250 PROPAGATION OF FISH. 



tacked on frames running in grooves set at an angle of 

 forty-five degrees (the top down stream), so as to expose 

 as much surface as possible to the water. 



Sediment falling on the egg keeps the water off and 

 destroys its life as effectually as if buried in the mud. If 

 sediment falls upon the eggs it may be removed by gently 

 agitating the eggs with a feather, or better still, by creat- 

 ing a current in the water with a feather. 



From the filter the water runs into the distributing trough 

 or pipe, which runs along the head of all the hatching 

 troughs. The water may be let into the hatching troughs by 

 faucets, or through holes cut into the trough. These holes 

 should be covered with netting, or the young fish will run 

 up out of the troughs into the filter, or coarse gravel may 

 % be heaped up at the head of the trough through which 

 the water will run, but through which the young fish 

 cannot work their way. The supply of water for one 

 trough should be equal to that coming through a three- 

 fourth-inch hole with three inches head ; just enough to 

 make a gentle ripple over the cross-pieces. J3e careful to 

 get the troughs level crossways, and the strips true, so that 

 when the water is running it will form an equal current 

 over every part of each strip along the whole length of 

 the trough. The length of time required to hatch out 

 the eggs depends upon the temperature of the water. 

 A general rule sufficiently accurate for all practical pur- 

 poses is this : At fifty degrees trout eggs will hatch out 

 in fifty days, each degree colder takes five days longer, 

 and each degree warmer five days less. The difference, 

 however, increasing as the temperature falls, and dimin- 

 ishing as it rises. The best temperature for hatching 

 is between thirty -five and forty-five degrees. 



