28o BULLETIN OF THE BUREAU OF FISHERIES, 



Adult Hemiptera — Ephemerida nymphs 2 



Cladocera — Copepoda i 



Cladocera — Adult Diptera i 



Cladocera — silt and debris i 



Diptera larvae — crayfishes i 



Diptera larvse — fish eggs i 



Fish — Odonata nymphs i 



Fish — frogs r 



Fish — Ephemerida nymphs i 



Amphipoda — Ephemerida nymphs i 



Amphipoda — Cladocera i 



Gastropoda — plant remains i 



Diptera pupae — silt and debris i 



Ephemerida nymphs — Oligochaeta i 



Both these comparisons give further support to the statements made under sec- 

 tion III, showing that different kinds of fishes have specific preferences for certain foods. 

 Nine species make their chief food the larvae of dipterous insects, which are far more 

 abundant than anything else. When these eat something different from their favorite 

 food, they do not all take the same kind of food but select five to seven new things. 

 It is difficult to group fishes into large classes on the basis of similarity in food. Essen- 

 tially the same conclusions were reached by Forbes" from a study of 1,221 Illinois fishes. 



VARIATION IN FOOD OF FISHES COLLECTED IN DIFFERENT LOCALITIES AND AT 



DIFFERENT TIMES. 



In order to ascertain how much each species of fish varied in the selection of its 

 principal food at different times and in different places, a study of the data for 1915 

 presented in section II was made. The chief foods taken at the different stations were 

 summarized as far as possible. If a species took a different kind of food each time it 

 was collected, it will of course be rated as one of versatile food habits; if its chief food 

 was the same in all collections, it is considered as having a limited range of diet. The 

 results of the comparison are shown in Table 5. 



It will be noted that some species, like the rock bass, bluegill, and black bullhead, 

 are rather versatile feeders; others (Johnny darter, miller's thumb, pickerel, gar) stick 

 to one food. All the species taken together show a change in the chief food with time 

 and place in about half the collections. These estimates, however, do not consider the 

 diversity in size among the fishes examined. 



VARIATION OF FOOD AT DIFFERENT PERIODS OF THE LIFE CYCLE. 



The data collected for this paper are not complete enough to make very satisfac- 

 tory comparisons possible between young and adult fish of each species. Of the 32 

 species studied, in only 20 were enough individuals of different sizes collected so that 

 comparisons can be made. 



Eight species feed more on amphipods, insect larvae, and adult insects and less on 

 entomostracans as they increase in size. Six change from insect larvae to fishes or 

 crayfishes. Each of the following changes is characteristic of a single species of fishes: 

 Snails and amphipods to plants ; oligochaetes to molluscs ; Hyalella to fish ; insect larvae 



o Forbes, S. A.: On the food relations of fresh-water fishes: A stunmary and discussion; pp. 497-504, 1888. 



