In our study, fancy southern platyfish Xiphophorus maculatus (Cyprinodontiformes, Poeciliidae) were examined due to breathing disorders and mortality. Fish came from Vietnam farm and were redistributed by international wholesaler. In fish, loss of appetite and gasping near the water surface was observed. Gill tissue showed small white spots, caused by metacercariae and areas of clearing surrounding the cysts. Primary branchial filaments were hyperplastic, necrotic, significantly deformed and shortened. Samples were fixed in 98% alcohol for molecular analyses. The identity of C. formosanus (Opisthorchiida: Heterophyidae) was confirmed by molecular methods (GenBank accession number OP808358). In this study, we present the first report of C. formosanus in Central Europe. Uncontrolled transport of fish can lead to health and economic concerns, including the transmission of zoonotic pathogens to non-native ecosystems.