AQUATIC PLANTS AND FOOD FISHES 



2 5i 



HOW BOOTING AQUATIC PLANTS INFLUENCE THE 



NUTEITION OF THE FOOD FISHES OF 



OUR GREAT LAKES 



By Professor RAYMOND H. POND 



NORTHWESTERN UNIVERSITY 



A THOROUGH investigation of the biology of our great lakes is 

 in itself a desideratum worthy the expense. From the purely 

 economic standpoint, however, our Bureau of Fisheries has long recog- 

 nized the necessity of knowing more of those conditions under which 

 products worth millions annually are produced. Until such an investi- 

 gation has been made the natural factors which determine the quantity 

 of food fishes these lakes can support must remain unknown. 



Fig. 1. Vallisneria spiralis after 7 weeks' growth rooted in lake soil. Plants in figures 1 



and 2 originally the same size. 



Fish, as all other living forms, reproduce in a geometrical ratio 

 and, other conditions being favorable, will multiply up to the limit of 

 their food supply. Thus it is that the problem of nutrition is very 

 fundamental. To determine the source of nutrition of our fresh-water 

 food fishes is in itself a considerable undertaking, but to ascertain what 

 factors regulate the quantity of this nutrition is a colossal task. 



The nutrient relations of aquatic life are perhaps no more compli- 

 cated than those of terrestrial, but they certainly are more difficult to 

 determine because of the numerous obstacles to observation and col- 



