ИСТИНА

The Danube, Dniester, Dnieper, Don, and Kuban are the largest rivers on the northern coast of the Black Sea. Berg summarized his own and literature data on ichthyofauna of these rivers in his famous monograph, which was published in 1949, before significant growth of human pressure on natural waters began. He included all of these rivers as part of the Danube-Kuban district of the Black Sea region and indicated endemic species when examining differences in their ichthyofauna. At that period, according to Berg (1949), ichthyofauna of the Danube River characterized by the most reach biodiversity included 81 species, whereas the ichthyofauna of the Kuban River was the most poor having only 57 species. The Dniester River according to Berg had 72 species, the Dnieper River - 73 species, and the Don River - 62 species. Further analysis of the main alterations in ichthyofauna of most aforementioned river systems occurred during about 50 next years revealed significant or even dramatic changes following dam construction, pollution, introduction, and other human activities (Vasil’eva 2003). As a result, the number of species recently recorded from every river of issue considerably changed and at the beginning of the XXI century ichthyofauna of the Dnieper River included 93 species (9 exotic), Dniester – 91 (13 exotic), Don – 78 (10 exotic), Kuban – 95 (16 exotic) (Vasil’eva 2003). In addition to introductions, invasions or progressive dispersal of alien species replacing native fauna in modified habitats, many native species lost their breeding sites, migratory ways and even suitable feeding biotopes in new hydrological regimes. And this process of modification still continues. For example, the Amur sleeper Perccottus glenii populated the Don and Dniester river drainages before the end of XX century recently is also well known from Dnieper and Danube rivers. The Danube River drainage being characterized by the largest catchment-area attributed to different landscape zones and countries, more than 20 large tributaries and numerous small ones certainly belongs to the most modified river system in Europe. As a result of damming anadromous fishes lost their spawning sites and migratory ways in the Danube River, and thus most sturgeon species randomly occur in the lower part only. Considerable changes of hydrological regime resulted in wide resettlement of euryhaline species, and now Neogobius eurycephalus dominates among other gobies in the lower part of Danube, and Proterorhinus semilunaris is recorded from Hungary and Austria. If summarize the lists of species presented for the Danube River in different countries the number of recorded species will reach more than 140 (in comparison with 81 species according to Berg 1949). And these surprising changes are caused not only by incorrect duplication of species names as a result of misidentification in some publications (for example, in g. Cobitis), the mixture of recent and previous taxonomic hypotheses (g. Rhodeus), unjustified description of new species or recover of some previously synonymized names (g. Coregonus), or by direct ignoring of recent knowledge (g. Carassius). Certainly, the main sources of increasing biodiversity are not taxonomic revisions and more detailed and careful studies of fish distribution, but continuing introduction and fish invasion and dispersion. The most “popular” introduced species entered native waters are Coregonus peled, Oncorhynchus mykiss, Salvelinus fontinalis, species of genera Gambusia, Poecilia, Hypophthalmichthys, Ictiobus. The species with the best penetrating and dispersing capacities is the Stone moroko Pseudorasbora parva, accidentally introduced together with Asian carps and recently recorded from different parts of the Danube River drainage.