102 REPORT OF THE SECRETARY OF COMMERCE 
pike perch in Saginaw Bay over the period 1929-85 showed no corre- 
lation with the plantings of fry in earlier years. Methods for the 
simplification of statistical procedure have been evolved. Racial and 
life history studies of several important commercial species were 
continued during the year. 
POLLUTION INVESTIGATIONS 
Investigations concerning the toxicity of industrial effluents on 
aquatic life have been continued in 22 States, so that to date some 
60 major groups of effluents representing over 200 kinds of indus- 
trial wastes have been studied, assayed, and the biological effects of 
their components standardized. For many of these substances de- 
toxifying procedures have been devised and tested. From these 
data on effluents and soil constituents the manuscript for the second 
part of the series of pollution studies, “Trade wastes, chemical ef- 
fluents, and natural pollutants,” has been prepared for publication. 
Part I of this series of studies, “Detection and measurement of 
stream pollution,” was published during the year. 
One of the striking findings in the investigations of natural pol- 
lutants has been the demonstration of the high toxicity of minute 
quantities of selenium to fish. This work is particularly significant 
in view of recent surveys which show this element to be a wide- 
spread menace in several Western States. Besides selenium, several 
other substances that occur in small quantities in some natural 
waters and soils, as boron, fluorin, titanium, and others, have been 
found to present previously unrecognized hazards to fish and other 
aquatic life. 
The investigations on fish physiology as related to water condi- 
tions have been greatly extended during the past year with the 
perfection of new apparatus for studying fish respiration, heart 
action, and internal metabolic activities. 
At Fort Worth, Tex., the long-time experiments on mussels in 
_ confined areas have been continued with satisfactory returns. 
These tests have confirmed the previous findings that the river 
mucket is the most promising species studied thus far for commer- 
cial propagation, and have given additional information on the 
survival of fresh water mussels under adverse conditions. 
AQUICULTURAL INVESTIGATIONS 
Trout investigations during the year consisted of field studies 
in streams of the George Washington National Forest and in 
various other waters; and of hatchery investigations at Leetown, 
W. Va., and Pittsford, Vt. The use of “test waters” in Vermont to 
obtain much-needed information on the productive capacity of 
streams under intensive fishing and the best methods of maintaining 
maximum production was increased to the full extent allowed under 
the State law, a maximum of four test waters. Arrangements were 
completed with the United States Forest Service for the operation 
of four experimental streams in the White Mountain National For- 
est for the purpose of obtaining information on the relative value of 
different sizes for stocking, and for the utilization of the streams 
