374 
BULLETIN OF BUREAU OF FISHERIES 
dissolved oxygen to be expected in flowing streams both polluted and unpolluted is in 
general from 0 to 14 p. p. m. 
For the final evaluation ol the various findings presented from the field studies on 
dissolved oxygen, experimental data covering the oxygen requirements of fresh-water 
fishes must also be considered, as both the amount of oxygen consumed by the fish 
and the minimal amount of dissolved oxygen which wall barely support life vary 
with the combinations of environmental factors operating at the time, and with the 
N. RIO GRANDE P. COLUMBIA RIVER SYSTEM 
DISSOLVED OXYGEN IN PARTS PER MILLION 
Figure 9. — Continuation of dissolved oxygen comparisons, stippled graph A figure 6, being the standard. 
size and species of the fish. Temperature, pH, and dissolved carbon dioxide are 
particularly important in this connection. 
Many observers have pointed out that the metabolism of, and consequently the 
oxygen consumed by, fishes and other aquatic animals follows in general the van’t 
Hoff law with reference to temperature so that the actual amount of oxygen removed 
from the water by the individual fish will vary with the temperature regardless of 
the amount of oxygen present until a near-lethal point is reached (Keyes, 1930). 
Ruttner (1926) states that the oxygen consumption of many aquatic animals is almost 
doubled with each rise of 10° C., within physiological limits, and Powers (1922 and 
1932) has pointed out correlations between the utilization of oxygen by fishes at low 
oxygen tensions and the pH and carbonate systems. 
