ABSTRACT
Data on freshwater gobies from the Mediterranean, the Black and Caspian Seas have been summarized recently by Kottelat and Freyhof (2007). Th ere are also detailed species accounts available in the books edited by Miller (2003) and Miller (2004). Th ese books comprise some original views and much past data especially from relatively inaccessible eastern European and Russian sources, not only systematic and distributional but much general biology. Western and northern European freshwaters are rarely colonized by gobies and only one euryhaline species, Pomatoschistus microps, is widely known also from the North, Baltic and Atlantic Sea basins as well as from some areas in the western Mediterranean Sea. On the contrary, freshwater
gobies are common and oft en dominant in littoral habitats even far from the sea in Italy and the Eastern Mediterranean and especially in the basins of the Black and Caspian Seas. In these areas, there are about 50 goby species being restricted to freshwater habitats or regularly enter freshwaters. With two exceptions (Padogobius), these gobies can be grouped within so called sand gobies (Economidichthys, Knipowitschia, Pomatoschistus) and Paratethyan gobies (Babka, Benthophiloides, Benthophilus, Caspiosoma, Mesogobius, Neogobius, Ponticola, Proterorhinus). The monophyly of Paratethyan gobies was recently supported also by molecular evidence (Neilson and Stepien, 2009). Freshwater sand gobies are most diverse in the Adriatic and Aegean Sea basins from northern Italy south to Greece and West Anatolia. In this area, two euryhaline species are commonly found in estuaries and adjacent freshwaters (Knipowitschia panizzae, Pomatoschistus canestrinii). Both are related to a number of local endemics which are characterized by reduced patterns of head canals and squamation. Paratethyan gobies are restricted to the tributaries of the Marmara, Black and Caspian Seas and none of them is ever recorded to permanently inhabit full marine waters. In this ecologically and morphologically diverse group of species, there are several real freshwater endemics (as Ponticola kesslerii) and several species which never enter pure freshwaters but are restricted to the brackish waters of the seas (as Ponticola ratan). Several species are euryhaline and are able to inhabit the sea as well as a wide range of freshwater habitats. Paratethyan gobies are a large radiation of real brackish-and freshwater gobies which has evolved in the today Black and Caspian Seas. Th ey are connected to one of the key events forming the today diversity of Western Palearctic freshwater biota, the palaeographic processes dividing the Tethys into the Mediterranean and Paratethys Seas. While the Mediterranean fell dry during the late Miocene (Messinian), the Paratethys became more and more freshened during this time. During the Pliocene, the Paratethys was divided into the Black-, Azov-, Caspian and Aral Seas. Th ese seas experienced massive water level fl uctuations during the Pleistocene when they were disconnected from each others and from the Marmara and Mediterranean Seas during glacial phases, but connected by eight brief phases of high global sea levels corresponding with glacial melting phases and interglacial’s. During the last glacial maximum, Paratethyan seas were fresh or slightly brackish lakes for at least 150,000 years and the sea level was about 150 m lower than today (see Aksu et al., 1999 for overview).