In February 2. – 28. 2. 2015I was in the internship at the University of Jyväskylä, Department of Biological and Environmental Science, Finland. The main goal of my stay was learning how to deal with natural abundance of carbon and nitrogen stable isotopes in freshwater ecosystems and how to plan an experiments connected with stable isotopes. Firstly I learned how dried and weighted samples correctly. Secondly it was shown me the correct way of stable isotopes result interpretation. Finally, I discus with Fabio Ercoli and other colleagues about my future projects.