Invasive (introduced, exotic) species represent a topical subject in many recent ecological studies. The impacts of invasive species are expected to be severe throughout all ecosystems, as increasing numbers of exotic species become established in new locations. Damage caused by invasive species results mainly from their high population densities. Escapement from the effects of natural predators and parasites is a frequent explanation given for the success of invasive species. In connection to low parasite infections of exotic populations, increased growth and lower mortality of invasive species may enhance the expansive distribution in new locations. The project aimed to (1) compare parasite fauna of invasive fish species Neogobius kessleri from its native populations (Danube River, Bulgaria) and site of its recent introduction (Danube River, Slovak Republic), (2) to estimate possible impact of introduced parasites on native fishes, and (3) to evaluate the effect of parasites on the host biology and ecology.