Description of the Species 161 



years after hatching, most of them probably 

 returning in the second season. 



It is not known whether the large-sized salmon 

 always found in the annual runs are individuals 

 which have encountered conditions unusually 

 favorable for their growth, or are fish that have 

 prolonged their stay in salt water far beyond 

 the customary period. 



The Blue-back Salmon 



The blue-back salmon (Oncorhynchus nerka) is 

 known under the name redfish, red salmon, Eraser 

 River salmon, blue-back, and sockeye. It is more 

 abundant than all other species combined, and is 

 the salmon par excellence of Puget Sound, the 

 Fraser River, and Alaska. The species may be 

 recognized by its small size, rather slender form, 

 slightly forked tail, and the following anatomical 

 characters: pyloric caeca slender and seventy-five 

 to ninety-five in number; gill-rakers long and 

 averaging thirty-two to forty ; anal fin with four- 

 teen to sixteen rays, branch iostegals thirteen to 

 fifteen; scales in longitudinal series about one 

 hundred and thirty. The fish when fresh from 

 the sea has a bright blue back and silvery sides 

 and under parts, there being no spots anywhere. 



