FLATHEAD CHUB 



The stomach contents of 19 flathead chub were removed and analyzed 

 qualitatively. Food organisms were well digested. An estimated 40-50 

 percent of the volume consisted of Cladocera. The remainder included remains 

 of Corixidae, Hydropsychidae, Isogenus, and unidentified organisms. 



OTHER SPECIES 



The qualitative results of stomach analyses for miscellaneous fish species 

 is presented in table 49. Forage fish were found in the stomachs of northern 

 pike, smallmouth bass, white crappie, and walleye. The carp, white sucker, 

 and freshwater drum fed on insects and organic detritus. 



FOOD SELECTION 



The values for Ivlev's electivity index (E) were calculated for the major 

 benthic food organisms eaten by shovelnose sturgeon, goldeye, and channel 

 catfish (table 50). The shovelnose sturgeon and goldeye selected for Baetis 

 and Chironomidae, but selected against Heptagenia, Rhithrogena, and 

 Hydropsychidae. The sturgeon consumed Traverella in proportions equal to 

 its availability, while the goldeye showed preference for Traverella. 

 Traverella nymphs and adults on the water surface were preferred by channel 

 catfish over other aquatic species during the study period. Sturgeon and 

 goldeye select for insects characteristic of a riffle habitat, while catfish 

 appear to take advantage of plentiful food types in any habitat. 



TABLE 50. Ivlev's electivity index for benthic food organisms eaten by 

 shovelnose sturgeon^, goldeye, and channel catfish. 



Shovelnose 

 Food Type Sturgeon Goldeye Channel Catfish 



0.15. -0.99^' 



-0.92^ -0.85b 



-0.65° -0.83° 



0.63 0.76 



-0.78 -0.92 



0.40 -0.75 



-1.00° -0.79b 



3 Because relative abundances of insects were unknown for these months, 

 sturgeon collected in May and June were excluded. 



b Less than 1 percent of benthic food items 



^ Less than 1 percent of benthic population 



131 



