18 U. S. BUREAU OF FISHERIES. 



endogenously, and the color of the tumors is due entirely to the mass 

 of black bacteria. In older tumors a slight pressure causes the libera- 

 tion of an inky black fluid, formed by the bacteria in suspension, and 

 microscopic sections show the presence of the bacteria throughout 

 the substance of the tumor. 



Inoculations of unaffected fish from another pond were made in 

 three ways: (1) by subcutaneous injection, (2) by abrading the skin 

 and rubbing in the fluid taken from a tumor, and (3) by grafting 

 portions of the tumor into the skin. Several of these developed and 

 showed some growth in the two months that the fish were kept under 

 observation. 



It seems probable that natural infection takes place through abra- 

 sions of the skin, as the tumors are usually located on the fins and 

 lips where such abrasions would more naturally occur accidentally. 

 The habits of the bullheads in schooling together render this mode 

 of transfer easy. 



As to the fatality of the disease we have no information. Cer- 

 tainly it is not rapidly fatal, for specimens with well developed 

 tumors were kept alive in aquaria in the laboratory for six weeks 

 without showing any appreciable change other than some slight 

 growth in area and thickness of the tumor. It would thus appear 

 that no active systemic poison or toxin is formed by the bacteria. 

 There is, however, a tendency for the tumors to become fungused 

 with Saprolegnia, a water mold, which would no doubt cause death 

 in time if the tumor did not. While dead catfish have not been ob- 

 served about the pond, the shores are such that they would not readily 

 be noticed. No other species of fish in the pond showed any indi- 

 cation of the tumors, and the probability is that the disease is specific 

 for the bullhead. 



GENERAL STUDY OF PARASITES OF FISHES. 



Systematic studies of the parasites of fishes are important for 

 several reasons. While the presence of some parasites is a normal 

 condition in fishes as well as in domestic animals, sueh as cattle, 

 sheep, and poultry, they may upon occasion become so numerous as 

 to cause the weakening or deatli of the animal infected. When not 

 leading to death they may yet so affect the condition or appearance 

 of the fish as to render them unacceptable to the housekeeper, which 

 means the loss of the fish as a possible article of food. In cases of 

 this kind, and they occur not infrequently, one can not approach 

 the question of cause or remedy or give proper advice to the public 

 unless there is a background of knowledge concerning the normal 

 degree of prevalence of different kinds of parasites in the several 

 species of fish. It is economically necessary, then, that observations 

 of parasites should be made systematically and a large body of evi- 

 dence obtained. Dr. Edwin Linton's studies in recent seasons have 

 covered about 40 species of fish in the region of Woods Hole, Mass. 

 Attention is being devoted now particularly to the round worms 

 (nematodes). The fear has been felt that round worms, which 

 occur on the viscera of certain fish and not normally in the edible 

 parts of the fish, might during storage of the dead fish burrow into 

 the flesh of the fish and thereby become objectionable. The experi- 

 ments conducted indicate that the worms do not penetrate the flesh 



