1 10 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



utilize the same supply by placing one after another, the upper end of 

 the lower trough being from 8 to 12 inches lower than the overflow of 

 the upper trough ; this gives a good aeration and will be found to answer 



Clark- Williamson Trousrh. 



nearly as well as though fresh water was conducted to the tank. 

 Should the supply be taken from a creek, lake, or other reservoir ex- 

 posed to changes of weather and drainage from the surrounding land, 



