9 



the same thing occurs with fish when they are kept in 

 one locality. They use up their food and increase the 

 list of their foes. So soon as this happens they sufier, 

 and should be supplanted by a different species, living 

 on difterent food, and having a totally different class of 

 enemies. Wherever this has been done, the effect has 

 been surprising, the new species increasing enormously 

 for the first few years, and then meeting the fate of its 

 predecessors. It is a curious fact that the stomachs of 

 fish are so often found to be entirely empty of food, 

 and the migratory varieties seem hardly to feed at all 

 while preparing to spawn. This would imply either 

 that they digest very rapidly, or can ,'go a long time 

 without nutriment, and, probably, both of these deduc- 

 tions are true. Heat and motion are the main consura 

 ers ot food, for animal bodies are physically machines, 

 which must be supplied with fuel if motion is to be gen- 

 erated, and will wear out with friction unless the waste 

 is restored. A man or a horse can only perform his 

 quota of work if his body is thoroughly nourished, and, 

 on the other hand, neither needs nor can digest his full 

 amount of food unless he works. The terrestrial ani- 

 mals are warm blooded and active, many of them, in 

 their natural state, getting their food by the chase, 

 whereas fish are cold blooded, and, although occasionally 

 making long journeys, are ordinarily quiet. 



The following points upon fish culture seem to be 

 established : First — Fish culture, extending to every de- 

 sirable variety of fish is entirely practicable. Second — 

 It may, under proper management, be made profitable to 

 'the producer ; as much so or more than the cultivation 

 of land, or of land animals, and on similar conditions. 

 Third — It may furnish to all classes an abundance of 

 cheap, and the most nutritious and healthful food. 



