BACTERIAL DISEASE OF FRESH-WATER FISHES. 263 



at temperatures below 75 ° F. the bacteria develop much more slowly and the fungus 

 growth may become evident before the fish succumbs. 



This is notably the case early in the fall. With the advent of cooler weather a con- 

 siderable number of the diseased fish may show characteristic fungus growths in connec- 

 tion with the bacterial lesions. But even in these cases there can be little doubt that the 

 lesions were primarily due to bacteria and that the Saprolegnia was a secondary invader. 



Occasionally fish may die from the disease without showing any lesions on the body 

 or fins. In such cases the gills are always badly infected, a large part of them being 

 entirely destroyed. In late stages of gill infection the fish often show characteristic signs 

 of suffocation, such as swimming at the surface and gasping for breath. In the majority 

 of cases, fish with infected gills will also shpw lesions on the surface of the body or fins, 

 but here again there is considerable variation in different species. 



OCCURRENCE OF THE DISEASE. 



It seems probable that most species of fishes are liable to attack by this disease, 

 although some species are much more susceptible than others. While it has been neces- 

 sary to confine our observations to a comparatively small number of species the disease 

 has been observed on the following fishes: The buffalofishes {Ictiobus bubalus and /. 

 cyprinella) , the sunfishes (Lepomis incisor and L. hum His), the carp (Cyprinus carpio), 

 the black basses (Microptcrus salmoides and M. dolomieu), the crappies {Pomoxis spa- 

 roides and P. annularis) , the warmouth (Chcenobryttus gulosus), the yellow perch (Perca 

 flavescens), the white bass (Roccus chrysops), the brook trout (Salvelinus jonlinalis) , the 

 minnow {Pimephales notatus), the channel catfish (Ictalurus punctatus), and the bull- 

 heads (A meiurus nebulosus and A . melas) . From the above list it will be readily seen that 

 the disease is widespread, and there is little reason to doubt that under favorable con- 

 ditions it may occur on nearly all species of fresh-water fishes. 



In one instance several tadpoles which were confined in a tank with a number of 

 infected buffalofish developed well-defined lesions on the tail. The tadpoles were just 

 beginning to metamorphose, which may have made them more susceptible to infection. 

 Attempts to inoculate adult frogs with the disease have proved unsuccessful. 



So far it has not been possible to obtain any data regarding the geographical dis- 

 tribution of the disease. However, while on a visit to the St. Lawrence River at Ogdens- 

 burg, N. Y., during the first week in July, 1919, the writer found the bacteria in lesions 

 on the smallmouth black bass and the common perch. In this case the fish did not 

 appear to be seriously injured by the bacteria which were evidently growing very slowly. 



CAUSE OF THE DISEASE. 



The disease is produced by an apparently undescribed species of bacteria for which 

 I propose the name Bacillus columnaris. It has not yet been possible to grow the organ- 

 ism in pure culture, but its appearance is so characteristic that it is always easily recog- 

 nizable if present in any numbers. It is a long, slender, flexible, rod-shaped organism, 

 5 to 12/J long and 0.5^ wide (figs. 246 and 247). The bacteria are very transparent and 

 unless present in considerable numbers are difficult to distinguish on this account. 

 They usually appear perfectly homogeneous, but rarely may exhibit a slightly granular 

 structure. The bacteria are motile and probably possess flagella, although owing to 



