BUREAU OF FISHERIES 327 
cipal lines. The first is related to the artificial propagation and rear- 
ing of game fishes; the second to the problem of controlling the para- 
sites and diseases of fish which frequently curtail the output of hatch- 
eries; and the third to field problems relating to fish management, 
such as the comparative survival and growth of hatchery and wild 
trout under natural conditions, the ecological requirements of differ- 
ent species of game and food fishes, and the possibility of increasing 
fish production in natural waters. 
In connection with studies of the artificial propagation and rear- 
ing of trout, progress has been made toward developing economical 
diets without sacrifice of growth. Other experiments have demon- 
strated that overfeeding of trout brood stock is distinctly detri- 
mental in that it reduces the number of eggs that hatch, while experi- 
ments in selective breeding have more than doubled both the rate of 
growth and the production of eggs. 
Studies of the pond culture of largemouth black bass were car- 
ried on in Florida with a view to determining the role of fertilizers 
and forage fish as they affect the production of bass fingerlings per 
acre. Similar work on a somewhat smaller scale has been conducted 
in West Virginia. Here, also, field studies of the spawning and sur- 
vival of smallmouth black bass are being made in selected tributaries 
of the Potomac River. 
The most important result of the studies in fish pathology during 
the year was the development of a safe, practical, and economical 
method of controlling the external parasites of fish. Other investi- 
gations contributed to an understanding of the causes and prevention 
of the Western type of gill disease and of the importance of several 
parasites of trout and bass. In addition to the hatchery studies, 
losses among wild fish in the field were investigated by the staff. 
The most important problem of this nature that is currently under 
study concerns the attacks of fungus organisms which inflicted con- 
siderable losses on adult chinook salmon and steelhead trout liber- 
ated in the Entiat River in connection with the Columbia River 
salvage operations. 
Fish-management studies on trout waters were carried on at the 
Pittsford (Vt.) and Leetown (W. Va.) Stations, in the Pisgah Game 
Preserve in North Carolina, and in Utah, Idaho, and California. One 
of the surprising results of the “test water” studies conducted in Ver- 
mont is the finding that fishing is maintained chiefly by natural 
reproduction of wild fish, and that stocking with hatchery trout has 
had little effect. Under conditions obtaining in those waters, stocking 
with legal-sized fish in the fall has been found to be wasteful, and 
tests are being made to discover whether stocking with smaller fish 
will yield better results. In the Pisgah Game Preserve, where the 
