BACTERIAL DISEASE OF FRESH-WATER FISHES. 269 



from a diseased buffalofish. Inoculation was made as usual by scraping away the 

 epidermis from a small area on one side of the body and rubbing the bacteria into the 

 wound. The bullhead developed a characteristic lesion, and within 3 or 4 days practi- 

 cally every bullhead in the tank became infected. The epidemic among the bullhead 

 was not confined to this tank but soon spread to bullhead in adjoining tanks. This 

 can be easily explained. On account of their apparent immunity to the disease no 

 precautions were taken to prevent the bacteria getting from one tank to another, and 

 they could easily have been transferred on the hands or nets. The epidemic developed 

 with remarkable rapidity, and within a few days nearly all the bullhead which had been 

 held in the tanks from one to several weeks without showing any signs of the disease 

 were dead or dying. Only by the use of control measures to be described later was the 

 epidemic checked and a few fish saved. It was noticeable that although the infected 

 bullhead were in several instances kept in the same tanks with buffalofish and bluegill 

 the disease did not spread among them nearly so rapidly as among bullhead, although 

 ordinarily both buffalofish and bluegill are more susceptible to the disease. 



It has also been observed in making artificial inoculations that while it is usually 

 not difficult to infect a fish with bacteria from another species a larger percentage of 

 positive results is often obtained when the bacteria are taken from a fish of the same 

 species. Further investigations along this line are greatly to be desired. 



As intimated above, while most species of fresh-water fishes are liable to be attacked 

 by the disease some species are much more susceptible than others. It is, of course, by 

 no means easy to determine accurately the relative susceptibility of different species, 

 but there can be no question that there is a great deal of variation in this respect. It is 

 possible to divide the fishes which have been most studied into two classes. The first 

 includes those species which are very susceptible and are almost certain to contract the 

 disease in large numbers if handled during warm weather. In this class we would include 

 the buffalofishes (Ictiobus bubalus and cyprinella), the crappies {Pomoxis annularis and 

 sparoides), and possibly the bluegill (Lepomis incisor). The second class includes those 

 fishes which are ordinarily only moderately susceptible and do not usually contract the 

 disease in such numbers, even in warm weather. Furthermore, a considerable per- 

 centage of the diseased fish may recover if kept under favorable conditions. In this 

 class we would include the largemouth black bass (Micropterus salmoides) , the channel 

 catfish (Ictalurus punctatus) , the bullheads {Amciurus nebulosus and melas), the sunfish 

 {Lepomis humilis), the carp (Cyprinus carpio), the warmouth {Chccnobryttus gulosus), 

 and the white bass (Roccus chrysops). Of course it is not to be understood that all of 

 the species in each class are equally susceptible, for that is certainly not the case, but in 

 the present state of our knowledge it does not seem advisable to attempt a more detailed 

 analysis of their relative susceptibility to the disease. 



It is also noticeable that the young of any species are, in general, more susceptible 

 than are the adults. This is especially true in the case of the carp, the young of which 

 are quite susceptible, while the adults are nearly immune. 



At first it was assumed that the bacteria must be widely distributed in the water, 

 since this would most readily explain the appearance of the disease when the fish are 

 handled, but we have no proof that this is the case, and there is some evidence that the 

 bacteria do not live for any length of time off the fish. If this is true, we are forced to 

 assume that they are able to live in small numbers on perfectly healthy fish without 



