nents. individual and average indices of stomach fullness (ratio of wei^t of food to body weight of 

 fish, multiplied by 10,000) were calculated. For a number of reasons, the index of stomach full- 

 ness does not reflect the natural course of feeding of the herring with complete accuracy . 



First of all, it should be noted that a herring is able to digest the food in its stomach after 

 having been caught in a drift-net. A series of drift-nets is usually in the water for a period of 8-9 

 hours; a considerable portion of the food in the herring's stomach is undoubtedly digested during 

 this time, since a herring can remain alive for a long while in a net. 



The character of the food is also reflected by the digestion and, of course, it alters the full- 

 ness index, since different organisms are digested at different rates. The fullness Index depends 

 to a certain extent on enzymes whose activity does not remain constant througtiout the year . Di - 

 gestion activity is influenced, and therefore varied, by the temperature conditions of the environ- 

 ment. The higher the temperature, the more^ rapid are the digestive processes. 



From the experimental data of G. C. Karzlnkin (5) and K. R. Fortunatova (11), it has been 

 established that the lower the water temperature the slower the food moves through the alimentary 

 canal. 



Battle (13), who studied the food of the herring off the American coast, came to the conclu- 

 sion that the food digests eig^t times more quickly at a temperature of 9.5°C than at a temper- 

 ature of 2.4"C. 



Despite the above-mentioned defects and discrepancies in our investigation method (absence 

 of analysis of different factors influencing the character of digestion, etc.), the results obtained 

 nevertheless enable us to make a general comparison of the food of the herring from season to 

 season and from year to year . 



Apart from the quantity -wei^t analysis of the stomachs of herrings, we also used data ob- 

 tained from field analyses during the period 1951-55 in which the degree of fullness of the stomachs 

 was determined by a five -mark scale: 



- stomach and intestines empty 



1 - small quantity of food present 



n - moderate quantity of food present 

 in - stomach full, containing a large percentage of food 



rv- stomach distended (walls of stomach distended to such an extent that food is visible 

 througji them) . 



A total of 36,821 stomachs were subjected to the field analysis. 



Specimens of plankton were taken (by means of a Nansen net with a closing device) at the 

 same time as the herring stomachs . 



Composition and Quantity of Individual Organisms 



in the Food of the Herring 



Our data show that the food of the Atlantic -Scandinavian herring consists of plankton organ- 

 isms (zooplankton) and young fish, irrespective of season. 



The ratios of food components vary in different years but some species always predominate . 



142 



