BACTERIAL DISEASE OF FRESH-WATER FISHES. 

 Summary op Experiment No. 4. 



2 75 



As in the case of the more dilute solutions, the 1 to 1,000 solution of copper sulphate 

 to be effective must be used before the appearance of any lesions. When the bacteria 

 have become abundant enough to produce visible lesions many of them are too well 

 protected to be reached by the solution during the short time the fish are exposed to it. 

 However, while this treatment is not recommended as a cure, it has been shown experi- 

 mentally that fish may be cured by its use, provided the gills are not infected. 



Experiment No. 5. — At 5 p. m., September 9, seven badly diseased fish, two crappie 

 and five buffalofish, were treated with a 1 to 1,000 solution for two minutes. These 

 fishes were so bftdly diseased that they would undoubtedly have died within a few hours 

 if not treated. They were so weak from the disease that three buffalofish turned 

 on their backs during the treatment, but two recovered later. The next morning, Sep- 

 tember 10, another buffalofish was found dying and the other fish showed no improve- 

 ment. The remaining fishes, two crappie and three buffalofish, were again treated with 

 a 1 to 1,000 solution for two minutes at 1 1 a. m. One buffalofish died shortly after treat- 

 ment. At 11.30 a. m., September n, the fish were again given a 1 to 1,000 treatment 

 for two minutes. No further treatments were given, and one buffalofish and one 

 crappie died on the 13th. The remaining fishes, one buffalofish and one crappie, showed 

 great improvement, and on the 1 6th, when the experiment was discontinued, had entirely 

 recovered. No doubt the relatively low temperature of the water, which averaged about 

 70 F. during this experiment, was an important factor in aiding their recovery. 



Of course a longer treatment with the copper sulphate would be more destructive 

 to the bacteria but would not be advisable on account of the bad effects on the fish. All 

 our experiments indicate that too strong a solution or too long a treatment with a weaker 

 solution is worse than no treatment at all. While the fish may not be noticeably injured 

 at the time, they may be so weakened as to easily succumb to a later infection. This is 

 well illustrated by one of our experiments in which five bluegill were treated with a 1 to 

 1,000 solution of copper sulphate for six minutes. These fish showed no ill effects from 

 the treatment at the time, but two days later all had become infected and died within 

 24 hours. In another series of experiments to determine the effects of various chemicals 

 six normal buffalofish were treated with a 1 to 1 ,000 solution of formalin for eight minutes. 

 The fish appeared in good condition after the treatment, but during the next three days 

 all developed a fatal case of the disease. 



In most cases it will probably not be worth while to attempt to cure fish with well- 

 developed lesions, but in case it should be thought advisable the most effective treatment 

 consists in local applications of a 1 per cent solution of copper sulphate. We have cured 

 a number of badly diseased fish in this way, and the treatment is successful in a large 



