— 4 — 



hardy and easily reared. And the element in which they have to be hatched and 

 reared, viz. fresh water, is very cheap to procure. 



The number of eggs deposited by these fish is as a rule small, the time of incubation 

 long and the protection rendered to each individual, even by hatching only, is therefore 

 important. Also the young fish when liberated remain entirely local. 



The pelagic eggs of salt water fish are on the contrary small and delicate. Each 

 individual produces an enormous number of eggs. The period of incubation is short. 

 The element, wherein they must be hatched viz. pumped up sea-water, is dear. And 

 when the small, helpless and exceedingly delicate larvae have left the egg the work of 

 the fish-hatcher is practically at an end. All he can do is to hurry these larvae into 

 the sea, where for many weeks they lead a pelagic life suspended in the waters and 

 subject to their movements. Where the work of the freshwater culturist in real earnest 

 begins, the efforts of the sea culturist cease. The whole process of rearing, so important 

 to all freshwater-culture, is as regards sea fish still technically and economically impossible, 

 at least on a large scale. 



From this short review of the main points of difference between the two kinds of 

 fish hatching, we will perceive, that the hatching of sea fish takes place under much 

 more unfavourable conditions than those characteristic of fresh water. 



The theory of those maintaining the utility of hatching opera! ions in the sea has 

 however been founded on hypothesis or suppositions, which reduced the importance of 

 the difference in conditions above mentioned. On the one hand the productivity of the 

 sea itself has been valued very low, and the numbers of hatched and liberated larvae 

 have been considered as very important compared with the production of the waters. 

 On the other hand the importance of the size of the waters was reduced by accepting 

 the doctrine that each area of the sea, even the smallest, possessed its own tribe of fish. 

 These tribes were supposed to be highly local during the whole life of the individuals. 

 They were easily injured by over-fishing and had to be replaced by the aid of man. 

 These theories variously attired, form everywhere the main argument of those who 

 advocate the efficiency of present seafish hatching. 



During the years of international cooperation for the study of the sea, immense 

 numbers of investigations have procured a large material illustrating the economy and 

 life of fishes in all North-European waters. Special experiments have been undertaken 

 in Norway in order to study the conditions which affect the hatching and liberation of 

 cod larvae in Norwegian waters. It is therefore interesting and justifiable to consider 

 the theories upon which the hatching of sea fish has hitherto rested in the light of all 

 this new knowledge. 



A. Special experiments and investigations on the hatching problem in the 



fjords of Southern Norway 



1. The hatching problem in Norway 



At the Fl0devigen hatchery near Arendal cod eggs have been hatched since 1884. 

 The following table is compiled from the reports on the hatchery and shows the number of 

 larvae hatched and, where recorded, the number of spawning cod. 



