Alien aquarium fish species found in open waters of Poland with new record of Amazonian Red Pacu Piaractus brachypomus, Cuvier, 1818 (Serrasalmidae) from Bzura river

Aquarium fish are often kept pets. Due to inappropriate actions of fishkeepers some of them are released into natural environment in many countries around the world, also in Poland. Species of exotic ichthyofauna usually do not have the possibility of survival and reproduction in a temperate climate, however the environment of thermally polluted waters in Poland could provide the tropical fish with appropriate living conditions. Cold water species may settle stable populations and threaten native fauna and flora. This work, based on the available scientific literature, describes the invasive potential of aquarium fish species introduced in Poland. The scale of introducing alien species of aquatic origin into Polish waters is difficult to estimate. It is recommended that monitoring should cover the largest possible number of water reservoirs in this country.