82 The Food of Yonnq Fishes. 



traca throughout its life. It is probable that all fishes 

 which are not especially adapted to the food requirements 

 of the more valuable fishes, are hurtful to them, because 

 they limit the food available for the young. The sun- 

 fishes, whose shape protects them from many enemies, and 

 the catfishes, with their armor of poisoned spines, are in- 

 stances in point While their young compete with the 

 young bass and wall-eyed pike for food, they do not fur- 

 nish the latter any important food resource in later years. 

 On the other hand, such species as the herbivorous min- 

 nows and the cylindrical suckers, which depend upon En- 

 tomostraca 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 itself 

 the most important food of predaceous fishes, may, by ex- 

 traordinary multiplication, so diminish the food of the 

 young of the latter as to cause, through its own abundance, 

 a serious diminution of the numbers of the very species 

 which prey upon it. To j)ut this statement into more con- 

 crete form, it is not certain that the excessive increase of 

 the gizzard-shad, for instance, would be a benefit 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 sup- 

 ply of Entomostraca, cause a corresponding reduction in 

 the numbers of all the^ species of that stream by starvation 

 of the young; and this decimation, applying to all in the 

 same ratio, would take effect upon the ordinary number 

 of the other species, but upon the extraordinary number 

 of the gizzard-shad, — wovild reduce the other species below 

 the usual limit, but might not even cut off the excess of 

 the shad above that limit. Consequently, important as is 

 the supply of food fishes for the predaceous species, it is 

 not less important that the predaceous species should be 

 supplied to eat up the food. Here, as elsewhere, only 

 harm can come from an imperfect balance of the forces of 

 organic nature, whether the excess be upon one side or the 

 other. 



