270 G. V. NIKOL'SKII 



Table I. Changes in stock fecundity in (a) Caspian roach in 1946 and 1947 

 {Chugunova, 195 1) and (b) herring of the Southern North Sea {Hickling 1940 

 and Cushing). 



1933 



1956 . 18,000 19,650 28,320 31,590 36,760 40,680 43,400 38,900 . 2,800,000 



How great the changes in stock fecundity can be is shown by the fecundity 

 alteration in a spawning fish population (computed to 100 fish), Caspian 

 roach in 1946 and 1947 (Chugunova, 195 1) and herring of the southern part 

 of the North Sea (Hickling, 1940 and Cushing's data) given in Table I. 

 When computing fecundity of 100 individuals we have used the observed 

 size composition of the spawning population. 



Fecundity of the Caspian pike-perch is shown by A. G. Kuz'min (1958) to 

 undergo some, though rather less, variation from year to year. As the result 

 of these variations and of some changes of spawning population structure the 

 average fecundity of the population of Volga pike-perch can change by as 

 much as I • 8 times. These changes of stock fecundity certainly cannot smooth 

 out all fluctuations brought about by changes in the conditions of existence 

 that determine the survival of a brood, as in some species the size of a genera- 

 tion can vary greatly; but the changes mentioned above can exert a smooth- 

 ing influence. An increase in stock fecundity, caused by an improvement of 

 food supply which takes place year after year under favourable conditions 

 of survival, provides a more rapid increase in the stock. 



Fluctuations are certainly determined not only by the environment factors, 

 but also to a great degree by the state of the population itself, in particular, 

 by the quality of the roe ; they also depend on the quantity of yolk and the 

 amount of fat in the eggs, the latter being related to the food conditions of 

 the mother stock in the previous year. As J. I. Cheprakova (i960) showed, 

 for instance, the amount of fat in eggs of Caspian roach is connected to a 

 great extent with the growth rate of fish for the previous year ; fish growing 

 more rapidly in the previous year, have a higher percentage of fat in their 

 eggs. 



