83] STUDY OF SOUTHERN WISCONSIN FISHES— CAHN 83 



Entomostraca: 



Cyclops 14.5% 



Daphnia 16.8% 



Bosmina 35.7% 



Other species 5.0% 



Rotifera: 



Anuraea 16.6% 



Diatomes, Algae etc 8.4% 



Unidentified 3.0% 



100.0% 



An examination of 250 stomachs of immature individuals taken August 12, 

 at night, while inshore, gives the following results: 



Entomostraca: 



Copepoda 5 . 5% 



Cladocera 10.8% 



Ostracoda 1.2% 



Mysis relicta 10.3% 



Plant remains 9 . 5% 



Insecta: 



Diptera 35.2% 



Coleoptera 9.0% 



Larvae 22.4% 



Unidentified 3.2% 



Arachnida 1.9% 



100.0% 



A comparison between these two tables will show very clearly that a great 

 change accompanies the initiation of the migratory habits of the species, 

 resulting in a much more varied diet when the fish enter the shallow waters. 

 A third series of stomach examinations, consisting of 45 stomachs of adults 

 taken on the night of August 14, gives the following tabulation: 



Entomostraca: 



Ostracoda 0.5% 



Copepoda 4.7% 



Cladocera 12.5% 



Plant remains 1-4% 



Insecta: 



Chironomus larvae 58 . 5% 



Diptera, adult 21.5% 



Miscellaneous 3.6% 



100.0% 



Thus there appears a transition from the micro-organism diet to a predomi- 

 nantly insectivorous diet, and this change in the food habits accompanies 

 the change in environment selection. However, since entomostraca are 



