Non-native freshwater fishes in Poland: an overview.

"The number of non-native fish species in Poland has already passed 30, and has being still growing consecutively from the end of 19th century. It is rather difficult to assess impact of all these introductions on native fauna, however it seems reasonable to say that most of them have rather negatively affected indigenous biocenoses. Due to increase of number of new alien fishes found in Polish inland waters observed in the last years, some regulations regarding limitations of introductions should be applied."