BLACK TUMOR OF THE CATFISH 
13 
division, may be observed commonly both in living and preserved material. Not 
being a bacteriologist, the writer will not attempt to describe or name the species. 
As to the fatality of the disease, there is no definite information. Doctor 
Jones informs me that he has seen no dead fish, but the nature of the pond is such 
that they would not readily be observed, for the shores are brushy to the water's 
edge and there are no beaches. Moreover, there is much vegetation in the pond, 
especially near the shores, which would help to make the discovery of floating dead 
specimens difficult. Certainly the disease is not rapidly fatal, for fish with well- 
developed tumors have been kept under observation in aquaria in the laboratory 
for six weeks without showing any changes except for some slight growth in the 
area and thickness of the tumors. It would thus appear that there is no active 
systemic poison or toxin liberated, at least at the time of the year during which 
these studies were made. Fish with large tumors were taken with hook and line, 
even those with large tumors on the jaws accepting the bait readily. However, it 
was noted that old tumors, from which the epidermis had been lost, were frequently 
infected secondarily with Saprolegnia, and there seems little doubt that this fungus, 
which only enters abraded surfaces, would soon cause the death of the fish. 
Doctor Jones believes that the disease has spread very rapidly since the sum- 
mer of 1916, when its presence was first observed. In 1917 about half of the fish 
taken had tumors of various sizes and degrees of development. In the summer of 
1919 it was a difficult matter to find any iminfected catfish in this pond. No doubt 
the habits of the bullhead in schooling together make the transmission of the dis- 
ease an easy matter. It was not noted on other species of fish in this pond during 
my work there nor on the same species of catfish in neighboring ponds. That this 
disease is capable of attacking the bullheads in other ponds is evident from my 
inoculation experiments. Under date of February 2, 1921, Doctor Jones wrote me 
as follows : 
A man who has been fishing through the ice on this pond tells me that he caught a pickerel 
the other day which was covered with the same dark colored spots observed on the hornpout. 
Unfortunately he had disposed of the specimen, but so far as I know this is the only instance 
where the disease has been observed on any fish except the hornpouts. 
As the evidence in this case is not complete, it may be well to suspend judg- 
ment as to whether the disease is capable of attacking other species than the bullhead. 
In the course of my work no measures satisfactory for the control of the dis- 
ease have been suggested. Salt and potassium permanganate solutions, both of 
which are useful in the control of Saprolegnia, were tried on individual specimens, 
but without any noticeable beneficial effect. Of course, it should hardly require 
mentioning that no species of fish from this pond, whether showing such infection 
or not, should be planted elsewhere. 
