From 16th to 19th  September 2019 T. Randák, P. Lepič, J. Turek, O. Palíšek, V. Plička, J. Martynková and students of the FFPW O. Bartoš, R. Kodras a V. Lexová performed monitoring of fish communities in the selected localities situated on Hron and Poprad rivers. The work was done in frame the “Grayling” project supported by the Slovak Fisheries Union. The performance of graylings tagged and released into the river in May 2018 and 2019 was evaluated.