176 



Part TIT. — Fifteenth Annual Report 



As already mentioned, artificial rearing of the post-larval fishes is of 

 great interest from the scientific point of view, for there is a gap in our 

 knowledge between the larval and adult stage of common fishes, which 

 only in a few cases is partly bridged over. But it is also of interest for 

 practical purposes in connection with the hatching and rearing of food 

 fishes, and will, no doubt, in the future become much more important. It 

 became desirable in 1885 at the Marine Hatchery at F.loderig to under- 

 take an experiment to clearly show the vitality of artificially produced cod 

 fry. A large tank was constructed on shore, into which cod fry from the 

 hatchery was placed in the spring, and most of the young fishes survived 

 the following winter. Some of them at that time had a size of about 10 

 to 12 inches; others were smaller. This experiment, which was carried 

 out by Capt. G. M. Dannevig, the director of that Hatchery, is described 

 in the annual report of that institution.* It is perhaps, the only one of 

 its kind on a large scale, where the young fry could find suitable condi- 

 tions for growth and development, and the only case, as pointed out by 

 Mr. Cunningham,! in which larvae artificially hatched from marine pelagic 

 fish eggs have been successfully reared in captivity ; the success he attri- 

 buted to the fact that the young fry were turned into a large reservoir of 

 clean sea water. 



Later, Cunningham described rearing experiments that he undertook in 

 the spring of 1894, | with whiting, flounder, and plaice. The fry were kept 

 in a tank in the laboratory ; it would seem that the two former species 

 soon disappeared, while the yolk was absorbed in the plaice larvae after 

 the elapse of five days, when the fry began to feed. They soon died, how- 

 ever, without haviug undergone any important change in development. 

 In another experiment he succeeded so far that two larvae were found 

 alive, thirty-seven days after the yolk had been absorbed ; but it appears 

 that the advance in development, also in this case, was very small. In 

 the first experiment the yolk was absorbed in so short a time, that it is 

 clear the temperature must have been high, probably at least about 12° C. 

 or thereabout, and there is little reason to think the water became 

 remarkably colder soon after. But then those two specimens that were 

 left at an age of thirty-two days, ought, according to the results of my 

 experiment this year, to have been far advanced in development, and 

 signs of the transformation should have been visible. When such was 

 not the case, the explanation can only be that one thing or another in 

 connection with Cunningham's arrangements were unfavourable to the fry. 

 The majority had died previously, and the two specimens left must have 

 been in an abnormal condition. I have taken notice of this here, as the 

 results of the above experiments partly correspond with what I experi- 

 enced in the same season (1894). (Twelfth Annual Report of Fishery 

 Board for 1895, part iii. p. 216.) 



Experimenting at the same time, we both follower much the same 

 system, trying filtered and unfiltered water in succession, and always 

 maintaining a constant current, and we both sought for the food chiefly 

 in tow-net collections. Our success was also much about the same, a 

 few individuals being kept alive for a considerable length of time ; but 

 the advance in development that these reached was very small. Although 

 these experiments were advances, and in the right direction, it was evi- 

 dent that something of importance was lacking with the arrangements, 

 that accounted for the sickly and abnormal state of the fry. 



* Berctning for femaaret, 1883-88. Arendal, 1889. 5th Annual Report Fishery 

 Board, Part III. 1886. 



t Jour. Marine Biological Ass., New Series, vol. h\, No. 3, May. 1892. 

 + Jour. Marine Biological Ass., New Series, vol. iii. No. 3. 



