22 



ILLINOIS BIOLOGICAL MONOGRAPHS 



[22 



The work of Shelford (1923), Powers (1921), Wells (1915), and others 

 has indicated that the H-ion concentration plays an important role in the 

 distribution and behavior of fishes. That this is true has been demonstrated 

 by the writer both in the laboratory and in the field, and will be discussed 

 in considerable detail in the subsequent sections of this paper, and in later 

 papers dealing with the life histories of the different fishes. 



ECOLOGICAL HABITATS OF FISHES 



It is well to glance for a moment at the various aquatic habitats existing 

 within the area. For this purpose one can divide the fresh water environ- 

 ments as follows: 



I. Rivers and streams. 



1. Rapids or rock-bottoms. 



2. Sand or gravel-bottoms. 



3. Silt, or sluggish-streams. 



a. Bare bottom. 



b. Vegetation. 



II. Lakes. 



1. Open water. 



2. Eroding rocky-shores. 



3. Depositing sandy-shores. 



4. Vegetation. 



a. Submerged vegetation. 



b. Emerging vegetation. 



