BREEDING BEHAVIOR OF SUCKERS AND MINNOWS. 29 



CONCLUSIONS. 



The breeding behavior of three species of suckers has been 

 studied, the white sucker (Catostomus commersonii), the red- 

 horse (Moxostoma aureoleum), and the hogsucker (Catostmits 

 nigricans). All three make use of similar breeding grounds, the 

 upper parts of rapids, where the water is moderately swift and 

 the bottom gravel and sand. They differ in that some of the 

 streams in which the white sucker breeds are smaller than any 

 frequented by the other two species. 



It is possible to discriminate the sexes of all three species on 

 the breeding grounds either by differences in coloration, size of 

 body and fins, pearl organs, behavior, or by some combination 

 of these characters. In all three species the males are seen to 

 congregate on the rapids while the females linger in the neighbor- 

 hood and enter the rapids at intervals, usually singly, sometimes 

 two or three at once. When a female has come to the rapid 

 she is at once pursued by as many males as happen to be near. 

 She flees, stops, flees as the males again approach, and so con- 

 tinues for some time alternately fleeing and stopping. Sooner 

 or later she comes to rest on the bottom and permits the males 

 to approach. When these have come to her, in the case of the 

 white sucker and the red-horse, two of them pair with her at one 

 time, one on either side. The fins of the males are without con- 

 spicuous colors or patterns. Nevertheless during pairing and 

 just before it the males spread their fins after the manner of 

 fish which thereby display conspicuous colors or markings. The 

 display movement occurs, although there is nothing to display. 

 Supernumerary males may approach and by crowding those 

 attempting to pair may interrupt the pairing act. In the hog- 

 sucker six or eight males may pair with the female at one time. 

 All appear to take an equal part so that no supernumerary males 

 can be distinguished. 



In all three species pearl organs occur on the male and in the 

 hogsucker effective organs occur also on the female. The largest 

 and most effective organs on the fins of the male occur on those 

 fins that exceed the corresponding fins of the female by the 

 greatest percentage of length. In all three species the pairing 

 attitudes are such as to bring into contact with the female those 



