BACTERIAL DISEASE OF FRESH-WATER FISHES. 27 1 



mat covering the lesions. Furthermore, potassium permanganate is expensive and 

 dissolves slowly in water. For these reasons the potassium-permanganate treatment 

 was later abandoned in favor of copper sulphate. 



A number of experiments with copper sulphate were made during the summer of 

 1918, and it was found that a 1 to 30,000 solution is more effective than a 1 to 50,000 

 solution of potassium permanganate and not so injurious to the fish. A solution of 

 this strength will not, however, kill bacteria which are well protected, such as those 

 beneath the scales. Our experiments showed that normal fingerling buffalo fish are not 

 appreciably injured when placed in a 1 to 30,000 solution for 30 minutes, but diseased 

 or weakened fish are not so resistant. Buffalofish over 1 year old are not injured by treat- 

 ment with a 1 to 25,000 solution for 30 minutes, and black bass and bullheads can 

 stand a 1 to 20,000 solution for the same length of time without injury. As a result of 

 these experiments the following treatment was recommended and used with much 

 success : The fish previous to the appearance of any lesions are placed in a 1 to 30,000 

 solution of copper sulphate for 20 minutes and are then removed at once to running 

 water. If properly handled they rarely suffer any permanent injury. Wooden vessels 

 are preferable, and if it is necessary to use galvanized vessels they should be painted 

 to prevent chemical action between the copper sulphate and the metal sides of the vessel. 

 A thin coating of melted paraffin over the inside of a galvanized tank serves the purpose 

 admirably. During the treatment some of the less resistant species of fishes may swim 

 around at the surface and show more or less signs of distress, but this does not neces- 

 sarily indicate any serious injury. 



It should be distinctly borne in mind that the treatment to be effective must be 

 given within a few hours after the fish have been handled and before any signs of infec- 

 tion appear. If the fish are to be confined in aquaria, two or three successive treat- 

 ments at 12 to 24 hour intervals are advisable. When this treatment is properly used 

 it is believed it will effectually prevent any serious outbreak of the disease. It must be 

 repeated, however, every time the fish are handled or subjected to injury in any way. 



In an experimental test of this treatment 30 fingerling buffalofish were seined 

 from one pond. They were handled quite roughly, and 14 controls were placed in a 

 small aquarium without being treated. The remaining 16 fish were treated with a 1 

 to 30,000 solution of copper sulphate for 20 minutes and then placed in a small aqua- 

 rium like that in which the controls were held. Throughout the experiment both 

 aquaria were supplied with running water, and the conditions in each were as nearly 

 identical as it was possible to make them. Two of the treated fish died within 12 hours, 

 probably as a result of mechanical injuries. At the end of 24 hours the fish were again 

 treated with a 1 to 30,000 solution for 20 minutes. Twenty-four hours later two of the 

 treated fish were found dead, but a careful examination failed to disclose any signs of 

 Bacillus columnaris. Since the remaining fish showed no signs of infection no treat- 

 ment was given at this time, but 6 hours later one fish showed a well-defined lesion at 

 the base of the tail. This fish was at once removed and the rest given the same treat- 

 ment as before. Since no further signs of infection appeared in this lot in three days 

 the experiment was discontinued. 



Among the controls 3 fish showed well-defined lesions after 24 hours, and at the 

 end of 48 hours 1 1 out of the 14 were dead, while 2 of the remaining 3 had well-developed 



