82 U. S. BUREAU OF FISHERIES 
cooperation with the Division of Fish Culture. These studies indi- 
cate that Costia may be a foreruner, and probably a direct cause, 
of the Western type of gill disease. It is believed, however, that 
Costia is not the sole cause of this type of gill disease, which pre- 
sumably may result from any prolonged irritation of the gill 
epithelium. Infection by Costa can be prevented by weekly treat- 
ments with a 1:6,000 solution of formalin. 
During the past year an effort was made to place the losses that 
occur at the Bureau’s trout hatcheries on an accurate statistical 
basis. Records, based insofar as possible upon actual counts of 288 
lots of fish at 22 separate hatcheries, were analyzed for the per- 
centage loss occurring among progressive size groups at half-inch 
intervals. The average loss between the eggs and 4-inch fingerlings 
was approximately 50 percent, which is much less than is believed to 
occur in nature. These results further emphasized the importance 
of hatchery losses and the need for more investigations of their 
causes. In 102 lots of fish, where both food and mortality records 
were available, it was found that the cost of food fed to these fish 
was $5,732. ‘The economic value of the dead fish among the 102 lots 
was conservatively estimated at $35 817. 
Several investigations of losses of fish at hatcheries in the general 
vicinity of Seattle, and losses among wild fish in the field, were 
made by Dr. Fish. Of the latter, losses among silver salmon, which 
apparently were caused by excessive sunshine, and attacks by fungus 
(Saprolegnia), which inflicted serious losses among adult chinook 
salmon and steelhead trout liberated in the Entiat River in the 
Columbia River salvage operations at Rock Island, were most note- 
worthy. 
At the Leetown Station, George E. Klak made a study of a 
strigeid worm which is very abundant in the black-head minnows 
He found that these worms caused sterility when their number was in 
excess of 1,000 per fish. In some cases they occurred in such num- 
bers as to rupture the abdominal wall. 
Dr. Davis continued his studies on a suctorian parasite of the 
smallmouth black bass. This parasite occurs on the gills, and when 
very abundant may seriously injure the host and eventually cause 
its death. It does not affect the largemouth bass, even when in the 
same pond with heavily infected smallmouth bass. 
Studies are also being carried on at Leetown on the common bac- 
terial gill disease of trout. It has been found that this disease 
may also affect largemouth and smallmouth black bass and has 
caused serious mortality among both young and adult fish. Other 
parasites of bass and trout are being studied for the purpose of 
clearing up certain points in their life history and developing: 
better methods of control. 
The disease service, which was inaugurated 4 years ago to assist 
fish-culturists in the control of hatchery diseases, continued to be 
heavily patronized during the past year. This service has proved 
to be very popular and has been an important factor in reducing 
losses. 
NUTRITION STUDIES AT THE CORTLAND HATCHERY 
The experimental hatchery at Cortland, N. Y., is operated under 
a cooperative agreement between the New York Conservation De- 
ra 
