52 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Yellowstone Lake and Heart Lake have one feature in common, and one shared by 
no other lakes containing trout with which I am acquainted (Shoshone aud Lewis Lakes 
being destitute of fishes). Both have a large influx of hot water from geysers aud 
from hot springs, some of them outside the lake, but many of them opening under the 
water. This suggests the theory that the existence of the worm itself, or perhaps its 
malignity as a parasite, is dependent on the presence of hot water, instead of the cold 
waters ordinarily frequented by trout. 
As bearing on this suggestion I may notice : In both lakes the trout actually frequent 
the warm waters, attracted apparently by the great abundance of fish food to be found 
there. It is perhaps not impossible that with the great variety of insect, crustacean, 
aud worm life, the germ of the worm may occur also. The streams in which wormy 
trout occur, so far as known, are all in easy access from Yellowstone Lake. Kiddle 
Lake, although tributary to the Yellowstone, has an outlet long, narrow and tortuous, 
being dry at both ends in the summer. It is so difficult of access that probably trout 
do not often ascend it. Only young trout were seen in the creek, and the trout found 
in the cold waters of Riddle Lake showed no sign of worms. The trout in Pelican Lake 
and other waters to the east of Yellowstone Lake and tributary to it are said to be 
infested with worms. These lakes receive much water from Hot Springs. 
Connected with this fact of the development of worms in warm waters is the fact 
that the suckers in the warm (largely geyser) waters of Witch Creek {Gatostomns 
ardens) are afflicted with another parasitic worm. I know nothing of the history or 
relationships of this worm, but it is hard to avoid the supposition that the warm 
water favors its development. Although the sucker is a small fish, the worm infesting 
it is larger than any other parasitic worm I have ever noticed among fishes, and, as 
elsewhere stated, it often occupies more space in the abdomen of the fishes than do the 
fish’s own viscera. 
The lakes of Washington, Colorado and Utah, abounding in trout of the same spe- 
cies, show, as far as we know, neither geyser water nor Dibothriuni. 
It will be interesting to know whether the trout introduced into Lakes Shoshone 
and Lewis, both of them with similar hot tributaries, will be afflicted with worms. It 
will also be interesting to know whether any other species of trout will show immunity 
from them. Possibly an abundance of other fishes as food for trout would draw them 
away from the hot waters, aud free them from worms. 
The “ wormy ” trout are leaner and more compressed than others, and the sides of 
the belly are likely to show ridges aud lumps. The flesh is said to be redder in the 
diseased fish, and the external color is more likely to be dusky or brassy. 
In the trout examined the presence of many worms was accompanied by a 
shrunken or irregular condition of the ovaries or testes. Perhaps spent fish are more 
likely to be wormy. According to Mr. Arnold Hague, the best trout are in swift or 
deep waters ; the wormy ones about eddies or among logs or masses of floating vege- 
tation. The wormy trout takes the fly freely but is in general little gamey. In fact, 
all the Yellowstone trout seem less active than is usual for the species. 
The value of these attempts at generalization can only be determined by the thor- 
ough study of some competent helminthologist in the field. The life-history of the 
worms is yet to be made known. When this is done possible remedies may be sug- 
gested. The probabilities are that the trout and the worm will never be divorced 
in Yellowstone Lake. 
