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conditions during the spawning time. We can show, in the first place, that all the 

 gadoids investigated are dependent during the spawning on definite conditions as to depth. 

 In the second place, we have found numerous examples, that the salinity and temperature 

 also play a most important part. In the more detailed description of the spawning places 

 of the different species we saw, that the coalfish and ling only spawn in the most 

 saline Atlantic water (over 35.2 °/oo)> *^hat in other words, the boundaries of the spawning 

 region coincide with the distribution of this high salinity. We saw that the cod every- 

 where preferred an essentially lower salinity and that its distribution at Iceland as at 

 Norway was restricted to water-layers with definite temperatures. The best evidence for 

 the close connection between definite natural conditions and the spawning of the fishes is 

 perhaps the fact, of which we have already had many examples, that the spawning 

 time of the fishes is different in the different regions, just according to the occurrence 

 of definite temperatures. We saw, for example, that the species Gadus pollachius and 

 minutus spawn in spring in the Atlantic Ocean, but first in summer in the North Sea 

 when the temperature there has reached the spring condition in the Atlantic. At Iceland 

 the cod spawns in February — March on the south coast, whereas it only spawns on the 

 colder west coast banks in May or later. In the North Sea we have seen that as spring 

 advances there is a gradual shifting of the spawning time maximum from the more south- 

 ern to the more northern banks. In the Norwegian Skager Rak fjords young pelagic 

 stages of the cod are constantly occurring from early spring right into the summer, which 

 presumably come from other localities where the spawning time is essentially later than 

 in the Norwegian fjords. 



The physical conditions are also of the greatest importance for the growth of the 

 fish. We have seen, for example, that the same year-groups of cod or coalfish attain 

 a very different size at different degrees of latitude, which must stand in agreement with 

 the different conditions of temperature at the different places. Compare for example the 

 cod of the North Sea with the cod of the White Sea. The stock is thus impressed by 

 definite, demonstrable factors in the surrounding medium. 



The conditions of life cannot however be the same throughout the entire life of the 

 fish or lie within the same limits, as is obvious indeed from what has been already said 

 above, namely, that the different stages are so different in their distribution. It is there- 

 fore only through a precise study of the regions occupied by the different stages and the 

 natural conditions there, that we shall learn to understand generally the conditions of life 

 of the species. 



We hope consequently that the results now obtained will facilitate to a substantial 

 extent further investigations in this difficult, but yet so important field of enquiry. 



3. How great is the natural increase in regard to eggs, young fishes 

 or earlier year-groups of the economically most important gadoids? It is 

 known generally, that Hensen subjected this question to a thorough analysis in his inter- 

 estirig investigations. He pointed out the possibility of calculating the number of fish 



