BACTERIAL DISEASE OF FRESH-WATER FISHES. 277 



a very considerable mortality each summer for several years. This mortality for the 

 most part has occurred in fishes which were being transferred from one pond to another, 

 or to aquaria for experimental purposes. It was not until the past summer (19 19) that 

 the disease was shown to occur on fish in the Mississippi River as well as in the ponds. 

 However, fish-culturists are well aware that is is impossible to handle many species of 

 fish during warm weather with any degree of success. Undoubtedly part of this mor- 

 tality among fish which have been handled is due to the direct effects of the treatment 

 to which they have been subjected, but there is no question in the writer's mind that a 

 much larger part is directly due to this disease and only indirectly to the handling which 

 has simply rendered the fish more susceptible to infection. We are convinced that a 

 great part of the mortality usually ascribed to fungus is in reality caused by Bacillus 

 columnaris. In fact the writer is inclined to doubt if fungus is ever an important cause 

 of fish mortality. In all probability Bacillus columnaris is widely distributed over the 

 country and during warm weather, at least, is the most important agent in the destruc- 

 tion of fish which have been injured in any way. 



Anglers are often advised to remove small fish from the hook and retnrn them to 

 the water. In the light of our experience with the disease at Fairport it is doubtful 

 if many fish which have been handled in this way actually survive. Since the disease 

 would not make its appearance until two or three days later, it is obvious that only 

 through carefully conducted experiments can their chance of survival be ascertained. 

 An incident which occurred at Fairport during the summer of 19 18 is very suggestive 

 in this connection. A number of largemouth black bass were needed for some experi- 

 mental work in mussel propagation. They were taken from one of the ponds on a hook 

 and line and placed in a large tank supplied with running water. Within two or three 

 days nearly every fish had become infected with Bacillus colutn naris. As previously men- 

 tioned, this species of fish is not very susceptible to the disease, and, furthermore, the 

 fish in this case were several years old. As the reader will recall the older fish are much 

 less susceptible than the young. 



During the last few years the Bureau of Fisheries has been rescuing large numbers 

 of young fishes from the small pools and ponds in which they are imprisoned when the 

 spring floods recede. These pools and ponds are widely scattered over the flood plain 

 of the Mississippi, often only a few hundred yards from the river. In some instances 

 they may be 2 or 3 miles from the main channel. As the waters recede these ponds 

 continually grow smaller and may eventually become entirely dry. They are often 

 crowded with fish and the shallow waters exposed to the hot sun of July and August 

 become heated to a relatively high temperature. These conditions combined with a 

 limited supply of oxygen often result in the death of large numbers of fish. The con- 

 ditions are such as to render the fish susceptible to infection by Bacillus columnaris, and 

 fishermen have told the writer of having seen large numbers of diseased fish in such 

 ponds. 



In transferring the fish to the river they must first be seined from the ponds, a 

 process which necessitates considerable rough handling, and then carried in galvanized 

 washtubs (often under a broiling sun) to the river. It is obvious that such treatment 

 is likely to result in infection by Bacillus columnaris. That the fish when liberated in 



