43 



the pike-perch eats, during the year, on an average, at this rate 

 per week for forty weeks, giving us a total per annum of six 

 hundred gizzard shad destroyed by one pike-perch. We cannot 

 reckon the average hfe of a pike-perch at less than three years, 

 and it is probably nearer five. The smallest estimate we can 

 reasonably make of the food of each pike-perch would therefore 

 be somewhere between eighteen hundred and three thousand 

 fishes like the gizzard shad. A hundred pike-perch, such as 

 should be taken each year along a few miles of a river like the 

 lUinois, would therefore require from one hundred and eighty 

 thousand to three hundred thousand fishes for their food- 

 Finally, when we take into account the fact that a number of 

 other species also prey upon the gizzard shad, and that the 

 whole number destroyed in all ways must not exceed the mere 

 surplus reproduced — otherwise the species would soon be extin- 

 guished — we can form an approximate idea of the multitudes 

 in which the food species must abound if we would support 

 any great number of predaceous fishes. The gizzard shad, 

 being a mud-eater and a vegetarian, taking little animal food 

 except when very young, can probably be more readily 

 maintained in large numbers in our muddy streams than any 

 other fish. 



The two species of black bass differ, according to my obser- 

 vations, in the character of their food, the large-mouthed 

 species eating more fishes, and the small-mouthed more cray- 

 fishes. Here, also, the gizzard shad made more than half the 

 food. 



The common sunfishes are readily divisible into four groups, 

 based on their feeding structures and their food ; one charac- 

 terized especially by the wide mouth, including the black 

 warrior and the blue-cheeked sunfish, took a noticeable amount 

 of fishes, the ratio varying from a third to a half, the remainder 

 of the food being chiefly insects, crayfishes, and smaller crus- 

 taceans. Those with small mouths, pointed teeth in the 

 throat, and short gill-rakers, like the most abundant of the 

 river species, took scarcely any fishes, but fed chiefly on 

 insects and crustaceans, the latter principally the forms of 

 medium size (amphipods and isopods). Some of this group 



