REPORT OF THE COMMISSIONER OF FISHERIES. 25 
it bores and encysts just beneath the cuticle. If the buffalofish eats 
the intected larva it obtains the young parasite, which very rapidly 
develops and assumes in the late summer the adult form ready to 
expel its eggs. The association of the buffalofish, the snail, and the 
May fly larva seems to be essential for the perpetuation of the para- 
site. ‘The probable importance of the form is suggested by the fact 
that a serious mortality occurred among the fishes that were so 
infested. 
The life history of a trematode parasite of the bluegill sunfish was 
also investigated. It is found in the larval stage in that fish and in 
the adult stage in the kingfisher. 
Investigation of protozoan parasites.—Investigations of protozoan 
parasites at the Bureau’s station at Fairport, Iowa, during the sum- 
mers of 1916 and 1917 produced interesting results which promise 
to be of practical value to fish culture. The myxosporidia are quite 
common on fish from the Mississippi River, and evidence seems to 
prove that they are to a degree seasonal in occurrence. Under cer- 
tain conditions they may cause serious injury to the host, but in the 
case of the buffalofish, and possibly of other species, it is believed 
that danger from infection in ponds might be lessened by a proper 
rotation of the fish in a series of ponds, as the young seem to become 
infected from the adults placed in the same pond to spawn. 
A hitherto undescribed species of coccidia is believed to have 
caused the death of young carp after transference from one of the 
ponds to hatchery troughs, as an exceptionally heavy infection of 
the intestines with these parasites was associated with a serious de- 
gree of mortality. Although infection of the pond fish with the 
ciliate parasites Ichthyophthirius, Chilodon, and Cyclocheta was 
quite common, a much heavier infection after transference of the 
fish from the ponds to the tank house, probably induced by change 
of environment, would seem to indicate that these parasites have been 
largely responsible for the previous heavy mortality of the fish in 
the tanks. 
Peculiar disease in brook trout—At a commercial hatchery in 
Rhode Island a peculiar disease of brook trout caused the loss of a 
large number of fish. The diseased fish at first became apathetic, 
then turned black and became blind. Just before death the fish 
would dart jerkily through the water for a time, losing equilibrium 
toward the last. As the result of the experiments conducted under 
the guidance of the fish pathologist of the Bureau, the cause of this 
unusual affection of trout was traced to the nonoil substances in lin- 
seed meal, the latter being a constituent of the food then used at this 
hatchery. The harmful effects of the linseed meal are believed to be 
due to action of a cyanogenetic glucoside or its decomposition prod- 
ucts, though the actual proof will require further experimentation. 
Miscellaneous studies of disease and parasites.—During the year 
a Serious condition of diminished vitality and disease of the blue pike 
was reported from several points on Lake Erie. Specimens of fish 
received from Cleveland, Ohio, were found to be unusually heavily 
infected with a species of parasitic copepod (identified as Hrgasilus 
centrarchidarum), which is known to occur abundantly on perch, 
sunfish, and bass, but is not generally found in numbers on blue 
pike and saugers. The fact of the peculiar abundance of parasites 
