18 College of Forestry 



has been found in any similar body of fresh-water in 

 America. Of the 92 species found in the lake, fully 50, or 

 about one-half, are known to be eaten by fish. 



The shellfish that are of the greatest value are the small 

 species that live among the vegetation or on the sandy 

 bottom, and are to the average person considered of no value 

 whatever. These include the little wheel-like Orb Snails 

 (Planorbis") which may be seen crawling over the plants 

 with their round shell carried perpendicularly on the back 

 of the animal, the little spiral snails (Amnicola) and the 

 broadly spiral shells, called Valva-ta. The young of the 

 Tadpole Snails (PJiysci) with their shiny shells, long-pointed 

 tentacles and pointed foot, and the young of the Pond Snails, 

 or Lymncca, with spiral shells and broad, flat feet, are also 

 favorite food for fish. The little clams or " finger nail " 

 shells, Sphcerium and Pisidium, are especially sought after 

 by many fish. A quarter of the food of such fish as suckers, 

 Dog-fish and Carp consists of the little bivalve shellfish 

 known as Sphcerium. The small snails and clams are shown 

 in Figure 7. 



SHELLFISH AS FOOD FOR FISH 



The examination of the stomach contents of fish has shown 

 that shellfish, snails and clams, form a large part of the food 

 of many species. Compared with their other kinds of food, 

 we find that shellfish bear an interesting relation to the com- 

 plete diet. Thus we find that on the average, fish consume 

 40 per cent of insects, 14 per cent of Crustacea (crawfish, 

 fresh-water sowbugs, scuds, fresh-water fleas, etc.), 20 per 

 cent of fish, 20 per cent of plants and mud, and 6 per cent of 

 shellfish. While the percentage of shellfish food is small for 

 the total number of fresh-water fish, it rises to large propor- 

 tions (24 per cent) when only the mollusk-eating species are 

 considered. In the different species the percentage of shell- 

 fish food ranges from 1 to 100 per cent, or from a trace to the 

 total food. 



A study of the fish of Oneida Lake, together with what 

 is already known concerning the food of our freshwater fish, 



