II28 



BULLETIN OF THE BUREAU OF FISHERIES. 



level of the bottom. The unfilled part of the trench — the pit in which the fish 

 are seen — lies at the lower end of the ridge. The sand washed by the current 

 from between the stones that have been moved in making the ridge collects 

 in a trail below the pit and is seen there in the figures. 



As the fish continues to work at the nest the observer may slowly, very 

 slowly, raise himself into a sitting position, and if he is careful the fish will not 

 be frightened by this. Then, after a time — a half hour, perhaps — he may 

 slowly rise to his feet, and in the course of time may slowly approach the nest 

 until he is within 8 or lo feet of it. How much of this he may do and how rap- 

 idly he may do any of it can only be learned by trial in each case, for it depends 

 on the individuality of the fish and upon the particular stage of his activities. 

 To the fish the relatively immobile observer becomes, after a time, a part of the 

 landscape and no attention is then paid to him. 



Fig. 4. — Showing the ceremonial behavior of the horned dace when a strange dace approaches the nest. The owner of 

 the nest is seen in the pit, P. Above this is the gravel ridge. G. /?.. and below it is the sand trail. 5. T. The direc- 

 tion of the current is indicated by the arrow at the right. The course of the two fish upstream to the point -V and 

 the return of the owner to his nest are indicated by the broken lines with the arrowheads. The heavy lines indicate 

 the banks of the stream. 



Protection of the nest against other fishes. — Other fish approach from time to 

 time as the dace works at his nest. Minnows of other species frequently attempt 

 to enter, but if smaller than the dace they are pursued and driven out. Fre- 

 quently other male dace approach the nest. If these are smaller than the nest 

 builder they are pursued and then invariably fiee. Such small males are dis- 

 tinguished from the larger ones by the presence of a dark lateral stripe (fig. 

 II to 1 6, pi. cxix and cxx). If the male dace that approaches the nest is of 

 the same size as the nest occupant a battle frequently ensues. The two 

 strike at each other with their heads in apparent efforts to inflict wounds 

 with the sharp pearl organs. They often struggle together fiercely in these 

 encounters, but neither fish appears to suffer any injury. The sole result seems 



