Turner and Kraats. — Food of Large-Mouth Bass 375 



This arrangement of the various articles of diet of the 

 fishes examined, brings to Hght some interesting facts as to 

 changes in food. For convenience the six chief articles are 

 shown in the graph, the figures and spaces running upright in- 

 dicating the percentage of the whole which each article forms, 

 and those running crosswise, the length of the fishes in which 

 each was found. 



First : The food of the very young specimens consists of 

 few forms and these are all minute. The Cladocera are 

 mainly Bosmina longirostris and Chydorus sphaericus, and 

 the Copepoda nearly all are species of cyclops. The midge 

 larvae are fairly abundant, but are very minute, the average 

 length being 1.97 mm. in the 10-15 mm. fish. 



Second : The food of the intermediate forms becomes more 

 complex. There is a distinct decline in the number of Clado- 

 cera, Copepoda and midge larvas, while the Amphipoda, of 

 which there are only a few very minute ones in the small fish, 

 become more important, forming 45 per cent of the total food 

 mass in fish of 35-40 mm. in length. There is also the intro- 

 duction of insect larvae and nymphs, such as those of may- 

 flies, damselflies, beetles and Corixa, and also of fish remains. 



Third : The larger forms have a relatively simple diet 

 again, in which larger insect larvae, fishes and crayfish become 

 more important. Rarely a larger fish is taken in which the 

 Entomostraca, Amphipoda and very small insect larvae con- 

 stitute a considerable part of the stomach contents; but the 

 tendency, as shown by the graph, is for the Entomostraca, 

 Amphipoda and midge larvae to disappear almost entirely. 



The question arises at once as to the reason for these defi- 

 nite changes in diet, and several solutions suggest themselves. 

 It is possible that part of the change may be accounted for 

 in the cycles of organisms that develop within the habitat 

 of the young bass. If this were the case, however, we should 

 expect a correlation between the appearance of an organism in 

 the habitat and its use as food. But in the case of Corixa, 

 for instance, one rather small species was found abundantly 



