268 BULLETIN OP THE BUREAU OE FISHERIES. 



port during September, 1919. With the advent of cooler weather there was a consider- 

 able decrease in the temperature of the water in the aquaria in which the experimental 

 fish were kept. After the first week in September the average temperature of the water 

 decreased from about 75 to 8o° to about 70 F. and there was a notable decrease in the 

 severity of the disease. The percentage of infected fish decreased, the disease developed 

 more slowly, and a considerable percentage of the infected fish recovered. 



The writer does not, however, wish to give the impression that there is no danger 

 of an outbreak of the disease when the water temperature falls below 70 F. There is 

 some evidence that an epidemic may occur at a comparatively low temperature, but it 

 is probable that under such conditions the disease is much less severe and more easily 

 controlled. That the bacteria may develop at lower temperatures is shown by an 

 experiment with brook trout. A number of fingerlings were shipped to Fairport from 

 the hatchery at Manchester, Iowa, and placed in a trough supplied with running water 

 from a well. The temperature of the water averaged about 62 ° F. On September 13 

 two badly diseased fish, one buffalofish and one bluegill, were placed in the trough among 

 the trout. At a temperature . of about 75 ° F. both fish would in all probability have 

 died in less than 24 hours. However, after being placed in the trough with the trout 

 the bluegill lived 48 hours and the buffalofish about 72 hours. One of the trout was found 

 dying with the disease on September 17. Unfortunately, owing to the writer's depar- 

 ture from Fairport, it was impossible to continue the experiment longer. 



During the first week in July, 1919, the writer found a slight infection on a yellow 

 perch and one on a smallmouth black bass from the St. Lawrence River at Ogdensburg, 

 N. Y. In each case the infection was in wounds on the side of the body. These fish 

 were in a tank with a large number of other fishes, and during the three days they were 

 under observation none of the other fish contracted the disease. Furthermore, the lesions 

 on the infected fish did not increase noticeably in size during this time and the fish 

 showed no ill effects from the disease. Since the temperature of the water averaged 

 about 65 ° F. it is probable that the failure of the disease to develop rapidly and spread 

 to the other fishes in the tank was largely due to this fact. Many of the other fishes 

 confined in the tank had been more or less injured when captured, so there would seem 

 to have been every opportunity for the disease to spread. However, in this case it was 

 impossible to determine definitely whether the failure of the disease to develop was due 

 to the low temperature or to the fact that the bacteria may have belonged to a much 

 less virulent strain than that at Fairport. It has not yet been possible to carry out any 

 detailed experiments to determine the effect of temperature on the virulence and growth 

 of the bacteria, but it is hoped to do so in the near future. 



There is also evidence that, in general, fish are more likely to contract the disease 

 from fish of the same species than from one of another species. This means, of course, 

 that physiological strains of bacteria may be developed on different species of fish. As 

 is well known such physiological strains are common among many species of bacteria. 

 The strongest evidence of the occurrence of physiologically distinct strains in Bacillus 

 columnaris was obtained in the course of some experiments with the black bullhead 

 (Ameiurus melas). This species is ordinarily not very susceptible to the disease, and 

 during the summer of 19 19 a number of these fish were kept in the same tank with 

 infected buffalofish and bluegill without any of them contracting the disease. After 

 several weeks one of the bullhead was artificially inoculated with bacteria obtained 



