68 U. S. BUREAU OF FISHERIES. 
2 inches thick, 1 foot wide, and 4 feet long is inserted in the grooves 
in the ends of the division wall to retain the fish, while the remaining 
portion of the pond is being cleaned. The dam board has a saw 
tooth edge permitting the overflow water to pass but preventing 
the escape of the fish. 
The “ push screen” consists of a frame made of 1 by 4 inch lum- 
ber, to which is attached poultry netting of 1-inch mesh or smaller 
if the size of the fish requires. The smaller dimension of the lumber 
forms the face of the screen, to offer but slight resistance when being 
pushed through the water. Its shape conforms to the shape of the 
ponds. At Manchester the sides flare outward. In size it 1s some- 
what shorter than the width of the pond for convenient handling, 
and to prevent the escape of fish around the ends strips of heavy 
duck or canvas belting are attached to each end of the screen. Iron 
staples driven into the bottom board at suitable intervals and shghtly 
protruding will serve to keep the board from dragging on the bot- 
tom of the pond and facilitate the easy movement of the screen 
through the pond. 
POND OUTLET AND “ KETTLE.” 
As being of possible interest and value to persons interested in the 
subject a drawing of the pond outlet and “ kettle” previously men- 
tioned (p. 64), with descriptive text and specifications for construc- 
tion, are given (Fig. 3). 
In referring to the cut of the pond outlet and “ kettle ” it will be 
noted that it contains features not embodied in other constructions 
of a similar character. The drain box is made in about the same 
manner as those now in use at many stations, but in place of the 
wooden dam boards it has a cement dam B, the height of which 
is determined by the water level when the pond is filled. If it is 
desired to raise the water level of the pond, the wooden dam boards 
can be dropped in the slot C. The screen / is the same as those 
now in use. To draw down the water in the pond, a gate valve A 
is so placed at the bottom that all of it can be drawn through the 
kettle. To make this removable, a flanged valve of the standard 
low-pressure type is used. A short nipple with a flange on one end 
is placed in the forms when making the drain box. Later a rubber 
gasket is cut to size and the gate valve is bolted into place. It is 
not necessary to bolt the valve around the bottom, since it may be 
desirable at some time to remove it, and it would be a difficult matter 
to get at bolts so located. A 6-inch gate valve as described above 
measures approximately 104 inches from face to face of flanges. 
Therefore, a standard valve should be used in place of the medium or 
heavy service valves. It will be necessary to place the flange of the 
nipple as close to the cement dam B as possible. Therefore, the 
bolts should be put in place before cementing. 
Another feature of the plan is the construction of a cement 
“kettle” in front of the drain box. It will be noted that the side 
walls of this kettle extend approximately 12 inches above the earth 
floor of the pond, so that in drawing down the water in the pond 
when it drops below this point it must then enter at the sluice gates J. 
The small fish will be drawn down through these gates and will 
immediately seek the more quiet water at the upper end of the kettle, 
