INTRODUCTION 23 



Biological research has also been systematic and all-embracing, covering 

 more or less uniformly both plant and animal populations throughout the sea 

 column from its tidal zone to its abyssal zones. This started as a systema- 

 tic study of the fauna and biogeographical characteristics of the seas, which 

 covered, however, some ecological problems, as well as the seasonal cycles of 

 development and the phenomena of biological productivity. The study of fish 

 feeding and their use of plankton and benthos forms a considerable section of 

 marine biological research. The results of biological research were used in 

 dealing with the problem of acclimatization in new places of marine fish and 

 the invertebrates used by them as food. The acclimatization of Mugil awatus. 

 M. saliens, Nereis diver sicolor, Syndesmya ovata, Leander longirostris and L. 

 squilla in the Caspian Sea and Clupea harengus membras and Leander squilla 

 in the Aral Sea were found most effective and interesting. 



