Spread and Ecomorphological Modifications of Ratan Goby Ponticola ratan (Gobiiformes: Gobiidae) in the Dnieper Reservoirs (Ukraine)

The ratan goby Ponticola ratan (Nordmann, 1840) is known as an inhabitant of the marine and brackish waters of the Black Sea, the Sea of Azov and the Caspian Sea. The paper presents data on its recent records in the freshwaters of Ukraine. The morphological features of the ratan goby in freshwater habitats were studied for the first time. Certain differences in morphological features between specimens from the freshwater and marine populations were revealed, probably reflecting adaptation to new freshwater habitats, characterized by more turbid water and other specter of available food. The records of mature specimens in the Dniprovske and Kaniv Reservoirs indicate its active progression upstream the Dnieper River, which enabled to confirm that the species should be considered both euryhaline and amphidromous. At the same time, low abundance of P. ratan in the Dnieper River enabled to consider its status in the fresh waters of Ukraine not as invasive but alien.