Abstract
Abstract — Based on the morphological features, four rare alien species in the Kapchagai reservoir were identified: Coregonus peled , Parasalmo mykiss , Megalobrama mantschuricus , and Oreochromis niloticus . The latter two species were recorded for the ichthyofauna of Kazakhstan for the first time. Self-reproducing P. mykiss populations have been known in the Balkhash Basin since the late 1990s, whereas the introduction of C. peled into the Ili basin in 1968−1969 and 1971 did not lead to the naturalization of the species. The reasons for the great diversity of invasive fish species in the Kapchagai reservoir are overviewed.