and flathead catfish were taken in 1965, and the maximum numbers of blue- 

 gill, flathead catfish, white bass, and bigmouth buffalo were taken in 

 1973 or 1974. 



The list of species which benefited from high-water levels includes 

 desirable game fish, such as largemouth bass, bluegill, black crappie, 

 and white crappie, which are in the sunfish family (Centrarchidae) and 

 have similar life histories. All of these sunfishes lay their eggs in 

 nests which are constructed in shallow water. They prefer to construct 

 nests on firm, rather than muddy substrates. The fry feed first on 

 zooplankton, then largely on aquatic insects and fish. The sunfishes 

 are generally less tolerant of low dissolved oxygen levels than species 

 such as carp and black bullhead . 



Increased flow of water in the Illinois has several beneficial ef- 

 fects on fishes. Flooded areas often provide good spawning sites, with 

 firm bottoms, whereas the bottom in much of the river and its bottom- 

 land lakes is covered with flocculent mud. Several people reported that 

 sunfishes were spawning on flooded gravel roads and areas of firm mud or 

 sand in the spring of 1973. Flooded areas also provide good nursery 

 areas for juvenile fish, provided the water does not retreat too soon. 

 An increased current velocity in the river stimulates spawning migra- 

 tions of species such as white bass. An increased rate of water flow 

 (discharge) can dilute oxygen-demanding or toxic wastes. Butts, et al. 

 (1975) report that increased flows in the Upper Illinois River initially 

 result in reduced dissolved oxygen levels because combined storm and 

 sanitary sewers overflow to the river, but that during sustained high 

 flows, the oxygen levels are higher than during sustained low flows. 



Carlson and Seifert (1974) have shown that oxygen levels at 

 35 percent saturation reduce the survival of larval largemouth bass by 

 13.7 percent, and oxygen levels at 70 percent saturation and below re- 

 tard the growth of larval largemouth bass. The tolerances of the other 

 members of the sunfish family to low dissolved oxygen are probably much 

 the same. The relationships among discharge, dissolved oxygen levels, 

 and largemouth bass populations in Chillicothe Island Chute are shown 



37 



