85 



the ice which forms over the pond serves to keep the 

 water below from being made colder by contact with the 

 air. 



If the water is so sluggish as to be likely to rise above 

 seventy degrees in summer, the ponds may be shaded in 

 some way. Trees and bushes look very nicely about 

 the borders of the ponds, and are very valuable so far as 

 ornament is concerned. But there are certain objections 

 to their use which will banish them pretty thoroughly 

 from the grounds of the practical trout-raiser. One ob- 

 jection is that the leaves, in autumn especially, clog up 

 the screens, and demand constant attention to prevent 

 an overflow of the water and trout. Or the leaves fall 

 to the bottom and decaying there, foul the pond. 

 The roots of the trees also will force their way towards 

 the water, and break the walls or banks of the pond. 

 If it is necessary to shade the ponds, floats may be used, 

 made of boards nailed together and moored in some con- 

 venient place; but the best plan of shading is by light 

 covers placed on beams running across the pond. If the 

 ponds are very large the floats will have to be used. 

 But the ponds must not be made large. We have said 

 that trout would not live in water which was raised 

 above the temperature of seventy degrees, and would do 

 better in water at forty degrees. This settles the ques- 

 tion as to how far south trout will live in the ordinary 

 rivers. 



California salmon will stand a much higher tempera- 

 ture than trout. The McOloud river from which the 

 eggs were obtained that have been distributed by the 

 United States Fish Commissioner through the eastern 

 states, often rises to 80 degrees, and occasionally as high 

 as 83 degrees. Its temperature through a large part of 

 the year is over 70 degrees, both at the surface and at 



