ZOOSYSTEMATICA ROSSICA, 18(2): 295–317 © 2009 Zoological Institute, Russian Academy of Scienсes 25 DECEMBER 2009 INTRODUCTION The Black, Azov, Caspian and Aral seas, remnants of the intracontinental Paratethys basin, possess a spectacular diversity of the biota. The term “Paratethys” was coined by Laskarev (1924) to designate the string of epicontinental basins originally stretch- ing from the Alps to what was the Aral Sea that has been separated from the rest of the Tethys by the uplift of the Alpine- Caucasian mountain chain since the Early Oligocene. Many groups of aquatic organ- isms including fishes have radiated in this region (e. g. Mordukhai-Boltovskoi, 1979; Dumont, 1998). Diversification in the Para- tethys has been traditionally linked to iso- lation events from the Mediterranean and the Atlantic and Indian Oceans resulted in restricted marine, brackish lacustrine, and freshwater lacustrine environments, and in- duced the evolution of endemic species and higher taxa among molluscs, ostracods, fish, and other groups of animals (e. g. Băcescu, 1940; Zenkevich 1963; Starobogatov, 1970, 1994; Bănărescu, 1991; Jones & Simmons, 1996, 1997; Dumont, 2000). It has been debated in literature if the Caspian Sea is really a sea though freshened, or just a giant lake. Dumont (1998) presents arguments for this water body being a true lake and not a sea. However, the Caspian biotic diversity clearly reflects its relation- ship to the Caspian geological history as an isolated basin of the world ocean, and also a complex process of immigration from the Mediterranean and Atlantic Ocean. Physical environment of the Caspian Sea A number of publications summarise much of the literature about the geomor- phological structure and hydrology of the Caspian Sea, e.g. Kosarev & Yablonskaya (1994), Mandych (1995), Golubev (1997), Mamaev (2002), Reid & Orlova (2002), Coad (2008). Below we briefly overview only those features which has the most sig- nificant impact on recent diversity and dis- tribution of fishes – salinity and its gradient, depth, seafloor morphology, and tempera- ture – in two major ecoregions of the Caspi- an Sea (for the ecoregions, see Bogutskaya, 2007 and Naseka & Bogutskaya, 2007). The Caspian Sea lies between 47°13´ and 36°34´35´´ north latitude and between 46°38´39´´ and 54°44´19´´ east longi- tude. Statistics for the Caspian Sea (Ma- maev, 2002): surface area approximately Fishes of the Caspian Sea: zoogeography and updated check-list A.M. NASEKA & N.G. BOGUTSKAYA A.M. Naseka & N.G. Bogutskaya, Laboratory of Ichthyology, Zoological Institute, Russian Academy of Sciences, Universitetskaya Emb. 1, St. Petersburg 199034, Russia. E-mail: dr_naseka@rambler.ru Geographic distribution of some 350 taxa from the Caspian and Black Sea basins were ana- lyzed with regard to recent taxonomy, phylogeny, endemicity and ecological classification. A check-list of the Caspian Sea fishes (taxa from families down to subspecies) is provided. Eighty species and subspecies permanently occur or occasionally recorded from the North Caspian while 33–35 species and subspecies being only distributed in the Middle and South Caspian. Forty-four species are common for the two ecoregions. A comparison of the Caspian and the Black Sea fish faunas and their historical evolution is given with special respect to palaeogeog- raphy and palaeohydrology of the basin. Key words: Caspian Sea, fishes, evolution, zoogeography, taxonomic composition