276 



PRACTICAL ZOOLOGY 



fertilized by the spermatozoa (milt) of the male which are poured 

 over them. At this time the fish are said to be spawning. Very 

 few of the eggs succeed in producing adult fish, since they are 

 eaten by numerous animals and destroyed by fungous plants 

 and by being smothered by sand and mud on the bottom. The 

 young fish lives for a time on the yolk stored up in the egg (Fig. 

 160, B); later it begins to feed on small crustaceans and insects 



Fig. 160. 



Photographs of three stages in the growth of the trout. (Fron 

 Bui. U. S. Fish Com.) 



(Fig. 160, C), and finally on larger crustaceans, insects, mollusks, 

 and other fish. 



Many fish migrate long distances to lay their eggs. For ex- 

 ample the chinook salmon (Fig. 172, D) lives in the sea along the 

 Pacific coast from Monterey Bay, California, and China, north 

 to Bering Straits. It enters the fresh-water streams to spawn, 

 especially the Sacramento, Columbia, and Yukon rivers. The 

 ascent takes place in the spring and summer, beginning in 

 February or March in the Columbia River. The salmon do not 

 feed during this migration, but swim at first slowly and then 

 more rapidly until they reach the small, clear mountain streams 

 often more than a thousand miles from the sea. Spawning 



