Yesterday we chose 29 fish that had the right size and today they went into surgery. They were anesthetized and then we implanted the hydroacoustic tag and stitched the small cut. Afterwards we observed them for several hours before they were released into the Danube. Together with Viadonau we already set up the receiver stations at the Nationalpark Donauauen last week and starting today we will learn more about their habitat use and movements. This will be supplemented via active tracking by boat.