458 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



whole post-Pontic period, and altered here under the effect of the freshening 

 of the waters of the Caspian Sea. There are, however, several serious objections 

 to this. To explain this phenomenon by the salt composition of the Azov and 



Fig. 220. Diagram of ancient estuary of river Danube 

 (Antipa, 1910). 



Black Seas or by competition (in virtue of the above-mentioned facts) with the 

 Mediterranean fauna, which pushed the ' Caspian ' forms into fresh waters, is 

 even more difficult. 



Fish and mammals 



The Black Sea ichthyofauna, with its 122 species of marine fish and 34 of 

 fresh-water fish, is about twice as rich as the Caspian Sea (77) and 25 per cent 

 richer than the Barents Sea (114) in its variety of species. The characteristic 

 difference from the fish of the Barents Sea consists of a much greater variety 

 of commercial fish. In the Barents Sea only 10 per cent of the species are 

 commercial, while in the Black Sea no less than 20 per cent are so. 



A. Krotov (1949) includes in the list of the Pontic relict species of fish: 

 Percarina demidoffi, Lucioperca marina, Clupeonella delicatula and six species 



