TROUT BREEDING. 49 



These four troughs will hatch from three to four hundred 

 thousand eggs. By increasing the supply of water and 

 lengthening the distributing trough, two or even four addi- 

 tional hatching-troughs can be used. 



The screens of the filterer are made by stretching and 

 tacking flannel to frames, which are slipped into grooves 

 made by nailing strips on the insides of the filterer, either 

 perpendicularly or at an angle inclining towards the outlet. 

 The flannel on the screen nearest the entrance of the 

 supply, should be of stout but open fabric ; the second, not 

 so coarse; the third, medium, and the fourth, closely 

 woven. A duplicate set should be provided, as the purest 

 water, to all appearances, in which one cannot detect the 

 most minute particle, will, in the course of four or five days 

 or a week, so clog the screens as almost to stop the flow. 

 At intervals of a few days the screens should therefore be 

 slipped out and a clean set put in. The flannel is cleansed 

 by allowing it to dry, and then brushing the dust ofi' with 

 a whisk broom, or better, by rubbing the screens with a 

 stiff hair-brush while wet. The filterer and supply trough 

 should both be kept covered. 



There should not be more than two inches fall from the 

 upper to the lower end of a trough of thirty-two feet, if the 

 aperture through which the water enters is a half inch 

 square. If the supply be doubled, the fall should not be 

 more than an inch. This will give a ripple about the six- 

 teenth of an inch deep over the strips dividing the trough 

 into nests. The bottom of the trough should be perfectly 

 true, and the strips fit neatly, so that the water may not 

 5 D 



