On the Food of Young Fishes. 83 
quently, important as is the supply of food fishes for the 
predaceous species, it is not less important that the pre- 
daceous species should be supplied to eat up the food. 
Here, as elsewhere, only harm can come from an imper- 
fect balance of the forces of organic nature, whether the 
excess be upon one side or the other. 
In the effort to increase the valuable fishes of a lake or 
stream, it is not sufficient that the food of these species 
should he increased alone, hut at the same time special 
measures must he taken to secure a corresponding multi- 
plication of the predaceous fishes themselves, otherwise 
precisely the reverse result may he produced from that 
intended. 
As a further illustration of some of the practical bear- 
ings of these facts, it may be noticed that the free access 
of fishes to the ponds, lakes and marshes connected with 
a sream is a matter of the highest importance. Eunning 
water is relatively destitute of Entomostraca, and hence 
fishes denied access while breeding to slow or stagnant 
water in which Entomostraca abound, have no chance to 
multiply. The condition of fish life in the lower Fox E. 
will illustrate this point. This stream takes its rise in the 
numerous lakes of northwestern Illinois and southern 
Wisconsin, but in its lower course has few branches and 
no stagnant waters draining into it. Its own current is 
swift and much of its bed is rocky, while the vast expanse 
of water of which it forms the outlet prevents any great 
oscillations of its level with the consequent flooding of 
adjacent lands. This part of the stream is therefore 
peculiarly unfit for breeding purposes, and we should ex- 
pect few fish to maintain themselves in it if denied access 
to the immense and teeming breeding grounds of the up- 
per part of the river. Such access is effectually cut off 
by several dams, unprovided with fishways, which have 
been thrown across the stream. A fish which enters the 
river from above therefore cannot get back to breed — a 
fact which must unfavorably affect the number of fishes 
in both river and lakes, and is apparently one cause of 
an unusual scarcity of game fishes in that stream. 
