248 BIOLOGY FOR BEGINNERS 



As development proceeds the form of the embryo fish may be 

 seen within the egg from which it soon emerges, retaining the yolk 

 of the egg attached to the body, to be absorbed as nourishment 

 until the tiny fish can shift for itself, and grow gradually to its 

 normal size. 



Life History of the Salmon. While no one fish can be taken as a 

 type of all, the life history of the Pacific salmon is as well known 

 as any and since it is so familiar an article of food, we shall take up 

 its breeding habits somewhat in detail. 



The adult salmon lives in the ocean all along the northern 

 Pacific coasts. In spring or early summer both sexes migrate in 

 enormous numbers up the Columbia and other rivers often to a 

 distance of one thousand miles. It is during these " runs " that 

 the canners make their annual catches by means of barriers or 

 machines which scoop up the passing fish. 



This migration may be for the purpose of finding greater safety, 

 cooler water, or better food, or it may be a relic of the time when 

 they may have been entirely fresh-water fish. At all events they 

 begin in March to make their last journey. Slowly at first and 

 later many miles per day they work their way against the current 

 to the spawning beds far from the sea. 



Here, in water not warmer than 54 degrees, each female deposits 

 about 3500 eggs. The male spreads over them the " milt " or 

 spermatic fluid at large in the water. It is much like wind pollena- 

 tion in flowers and many eggs are not reached by the sperms, 

 hence do not develop. 



The males are brilliantly colored at the breeding season but 

 both sexes soon lose their beauty and strength, partly in fighting 

 other fish and partly by injuries from the stones in the spawning 

 beds. 



The eggs are deposited on fine gravel and the process extends 

 over several days after which the strength of the parents seems 

 to be exhausted and both die. 



After from thirty to forty days the eggs hatch, but as usual with 

 fish, the yolk remains attached until all is absorbed in growth and 

 the fry, as they are called, can shift for themselves. 



