44 



IT. S. BUREAU OF FISHERIES. 



The screen is arranged to slide vertically between beveled cleats, so 

 that it may be cleaned more readily. An iron standpipe of suitable 

 length to give the desired water level in the trough is screwed into 

 the discharge pipe from the inside of the trough. Each trough should 

 be provided with two of these standpipes of different lengths, mak- 



Q_ a D a P 



LONeiTUOINAL SIGTION OF HATCHING THOUGH.SHOWNG POSITION OF HATCHING TRAYS, DAM, £TC. 



Fig. 13. — Hatching troughs, guard screen, and qz% trays. A, guard screen ; B, horizontal 

 sliding screen ; C, hatching tray ; D, position of hatching trays ; E, tin tray for use in 

 muddy water ; F, block for water to fall on ; G, hrackets ; H, feet. 



ing it possible to reduce the water level in the trough when desired 

 for reasons which will be discussed in subsequent pages. 



In the upper end of the trough a horizontal screen made of per- 

 forated tin, shown at B (fig. 13) is used. This is so constructed that 

 it can be slipped forward or raised up (as shown in the illustration) 

 when the fry are fed or the troughs cleaned. The water falling upon 

 a small wooden block in the center of the screen is thoroughly aer- 



