Trautman (1957) reported that hybrids might be expected wherever 

 carp and goldfish occur together, and that in some areas in and near 

 Lake Erie the number of hybrids exceeds the number of both parent 

 species. In the Illinois electrof ishing collections, goldfish were 

 most abundant in the Dresden Pool, carp in LaGrange Pool, and carp x 

 goldfish hybrids in Starved Rock Pool and Peoria Pool (Tables 10, 11, 

 and 12). 



Virtually all the goldfish and carp x goldfish hybrids taken in 

 the Des Plaines River had one or both eyes protruding, a condition re- 

 ferred to as "popeye" by fishermen. In the course of weighing and 

 measuring these fish, some of the eyes would fall out. Some individuals 

 had evidently survived a considerable time after losing one or both 

 eyes, because the empty sockets had filled with scar tissue. The cause 

 of this popeye disease is not known, although the disease appears to be 

 associated with polluted water in the Upper Illinois River. The in- 

 cidence of popeye disease decreases in the downstream direction, away 

 from Chicago. 

 Carp (Cyprinus carpio) 



Carp and gizzard shad were the only species that occurred abun- 

 dantly in the electrof ishing collections in all pools of the river. 

 Carp were introduced into the Illinois River in 1885. By 1898, carp 

 brought more money to commercial fishermen along the Illinois River than 

 all other fishes combined. The carp catch was 6 to 8 million pounds per 

 year and was worth more than $200,000 (Forbes and Richardson 1908). In 

 1908 the catch was over 15 million pounds, according to Thompson (1928). 

 At present, carp and bigmouth buffalo comprise the bulk of the commer- 

 cial catch in the Illinois River, although carp have decreased from 

 4,041,000 lbs in 1950 to 213,000 in 1973. Mills, et al., (1966) dis- 

 cussed the decline in the carp catch: 



"Much of the decline in the commercial catch since 1950 has 

 resulted from the scarcity of carp of commercial size 

 (17 inches or more in total length) in the middle section 

 of the river. Small carp are often abundant in this section 

 but most of them disappear before attaining commercial size. 



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