Mar., 1920] Food and Fish Associates of Young Perch 147 



5. Diet of the Perch. 



In the present study the articles of diet found are classified 

 as follows : 



The proportion which each article of diet forms of the 

 whole, the length of each fish examined and the number of 

 each length have been set down in the accompanying table while 

 the quantitative variation of the principal items of diet is shown 

 in graphic form. Algas, plant remains, the different worms,, 

 ostrocods, isopods, adult insects, mites, fish eggs, fish remains, 

 and inorganic debris are purposely excluded from the graph 

 because they form such a small proportion of the entire diet. 



Specimens of 26 and 27 millimeters in length are found to 

 have eaten copepods only but the pure diet is soon given up 

 for one composed almost wholly of copepods but with a slight 

 admixture of cladocera and minute chironomid larvas. May 

 fly larvce are soon added and an occasional adult insect. From 

 30 to 40 millimeters, cladocera become increasingly important 

 while copepods drop below fifty per cent of the total. Medium 

 sized Crustacea are first taken at this stage and form a small but 

 rather consistent article of food. Insect larvae, other than 

 chironomids and may files are also taken at this time and 

 together with the may files and chironomids constitute the 

 chief food up to a length of 120 millimeters. The larger snails 

 and crayfish are not used till the fish has reached a length of 

 about 100 millimeters although some smaller snails are eaten 

 earlier. 



Forbes (1880,2) reports the food of the adult perch to consist 

 of crayfish and fish in the larger specimens and of fish, crayfish, 

 molluscs, amphipods, isopods, and insect larvas in the others. 



