herring at different times of the year. In winter, the sexual glands are slightly developed, in 

 March they double their size, in April they are more than four times the winter size. 



In 1946, Smimov (64) made experiments in order to show the direct connection between the 

 development of the sexual glands of the Caspian herring and the magnitude of the radiation from the 

 sun. He stated that the weight of the gonads of the Caspian puzanok ( Alosa ) increased with the in- 

 crease of the direct radiation. 



We have tried to compare the development of the roe in the Murmansk herring with the 

 light conditions (Table 10). This comparison must necessarily be a mechanical one, for in most 

 of the experiments with living creatures no positive correlation has been found between the develop- 

 ment of the gonads and the light. This question can only be answered correctly by experiments, as 

 the influence of ligjit cannot be treated in an isolated manner, but must be considered in connection 

 with other factors . 



TABLE 10. THE VARIATION IN WEIGHT OF THE ROE OF MURMANSK HERRING 

 AND THE VARLA.TION OF THE AMOUNT OF SOLAR RADIATION. 



With respect to the lig^t conditions, the Polar Basin is sharply distinguished from the south- 

 ern oceans. Even in summer, bri^t days without clouds are comparatively rare. From the data 

 (Table 10), it migjit be concluded that a connection exists between the sexual cycle of the herring 

 and the order of magnitude of the solar radiation. The greatest radiation corresponds with the two 

 most important steps in the sexual cycle, the beginning of the ripening of the sexual products, and 

 the period of maximiun mature gonads . 



In the Murmansk herring, the gonads usually begin to ripen in July. This period corres- 



ponds with a maximiun of the direct solar radiation (5400 cal/cm, 

 gonads pass from stage I to II, in adults from II to HI. 



) . In immature individuals , the 



During the Polar ni^t the direct radiation from the sun decreases to 5 cal/cm. . In this 

 period, the growth of the gonads continues, until they constitute 9.6% of the fish weight. The cor- 

 relation between the development of the gonads and the solar radiation is therefore very poor . In 

 March and April, the radiation increases very strongly (1592 cal/cm.'^) for we have the largest 

 number of bright days and maximum weig^ of the roe of the herring (13.9%). Most of the herring 

 spawn in these months, but the spawning process itself has probably no relation to the lig^t. The 

 spawning is the climax of the sexual cycle . After the spawning, a new cycle begins . 



Before the spawning period, the organism is biologically prepared for the spawning. A 

 great accumulation of fat on the intestines and in the muscles is caused by the heavy feeding during 

 the period previous to the spawning. This fact probably explains the increase in the hemoglobin 

 content of the blood . 



240 



