SPAWNING HABITS OF CHROSOMUS. 



13 



active spawning operations on the same ground, forms a series of 

 events which occur on different occasions with unfailing regularity. 



On the up stream journey, occasional isolated cases of spawn- 

 ing occur. Several males pursue one female ; as the foremost 

 males gain a position alongside the female, the flight and pursuit 

 attain almost lightning-like rapidity. At length two males 

 spawn with the single female as follows: One on each side 

 presses the side of his head against that of the female, all three 

 facing up stream. The two males then crowd laterally against 

 the female, held between them (see Fig. 

 3) : their entire flanks are thus pressed 

 against the sides of the female. While 

 the males are in this position, a rapid 

 vibration of their bodies occurs. The 

 wave of pressure begins at the anterior 

 end of the body and passes backward as 

 a sidewise undulating movement. Other 

 males may attempt to crowd in. So far 

 as observed, the female remains passive. 

 The entire performance occurs so quickly 

 that the details are made out only after 

 considerable practice in observation. 



Spawning under these conditions seems 

 to be attended with difficulty. The act 

 of clasping lasts but for an instant; the sp-ning position. Natural 

 males seem unable to keep their position 



after the impetus of their rush up stream is overcome by the 

 current, for swimming movements are necessarily discontinued 

 during spawning. It is doubtful if spawning in the open, with- 

 out contact with the bottom, is very efiective ; milt was not ex- 

 truded in sufficient quantities to be seen. Although the eggs 

 (almost transparent, with light-brown yolk, always difficult to 

 see in the water) could not be seen, it was evident that some 

 were extruded, for immediately after the spawning other fishes 

 poked their noses into crevices between pebbles, just down 

 stream from where the spawning occurred, evidently trying to 

 get at the scattered eggs to eat them. 



As the school in its circling movements nears the shallows, a 



Fig. 3. Ch 7- s in ii s in 



