44 



DEPARTMENT OF TEE NATAL SERVICE 



greatest numbers, there also the number of those newly-spawned is at a maximum, its 

 minimum falling there where the yield as a whole is poorest. We notice, moreover, 

 that advanced stages are not yet present in the samples, this being doubtless due to 

 the fact that the season is only just commencing. 



If we now consider the results from Canada in conjunction with this sample from 

 the Lofoten material, we obtain a table for comparison of the stages of development 

 in the eggs from the different waters. 



Stage I . . 

 Stage IT. 

 Stage IIT 



Lofoten 



(12% 



38% 



0% 



4«% 

 40% 

 12%, 



Acadia I 



43% 



2% 



35% 



49% 

 16% 



Fri 



a 



St% 



16% 



0% 



> 



86% 

 13% 



1% 



Acadia II 



52% 

 35% 

 13%. 



6S% 



2!)% 



3% 



Princess II 



64% 

 32% 



4% 



«4% 



15% 



1% 



"33' 



03 



!'5% 

 5% 

 0% 



83% 

 14% 



3% 



From this it will be seen that the gulf of St. Lawrence is considerably behind the 

 other localities with respect to the occurrence of later stages, both in the case of the 

 earlier investigation and those made subsequently (Princess I, Princess II, and 

 iV 0. 33). The ova have here evidently a far poorer chance of being developed and 

 hatched than in the other places; in the gulf of St. Lawrence the eggs must — at any 

 rate occasionally — be liable to a high degree of mortality, either due to the hydrogra- 

 phical conditions or to their being preyed upon with unusual intensity. 



The task of solving this question must be left to fjiture investigations; I may, 

 howeven, in conclusion, set forth such material as we have available for the considera- 

 tion of what factors should be regarded as detrimental to the development of cod eggs 

 and the growth of the young. 



VI. — I^FLUE^cE OF Temperature and Salinity upon the Development of Eggs and 



Growth of the Young. 



In order to ascertain what effect the low bottom temperatures might possibly have 

 upon the development of the ova in the gulf of St. Lawrence, Dr. Hjort approached 

 Dr. Johansen and Dr. Ivrogh, of Copenhagen, who had previously at the Zoo-physiolo- 

 gical Laboratory there, carried out a whole series of experiments with hatching of 

 eggs at constant temperatures, with the request that they would repeat their investi- 

 gations having the special object at present in view. 



We are aware that cod in the gulf of St. Lawrence spa%vn near the bottom, i.e. in 

 water frequently below 0° ; the inherent upward tendency of the ova then lifts them 

 to the water layers above, where they develop at considerably higher temperatures. 



Dr. Johansen and Dr. Krogh then cemmenced experiments with fertilization of 

 ova at low temperatures, from 0° to -^ 2° C, the eggs being thereafter either main- 

 tained at various low temperatures or gradually transferred to warmer water, vip to 

 6.6° C. 



According to Dr. Johansen, the resiilts showed : — 



1. That fertilization can take place at a temperature between-=-0-6° and 

 -^2 = C. 



2. That full development can be obtained by ova fertilized at such temper- 

 ature and thereafter exposed for nine days to a temperature between -;- 0-7° C. 

 and -4- 1-4. mean value -h 1°, and afterwards transferred to warmer water 

 (e.g. 0° to 3.3° C.) 



3. That full development can be attained by ova fertilized at 0° C. and 

 constantly kppt in water at that temperature. 



