GENERAL BIOLOGY 759 



It has been discovered that in various boreal fishes the 

 seasonal changes in their growth leave certain traces in all the 

 osseous structures, such as vertebrae, gill-covers, otoliths, and 

 scales, a difference being plainly seen between the parts formed 

 during rapid growth (in summer), and the parts formed during 

 feeble growth (in winter). In this way visible rings or zones Age and 

 are formed in the structures mentioned, varying according to Ish^s ae°noted 

 summer and winter, thus enabling us to count the number of by their 

 winters and summers passed by the fish in question, and to^'^^^^' 

 ascertain its growth in various phases of life. This was first 

 discovered by Hoft^bauer in the scales of the carp (1899), ^"^ 

 has also been observed to hold good in the case of the otoliths 

 of the plaice (Reibisch), and of the scales of gadoids (Stuart 

 Thomson), while Heincke and others have proved various 

 bones to be good indicators of growth. A voluminous 

 literature ^ has accumulated as the result of these methods, 

 which assumed greater importance when in 1904, upon the 

 recommendation of Heincke, the international fishery investi- 

 gators adopted them and applied them to many special 

 and general problems. In recent years during the fishery 

 investigations of several countries the growth and age of 

 various commercial species have been subjected to analysis. 



In Norwegian fishery work the scales have mostly been 

 employed for age assessments, and in this way a number of 

 species belonging to the cod family have been treated by 

 Damas, while Sund has studied the age of the sprat, Broch, 

 Dahl, and Lea the age and growth of the herring, and Dahl 

 of the salmon and trout.' 



Fig. 554 represents a series of scales of saithe, ranging from 

 17 to 67 cm. in length, taken on the west coast of Norway. 

 They have been represented in proportion to the size of the 



1 See Knut Dahl, " The Assessment of Age and Growth in Fish," Internationale Revjte der 

 ges. Hydrobiologie 21. Hydrographie, Bd. II., 1909, containing review of literature. 



- Desire Damas, "Contribution a la biologic des Gadides," Rapp. et Proc.-verb. de la 

 coin. perm, pour Texpl. de la mer, vol. x., Copenhague, 1909. 



Hjalmar Broch, " Norwegische Heringsuntersuchungen wahrend der Jahre 1904-1906," 

 Bergens Miis. Aarbog, 1908, No. i. 



Oscar Sund, " Undersokelser over Brislingen i Norske farvand," Aarsbcretning vedk. Norges 

 Fiskerier igio, Bergen, 191 1. 



Knut Dahl, "The Scales of the Herring," Report on Norwegian Fishery and Marine^ 

 Investigations, vol. ii. No. 6, Bergen, 1907 ; " Age and Growth of Salmon and Trout in Norway," 

 Salmon and Trout Association, London, 191 1. 



Johan Hjort, "Report on Herring Investigations until Jan. 1910," Publications de 

 Circonstance, No. 53, Copenhague, 1910. 



Johan Hjort and Einar Lea, "Some Results of the International Herring Investigations, 

 1907-1911," Picbl. de Circonstance, No. 61, 1911 ; " Einige Resultate der internationalen 

 Heringsuntersuchungen," Mitteihlngen des Deiitschen Seefischerei- Vereins, No. i, 1912. 



Einar Lea, "On the Methods used in the Herring Investigations," Pitbl. de Circonstance, 

 No. 53, 1910 ; " A Study on the Growth of Herrings," Publ. de Circonstance, No. 61, 191 1. 



