Four lamprey species and 55 fish species are considered autochthonous taxa in the Czech Republic. In recent years, as a result of spontaneous migrations, the native ichthyofauna has been increased by three species Sander volgensis, Gymnocephalus baloni, Proterorhinus marmoratus) which, in view of their autochthonous occurrence in the Central European region, are evaluated as native. At present, according to the criteria of the IUCN (2001) version 3.1, two lamprey species and 6 fish species are evaluated as “regionally extinct”. Most of these taxons are denoted as anadromous. One species has been classified in the category “Extinct in the wild”. Two lamprey species and 25 fish species are considered to be endangered to various extent: one lamprey species and 10 fish species are classified as “Critically endangered”; one lamprey species and 5 fish species as “Endangered”; ten fish species as “Vulnerable”. In the course of the past two centuries, attempts have been made at introducing about 30 fish species (see Lusk et al. 1998, Hanel 2003); of these, the introduction of 11 species can be evaluated as successful. Only four non-native species have established stable and naturally reproducing populations in natural conditions (Pseudorasbora parva, Carassius auratus, Ameiurus nebulosus, Gasterosteus aculeatus).