American Fisheries Society 381 



when it is seen that the disease is not exclusively among 

 trout and salmon nor only among the subjects of fish cul- 

 ture. An adult whitefish was taken during the past winter 

 from Lake Keuka, N. Y., with a well developed thyroid 

 tumor. There has recently come to light a museum speci- 

 men of an adult brook trout caught in 1902 in Hosmer's 

 Creek, a stocked stream in western New York, having a 

 large thyroid tumor. This was to all intents and purposes 

 a wild trout, though it may have been derived from a 

 domesticated fish. The whitefish, however, are not arti- 

 ficially fed in hatcheries and are held scarcely beyond the 

 hatching period. The causative factors of the disease which 

 are intensified in the artificial fish ponds are present also 

 among the natural conditions surrounding wild fish. The 

 prevalence of the disease among salmonoids has doubtless 

 to do with the great extent to which these fish are cultivated 

 as well as with a natural susceptibility to thyroid en- 

 largement. 



The disease runs usually a slow chronic course, with 

 occasional acute outbreaks of more rapid progress and 

 higher death rate. Ordinarily only a low mortality ac- 

 companies it but it is difficult to say just what this is, since 

 secondary causes are probably the immediate cause of death 

 of many tumor fish. There is no definite picture of symp- 

 toms and effects of tumor growth upon the fish. The mere 

 mechanical efifect of the growth by interfering with breath- 

 ing and eating is certainly considerable but does not explain 

 all the cases of marked anemia and poor condition, reaching 

 sometimes to extreme emaciation. The material of which 

 the tumor is composed contains some substance, probably 

 identical or similar to the extract of the thyroid gland, 

 which is highly toxic to the fish when injected into the cir- 

 culation. When the tumor is ground up, mixed with one 

 to three volumes of physiological salt solution, and about 

 1/10 c.c. of this injected directly into the thyroid region 

 many of the fish are killed, in some cases nearly everyone 

 injected. This fact interferes greatly with efforts to trans- 



