BREEDING BEHAVIOR OF SUCKERS AND MINNOWS. 



II 



organs (Parker, 1917). In many fishes the spreading of the 

 dorsal at the breeding season results in the display of a con- 

 spicuous marking or color pattern (Reeves, 1907 and citations). 

 This is true of some of the minnows to be described in later num- 

 bers of this series. // is noteworthy that in the suckers, although 

 the dorsals are unmarked, the display movement (Fig. 2) does not 

 differ from that of those fishes that have a conspicuous dorsal. 



As the male approaches the female another change becomes 

 evident. The dark stripe on his side (Fig. 4), which may have 

 become rosy a little while before, now suddenly turns to a vivid 

 scarlet and remains so during the pairing. At the same time 

 the eye becomes red and continues so while the female is present. 



The males with fully extended pectorals and erected dorsals 

 now press close against the female one on either side (Figs. 2,3). 



FIG. 3. Diagram showing the pairing of Catostomus commersonii as seen from 

 the dorsal side. Compare Fig. 2. 



The smallest males that I have seen pairing were about six 

 inches long. The two are usually of the same size and commonly 

 are a good deal smaller than the female. But they are not always 

 of the same size and one or both may be as large as the female. 

 When the males are in position (Figs. 2, 3) their adjacent 

 pectorals are spread beneath the female. Their caudal fins press 

 on either side against that of the female, but may extend for 

 some distance behind and below it, so that their distal parts 

 press against each other. Their anals are spread and extended 



