118 FISH CULTURE 



an inch to an inch lower than the upper end; 

 but the lower end of the supply-trough should 

 be not more than an inch below the upper end 

 or intake. 



For a 40-feet-wide house equipped with three 

 tiers, each set of troughs can only be 12 feet 

 long ; this will allow a four-foot walk the whole 

 length of the opposite side of the house. The 

 troughs are made in pairs and of lumber one 

 inch thick when dressed, 33 inches wide outside 

 measurement, with a one-inch division-board 

 down the centre, making two troughs each 15 

 inches inside measurement. They are usually 

 eight inches deep, but may be 10 inches to ad- 

 vantage. 



At the lower end of each trough, if two or 

 more tiers are used, there must be bored two 

 holes, one in the centre and one at the side, 

 each not less than one inch in diameter. One 

 is to carry the water from one trough to the 

 other; and the other to be used only when the 

 trough is being cleaned, at all other times being 

 kept plugged. Six inches from the end, and 

 above the hole, two cleats are set on each side, 

 three-fourths of an inch apart, and two others 



