Quantification of <i>Saprolegnia parasitica</i> in river water using real-time quantitative PCR: from massive fish mortality to tap drinking water

Since 2010, the Loue River (Franche-Comté, East of France) has been suffering from massive fish kills infested by <i>Saprolegnia parasitica</i>. The river supplies inhabitants of the city of Besançon in drinking water, raising the question of a potential risk through both water consumption and use. We developed a real-time quantitative PCR (qPCR) to quantify <i>S. parasitica</i> in the Loue River as well as in the drinking water. A weak spatial trend is suggested with greater quantities of <i>S. parasitica</i> observed at the sampling station close to the main pumping station. No <i>S. parasitica</i> DNA was detected in the tap water connected to pumping stations. The use of qPCR, which combines specificity, practicality, speed and reliability, appears to be an effective tool to monitor the spatial and temporal dynamics of this oomycete and identify the risk period for wild salmonid populations in the field, for fishery management or in aquaculture.