Trout Breeding. 127 



inches with four strips to stiffen the cylinder and cover 

 this with No. 2 wire cloth. Run an axle through it and 

 set it so that it will revolve in the current, with six 

 inches of water to turn it ; *. e., set it in water to that 

 depth. A half inch btlow the cylinder set a board 

 edgewise under its centre, and all leaves and fine trash 

 will be passed without clogging. This can be made to 

 fit a trough or box. A coarse screen should be placed 

 in front of it to catch sticks. 



CHAPTER IX. 



TEMPERATURES. 



There are extreme temperatures which limit the lives 

 of all things, animal or vegetable ; and of all animals 

 the fishes are the most sensitive to sudden changes. 

 Water in lakes or streams is slow to change, and, while 

 animals which live on land endure changes of a dozen 

 degrees in twenty-four hours occasionally in our north- 

 ern climate, it takes many days or even weeks to make 

 such a change in running waters or in a large, deep 

 pond. Even after the surface of a pond is frozen the 

 water at the bottom will be found warmer than near 

 the surface if the pond has much depth or if there are 

 bottom springs. 



I think our brook trout would prefer an even tem- 

 perature of about 60 Fahr., equal to 10 Reaumur or 

 to 13 centigrade. It ranges "from Maine to Dakota 

 and north to the Arctic Circle and south to the Chatta- 



