1 . For Aspius , Lucipperca , Esox , Cyprinus , Chalcalburnus and Abramis there is in fact 

 one scale only, according to whiqhithe criteria of maturity are only schematic and not real. 



2. The greater part of the scales (18 of 27) are only adapted for 9 species in all, although 

 they have been worked out for marine fishes. There are 12 scales for clupeoids, 4 scales for cod- 

 fish, and 2 scales for flatfish. The remaining 9 scales have been worked out for semi-migxatory 

 fishes and freshwater fishes (sterlet, pike-perch ( Lucioperca ) perch, carp, bream, vobla, Aspius , 

 carp (sazan), and Coregonus lavaretus ). 



During the development of the investigations the principles of the maturity scales were 

 changed. The first scales (Heincke 1898, Maier 1906, Lea 1910, and others) were based on sub- 

 jective criterions (color of the gonads, transparency, visibility of the ovocytes with the naked eye, 

 and so on). Later, measurements of the ovocytes and their nuclei were very much used. 



In 1927 Meien introduced the index of maturity , the relation of the weight of the sexjjal pro- 

 ducts to the weight of the fish. This index is a very important indicator of the biological state of 

 the herring (Table 7). 



TABLE 7. STAGES AND INDEXES OF MATURITY OF THE SEXUAL PRODUCTS IN FISH. 



Some of the criteria used in the determination of the maturity stages are given below: 



Macroscopic criteria: 



1 . Relation: roe weight to body wei^t . 



2 . Degree of transparency of the ovaries . 



3 . Shape of the ovaries as a whole . 



4 . Color of the ovaries . 



5 . Elasticity of the ovaries . 



6. Characteristic feature in the membrane of the ovary (macroscopical) . 



7. Etegree of development of the blood vessels in the ovary. 



8 . Degree of filling of the body cavity, a) relation: length of the ovaries to length of the 

 cavity, b) relation: hei^t of the ovaries to height of the cavity. 



9 . Degree of development of the cavity of the ovary and its filling with ovarial fluid . 



10. Shape of the eggs. 



11 . Diameter of the ovocytes . 



12. Pigmentation of the yolk. 



13. Degree of transparency of the various eggs. 



14. Visibility of the nucleus and egg cells . 



15. Degree of separability of the sexual products. 



226 



