430 



hole, and several carloads of carp and buffalo were taken here during 

 the last two weeks of January. A rise in the stage of the river largely 

 diluted this better water with the oxygen-deficient river water, and large 

 numbers of minnows, large-mouth black bass fingerlings, crappies, sun- 

 fishes, etcetera, died ; and the carp became much distressed and swam 

 at the surface with their heads out of the water. Part of the ice then 

 went out of the channel, the dissolved oxygen in the river water increased, 

 and the fishes no longer were attracted to this place. The unusually large 

 numbers of gulls that frequented the river at that time may indicate an 

 unusually large number of dead fishes ; but, with the above exception, 

 no dead fishes were seen by the writer except where they had been con- 

 fined in live-boxes, traps, and nets, and could not escape from the oxygen- 

 deficient water. 



Those animals which are more sedentary in their habits and can not 

 so readily avoid oxygen-deficient water suffer more severely than the 

 fishes. After the recent prolonged period of ice, large numbers of dead 

 snails were washed up on the east shore of lower Peoria Lake. Fisher- 

 men in the vicinity of Meredosia and Beardstown have in recent years 

 remarked the growing scarcity of air-breathing animals that hibernate 

 on the bottom of the river, such as bull-frogs, snapping turtles, and soft- 

 shelled turtles. Some of the turtles, however, such as the painted turtle, 

 the ridge-back turtle, and the terrapin, do not bury themselves in the mud 

 and hibernate, but remain active, as shown by the fact that they are caught 

 in hoop-nets and traps throughout the winter. These latter species of 

 turtles are much more plentiful in the lower Illinois River than the 

 hibernating species. In cold water, frogs and turtles utilize the oxygen 

 in the water and can dispense with the use of their lungs. If they re- 

 main active they select the better water the same as the fish; but if they 

 bury themselves in the mud and become dormant, it may be that they 

 die there from deficiency of oxygen during times of stagnation. 



In the attempt to determine what dissolved oxygen concentrations 

 the different fishes avoid and what concentrations are fatal to them, dis- 

 solved oxygen determinations were made where fish were being taken, 

 where they customarily had been taken but were absent at the time, and 

 where fish were dying. The procedure followed was to accompany a 

 fisherman who was raising hoop-nets and take dissolved o.xygen samples 

 at the nets. This was done at nets which had been fishing one, two, or 

 at most three days, and, when convenient, both when the nets were set 

 and when they were raised. The samples were usually taken near the 

 bottom because that is where the fish spend most of their time. One 

 advantage of hoop-nets is that they can be used in all kinds of situations 

 where the hauling of seines is often impossible. For the purpose of 

 ascertaining the relations of fish life to dissolved oxygen, hoo])-nets 

 have the further advantage, that they fish a very restricted area. The 

 amount of fish taken by them depends on conditions which cause the fish 

 to move about, such as high winds, changes in the stage of water, changes 

 in the quality of the water, and changes in temperature. What may be 



