THE CASPIAN SEA 



635 



Benthos-eating fish of the Caspian Sea can be divided into four groups : 

 worm eaters in a wide sense (including chironomids), and those which live on 

 molluscs, crustaceans and fish (usually called predators) ; moreover, individual 

 fish are transitional types as regards their diet. As may be judged from Table 

 271 sturgeon and two species of bullheads — Pomatoschistus (Bubyr) causasicus 

 and Knipovitschia longicaudata — feed on worms ; vobla, Benthophilus stellatus 

 and B. macrocephalus and the bullheads Gobius melanostamus affinis and G. 

 kessleri feed on molluscs. Predators and crustacean eaters often have a mixed 



Table 271. General character {percentage basis) of . fish diet in Northern Caspian 



diet. The bullheads Hyrcanogobius bergi, Gobius fiuviatilus pallasi, G. caspius, 

 pike perch and carp may be considered typical crustacean eaters ; while the 

 typical predators are belugam pike perch, Caspialosa saposhnikovi, Caspialosa 

 brashnikovi and C. sphaerocephala. Starred sturgeon and sturgeon also have a 

 mixed diet. 



Some less pronounced transitions also exist between the typical crustacean 

 and mollusc eaters. Gobius melanostomus affinis, G. kessleri, G. pallasi, G. cas- 

 pius, golden shiner and carp have a mixed diet of this type. However, in all 

 these cases except for the first two, the consumption of crustaceans is greatly 

 in excess of that of molluscs. 



A comparison between the main nature of diet and the average index of 

 repletion brings out a definite dependence : the higher the calorific value of 

 food the lower the index of repletion. Moreover, the indices of repletion 



