The Wels catfish (Silurus glanis) is a large species of catfish native to wide areas of central, southern, and eastern Europe. In the Netherlands a native population exists as well as possible introduced populations in the Rhine-Meuse system. The population in the Netherlands is expanding and increasing while hardly any information is available on the habitat use, diet and migration patterns. In this project we aim to gain insight in these matters and whether they adapt their behaviour to the absence/precence of migratory fishes that congregate at the weir and hydropower station "Lith" in the river Meuse. The European eel (Anguilla anguilla) is an eel species that is critically endangered. Glass eels migrate from the Sargasso Sea towards Europe and spend most of ther life in freshwater. After 5-20 years the eels start to mature and become "silver eels". These silver eel migrate downstream towards the sea to start their long spawning migration back to the Sargasso Sea. During this spawning migration, silver eels encounter several anthropogenic migration barriers. This project aims to gain insight in when, how and where silver eels pass these migration barriers at Lith and Linne in the river Meuse and whether this results in losses of silver eels.