50 DOMESTICATED TROUT. 



the mercury is 10 below zero, the water at the hatch- 

 ing house loses only two degrees in passing through 

 one hundred and twenty feet of channel. 



THE FILTERING ARRANGEMENTS. 



Next to fungus, sediment is the most dangerous 

 enemy to trout eggs, and, like fungus, it is the more 

 to be dreaded because it is invisible ; that is, as it 

 is held naturally in the water. A stream or a spring 

 may look to you as clear as crystal, you may examine 

 most carefully and not find any traces of dust or foreign 

 matter in it, yet the same water in running sixty days 

 over any given spot will very likely deposit enough 

 sediment to kill a million eggs. Some few springs are, 

 I believe, sufficiently free from sediment to be used 

 without filtering, but such springs are exceedingly 

 rare, and are the exceptions. As a rule, all springs 

 and streams, however clear they may appear, will in 

 time deposit a fine layer of dust, or sediment, as' it 

 is usually called, which is sufficient to destroy or de- 

 form all the fish embryos that are exposed to it. 



It is very important, therefore, to have this sediment 

 kept away from the eggs ; and to effect this, the water 

 is conveyed through a very efficient filtering apparatus. 

 This usually consists of a large tank containing a 

 series of flannel screens. These screens consist sim- 

 ply of light wooden frames, with flannel fastened on 

 them, which are made to slide in grooves prepared 

 for the purpose, on the inside of the tank. 



The flannel should be drawn tight over the frames, 

 and the frames themselves should slide obliquely into 



