370 
BULLETIN OF BUREAU OF FISHERIES 
Fish 
The fish fauna was studied from collections made with various types of nets and 
seines. Several hauls were made in each of the various portions of the habitat under 
consideration and usually the entire catch preserved. If the entire catch were too 
large, representative collections from it were made and the total bulk of the catch 
noted. 
EQUIPMENT 
In the field studies reported in this discussion several types of equipment have 
been used. In the major stream surveys U. S. Quarterboat 348 (see fig. I), which is 
fully equipped with chemical and hydrobiological laboratories, together with living 
quarters for 12 people, was used as the base from which the operations were con- 
ducted. Attached to the quarterboat for these investigations were two 35-foot 
cruisers (U. S. Fisheries 53 and U. S. Fisheries 56 , see fig. 2) which were specially 
equipped with dredging, sounding, and sampling apparatus, together with portable 
chemical units for such determinations and preparations as required immediate 
attention in the field. On certain streams where it was not feasible to move the 
quarterboat and cruisers, support and cooperation in equipment was given by various 
Government, State, and private agencies, including the loan of vessels and the use of 
equipment at hand. 
For certain stream studies automobile trucks carrying compact biochemical, 
biophysical, and hydrobiological apparatus were also used extensively. These mobile 
units were found to be very effective, as long distances could be covered quickly and 
the equipment taken to the specific site of the pollution problem to be investigated. 
(See fig. 5.) 
The detailed experiments, most of the bioassay work, and various analyses and 
tests which could not be made in the field were conducted at the United States Bureau 
of Fisheries laboratories at the University of Missouri. Here, through the excellent 
cooperation afforded by the University of Missouri, the Bureau has a research labora- 
tory suite of eight rooms specially equipped for biochemical, physiological, and bio- 
logical work, in which various pieces of apparatus devised particularly for these pol- 
lution studies are in operation. 
DISSOLVED OXYGEN 
The modifications of the Winkler method for oxygen determinations as described 
by Kemmerer, Bovard, and Boorman (1923) and as given by American Public Health 
Association (1933) were followed in both the field and laboratory analyses for dis- 
solved oxygen. The data are reported in parts per million (p. p. m.) unless other- 
wise specified. 
In figures 6, 7, 8, and 9 are presented the results of 5,809 determinations of 
dissolved oxygen made at 982 stations on fresh-water streams and rivers of the 
United States during the months of June to September, inclusive, 1930-35. Natural 
lakes and ponds are excluded, the data covering only conditions in stream and river 
waters during the warm season. This season was chosen since the oxygen carrying 
power of water decreases and the metabolic demands of aquatic animals for oxygen 
increase as the temperature of water rises. 
