82 
On the Food of Young Fishes. 
for without them all our waters would be virtually depop- 
ulated. Other facts of eminent interest thus brought to 
view are the magnitude and intensity of the competition 
for food among the young of all orders of fishes, where a 
stream is fully stocked, and the injurious character of 
such a species as the shovel-fish, which feeds on Ento- 
mostraca throughout its life. It is probable that all fishes 
which are not especially adapted to the food require- 
ments of the more valuable fishes, are hurtful to them, be- 
cause they limit the food available for the young. The 
sunfishes, whose shape protects them from many ene- 
mies, and the catfishes, with their armor of poisoned 
spines, are instances in point. While their young compete 
with the young bass and wall-eyed pike for food, they do 
not furnish the latter any important food resource in 
later years. On the other hand, such species as the her 
hivorous minnows and the cylindrical suckers, which de- 
pend upon Entomostraca to a less extent when young, or 
take up other food at a relatively early period, are those 
which seem to promise best as food for the higher fishes. 
It is a curious corollary from the above reasoning that 
a prolific species having an abundant food supply, and it- 
self the most important food of predaceous fishes, may, 
by extraordinary multiplication, so diminish the food of 
the young of the latter as to cause, through its own abun- 
dance, a serious diminution of the numbers of the very 
species which prey upon it. To put this statement into 
more concrete form, it is not certain that the excessive in- 
crease of the gizzard-shad, for instance, would be a bene- 
fit to the black bass and pike-perch which feed so largely 
upon it. In fact, it is clear that the great overstocking of 
a stream with gizzard-shad would, by eventually reducing 
the supply of Entomostraca, cause a corresponding re- 
duction in the numbers of all the species of that stream 
by starvation of the young; and this decimation, apply- 
ing to all in the same ratio, would take effect upon the 
ordinary number of the other species, but upon the extra- 
ordinary number of the gizzard-shad— -would reduce the 
other species below the usual limit, but might not even 
cut off the excess of the shad above that limit. Conse- 
