PROPAGATION OF FISH. 249 



These strips may be made of half -inch stuff and cut two 

 inches in width. There is no necessity for nailing them 

 to the bottom ; fit them in accurately and set them edge- 

 ways at intervals of eighteen inches. As they do not 

 need to be removed often, it is better to make them fit 

 tightly. Other strips of the same stuff must be pro- 

 vided, to fit upon these and made wide enough to raise 

 the water within an inch of the top of the trough ; as 

 these need to be often moved, they must be made loose 

 enough to take out, and yet fit accurately enough to raise 

 the water over them when they are put in. New wood 

 under the action of water develops a slimy sap, therefore 

 it is necessary to paint the troughs with hot coal tar 

 mixed with enough turpentine to thin it to about the con- 

 sistency of paint. The troughs should have an inclina- 

 tion of about one inch in eight feet just enough to let 

 the water ripple gently over the cross strips. They should 

 not be longer than twenty feet, or the air in the water will 

 be exhausted before the water reaches the end of the 

 trough. There is more danger of this after the eggs are 

 hatched out and the troughs are full of young fish. If 

 possible, the hatching house should be so far below the 

 level of the spring from which its supply of water is de- 

 rived, as to allow the troughs to be raised two or three feet 

 from the floor. 



The filter is a box six feet long by one and a half feet 

 wide and one and one-half feet deep; in which four or 

 five flannel screens can be placed through which to filter 

 the water before it passes into the troughs. The coarsest 

 and cheapest red flannel is the best. It will rot and must 

 be renewed once or twice in a season. Red flannel will 

 last twice as long as any other. The flannel should be 



