CANAblAS FlsHKRlf-Js EXPElJlTlOS, lOl'rlS 45 



The mortality observed in the course of these experiments was considerable; 

 as, however, these were carried out under conditions which in several respects must 

 be less favourable than those prevailing in the sea, we should not, as Dr. Johansen also 

 points out, attach too much weight to this. Even at the most favourable temperatures, 

 the mortality was, in the apparatus employed by Dr. Johansen and Dr. Krogh, still 

 considerable. 



Dr. Johansen's experiments show, however, that the low temperature at the 

 bottom in the gulf of St. Lawrence where the cod are to be found during spawning 

 time, cannot be regarded as a general hindrance to the development and hatching of 

 the ova. 



With regard to the influence of high temperatures upon the development of the 

 ova, we may refer to the experiments previously made bj' Johansen and Krogh 

 (The Influence of Temperature and certain other Factors upon the Rate of Develop- 

 ment of the Eggs of Fishes; Publications de Circonstance Xo. 08). These show that 

 cod eggs may be hatched in water up to 12° C. H. C. Dannevig (late Director of 

 Fisheries for Australia) has even hatched them in water at 14° C, (Scottish Fishery 

 Board, 13th Report for 1891.) 



At Flodevigen, where several hundred million cod eggs are annually hatched, low 

 temperatures (down to 0° C. ; the lowest figure at which we have worked) never seem 

 to have any detrimental effect; the most favourable temperature would seem to be 

 about 3°-5° C, while temperatures up to 8° or 10° occasion a higher degree of mortality. 

 As the quantity of ova in the apparatus is very great, the direct cause of such mortality 

 might possibly be lack of oxygen, or poisoning, despite the fact that the water is 

 constantly renewed. 



That the young can thrive at considerably higher temperatures in a greater mass 

 of water is shown by an experiment which I made in the culture basin at Flodevigen 

 during May and June, 1909. The basin is situated in the open air; it measures 34 by 

 22 by 5 m. and is used in the hatching oi^erations as a water reservoir for the apparatus. 

 It is supplied with sea water by means of a steam pump, and in order that the water 

 may be constantly renewed, as well as for other reasons, the water for the hatching 

 apparatus is always drawn from here. 



On the 25th of May, when the hatching experiments were brought to a close, and 

 the circulation of the water consequently ceased, about 100,000 young cod, from one to 

 two days old, were liberated in the basin. The eggs from which these young were 

 hatched had been spawned at about 7° C, and the development had taken place in 

 the course of about nine days at temperatures between 7-6° and 9*5° C. At the time 

 of liberation, the water in the basin at 3 m. depth had a specific gravity of 1-026 at 

 9-5° C. The young could now be seen every day in the water, at first near the surface, 

 and later swimming for the most part in great shoals in the intermediate water layers. 



On the 16th of June, I noted in my journal that up to fifty young could be 

 counted at one time. On that day also, feeding was commenced with finely chopped 

 Mytilus edulis. The water in the basin, by the way, was extremely rich in plankton, 

 especially larvae of molluscs and crustaceans, which, with some few copepods. made up 

 the stomach contents in such ofi the young fish as were examiAed. On the same 

 day, the water in the basin had reached a temperature of 20° O. at the surface, with 

 a maximum, at 1 m. of 21-4° C, and a bottom temperature of 21-1^ C. 



On the ISth of June, eight fish were taken up and measured; they showed the 

 following lengths : 25, 25, 27, 24, 24, 23, 23, 22 mm. The fish were by this time moving 

 nearer the bottom. 



The weather now set in colder for a time, with cloudy sky, and the temperature 

 of the water sank somewhat. On the morning of the 21st, the surface showed 18-9° 

 C. ; maximum of 19-5° at 2 m. On that day, fresh sea water was pumped in (tem- 

 perature 8-3° C.) and in the evening, after the surface water had been drawn oil, and 

 replaced h^ a new supply, the surface temperature was 19 -4". this being the maximum, 

 while at 3 •4m. a minimum of 15-7° C. was recorded. 



