96 The First Food of the Common White - Fish. 



existence. Disturbances of the natural balance of life, of the 

 primitive and spontaneous system of reactions by which the dif- 

 ferent groups of organisms are related, will therefore be unusually 

 serious and lasting; and where such disturbances result from 

 human interference, as by the yearly capture of large numbers of 

 any important fish, it is especially desirable that artificial means 

 of compensation be taken to restore the disturbed balance as 

 nearly as possible. Excessive loss will be made good by natural 

 reactions far more slowly than if it occurred to a pond or river 

 species, accustomed, as most of the latter are, to fill up rapidly 

 enormous gaps in their numbers. 



On the other hand, to multiply unduly by artificial measures any 

 species naturally abundant in such a lake, will have scarcely a 

 less disturbing influence than to diminish its numbers in the same 

 ratio. The relatively nice balance between the demand for food 

 and food supply which here naturally obtains, is such that an ex- 

 traordinary increase in a species must soon react to diminish 

 greatly its food resources — a fact which will then take effect on 

 the species itself, reducing it below its natural, original level; 

 and if both excessive capture and excessive multiplication go on 

 side by side we shall have this result finally aggravated to an ex- 

 treme degree. 



As fishes are caught before the end of their natural lives, but 

 planted by the fish culturist when young, it is evidently the food 

 of the young which will be first and most seriously afi'ected by 

 over-production. Only a part of the adults, perhaps a small frac- 

 tion, will live a life of ordinary natural length, many being cap- 

 tured before they have attained even the average size; but a far 

 greater number, perhaps nearly every one, must survive the earli- 

 est period and must consequently draw most heavily upon the 

 earliest food resources of the species when these differ from those 

 of the adult. 



The above considerations are brought forward here to show the 

 especial importance, to us, of a study of the system of natural 

 interactions by which the animals of our great lakes affect each 

 other, if we would avoid the necessarily injurious consequences of 

 our own interference with the natural order there obtaining, and 

 above all to show the extraordinary value of a knowledge of the 

 food habits and food capital of the young. They apply perhaps 



