A NEW BACTERIAL DISEASE OF FRESH-WATER FISHES. 



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By H. S. DAVIS, Fish-Pathologist, V . S. Bureau of Fisheries. 



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 Contribution from the U. S. Fisheries Biological Station, Fairport, Iowa. 



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CONTENTS. 



Page. 



Introduction 261 



Description of the disease 262 



Occurrence of the disease 263 



Cause of the disease 263 



Pathogenesis 265 



Methods of infection 266 



Treatment and control of the disease 270 



Economic importance of the disease 276 



Explanation of figures 280 



INTRODUCTION. 



While working on the protozoan parasites of fishes at the U. S. Fisheries biological 

 station, Fairport, Iowa, during the summer of 1917 a number of fish which had been 

 recently placed in aquaria were found to be dying from the effects of a bacterial infection. 

 Later in the season the disease was quite prevalent among fishes confined in aquaria, 

 but owing to the pressure of other work no particular attention was paid to it at that time. 



Early the following summer (1918) the disease again made its appearance, this time 

 in one of the ponds. In the course of a series of feeding experiments being carried on at 

 the Fairport station a large number of fingerling buffalofish were held in a pond in which 

 had been placed a considerable quantity of horse manure. These fish grew rapidly for 

 some time and appeared to be in a healthy, vigorous condition. However, early in 

 July they began to die in large numbers, and a careful examination showed that the dying 

 fish were infected with the same species of bacteria found the previous summer on fish 

 in aquaria. A little later in the season the disease appeared among fishes that had 

 recently been transferred to troughs for feeding experiments and caused considerable 

 mortality. 



On account of its evident importance it was decided to undertake an extended 



investigation of the disease to determine, if possible, a practicable method of control. 



This investigation was begun during the latter part of the summer of 1918 and continued 



during the summer of 1919. During the summer of 1919 the writer was assisted by 



Miss Miriam Mackenzie. 



261 



