Food Relations of Fresh-Water Fishes. 487 



Asellus, or water wood louse, was less generally eaten ; by only 

 two of the miller's thumb, a single sheepshead, a white bass, 

 four perch, two young black bass, eight sunfishes (Lepomis), 

 two pirate perch, a grass pickerel, three small catfishes, and 

 a dog-fish. 



The minute crustaceans commonly grouped as Entomos- 

 traca are a much more important element. Among full- 

 grown fishes, I find them especially important in the shovel 

 fish, where they made one third the food of the speci- 

 mens studied, in the common lake herring, 1 in the brook 

 silversides (forty per cent.), in the stickleback (thirty per 

 cent.), in the darter family (eleven per cent.), and in the 

 mud minnows (ten per cent.). The perch had taken scarcely 

 a trace of them. Among the sunfishes at large they were 

 present in only insignificant ratio; but two genera (Pomoxys 

 and Centrarchus), distinguished by long and numerous rakers 

 on the anterior gill, had derived about one tenth of their food 

 from these minute crustaceans. In the early spring especially, 

 when the backwaters of the streams are filled with Entomos- 

 traca, the stomachs of these fishes are often distended with the 

 commonest forms of Cladocera. 



Notemigonus and Notropis among the minnows, repre- 

 sented in my collections by one hundred and twenty-five and 

 one hundred specimens respectively, had obtained about a sixth 

 of their food from Entomostraca. 



Ten per cent, of the food of the sucker family consisted of 

 them, mostly taken by the deep-bodied species Carpiodes and 

 Ictiobus, in which they made a fourth or a fifth of the entire 

 food. This fact is explained, it will be remembered, by the 

 relatively long, slender, and numerous gill-rakers of these fishes. 

 Large river-buffalo were occasionally crammed with the smal- 

 lest of these Entomostraca, the minute Canthocamptus, only 

 a twenty-fifth of an inch in length. 



I have several times remarked the peculiar importance of 

 Entomostraca to the shovel fish, one of the largest of our 

 fresh-water animals, a fact accounted for by the remark- 

 able branchial strainer of this species, probably the most 

 efficient apparatus of its kind known to the ichthyologist. Here, 



^oregonus artedi. 



