274 



BULLETIN OF THE BUREAU OF FISHERIES. 



These two experiments indicate what the copper-sulphate treatment can accom- 

 plish when used under favorable conditions. If the fish have been greatly weakened 

 before being given the treatment, however, the results are far from encouraging. 



As pointed out, fish which have been seriously weakened by previous treatment 

 are often killed by the copper sulphate, and it is doubtful if any treatment can be 

 devised which can be safely used while the fish are in this condition. This is especially 

 true if the fish just previous to being treated have been confined for some time in a 

 small vessel where the oxygen supply is deficient. Several experiments were carried 

 out with fish seined from small ponds which had been isolated from the river when the 

 waters receded after the spring floods. These fish were transported in galvanized 

 washtubs, often for a distance of 2 or 3 miles, and held in the tubs an hour or two before 

 reaching the station. A large number of fish were carried in each tub, and although 

 attempts were made to keep the water aerated they were partially asphyxiated when 

 reaching the station. All our experiments in treating such fish were unsuccessful, the 

 great majority being killed by the copper sulphate. Possibly the fish could be suc- 

 cessfully treated if first held in running water for several hours. The two following 

 experiments are typical of results with these exhausted fish. 



Experiment No. 3. — The fish were brought to the station at 5 p. m., September 10, 

 in a greatly weakened condition. Part were treated with 1 to 1,000 copper sulphate 

 for two minutes and then placed in an aquarium well supplied with running water. 

 The remainder were placed in a similar aquarium without being treated. Most of the 

 fish in the treated lot died within 24 hours. In the following summary all fish which 

 died during the first 48 hours are tabulated as having died from the effects of the copper- 

 sulphate treatment or injuries sustained on their way to the laboratory. These fish 

 showed no well-developed bacterial lesions, and our previous experiments had shown 

 that fish rarely die from the effects of bacteria until more than 48 hours have elapsed. 



Summary of Experiment No. ?. 



This case is remarkable for the small number of infected fish among the controls. 

 Possibly this can be explained by the fact that although the fish had been much weak- 

 ened from lack of oxygen they had evidently been handled carefully and showed only 

 slight mechanical injuries. 



Experiment No. 4. — September 1 1 a number of buffalofish and bluegill were brought 

 to the laboratory from the same pond as in the preceding experiment and were treated 

 in the same way. 



