32 ILLINOIS BIOLOGICAL MONOGRAPHS [32 



the fish behaving in normal minnow fashion. They are bottom feeders, 

 taking in much silt from which the plankton organisms are strained and 

 retained as food. Diatoms, algae, Sphaerium, small bivalves, Physa and 

 Planorbis, insect larvae and an occasional insect form the chief items of 

 food, the vegetable matter dominating to the extent of about 70%. 

 Of no value as a food fish because of its small size. 



17. Catostomus commersonii (Lacepede). Common Sucker. 



A common sucker in the Oconomowoc, Ashippun, Bark, Muckwonago 

 and Menomonee river systems, being almost wholly confined to these 

 streams. In the rivers the fish attain a length of from 10 to 12 inches, 

 rarely more, but I have taken specimens 13 and 15 inches long from 

 Oconomowoc lake. Those individuals which inhabit the lakes of these 

 river systems often ascend the streams soon after the ice goes out in the 

 spring, and spawn on the riffles, usually about the middle of April. The 

 young remain for the most part in the rivers, going down to the lakes only 

 when they are nearly fully grown. That some of the fish spawn in the 

 lakes is indicated by the presence of young fry taken in minnow nets along 

 the shores of Oconomowoc, Silver, Golden, Keesus, Pine and La Belle 

 lakes. The chief economic value lies in their being used as food for bass, 

 pickerel and other valuable food fish. 



18. Hypentelium nigricans (Le Sueur). Hognosed Sucker; Stone-roller. 

 This sucker is confined strictly to the rivers, and I have no lake records 



for the species. The Bark river contains the greatest numbers of these 

 interesting fish, and I have taken them in the Oconomowoc river as well. 

 They show a preference to swiftly flowing water, avoiding those reaches of 

 the river where silty bottom or deep water slows up the current. Like the 

 darters they come to rest heading upstream, the large pectoral fins acting 

 as a brace against the current. Very fast of movement, when disturbed 

 they dart off at great speed, but only for a very short distance, while the 

 dark mottled coloration of the back acts as a protection, rendering the 

 fish almost invisible against the mottled river bottom. The food consists 

 almost entirely of animal matter, largely insects and larvae, with only a 

 small proportion (6%) of mollusca, and 12% of vegetable material. Of no 

 economic value. 



19. Moxostoma aureolum (Le Sueur). Common Red-horse. 



A very common sucker of the Rock river, the red-horse is found in all 

 streams tributary to the rock, and only as far as dams prevent their distri- 

 bution. Thus they are found abundantly in the spring in the Oconomowoc 

 river as far as the Lac La Belle dam, where many are speared every year. 

 The Ashippun river and the Bark river, together with the Scuppernong 

 river also contain red-horse and the fish are caught in some numbers from 

 all of these streams. They are used as food by many, but during the summer 

 (August) when they can be caught on hook and line, the meat is soft and 



