20 0. Nordgaard. [No. 4 



ferred from salt water to fresh before it bad acquired the peculiar 

 shining appearance, it did not turn white-, but retained its nor- 

 mal appearance. It thus, in my opinion, admits of no doubt 

 that when salmon spawn bas become shining and transparent, with 

 a marked reddisb yellow spot, it is actually dead, and further 

 development is an absolute impossibility. 



Subsequently botb salmon and sea- tr out spawn were tried in 

 saltwater. The salmon spawn was then about one month old, and 

 tbe sea-trout spawn had lain in fresh water for about 3 weeks. 

 The result was also here a similar one; the sea-water bad a deleterious 

 effect upon the spawn. Further experiments were made with sal- 

 mon spawn that was so far developed (in fresh water), that distinct 

 movements could be perceived in the embryoes. The result was that 

 the movements very soon ceased, though not instantaneously. 



While hatching experiments in greater degrees of saltness were 

 exclusively productive of negative results, in weakly saline water 

 they were successful. Four hundred pieces of the sea-trout roe fer- 

 tilized in fresb water on the 6th Nov. were immediately placed in 

 brackish water of which the saline strength, during the period of 

 development, varied between 8 and 9 per mille. The number was 

 increased on the 21st Jan. 1896, by 200 fresh trout roes, which 

 bad been in fresh water since tbe 6th Nov. 1895. In this hatching 

 tank, development proceecled normally; on [the 4th Dec. I distinctly 

 saw the embryo rudiment as a white stripe, and movements were 

 first observed in the embryo on the 13th Dec. On the 17th Feb. 

 1896, the first young fish emerged; during the remainder of February, 

 11 were batched, and in the first hall of March, 509 young sea- 

 trout appeared, making 521 in all. The few eggs that diecl had 

 the same shining appearance as the salt-water spawn. Only in 

 a single instance, when mud had accumulated at the end of the 

 glass tube which conveyed tbe sea-water, did one or two eggs 

 become white. In another instance, the fresh water tube became 

 obstructed, so that the saltness rose to 31.54 %o ; but this was 

 observed sufficiently soon to prevent destructive consequences. It 

 was thus ascertained by this experiment that sea-trout spawn, fer- 

 tilized in fresh water, can develop in water of which the saltness 

 is about 9 % . 



On the 15th Nov. the fertilization of sea-trout spawn in 

 slightly salt water (4 %o) was tried. The spawn was placed in a 

 tank in which tbe saltness varied from 3 to 4 per mille. The 



