154 College of Forestry 
eaters; 2, crustacean eaters; 3, molluscan eaters; 4, fish 
eaters, and 5, plant and mud eaters. Of these the first and 
second are the most important, providing food for many 
young and for a majority of the adult fishes. The ratios of 
these five varieties of food as used by adult fish may be 
expressed as follows (the data is principally from Forbes, 
1888, b): 
eI S CCK OROWESE (ON si, Heian bc cedinid sci 40 per cent (p. 482) 
PEA@nUStacea uw... ee te. Levy ie mel ke 14 per cent (p. 486) 
BS eeMOMUSCAM wre raylece «ove rocbd elo ae «ie 6 per cent (estimated) 
ARBISIU Me snk iafe coer s, aay ane roe 20 per cent (estimated) 
5. Miscellaneous (mud, plants, ete.y.. 20 per cent (estimated) 
Mollusk-Eating Fish. 
As has already been stated, the Mollusca form about six 
per cent. of the total food of our fresh water fishes and up- 
wards of 24 per cent. of mollusk-eating fishes. The propor- 
tion of this element of food varies greatly in different species 
of fish. A few species, as the Sheepshead (A plodinotus grun- 
niens ) subsist almost entirely upon mollusks when adult, while 
others, as the Gizzard Shad (Dorosoma cepedianum) eat only 
an occasional mollusk. Many fish eat no mollusks. The food 
supply also varies greatly with age, some species, as the 
Sheepshead noted above, passing through three stages; begin- 
ning with the plankton when very young, it changes to an 
insect eater when a few inches in length, and as it attains 
adult size it becomes a mollusk eater, the jaws developing a 
powerful crushing apparatus which is able to crush the 
heaviest shells of the clams and snails upon which it feeds. 
The Perch (Perca flavescens) is a good example of this food 
variation passing through three distinct food eating stages, as 
noted in the table below. 
