460 COLLEGE ZOOLOGY 



time. It migrates to shallow water again in the autumn to 

 spawn. The mouth is on the under side, and the crustaceans, 

 mollusks, and other animals used as food are picked up from the 

 bottom. The eggs are laid over honeycomb rock, and, since 

 many of them are covered by sediment or fall prey to mud- 

 puppies, yellow perch, crayfishes, and other enemies, very few 

 reach the adult stage. Because of this fact the government each 

 year gathers, rears, and distributes millions of whitefish eggs. 

 Whitefishes are captured in deep water by means of gill-nets 

 which hold the fish just behind the gill-covers. The average 

 weight is about four pounds, but they may become as heavy as 

 twenty pounds. 



The lake-trout, Cristivomer namaycush, is another important 

 food-fish of the Great Lakes region. It is the largest of our 

 trouts, averaging about eighteen pounds, but occasionally attain- 

 ing a weight of over one hundred pounds. Lake-trout are cap- 

 tured usually in gill-nets. They are omnivorous, but show 

 special preference for lake herring. The spawning season ranges 

 from September to November, according to the latitude. Mil- 

 lions of eggs are cared for and distributed by the government 

 each year. 



The brook or speckled trout, Salvelinus fontinalis, is one of 

 Dur most beautiful and well-known game-fishes. It prefers clear, 

 cool streams with a swift current and a gravelly bottom. 



The mountain or cut-throat trout, Salmo clarkii, is a large 

 species inhabiting the streams and lakes of the Rocky Mountain 

 region. The rainbow-trout, Salmo irideus, is also a Western 

 species. It is a good game-fish and takes the fly readily. In 

 weight it averages about two or three pounds. The steelhead 

 or salmon trout, Salmo gairdneri, is found in the streams along 

 the Pacific coast. Like the salmon it migrates upstream to 

 spawn. Its average weight is about eight pounds. Thousands 

 of steelhead trout are taken each year for canning purposes, 

 especially in the Columbia River. They are also considered 

 excellent game-fish. 



