23] STUDY OF SOUTHERN WISCONSIN FISHES— CAHN 23 



Rapids or rock-bottoms: In this group one finds those species which 

 are found commonly associated with swiftly flowing water which, in 

 the region under discussion, is normally over a rock bottom. These fish 

 have a common ability to maintain themselves in the swiftly flowing water, 

 and agree in an ecological sense in at least two factors: 1) a thigmotactic 

 reaction to large objects; and 2) a positive rheotaxis. Among the most 

 typical fishes are the darters, the miller's thumb, the stonecat and the 

 hog-nosed sucker. 



Sand or gravel-bottoms: Normally a habitat of less swiftly flowing 

 water and a bottom of finer material than the preceding. This is the 

 habitat which comprises most of the rapid water streams of the region. 

 It is for the most part without heavy vegetation, though islands of Potamo- 

 geton and other aquatic plants intrude and afford regions of very temporary 

 shelter to the fish of the open waters. Here one finds the chubs, shiners, 

 various species of darters and stone rollers as typical species. 



Silt or sluggish- waters: These are the waters found commonly in 

 regions where the streams traverse swampy lowlands. The banks are 

 usually steep, the bottom offering very uncertain footing to one who would 

 seine. The current is slow and sluggish, the water often a dark color 

 both because of the organic matter in solution and because of the black 

 silty nature of the stream bed. The non-vegetated areas are in this condi- 

 tion because of the lack of solid bottom for the insertion of the roots of 

 aquatic plants, and the shifting nature of the bottom material. Such 

 habitats ordinarily have fairly deep water, and are inhabited by carp, 

 suckers, pickerel and a few darters. The vegetated associations are of a 

 similar structure but with a bottom hard enough to afford footing for 

 Potamogetons, Elodea and various other aquatic plants, including masses 

 of filamentous green algae. 



Open waters: The deep water habitats of the lake, and including 

 everything from the surface over deep water to the bottom. These are the 

 least populated habitats of the lake; the fish are mostly suckers and ciscos 

 on the bottom, and silversides and gar on the surface, with a large zone 

 between which is for the most part uninhabited by fishes or at best receives 

 but a transient population. The lower regions of this habitat are rendered 

 uninhabitable during the summer by the formation of the thermocline. 



Eroding rock-shores: For the most part shallow water habitats, which 

 are characterized by the eroding action of the waves. These are rough of 

 bottom, and afford certain ecological affinities with the rocky-bottom 

 communities of the streams and rivers. Vegetation is practically lacking, 

 due to the character of the bottom and the action of the waves. It is the 

 home of various darters, minnows of many species and the young of 

 several species of the Centrarchidae. 



