BRIEF NOTES ON FISHES. 421 



The sixteen species of fishes that have been so briefly 

 referred to in the preceding pages are worthy of much 

 study, but collectively, rather than with a view of deter- 

 mining just in what particulars they differ among them- 

 selves. As a group, they are of much importance in the 

 economy of nature, as must necessarily be the case where 

 any animal exists in vast numbers in comparatively 

 crowded quarters. 



During the past few summers I have studied these 

 fishes as a group, in the hope of discovering the influence 

 they exerted upon the general fauna of the locality, and 

 have reached the conclusion that the part that cyprinoids 

 play is mainly that of a check upon the undue increase 

 of lower forms of aquatic animal life. In consequence of 

 their vast numbers, they prevent the fouling of much 

 water that would otherwise become offensive, and yet do 

 not, of themselves, contaminate the water, however nu- 

 merous they may be. 



Cyprinoids, as a class, are carnivorous, or more prop- 

 erly omnivorous ; and although with weak, toothless 

 jaws, the arming of their pharyngeal bones with power- 

 ful cutting and crushing teeth enables them to feed 

 upon animal substances as readily as do the predatory 

 species of fish. I judge that the great bulk of their 

 food is the minute animal life that teems in all water, 

 and also the small mollusca, of which they devour 

 enormous quantities. The result of rny studies of such 

 of these fishes as I have kept in aquaria is, that young 

 mollusca are the favorite food of cyprinoids, for I found 

 it very difficult to so plentifully supply them as to sur- 

 feit the fish to which they were offered. It is in this 

 way, I believe, that the cyprinoids aid materially in 

 keeping our streams in that condition which we call 

 " pure." 



