86 U. S. BUREAU OF FISHERIES 
cause-effect complex that is involved in every type of situation. Be- 
cause immediate and epidemic situations are frequently of a tran- 
sient nature, the research program is more concerned with an analysis 
of the cumulative physiological effects of pollutants related to the 
fish themselves than with the application of palliatives. The inves- 
tigational program also attempts to determine the precise agent or 
agents in pollution situations that are responsible for deleterious 
effects on the fish populations and their habitat. 
Three major lines of investigations organized in 1938 were carried 
forward in 1939 by the Columbia, Mo., field unit in conjunction with 
the laboratories at Columbia, and at Fort Worth. 
Analytical studies —Waters, muds, and aquatic organisms collected 
in the field are sent to the central laboratory for detailed analyses, 
which are carried out by Dr. B. A. Westfall and his assistants. In 
addition to the materials collected by the staff, in the course of field 
work, a large number of samples are sent in for examination by the 
various State agencies. 
Bioassays. —As during previous years, the specific effects of mate- 
rials found in waters, muds, and pollutants, on living fish, and other 
aquatic animals, were determined by the bioassay method. The 
bioassays of pollutants sent to the Columbia unit, by State authori- 
ties and other agencies, have become an important function of the 
laboratory, and many determinations are constantly m progress. 
Physiological investigations —The underlying causes for the 
actions of the various substances found in natural waters and _ pol- 
lutants on living fish are sought through studies of the physiology of 
fish conducted under the direct supervision of Dr. Ellis at the Colum- 
bia and Fort Worth laboratories. As in 1938, one of the major fields 
of physiological investigation during 1939 was a study of the effects 
of various components of larvacides and herbicides on fresh-water 
fishes, and their associated aquatic food organisms. Because the 
biochemiéal and physiological tests necessitate technique of consider- 
able precision, each fish is maintained and studied separately and 
receives individual feeding and care, frequently for several months. 
More than 300 fish are constantly under observation at Columbia, and 
numbers of catfish, bass, and other fishes are under observation as 
part of this investigation at Fort Worth. These studies have pro- 
gressed to the point where it is possible to conclude that there is 
Impairment of the growth and nutrition of fishes in waters treated 
even with smail quantities of asenicals and several other materials 
commonly used as mosquito larvacides. A separate report on this 
subject has just been presented to the Malaria Control Committee as 
part of the cooperative program on mosquito-control measures con- 
ducted in the T. V. A. area. 
Throughout the year physiological studies, with concurrent analy- 
ses, have been made on the effects of several substances dangerous to 
fish life which were found in natural waters in the West in the course 
of the field investigations, with particular reference to the natural 
pollution picked up by waters used for irrigation during their pass- 
age over fields and through irrigation ditches. Marked concentra- 
tions of various mineral salts have been discovered in many return 
irrigation waters, and the detrimental effects on fishes noted. 
Through the application of physiological, biochemical, and metabolic 
methods to the study of fishes from irrigation waters, it has been 
