VALUE OF NORWEGIAN LAKES FOR FISH CULTURE. 575 



species to many lakes, and to greater heights than those at which they 

 now occur ; and they will then, even if one may not wish to use them 

 as food for mankind, be particularly useful as food for other larger fishes 

 which persecute them with eagerness. 



As being closely related to fishes, must another class of animals which 

 may serve as nourishment both for larger and smaller fishes not be Teft 

 out of consideration, namely, frogs and toads. Just as the grown an- 

 imals are relished by the larger fishes, so are their eggs and tender 

 young a favored food for smaller fishes of choicer kinds. To transfer 

 these animals from one water to another will, of course, hardly be suc- 

 cessful, since they are just as much laud animals as they are water ani- 

 mals ; but nothing is easier than to transfer their eggs or spawn laid 

 here and there to basins or waters where it may be of use. 



As is seen from the foregoing brief representation, the ability to pro- 

 cure natural food for the larger fishes is all the greater and easier the 

 lower the water-basin lies which shall be prepared or preserved for fish- 

 cnlture. This is a very favorable circumstance, because the lower the 

 level becomes, the higher the water's average temperature, and the less 

 uniform the water supply, the more voracious, as it aiiiiears, become the 

 species of fish which may be made the object of successful culture. Even 

 the trout becomes in the less elevated warmer waters more of a preda- 

 cious fish than at greater heights. Whether this is because of the 

 greater wealth of insect food in the elevated regions than in the waters of 

 the lowland, or owing to other circumstances, we have as yet scarcely 

 any certain knowledge or conjecture about j the fact is in the meantime 

 as stated. A commonly received opinion, especially with regard to the 

 trout, which, with the exception of the red char, is regarded as th e best of all 

 our fresh-water fishes, perhaps because it is the most common — is at the 

 same time that fish of the salmon family become all the fatter and more 

 savory the greater the supply they find of insects, crustaceans, and mol- 

 lusks. This supply is meanwhile, as experience teaches, very diiferent 

 in different waters. It shows, therefore, of itself that also in this direction 

 one ought to provide, as far as possible, for iirocuring himself a supply 

 of food by stocking the waters in which fish-culture is prosecuted with 

 the species of these kinds of animals which admit of being transferred 

 from one place to another. 



The same opinion is stated by Prof. G. O. Sars, in a jmze essay on 

 Norwegian Crustacea, issued as a iiublication of the university in 1865: 

 " One will be able to form a still clearer idea of the enormous numbers 

 of these animals if one reflects that tliey, notwithstanding their small 

 size, constitute the chief food of most fresh-water fishes, a fact which is 

 sufficiently established by Leydig, who, upon the dissection of very many 

 different kinds of fresh-water fishes, always found the stomach's con- 

 tents almost exclusively to consist of entomostraca and copepoda. It is 

 thus most highly probable that the good quality of fish in different lo- 

 calities largely depends upon the greater or lesser quantity of these small 



