then can be turned into notification in cooperation between the farmer and the competent authority. All the challenge relies on starting from individual perception and knowledge of increased mortality to a collective alert onset informing potential control actions having a community interest. We made an inventory of the criteria used by surveillance stakeholders to define and detect increased oyster mortality, and of their perceptions of the system purpose and usefulness. This constitutes the prerequisite to bridge the gap between theory and application for a stable and sustainable early warning surveillance