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



frequently two breeds of each species present — the 'winter' and 'spring' ones 

 (L. Berg, 1934), differing in the time of their entry into the river and in their 

 wintering place (either in the river or in the Sea). 



The migrations of Salmonidae {Stenodus leucichthys and Caspian salmon) 

 are of special interest. Stenodus leucichthys moves from the Caspian into the 

 Volga, Kama, Belaya, and finally into the river Ufa, travelling about 3,000 km. 

 A certain number of Stenodus leucichthys also enters the river Ural; salmon, 

 on the contrary, mostly enter the rivers on the Caucasian shore, and only 

 single specimens of it enter the Volga.* Acipenseridae have been observed to 

 choose some individual rivers for spawning ; it has been known for centuries 

 that some rivers are preferred by the Acipenseridae (the rivers Volga, Samur, 

 Gyurgenchai and Sefidrud) and others (Kura, Terek, Sulak, Ural) by starred 

 sturgeon. 



Among the migratory fish of fresh-water genesis the following should be 

 mentioned; Rutilus rutilus caspius, Rutilus frisii kutum, Abramis brama, Bar- 

 bus brachycephalus caspius, Cyprinus carpio, Pelecus cultratus and Lucioperca 

 lucioperca. They all spawn in fresh water (except for some shoals of carp) and 

 fatten in the Sea ; but they spawn in the deltas and lower reaches of the Caspian 

 rivers and therefore they do not make long migrations. Autumn migration 

 into rivers for wintering, apart from the spring spawning migration, is most 

 characteristic of this group of fish. All the above mentioned fish, except for 

 vobla and to some extent carp, winter in the lower reaches of the rivers in 

 deep places or 'pits', where they ' spend the winter either completely or almost 

 completely motionless, being covered by a thick layer of slime as if by a fur 

 coat' (V. Meisner, 1933). Vobla approaches the shores for wintering, bedding 

 down in the pits of the Volga delta ; but it does not enter the river. Carp 

 winter either in the pits or in the Sea. In the same way various shoals of carp, 

 apart from the carp which spawn in the river, also spawn in different places, 

 in brackish water, in inlets and in the bays and inlets of the Northern Caspian. 



P. Schmidt (1938) believes that there is a great difference in principle 

 between the movements of migratory fish of marine and of fresh-water origin. 

 'Whereas the true marine fish acquire a new element in their biology in the 

 shape of spawning migration into fresh waters, the fresh-water, semi-migratory 

 fish are only extending their feeding migration, covering the neighbouring 

 parts of the Sea, in as much as they succeed in restoring their long-lost capacity 

 for enduring an increase of salinity in the water. In the first case it is an acquisi- 

 tion of new properties and instincts, a reconstruction of the whole process of 

 breeding and development ; in the second it is only the renewal of a capacity 

 they had possessed. . . . ' 



Semi-migratory fish like Abramis sapa, Abramis ballerus, Blicca bjornca, 

 Aspius aspius and Si/urus g/anis do not move farther than just outside the delta, 

 as they are strictly limited in their propagation by fresh water and can tolerate 

 only a very slight increase of salinity. 



As for the marine fish listed above, almost nothing is known as yet about 



* Judging by archival material collected by A. Derzhavin (1939), salmon were abundant 

 in the Volga in the seventeenth and eighteenth centuries; their numbers have greatly 

 decreased since then. 



