32 College of Forestry 



a large number of fish. By using Illinois and Oneida Lake 

 data, a single individual of this game fish is calculated to 

 eat from 250 to 600 small fish in a year. When we remem- 

 ber that there are hundreds of individuals of the Pike Perch, 

 as well as other predatory fish, in Oneida Lake, it is at once 

 seen that the number of small fish in this lake must be very 

 large to supply these fish with food. It also follows that a 

 large number of invertebrate animals as well as an abun- 

 dance of vegetation for these smaller animals to feed upon 

 is necessary to provide food for these small fish. It has 

 been shown by these investigations that Oneida Lake meets 

 all of these conditions favorable for fish in full measure, 

 and these provide the essentials for a large and varied 

 population of food and game fish (Fig. 15). 



Conclusions. A fresh water pond or lake has been com- 

 pared to a microcosm or miniature world. It is isolated 

 from the rest of the world and the animal life of the sur- 

 rounding country might be shut off without greatly modify- 

 ing the life of the water. This life has not reached the high 

 state of complexity that the life on the land has attained. 

 The life of the w r ater is intimately related and bound together 

 so that it is quite likely that any agency that tends to influ- 

 ence any group would sooner or later upset the balance of the 

 whole community of animals. 



It is when we come to study the natural history of a single 

 water animal that we realize how closely related this is to 

 all the other animals and to the environment in which it 

 lives. Thus if we wish to learn what we can concerning the 

 Yellow Perch we soon find it necessary to consider the other 

 animals that the Perch preys upon, as well as those which 

 prey upon the Perch. We learn that this fish feeds upon 

 insects, crustaceans, shellfish, and small fish. These animals- 

 in turn feed upon other insects, crustaceans, and plants, and 

 these in turn feed upon plants, mostly algse. The plants 

 feed upon the mineral and organic matter in the water and 

 soil. The physical environment, also, must be favorable in 

 order that the plants may find a suitable place in which to> 

 grow. And so in our study of this familiar fish we have 



