820 Puget Sound Marine Sta. Piib. Vol. 1, No. 28 



The Chinook salmon (Oncorynchus tschawytscha) is found on the 

 shores and in the streams along the Pacific Coast from Kamchatka to south- 

 ern California. It spends most of its life in the ocean, returning to the 

 rivers during certain seasons to spawn. The gonads are immature when 

 the fish enters the river. Secondary sex characters appear during the 

 migration to the spawning beds. The males develop long, sharp teeth, 

 hooked jaws and a hump at the shoulders. The back and sides of the fe- 

 male become thin and the abdominal cavity distended with eggs. 



At the spawning beds the adult pair construct a nest in the gravel 

 by pushing on the bottom with their heads and the sides of their bodies. 

 The female deposits the eggs in the nest and the male extrudes sperms 

 over them. Both adults then soon die, never returning to salt water. 



The eggs hatch in 40 to 180 days, according to the temperature of 

 the water in which they are incubated. The fry are nourished for two 

 months by the food in the yolk sac. When the yolk sac is nearly absorbed, 

 they begin to swim about and feed on microscopic plankton, small Crustacea 

 and insects. They are then known as fingerlings. 



Usually the fingerlings begin to drift down to the ocean as soon as 

 they are able to swim. Chamberlain (4), Gilbert (14) and Rutter (43) 

 mention cases of Chinook fingerlings that remain for a time in fresh water 

 and migrate to the ocean as yearlings. Such fish are inferior in size to 

 those that spend their first year in salt water. 



Practically nothing is known about the life of the salmon in the 

 sea except that they remain near the mouth of their parent stream during 

 their first year. The Chinook salmon spends from 2 to 7 years in the 

 ocean and usually returns to fresh water in 4 years. Gilbert (14), who 

 made the above estimates of the age of the Chinook, based his figures on the 

 marking of the scales. He finds that the growth of the scales is retarded 

 during the winter and accelerated in the summer, and this periodicity of 

 growth is recorded by the striations on the scale. 



DESCRIPTION OF THE SPERM AND EGG 



The head of the sperm of the Chinook salmon is 0.0026 mm. in length 

 and tapers forward from the base, which is 0.002 mm. in diameter, to a 

 blunt tip. A common length for a sperm is 0.0196 mm. from tip to tip. 



The diameter of the eggs varies from 7 mm. to 9 mm. and averages 

 7I/2 ™iii- The weight of the living eggs examined varied from 0.26 grams 

 to 0.33 grams, but not a sufficient number of eggs was weighed to give 

 a reliable average. The live egg has a specific gravity greater than water 

 and sinks to the bottom when laid. The freshly laid eggs are usually 

 spherical, though often irregular in shape, owing to a crowded condition in 

 the body cavity of the female before the eggs are deposited. 



