26 . U. S. BUREAU OF FISHERIES. 
place through invading cells, but is not always successfully accom- 
plished; it apparently makes a demand upon the body of the fish, 
which, if excessive, may lead to death. 
DISEASE OF RESCUED FISH. 
Dr. H. 8. Davis, temporary investigator at the Fairport biological 
station, has found that a high mortality may occur among rescued 
fishes immediately after the handling incident to rescue operations. 
This heavy death rate is especially characteristic of the crappies, 
buffalofish, and bluegills, when taken in warm weather, the first- 
named species being the weakest. While the mortality may be 
founded in part upon “shock” sustained during the seining and 
handling operations, it is due more directly to bacterial infection 
following slight injuries and gaining headway from the weakened 
condition of the fish. Immersion for one minute in a solution of 
copper sulphate in 1 to 1,000 dilution reduces the loss among rescued 
fishes to a minimum. 
In certain experiments 75 to 100 per cent of the crappies rescued 
from inland sloughs and untreated were lost through death. Under 
similar conditions, except for a one-minute treatment with 1/1,000 
copper-sulphate solution after the fish were allowed to remain a 
short time in fresh clean water, this experimental loss was reduced 
to 30 or 40 per cent. The necessity and practicability of the treat- 
ment depend upon the conditions attending work in particular fields 
and at particular times. It is believed that frequent tests should be 
made in connection with rescue operations and the prophylactic 
measures taken wherever a substantial mortality rate is to be ex- 
pected. Dipping in a simple disinfectant can not be very expensive 
and will be worth while if it will increase appreciably the percent- 
age of survivors. 
Dr. Davis’s experiments not only point out the possibilities of loss 
and the means of prevention, but they also emphasize the necessity 
for great care in handling rescued fish. Rough methods, including 
the throwing of fishes into receptacles and the abrasion of the fishes’ 
bodies by seines, hands, or débris are the main causes of a high 
death rate. 
PARASITIC. FLATWORMS OF FRESH-WATER FISHES. 
The parasitic flatworms which infest the body surface and gills of 
fishes (ectoparasites) may be more of a nuisance to fish culture in 
ponds, tanks, or aquaria than those which live within the body of the 
fish. The endoparasites generally can not complete the life cycle 
without passing different stages in two or more hosts, which are 
likely to be animals of widely different groups. Therefore, as re- 
gards these parasites, fish can not directly infect fish. With external 
parasites it 1s otherwise; there being no alternation of hosts, infec- 
tion may proceed from fish to fish and thus multiply in such abun- 
dance as to cause extreme weakness or death of the fish. Such a 
parasite is Gyrodactylus fairporti, a new species described by Dr. 
H. J. Van Cleave from bullhead and carp of certain ponds at the 
Fairport (Iowa) station. These flatworms are very small, usually 
