Background. The aquarium fish trade is characterized by an enormous number of species. Aquarium fish may have an impact on native biota by means of their invasiveness as well as through pathogen transfer. The Czech Republic has become a gateway for aquatic pets into the European Union. The aims of this study were to identify the most common aquarium fish species on the wholesale market, to estimate temperature suitability for seasonal (winter and summer) survival in the EU, and also to assess the invasiveness risk of the most common aquarium fishes with the strongest temperature matching. Materials and methods. Data on aquarium fish species, their origin, and availability from producers and traders based in the Czech Republic were collected based on all available sources. The target area was defined as all member states of the EU. Estimation of the temperature suitability for each species was done using Climatch 1.0 software. The Freshwater Fish Invasiveness Screening Kit (FISK) was employed for species with temperature suitability within the target area exceeding 10% in the coldest quarter of the year. Results. In total, 1118 fish species representing 51 families were identified. Thirty-three species belonging to 13 families were classified as “very common”. Three sources of origin were identified: domestic production within the EU, farm production outside the EU, and wild harvests in the region of origin. The major suppliers outside the EU are in south-east Asia. Only one common species originated from wild harvests. FISK scoring divided the 11 species evaluated as having the strongest temperature suitability in the EU (TSEU) into seven species bearing medium risk and four species representing high risk. The family Cyprinidae was the most frequently represented among all evaluated taxa (seven species), but the majority of high-risk fishes belonged to the family Poeciliidae (three species). The highest score was earned by Carassius auratus (Linnaeus, 1758). Conclusion. The risk potential of aquarium fishes most traded in the EU seems to be not alarming. Attention should be focused on the possibility of novel pathogen transfer to native aquatic biota as an important aspect of regulating the aquarium fish trade.

introduction pathway, aquarium trade, invasive species, freshwater fish, risk assessment, FISK