UTILIZATION OF THE EXOTIC CLADOCERAN, DAPHNIA LUMHOLTZI, BY YOUNG-OF-YEAR FISH 
WITHIN AN ILLINOS RIVER FLOODPLAIN LAKE

A. Maria Lemke, James A. Stoeckel, Amy E. George, Mark A. Pegg
Illinois Natural History Survey, Illinois River Biological Station, Havana, IL  
62644

Lake Chautauqua is a floodplain lake on the Illinois River managed by the U.S. 
Fish and Wildlife Service for migrating waterfowl and shorebirds.  Researchers 
at the Illinois River Biological Station have conducted a long-term study since 
1996 designed to assess the suitability of Lake Chautauqua as habitat for larval 
fish production.  One component of this study is the analysis of young-of-year 
(YOY) fish diet composition in relation to zooplankton prey availability.

A particular aspect of the diet composition study focused on the utilization of 
the non-native cladoceran, Daphnia lumholtzi, as a food resource by YOY fish.  
Previous reports from Lake Chautauqua have shown that native Daphnia species 
typically attain maximum abundances during late spring and are replaced by D. 
lumholtzi during early to mid summer.  High abundances of D. lumholtzi during 
late summer increase their potential importance to zooplanktivorous fish; 
however, the large spines produced by this cladoceran may preclude its value as 
forage for certain YOY fish species or size classes.  Our objective was to 
quantify the relative importance of D. lumholtzi as a food resource to various 
larval and juvenile fish species in Lake Chautauqua.  

Diet compositions were analyzed for YOY fish species collected from escapement 
sampling during late summer of 2000 and 2001.  Daphnia lumholtzi were consumed 
by bluegill juveniles 8-50 mm in size, but comprised the largest proportion of 
diet items for bluegill 21-40 mm (20-30%, 2001) and 41-63 mm (47%, 2000).  
Similarly, D. lumholtzi comprised 23-34% of the items consumed by white bass 31-
60 mm (2001) and 60-140 mm (2000).  Daphnia lumholtzi were consumed by white and 
black crappie juveniles 9-70 mm in size (2-40% of diet), but were utilized 
primarily by juveniles 50-70 mm (22-40% of diet).  Several additional species 
utilized D. lumholtzi (e.g., largemouth bass, emerald shiner), however data for 
these species were not consistent between years. 

Our results indicate D. lumholtzi are an important food resource for juvenile 
fish, especially white bass, bluegill, and crappie, during late summer periods 
when native zooplankton abundances are lowest in Lake Chautauqua.