276 G. V. MKOL'SKII 



has shown (1961) that the yearhngs of Baltic herring when feeding mainly 

 on the stage V of Calanus appear to be better provided with food than those 

 feeding mainly on stages I and II. In the first case the variation coefficient 

 of the size appears to be lower — on average 11-85 (by five tests), and in 

 the second case higher — 15*27 (by four tests). If, for the population as a 

 whole, its density and biomass are determined, as a rule, by the food supply 

 of the fish in the post-larval period of development, the survival of separate 

 generations depends to a great extent on the food supply available for the 

 earher developmental stages as was found by T. F. Dement'eva (1953)- 

 Though naturally these phenomena are interrelated. 



One of the forms of the adaptive response of population to the deteriora- 

 tion of the food supply is the increase of the diversity of the egg size, i.e. the 

 increase of the difference in the yolk reserve in the eggs. L. E. Anokhina 

 (i960) showed that the variability of the egg size in the White Sea herring 

 {Ckpea harengus maris alhi Berg) was greater in lean fish than in fat ones 

 (Table VI). 



Table VI. Differences in the variability of egg size in Onezhskaya herring of 



different fatness {after L. E. Anokhina, i960) 



Percentage of fat Egg size t for difference 



^ A ^ ^ ^ ^ between 



Group of Wet Dry Mean and Standard standard 



fish substance substance standard error deviation deviations 



For all fish between 14-5 and 16-5 cm in length 

 Lean . . 3*22 — . 4'35±o-23 0-69 . 3-41* 



Fat . . 7-74 — . 3-36±o-i7 0-44 



For three years' fish between 14-5 and 15-4 cm in length 



Lean . . 3-16 14-82 . 4-03±o-09 0-24 . 8-17* 



Fat . . 7-12 28-73 • 3-05±o-o8 o-i6 



* Both values of t are highly significant. 



The mechanism of egg formation with different reserves of yolk was 

 revealed by V. A. Meien (1940). He has shown that the difference between 

 the yolk amount in different eggs of one and the same fish depends to a 

 great extent on the position of a given egg with respect to the ovarian 

 blood-vessels. NaturaUy, the greater the amounts of nutritive substances that 

 enter the egg, the more favourable the conditions of yolk reservation that 

 are created. In fish that are well provided with food all eggs receive a sufficient 

 amount of nutritive substances to accumulate the necessary amount of yolk, 

 and all the eggs appear to be more or less similar in size. Upon the deteriora- 

 tion of the food supply some eggs receive a larger amount of nutritive 

 substances than others and thus the heterogeneity of eggs is brought about 

 which was mentioned above. 



