884 BULLETIN OF THE BUREAU OF FISHERIES. 



sufficient water to compensate for evaporation, seepage, etc. If the bottom of 

 the pond has considerable springs of water the volume delivered may be taken 

 into account as far as it is possible to do so in calculating for the dilution, unless 

 it is small enough to be igtiored. 



The first step is to determine the susceptibility of whatever fishes are held 

 in the water to be treated. This will be done in quite the same way as already 

 described under the siphon treatment. Pond-culture fishes will for the most 

 part endure more copper sulphate than trout. The total volume of water in 

 the pond must then be ascertained. The dilution to be used will be 

 indicated by the susceptibility, allowing an ample factor of safety. The milli- 

 grams of water in the pond divided by the dilution will give the milligrams of 

 copper sulphate to be used. This will be readily reduced to pounds or ounces 

 or other unit and the amount weighed out. It may be placed in a bag of cheese 

 cloth, burlap, or of other loose-meshed material, and dissolved in the pond by 

 dragging it about at the surface from the stern of a boat." The more thor- 

 oughly all parts of the pond are traversed the more uniform the distribution 

 of the sulphate. 



If the algal growth is very abundant only part of it may be killed by the 

 first treatment. When there are large masses of algae all the copper may be 

 used up before the whole of the mass is destroyed. After algse have grown 

 unchecked in ponds for a long time the growth may mat heavily together, or 

 where there is a current it may form long strings or ropes. These more densely 

 massed bodies of algal growths are less susceptible to treatment. The outside 

 strands may be killed while the inner portions remain alive, being protected 

 by the outer. In such cases as these the dose may be repeated after an interval 

 of time, as a few days or a week. If the pond can once be made free of algae, 

 it is much easier to keep it so than to kill off heavy growths. It is not always 

 possible, however, to eliminate all growths while fish remain present. The 

 species of alg£e vary considerably in their susceptibility to copper, and some 

 may therefore survive on account of their natural resistance to the strongest 

 dilution the susceptibility of the fishes concerned permits to be used. 



MISCELLANEOUS DIRECTIONS AND CAUTIONS. 



To make the siphon which is to be attached to the float, glass tubing with 

 rubber connections should be used. The smaller sizes of tubing are preferable, 

 that with an outside diameter of 4 to 6 millimeters, or five-thirty-seconds to 

 one-fourth inches, being convenient. The tubing should be bent approximately 

 at right angles to make the turns at the top of the float, the bending being done 

 best by heating in the yellow flame of an ordinary gas jet. The tubing should 



" Moore and Kellerman, op. cit., 1904. 



