PROGRESS IN BIOLOGICAL INQUIRIES. 17 



The disease does not ordinarily attack healthy or uninjured fish, 

 but even a slijjht injury or the lowering of the vitality in any way 

 renders the fish susceptible to infection. Fish are especially liable 

 to contract the disease within a day or two after bein<j: handled. 



It has been found that the disease can ordinarily be controlled by 

 treatino: the fish after they have been handled with a 1 to 1000 solu- 

 tion of copper sulphate for two to three minutes. When properly 

 used it has been found possible to reduce the loss from this disease 

 from about 50 per cent to 5 per cent or less. 



Studies on protozoan parasites of fishes have been continued and a 

 paper is nearly ready for publication describing the development 

 of the cysts and the formation of spores in a species of Myxobolus 

 which is abundant on the gills of the buffalofishes. The early devel- 

 opment of the myxosporidian cysts has not previously been worked 

 out. It has been found that the young parasites reach the gills in the 

 blood stream and become permanently fixed in the capillaries of the 

 gills, where they develop into large, saclike cysts, which may cause 

 considerable injury to the gills. The results of studies on several 

 other species of myxosporidian parasites, several of them new, are 

 also nearly ready for publication. 



BLACK-SPOT DISEASE OF THE BULLHEAD. 



A conspicuous and unsightly disease of the common bullhead or 

 hornpout {Ameiurus nehulosus) became very evident in a pond near 

 Falmouth. Mass., in the summer of 1917. The matter having been 

 brought to the attention of the Biu-eau, and no information regarding 

 a disease of this description being available. Prof. Raymond C. 

 Osburn was engaged as a temporary investigator for a study of the 

 disease. 



The disease takes the form of swollen, rough, tumerous, intensely 

 black areas, affecting the skin externally ordinarily, but sometimes 

 entering the mouth cavit}?^ and the gill chamber. The subcutaneous 

 tissues are but little affected, the disease being confined almost en- 

 tirely to the skin, and there is no evidence of spread to other parts of 

 the body. The tumors appear to grow very slowly, but there is 

 evidence that they are infectious, for in 1919 the percentage of in- 

 fected fish taken in the pond was much greater than in 1917, and 

 nearly all the bullheads taken showed the disease. 



Careful study and experimentation proves the disease to be of 

 bacterial origin, the causative organism being a very minute coccus, 

 or bacterium of that general class, probably undescribed. The dis- 

 ease appears to l)e unknown to science and a widespread inquiry has 

 brought out only the information that no one has ever observed it. 

 The one exception in the literature is found in Thoreau's Journal, 

 where he twice makes mention of observing such black tumors on 

 bullheads in tlie (^oncord Kiver and one of its branches. 



With the cooperation of Dr. W. W. Browne, bacteriologist, cul- 

 tures of the bacteria were made on agar mixed with the juices of the 

 fish to produce a proper medium. Though the bacteria grow" very 

 slowly, a number of colonies were developed to a diameter of one- 

 eighth of an inch or more in from 12 days to 2 weeks. These had 

 the same intensely black color as the tumors. The color is produced 



