— 153— .TORS. SCHMIDT 



at Frederikshavn in the Northern Kattegat (Denmark), according to inCormation received 

 from Dr. A. C. Johansen '. 



It thus appears that the coalfish, which oC all the Gadus-s\)ec\&s (excepting the deep- 

 water species G. Poutassou and Gudiculus) requires the greatest salinity and depth during 

 spawning, is yet the species which outside the spawning time can live in the shallowest 

 waters and likewise under a much smaller salinity than at the spawning time, so that it 

 may be distributed over a considerably larger area than merely the spawning region. 



As a last example in this direction the cod (G. callarias) at Iceland may be men- 

 tioned. The spawning occurs there chiefly, practically only, in the warm Atlantic water 

 and mainly at depths from ca. 50 to ca. 100 meters. The spawning region is thus limited 

 to a rather narrow belt ofl' the south and west coasts. When the spawning is over the 

 spent cod swarm in immense quantities round all the coasts of Iceland, both the cold and the 

 warm but especially the former, and can thus be taken in numbers even at so great depths 

 as 300 meters and in waters of less than 1°. — The special insensitiveness of the young and 

 adolescent stages towards outer conditions, for example temperature, shown by the fact that 

 enormous masses of them live and overwinter in the ice-cold waters on the east coast whilst 

 others of their kind remain in waters which as ont he south coast and at the Fseroes never 

 sink below ca. 6°— 7°, has already been described (p. 27). I need only remark here that the 

 early bottom stages, which we know best from their occurrence in quite shallow, tidal 

 waters along with similar stages of the coalfish (see hauls pp. 23—27), are far from 

 being bound to these waters but can also be found in much greater depths. At Iceland, 

 for example, I have taken the bottom stages of the year in depths of ca. 200 meters and 

 in the Skager Rak near the Skaw I have found them in great quantity in water of 

 100 meters in July 1907. 



"We have thus seen several examples of the fact, that the spawning region of a spec- 

 ies, owing to the greater sensitiveness of the spawning fish towards outer 

 conditions, may be much more restricted both in a horizontal and vertical direction 

 than the distribution of the species as a whole. I have emphasized this condition so 

 strongly, because in my opinion it contains a very important principle which enables us 

 to understand both the biology and geography^ of the species, as for example how the 

 spawning fish collect together on definite, small areas and how from there the fry can 

 spread far out either passively or actively over widely different waters and yet find every- 

 where favourable conditions for their growth. 



The different species have different requirements in regard to the outer 

 conditions (depth, temperature and salinity) and the regions are subdivided 

 accordingly — "vicarious" species. 



On reviewing the lists (p. 139 et seq.) where the depth, temperature and salinity 

 which each species requires for its spawning are noted, we see at once that these 



' On May 12th 1907 Dr. Johansen examined a number of siioh small coalfish taken in Frederiks- 

 havn harbour whilst pursuing small herrings. They had a length of 19—26 cm. and belonged to the 

 group of the previous year, as determined by Dr. Johansen from examination of the otoliths. 



'■^ Though it is almost superfluous, I may just mention that it is naturally not my meaning that 

 because the fish are specially sensitive during the spawning time, they are quite insensitive towards 

 outer conditions at other times. This is indeed far from being the case, as all who have been engaged 

 in the study of marine biology ivill know. 



20 



