In recent years, gobies of the genus Neogobius and western tubenose goby have spread extensively from their native Ponto-Caspian region due to human activity (navigation, connecting canals, angling). Their occurrence usually shows the characteristics of invasion in the non-native areas of distribution. Following a previous pilot project, the proposed project will provide an objective evaluation of the direct and indirect impacts of gobies on local fishes. The project, consisting of intensive field work, experiments and laboratory analyses, will address specific questions of colonisation, movement activity, genetic characteristics, inter-specific interactions between gobies and local fishes and parasite infection. Knowledge of fish assemblages, obtained during long-term monitoring of the lower River Morava (Czech Republic), allows for an objective evaluation of the impact of these non-native species. The complex data obtained will provide a comprehensive framework for risk assessment of invasive populations and facilitate future legislative and management steps.