588 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



the same genus, ought to be kept separate ; likewise should the young 

 of the same species and the same age be separated according to size. 

 The development of diflerent indiAiduals is considerably different in ra- 

 pidity, and the larger will quickly attack the smaller if they live together. 

 The most important thing to observe in a structure for the culture of 

 salmonoids is to secure a constant sui)ply of clear water, and the colder 

 this is the better. 



For the rearing of the young newly-hatched is naturally required a 

 larger place than for their hatching. The larger the place one gives 

 them, and the purer, the colder the water one has for use, the more cer- 

 tain is one that they will thrive well, and that the loss at this most sensi- 

 tive age will become the least possible. 



These are a few of a great multitude of examples of more or less suc- 

 cessful fish culture prosecuted on different scales. That there are plenty 

 of examples of less successful or even quite unsuccessful culture is self- 

 evident. Everything depends in this as in all other practical undertak- 

 ings, on how far one properly appreciates the conditions, and does all 

 that is necessary in pursuance of them, in order that the affair shall suc- 

 ceed; if these things are done, the examples mentioned show that the 

 business can and will yield a good profit. It is particularly the hatching 

 of the salmonoid fishes that is unsuccessful, and the reason is easily 

 given. They have partly lacked a sufflcient water supply, but espe- 

 cially the comparatively low temi)erature of the water in summer, which 

 is an irremediable condition for the thriving of the salmon. 



With regard to the quantity of food that fish require in comparison 

 with what warm-blooded land animals need, the fish commissioners of 

 New York state the following : 



" The food consumed is used by all animals chiefly for the produc- 

 tion of motion and heat, because all animals are physical machines, 

 which must be furnished with fuel if motion is to be developed, since 

 they will wear out with friction if this wear and tear is not comi)ensated 

 for by new nourishment. A man or a horse can only perform his full 

 quantum of work when his body gets the full nourishment required, 

 and on the other hand he can not consume the full quantity of nourish- 

 ment unless he works. The dry-land animals are warm-blooded and 

 movable ; many of them, in natural state, find their food only by hunt- 

 ing it ; while fishes are cold-blooded, and although they sometimes un- 

 dertake long journeys, as a rule they keep themselves still in the same 

 place. A trout will remain by the week in the same place in a pool or 

 a hole. A pike will lie still like a sunken stick between the rushes, ex- 

 cept when it between times plunges oft' after its prey, after which it 

 usually returns to the same place ; in the possession of all the senses 

 except hearing, in the fullest development, it resumes its condition — 

 that of motionless, sleepless attention. 



" The consequence of this is, that while the warm-blooded animals 

 use a considerable quantity of nourishment to produce the high tern- 



