Figure 6 shows graphs of indices of the physiological condition of adult Atlantic -Scandina- 

 vian herring throughout the year. Owing to the lack of data from quality -weight analyses for the 

 winter-spring months, we have given in Figure 6A the mean weight of food in the stomachs of feed- 

 ing herring, disregarding empty stomachs . 



The mean weight of food in the winter-spring months is very high, but the number of feed- 

 ing fish at this season is very small. During the following months, the mean weight of food in the 

 herring stomachs declines slightly, whereas the number of feeding fish increases sharply. 



The maximum mean stomach fullness index for all the years (1951-55) falls in the summer 

 months (June-July) when the maximum number of feeding fish were observed (Figure bB)- 



In order to illustrate the fat accumulation in the body cavity we used thedata from biolog- 

 ical analyses in which the quantity of fat in 36, 450 herrings was assessed visually and evaluated by 

 a system of grades— . 



A noticeable accumulation of fat on the internal organs appears from May onwards and con- 

 tinues to increase during the following months . Visual observations show a slight reduction in 

 fatness by September -October. An abrupt fall in general fatness occurs at spawning time - in Feb- 

 ruary and March (Table 7, Figure 6B). 



On the fatness of the flesh of the herring, we have the data obtained in 1953 by the Industrial 

 Chemical Laboratory (Figure 6?). 



The flesh has the minimum fat content, 8%, in Ma^ch, after which the fatness increases 

 and reaches its maximum of 22.5% in August; it then gradually falls until the end of the year. 



A good index of the condition of the herring after spawning and feeding is its weight . We 

 observed the variations in weight for different size groups during the course of the year; in 1954, 

 the weight was calculated from 1, 678 specimens and in 1955 from 3, 329 specimens (Table 8, Figure 



We find that herrings of all size groups show the minimum weight immediately after spawn- 

 ing, in March or April . 



The reduction in weight after spawning is in fact relatively abrupt, since the release by the 

 fish of its gonads immediately reduces its weight by 20-25%. 



The weight is at its minimum during the period of intensive feeding. 



There is a gradual increase in the weight of the herring during May and July. The maximum 

 weight is attained in August, a month after the highest average stomach fullness grade. The aver- 

 age weight of the herring in 1955 for all size groups was somewhat below that of the preceding year 

 (Table 8). 



2/ 

 The nutritional condition factor— of the fish varies in complete conformity with their weight 



(Table 9, Figure 6r). 



V 1 grade = small deposit of fat on the stomach and Intestines; 2 grade = fat in considerable 

 quantities on the stomach, intestines and pyloric appendages; 3 grade = abundant fat - 

 stomach, intestines and pyloric appendages covered in a thick layer of fat. 



2/ The nutritional condition factor is calculated from the formula Ky = = — 2 



157 



