Figure 12. — Magnified central portion of a masu salmon 

 scale; entire scale Is superimposed to show fresh- 

 water and ocean zones in detail, age 2.1. 



2. The number of circuli that are com- 

 plete below the focus of the scale is vari- 

 able, but usually there are many. 



3. The circuli often invade the posterior 

 field from their bases; often many can be 

 traced through that area of the scale. 



4. Reticulations are usually absent, but 

 if present they are few in number and net- 

 like. 



The features that differ from those of the 

 echo salmon are: 



1. Masu salmon have no radial stria- 

 tions . 



2. Compared with scales of coho sal- 

 mon, the scales of masu salmon tend to be 

 small for the age of the fish (scales of 

 masu salmon are about the same size as 

 those from pink salmon). 



Steelhead Trout (figs. 14, 15, and 16)* 



Scales of this species usually show con- 

 siderable fresh-water growth, often with bold 

 appearing circuli. A wide range of age com- 

 binations may be found: one to three, or more, 

 winter marks in the fresh-water zone and from 

 one growing season (no winter mark) to four, 

 five, or occasionally even more winter marks 

 in the ocean zone. Many of the circuli of the 

 fresh-water growth are continued around the 

 scale into the posterior field; in fact, the whole 





Figure 14. — Scale of steelhead trout with a magnified 

 portion of the center, age 3.1. 



Figure 13. — Scales of masu salmon: A, B, and D, age 

 1.1, and C, age 2.1. 



^The incidence of regenerated or atypical scales Is 

 high in this species; it is often necessary to examine a 

 number of scales to find a suitable one to study. 



