24 



U. S. BUKEAU OF FISHERIES. 



It is well to paint the pipes with waterproof paint, and a mixture of graphite 

 and oil is recommended for use in the elbow and coupling threads. Pipe 

 threads should penetrate elbow 1 inch, hand screwed. When the drainage line 

 is to be of terra cotta its joints should be sealed with cement throughout the 

 line rather than laid partly open, as is sometimes done. 



The elbow and two pieces of threaded pipe comprising the outlet proper and 

 modifications as to size and detail of the L outlet and appurtenances may 

 be made to suit requirements and material available. If it is necessary to 

 reduce expense, the kettles may be reduced or omitted entirely, but the installa- 

 tion of a kettle, even though of small size, is recommended because of its use- 

 fulness when drawing the pond and sorting the fish. The cement blocks, the 

 chief use of which is to protect the outlet drainage line against water working 

 an opening about it, and which also prevents animals such as crayfish and 

 muskrats following it through the embankment, must not be omitted because 

 without the blocks to protect and stay the drainage line leakage is certain to 

 occur. The depth of these blocks should not be reduced, but in unfavorable 

 soil may be increased to advantage. 



All surfaces over which embankments are to be laid should be plowed before 

 the fill is commenced, so that the earth will bind satisfactorily, and all foreign 

 matter such as brush, rock, etc., should be excluded from the fill dirt. 



The outlet is placed at the drain point and stayed as described, after which 

 the fill is laid over it, the outlet being ready for service as soon as the fill is 

 started. Pipe 4 to 6 inches in diameter is sufficiently large for ponds of less 

 than 1 acre in area. It is always better to have the outlet pipe too large 

 rather than too small. 



Many of the spillways and outlets in general use give more or less trouble 

 through leakage, and those of cement construction often freeze and crack, or 

 settle and crack, causing serious trouble and considerable expense. Many of 

 the outlets in use are built into the embankment, thereby weakening and sub- 

 jecting the embankment to the danger of washouts. Loss of fishes often arises 

 from screens below the water surface becoming damaged, and many outlets, 

 when the pond is being drawn, have too much suction for the good of the little 

 fish. These and other troubles have been eliminated in the L outlet, some 

 favorable features of which are enumerated below : 



The action of the outlet is quick and easy. 



Leakage and freezing difficulties have been overcome. 



The outlet operating from the surface provides minimum suction, which 

 works to the benefit of small, fish. 

 The screen is visible, therefore safe, and easily cleaned. 

 The outlet does not weaken the pond embankment. 



The outlet may be assembled, installed, and maintained at low cost, and 

 is so simple of construction that any " handy man " can build and install it. 



ERADICATION OF SOME OBJECTIONABLE PLANTS. 



The rank growth of cat-tails in ponds and lakes, particularly at 

 fish-cultural stations, has often become a serious nuisance, causing a 

 substantial reduction in the effective area of the pond. Hitherto 

 there has been no inexpensive or practicable method of combating 

 them, since removal by cutting alone is quite ineffectual. Superin- 

 tendent Canfield has devised and demonstrated the efficacy of a 

 method of elimination of these plants, based upon the necessity of 

 areation through contact of the plant or its landward roots with 

 the air. 



The water level in the pond is lowered below the limit of growth 

 of the cat-tails, which should then be mowed as low as practicable. 

 With spade or plow a ditch is made below the normal water line and 

 between the cat-tails and the shore. The ditch must be sufficiently 

 deep to sever the roots that connect the plants in the pond with the 

 shore or with any plants that are allowed to remain above the ditch. 

 In this way the air supply from the land roots is completely cut 

 off. The pond should then be immediately flooded and the water 



