THE CASPIAN SEA 



637 



and more molluscs (Cardidae, Mytilaster and Nereis). When a sturgeon reaches 

 170 to 180 cm it feeds exclusively on molluscs and Nereis. This change is 



С 3 10 12 /4 16 Id 20 



28 Cm. 30 50 70 90 110 130 /SO 170 190 210 230 Clll. 



100 

 80 

 60 

 40 

 20 

 



{Crust a 





Cordylophora 



30 50 10 90 110 130 150 ПО 190 200 gr. 



% 

 /00 



60 



40 

 20\ 

 



Ш 



\Crustacea 



+*«. x '*"*" 



Corophiidae 



Gobijdae 

 Clupeidae Vi 



5 10 IS 20 25 30 35 40 45 SO 55 60 С1П. 



Fig. 299. Change of diet with age of some Caspian Sea fish (Schorygin). / Vobla ; 

 // Benthophilus macrocephalus ; /// Gobius kessleri; IV Sturgeon; V Caspialosa 

 saposhnikovi ; VI Pike perch. 



connected with the approach of sexual maturity. Generally speaking sturgeon 

 is a typical euryphague. 



Competition for food. The examination of the inter-relation in feeding among 

 the different species is one of the essential problems in the study of fish nutri- 

 tion ; moreover, as has been noted by Schorygin it is equally important ' to 

 establish between which species, where, when, and for which foodstuffs such 

 competition arises, and also, if possible, to determine the degree of competi- 

 tion. It is equally important to study the nature of the effect of the consumers 



