SALMON AND TROUT— SCHULTZ 373 



steelhead, all indicate that the details of actual egg laying are essen- 

 tially the same for the various species. The spawning act or egg- 

 laying act may be summarized as follows from Needham's (1934, 

 pp. 334-335) account for the steelhead: 



The female dropped back in the center of the pit with her vent and anal fin well 

 down in the deepest part. The male instantly moved into position parallel to her. 

 Their vents were opposite and, since he was considerably shorter, his head came 

 only about to her pectorals. Both fish opened their mouths wide, the female 

 particularly was seen to arch her body, raising her head so that the tip of her 

 snout was out of water. Eggs and milt were exuded with a quivering motion by 

 both fish at exactly the same instant. The snout of the female, where it pro- 

 truded from the water, was seen to cause ripples on the surface from the quivering 

 motion as the eggs were deposited. The white cloud of milt partially obscured 

 the eggs from our view, but we could clearly see the stream of bright pink eggs 

 dropping into the bottom of the nest. They appeared to stay in a very compact 

 group and none were observed floating from the nest. The milt settled in a more 

 or less compact way about the eggs, though some of it was carried away by the 

 current. The whole process did not require much more than 2 seconds. The 

 male during this process was on the left side of the female as she faced upstream. 

 The female remained in a vertical position. The male inclined slightly toward 

 and appeared to be in definite contact. 



FERTILIZATION AND WATER-HARDENING 



Both eggs and milt are discharged at the same time during the 

 spawning act, and Nature has so beautifully coordinated each step 

 in the breeding activities of salmon and trout that the eggs or ova are 

 fertilized the instant they are shed; otherwise they would probably 

 not be fertilized at all because the sperm would be carried by the 

 current downstream away from the nest. The millions of spermatozoa 

 making up the milt are inactive until they enter the water, then for 

 about 45 seconds they swim about with great rapidity, but by the 

 end of 1 ji minutes all have become inactive and probably many have 

 died. The eggs, once they enter water, change rapidly too. For 

 about 1 minute after the eggs are in water it is possible for nearly 

 100 percent of them to be fertilized when active spermatozoa are 

 present, but at the end of another 4 minutes in the water the shell of 

 the egg has so changed that it is nearly impossible for a spermatozoan 

 to enter. All spermatozoa must enter fish eggs through a single 

 minute pore, the micropyle, in the egg membrane or outer shell of the 

 egg and after one spermatozoan has entered (it takes but a single 

 spermatozoan to start the development of the egg) it is impossible 

 for another one to do so. Should no sperm enter the egg within the 

 first few minutes that the egg is in the water, the micropyle closes, and 

 that egg can never be fertilized beibause "water-hardening" has 

 already begun. 



"Water-hardening" is a physiological process by which water 

 passes through the egg membrane (outer shell of the eggs) into the 



