TREATMENT OF FISH-CUI^TURAL WATERS FOR REMOVAL OF ALGJE. 



875 



tion which tend to modify the effect of the copper salt, while the physiological 

 resistance of the fish varies with individual fish and with different broods of 

 the same species. As a matter of fact, fish in general resist the action of copper 

 sulphate better than algse. The salmonoid fishes have less resistance than any 

 group with which experiments have been made; nevertheless, it has been found 

 in most cases thus far that the necessary margin between the death point of 

 fish and the death point of algse does exist. Algae, including some species that 

 cause annoyance, are sometimes killed by much weaker solutions than the 

 weakest known to be fatal to the most susceptible fish, even as weak as i part 

 copper sulphate to 50,000,000 parts of water. 



The variation of the two important facts, however, susceptibility in indi- 

 vidual broods of fish and in the dissolved content of the water, giving rise to 

 wide differences in the quantity of copper sulphate that may be fatal, makes it 

 necessary to determine in each case the susceptibility of the fishes in question 

 in the particular water concerned. It follows that no general formulce for the 

 proportion of copper sulphate can be stated. Some results actually obtained 

 will be of interest, however, and useful for comparison or to some extent in 

 approximating the strength of the solution which must be fixed more accurately 

 by experiment. 



Moore and Kellerman give the following as the number of parts of water 

 to one part of copper sulphate in dilutions which will not injure fish of certain 

 species : " 



Trout 7, 000, 000 



Goldfish _. 2,000,000 



Sunfish 750, 000 



Perch 1, 500, 000 



Catfish 2, 500, 000 



Suckers 3, 000, 000 



Black bass 500, 000 



Carp 3, 000, 000 



These dilutions are presumably close to the death points in the particular 

 water used and with the particular fish experimented with.* The trials on 

 which the figures for trout {Salvelinus fontinalis) are based show the greatest 

 susceptibility to copper sulphate yet observed for fish. They were made at 

 Cold Spring Harbor, N. Y., and fatal results were obtained at i to 6,500,000 

 with fingerling trout during 24-hour exposures. At Bayfield, Wis., however, 

 adult trout resisted i to 500,000 during this period. These are probably 

 extreme cases. In the former algse probably could not be killed in the presence 

 of the trout, and it is the only case of its kind that has come to the attention of 

 the writers. 



o Copper as an algicide and disinfectant in water supplies. Department of Agriculture, Bureau 

 of Plant Industry, Bulletin No. 76, p. 11, 1905. 



6 It is of interest to note in this connection that, according to Mr. Kellerman, copper-killed fish 

 are of little use for table purposes on account of the rapidity of decomposition, which seems to proceed 

 more rapidly than with those killed in the ordinary ways. Moreover, the dead fish have usually an 

 unattractive appearance, due to the distention of gills and jaws. 



