TREATMENT OF FISH-CULTURAI, WATERS FOR REMOVAL OF ALG^. 889 



trout it was not noticeable under 20 hours, but after this period they also 

 refused food. If the treatment was discontinued at the end of 24 hours, both 

 fry and adults would resume feeding with their accustomed vigor within the 

 next 24 hours. 



The use of the i to 4,000,000 dilution, repeated about once a week 

 for a duration of 8 hours each time, proved sufficient to keep down the algal 

 growths without harm to the fish. The cost of the copper sulphate used in this 

 treatment was at the rate of about 30 cents per 24 hours. 



In the summer of 1907 a pond of an area of 0.68 acre and with an average 

 depth of 18 inches, containing 28 adult large-mouthed black bass and several 

 thousand advanced fry, was treated with 4 pounds of copper sulphate in 

 single dose. The treatment was entirely effective in destroying the algge and, 

 as far as could be seen, without the loss of a fry or an adult. 



AT FISH LAKES, WASHINGTON, D. C. 



As a part of some joint experiments conducted by the Bureau of Plant 

 Industry and the Bureau of Fisheries two small ponds, each containing a few 

 adult bass ready to spawn, were treated on April 22 with copper sulphate in a 

 dilution of i to 5,000,000. The water subsequently became roily, so that obser- 

 vations could not be made on the nesting and spawning bass, but on May 8 a fine 

 brood of bass fry was observed. With the disintegration of the algae myriads of 

 Daphnia appeared. On June 12 a pond of 1.55 acres, with an average depth of 

 2o|<f inches, was treated with i to 5,000,000. This pond contained adults, fry, and 

 baby fingerlings of the large-mouth black bass. Careful observations about the 

 pond and of the young fish seined from it daily after the copper was administered 

 showed no harmful effects upon the fish. By June 22 much of the algae had dis- 

 appeared, comparatively little remaining. Its disintegration caused the water 

 to impart a very offensive odor when stirred. 



This dilution was far weaker than any which, as far as experiments indicate, 

 could in the least harm the species of fish concerned, but it was nevertheless 

 strong enough to eradicate the particular growths of algae then existing in the 

 ponds. 



FURTHER POSSIBILITIES OF THE TREATMENT. 



The success of the copper-sulphate method of treating fish-cultural waters 

 for the removal of a mechanical nuisance indicates successful fish-cultural 

 application of the remedy in other directions. The administration of remedies 

 for disease in the lower animals is familiar in the case of the farmer's live stock 

 and other domestic land animals, being the science of veterinary medicine. 

 Upon fishes, however, medical treatment has been practiced but inconsiderably, 



B. B. F. 1908— Pt 2—14 



