of the herring (fat content, condition) is evidently sufficient to re sorb the remaining ripe eggs, as 



well as the empty follicles, - and to start a new sexual cycle. 



2) From the histological state of the ovary it can be decided at any time of the year if one 

 or other individual has spawned. 



Fro^m the Polar Institute we received 10 roes from Norwegian herring taken in February 

 1947 near Alesund (Table 6), sufficient for a brief characterization. 



TABLE 6. A TYPICAL SAMPLE OF NORWEGIAN HERRING IN THE PRE -SPAWNING 

 PERIOD. 



The macro- and microscopical structure of the ovary of the Norwegian herring is very 

 similar to that of the Murmansk herring. 



Histological Control of the Maturity Stages 



In field work, the scale of maturity used is based on macroscopical criteria . The estimate 

 of the degree of maturity will then be mostly subjective . It is very important to know the time 

 when the gonads pass from stage VI into stage II, and from n to HI. In the first case gonads from 

 spent fish (VI) in which the re -establishment of the gonads already started some time ago, may 

 very well be determined as stage II in field work. However, the same stage may also be found in 

 immature fish . In the second case (transition from II to III) one may miss the time when the sexual 

 products begin to ripen. 



In order to get an exact picture of the degree of maturity it is proposed to supplement the 

 field determinations with a histological control in the laboratory . A freezing microtome may be 

 used to make sections within one hour. 



The Scale of Maturity for Sexual Products in Fish 



The necessity of establishing a "scale of maturity", also called "table of maturity" of the 

 sexual products, arose long ago in fishery investigations. In 1937, Meien (47) numbered 20 such 

 scales. At present there are about 30 scales. 



Scales for maturity have been worked out for many of the important food fishes. TTie follow- 

 ing items must be taken into account: 



225 



