and earlier, 1,000 lbs of northern pike were caught at a time at Havana 

 (Forbes and Richardson, 1908). 



Pike are sight predators and often lie in ambush for prey in weed 

 beds in clear, shallow water. They spawn in marshes and backwaters 

 where the water is clear and there is abundant aquatic and flooded ter- 

 restrial vegetation. The decline in northern pike populations is prob- 

 ably attributable to increasing turbidity and to loss of suitable habitat 

 due to leveeing and siltation. The sporadic abundance of young northerns 

 in 1973 is attributable to favorable high-water conditions in 1972 and 

 1973. 

 Goldfish (Carassius auratus) and goldfish x carp hybrids 



Goldfish were probably introduced to the Illinois River between 

 1908 and 1935 because Forbes and Richardson did not mention them in The 

 Fishes of Illinois (1908) and O'Donnell (1935) mentioned that they oc- 

 cur infrequently in the Illinois River. O'Donnell (1935) also mentioned 

 that two carp x goldfish hybrids were taken at Peoria. 



Goldfish were abundant in the electrof ishing collections from the 

 polluted Upper Illinois River and the Des Plaines River (Table 10) . In 

 1962 for example, 101 goldfish were taken in 30 minutes of electrof ishing 

 in the Des Plaines. 



Goldfish are more tolerant of low oxygen concentrations than many 

 native species, and appear to thrive where populations of native species 

 are sparse or absent. Goldfish are sometimes used as bait, so it is pos- 

 sible that native predators reduce goldfish populations in relatively un- 

 polluted areas. It is also possible that goldfish do not compete well 

 with native species of similar ecological habits in unpolluted areas, 

 but thrive in polluted environments where there is absence of competi- 

 tion. 



If one uses goldfish as a pollution indicator and judges the quality 

 of the Upper Illinois by the catch of goldfish, then the low goldfish 

 catches in 1973 and 1974 in the Marseilles and Starved Rock pools indi- 

 cate that conditions improved during, and following, a high-water peri- 

 od. However, conditions in the Des Plaines River did not improve to an 

 extent that there was a marked reduction in goldfish. 



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