FRESH WATER FISHES AND THEIR ECOLOGY* 
By StepHEeN A. ForBEs 
When we watch a summer thunder storm, which covers the earth 
with a sudden flood and makes rivulets by the road-side, each carrying 
down to the smaller streams its load of leaves and other organic debris, 
together with the lighter parts of the soil, and when we see these silt- 
laden streams unite in rivers turbid with the rich spoil of the land, we 
are inclined to lament the enormous and oft-repeated waste, seeing no 
way in which it can be recovered in any considerable measure to the use 
of man; but if we follow it to the lake bottom and the river bed we shall 
see much of it arrested there, to become an aquatic soil, partly muddy 
water and partly wet mud, more fertile even than the richest fields, and 
sustaining a new population of plants and animals, of many grades and 
classes, one climbing upward, as we may say, upon the shoulders of 
another, to reach a level which makes them accessible again to our use. 
Since the waters which wash the surface of the earth fall virtually 
lifeless and sterile from the sky, whatever population they eventually 
contain must evidently be supplied from the contributions made to them 
by the earth, including, of course, the organic and inorganic substances 
dissolved out of the earth by surface wash and underground filtration. 
The aquatic population of a lake or stream is thus sustained by the wastes 
of the land—materials which would otherwise be carried down prac- 
tically unaltered to the sea; and our rivers and lakes may be looked upon 
as a huge apparatus for the arrest, appropriation, digestion, and assimila- 
tion of certain raw materials about to pass from our control, valueless 
and sometimes deleterious as they leave us, but capable of being worked 
over, renovated, and returned to us in new and valuable forms, mainly 
as fishes available for food. 
The raw materials thus contributed by the land vary according to 
their origin. In uncivilized nature they were mainly the washings and 
sweepings of the primitive prairie and forest, rich in carbon but with a 
minimum amount of nitrogen. With the occupation of the country, the 
cultivation of its lands, and the building of towns and cities, the animal 
wastes are increased, with their larger increment of nitrogen, and larger 
quantities of the soil itself are swept into the streams—all alike available 
* Read at the University of Chicago, August 20, 1913. 
