However, the long point is easily and commonly broken or eroded, so that 

 positive identification is difficult. Also, young fish (less than 3 in. 

 long) of both species resemble each other. Therefore, carpsuckers with- 

 out high dorsal fins were divided into two classes: quillback carp- 

 suckers and Carpiodes spp . Most of the fish in the latter group were 

 probably river carpsuckers. Carpsuckers with dentary nipples and high 

 dorsal fins were identified as highfin carpsuckers. 



The three species of the genus Carpoides were all found in the 

 Illinois River (Tables 13 and 14) . Most of the fish in the Carpiodes 

 spp. group were taken from the three lower pools of the river, Alton, 

 LaGrange, and Peoria, prior to 1973. For 1973 and 1974 combined, most 

 were taken in Starved Rock Pool, so their distribution in the river may 

 have changed after the high-water period of 1971-1973. 



Carpiodes spp. populations do not appear to have changed greatly 

 since 1908. Forbes and Richardson (1908) reported that Carpiodes 

 carpio were found mainly in the Illinois and Mississippi Rivers and 

 were not anywhere abundant. At that time, most of the river carp- 

 suckers from the Illinois River were taken at Havana and Meredosia, in 

 what today are the LaGrange and Alton pools. 



River carpsucker (Carpiodes carpio) . River carpsuckers feed on 

 diatoms, desmids, filamentous algae, rotifers, microcrustaceans, and 

 midge larvae (Bucholz, 1957), so they were not noticeably affected by 

 the die-off of fingernail clams and rooted aquatic vegetation which oc- 

 curred in the middle section of the Illinois River in the mid-1950 's. 



Quillback carpsucker (Carpiodes cyprinus) . In 1957, Trautman 

 listed two species of Carpiodes, C_. cyprinus and C. forbesi , and two 

 subspecies of C_. cyprinus , the eastern quillback carpsucker (C. c_. 

 cyprinus ) and the central quillback carpsucker (C . c^. hinei) , but in- 

 dicated that environmental factors strongly influenced the morphological 

 characteristics of these fishes: 



"Central quillbacks, living in large waters of 

 relatively low turbidity having an abundance of 

 food, such as at Buckeye Lake, grow very rapid- 

 ly, are excessively fat, deep-bodied and small-eyed. 



27 



