306 ANIMALS IN INLAND WATERS 



level in the Swiss Alps, and the miller's thumb, Cottus gobio, which 

 is found even at a height of 2300 m. Next to this region upstream is the 

 barbel region with deep, moderately warm, swiftly running water 

 which is not entirely clear, and which has a partly soft and partly 

 gravelly substratum. The extremely flattened fishes are wanting; 

 moderately compressed forms like the roach still occur; the charac- 

 teristic fish, the barbel, Barbus fluviatilis, has a rounded body. A 

 limited number of stenothermal forms also occur, such as minnows of 

 the genus Leuciscus. Graylings are found here, which are absent in the 

 carp region. The grayling region usually forms the transition to the 

 uppermost or trout region, but it may be absent. This includes larger 



Fig. 82. — Cross sections of fishes of swift streams (upper) compared with those 

 of standing waters. Left to right, upper: trout, Salmo fario; European minnow, 

 Phoxinus; roach, Misgumus; miller's thumb, Cottus; lower, bream, Abramis; 

 crucian carp, Carassius; carp, Cyprinus carpio; bitterling, Rhodeus; red-eye, 

 Scardinius. After Bloch. 



creeks and middle-sized rivers, with rapidly moving water, as a rule, 

 deep, moderately warm, with sandy or partly soft substratum. Besides 

 grayling a number of fish from both neighboring regions occur here. 

 The trout region, finally, includes brooks and smaller rivers with 

 rocky and coarsely graveled bottoms, and clear, cool water with 

 stronger currents. All the fishes of this region have rounded bodies 

 (Fig. 82, a-d) . The characteristic form is the trout, Salmo fario. With 

 an increased fall the number of accompanying fish decreases more and 

 more; those going farthest up are the minnow, Phoxinus laevis, the 

 roach, Cobitis barbatula, and the miller's thumb. Though the species 

 differ, there is an essentially similar distribution of fishes in the Chi- 

 cago region. 8 



The boundaries of these regions naturally are nowhere sharply 

 defined; their order may even be changed according to the topography 

 of the bottom, and a creek may be typically a trout region in the 



