GENERAL BIOLOGY 



7Z2, 



I. Spawning in the Atlantic, in the 

 North Sea, and in the Norwegian 

 Sea. 



A. On coast banks in depths less than 

 100 metres. 



Gadus vierlangiis, Optimum 20 to 60 metres. 

 „ callarias,^ ,, 40 to 80 ,, 



,, cBgleJinus, ,, beyond 60 ,, 



,, esi7iarki, ,, ,, 80 ,, 



B. On the slopes of the coast banks. 

 Molva molva, Optimum 60 to 200 metres. 

 Gadus virens, ,, I GO to 200 ,, 



C. On the edge of the coast banks. 

 Brosmius brosine, Optimum 100 to 500 metres. 



II. Spawning entirely, or almost 

 entirely, in the Atlantic. 



A. On coast banks beyond 100 metres. 



Gadus liiscus. 

 ,, mi nut us, 

 „ pollac hilts. 



B. On the slopes towards the edge. 

 Alerluccius vulgaris. Opt. 100 to 200 metres. 



C. On the edge of the coast banks. 



Gadiculus argenteus,^^ 

 Gadus poutassou, \ Optimum from 



Molva byrkelange,^ j" 200 to 1000 metres. 

 ,, elongata j 



floating eggs. 



From the point of view of general biology it is interesting 

 to note from this table that species, which in shape and general 

 anatomy are very similar, present such pronounced differences 

 as to their habitat during this most important process of life 

 (see the chart, Fig. 522, showing the spawning area of the three 

 ling species). 



C. G. J. Petersen" was one of the first to draw attention Effect of 

 to the influence exerted by currents on pelagic eggs. After '^^^"■entson 

 his investigations in the Lesser Belt (Faenoe Sund) he sums 

 up as follows : " It is one of the facts that have astonished 

 me most during these researches that the fry of pelagic eggs, 

 which were sometimes found in such huge numbers in 

 Faenoe Sund, was not hatched there, or at any rate was 

 only to be found there quite exceptionally. This condition did 

 not only apply to the cod, but indeed to all species which 

 possess floating eggs, in contrast to the fishes which deposit 

 their eggs on the bottom." It has proved very important to 

 investigate the drift of pelagic eggs, and this study has yielded 

 important results regarding the different species. The drift of 

 the eggs depends on physical as well as biological condi- 

 tions. The direction and velocity of the currents, the tem- 

 perature, the duration of the hatching and development, the 

 actual duration of the pelagic life which varies in different 

 species, all these are important points. Finally, the specific 

 gravity of the eggs and larvae is of great importance in 

 determining the depth at which they float. From my investiga- 

 tions on the distribution of cod eggs, larvae, and pelagic fry in 



1 Also spawn in the Norwegian fjords. ^ Report of the Danish Biol. Station, 1893. 



