876 BULLETIN OF THE BUREAU OF FISHERIES. 



Some laboratory experiments were made at the Bureau of Fisheries with 

 brook trout fry and yellow perch. The trout fry were held in shallow dishes 

 with about one liter of water. The dishes were floated on the surface of cold 

 water to maintain a proper temperature, which was 52° F. or under during the 

 trials. The dilution in the dish was aerated only by contact with the air. In 

 every dilution tested 10 fry were used in each trial; i to 500,000 was fatal to 

 most of these fry within 24 hours; i to 1,000,000 killed no fry during 48 hours. 

 Intermediate dilutions killed a portion of the sample of 10 during 48 hours. 

 Potomac water was used, having at this time an alkalinity of about 53 parts 

 per million. 



Adult yellow perch {Perca flavescens) were tried in 10 liter samples of the 

 dilution made with Potomac water held in tall glass jars with only air surface 

 aeration. One perch only was used in each trial. A dilution of i to i ,000,000 

 killed the fish within 24-40 hours; i to 2,000,000 was fatal after 48-64 hours in 

 one case, while in another the same dilution was safe during 5. days; i to 2,500,000 

 was fatal after 68 hours; i to 3,000,000 was safe during 7 days. 



Fingerling large-mouth black bass (Micropterus salmoides) proved much 

 more resistant than adult perch. Under the same general conditions as those 

 above described for perch a dilution of i to 100,000 killed the fish within 

 24 hours, while i to 200,000, as well as several weaker dilutions, did no harm 

 during 5 days. 



Moore and Kellerman in laboratory experiments found that the eggs and 

 fry of large-mouth black bass and very young crappie fry were not injured by 

 I to 1 ,000,000. Carp were found usually to succumb to i to 500,000. 



Sunfish (Eupomotis gibbosus) in a turbid Potomac water dilution were not 

 killed by i to 400,000 during 21 hours. Mummichogs (Fundulus heteroditus) 

 were killed by i to 750,000, but not by i to 1,000,000. The temperature of 

 the dilution in these cases was 78°-8o° F.. 



Silver nitrate has also a very high toxicity both to algse and to fish. It is 

 probably its expense alone that prohibits its usefulness for some of the same 

 purposes for which copper sulphate is used. Chinook salmon fry about three 

 months old are killed within 48 hours by a solution of i part of silver nitrate 

 to 22^ million parts of water, while i part to 25 million parts of water is on 

 the border line of safety, and killed a portion only of the several fry used in the 

 test. No substance more poisonous to fishes is known to the writers. 



METHOD OP ADMINISTERING THE TREATMENT. 



In the treatment of fish-cultural waters with copper sulphate there are, of 

 course, from the mechanical standpoint, two kinds of water to be dealt with, 

 namely, still water and flowing water. For still water the process is compara- 

 tively simple, only a single " dose " being required. Such treatment is, however, 

 applicable only where renewal of the water may be dispensed with for the period 



