Figure 15.— Scale of steelhead trout with a magnified 

 portion of the center, age 4.1. 



Figure 16. — Magnified central sections of steelhead trout 

 scales: 



Upper left — 3 winters In fresh water. 

 Lower right — 4 winters in fresh water. The last two 

 winter marks may also be fresh-water spawning 

 checks. 



fresh-water zone, with sometimes more than 

 30 circuli, may be complete in this area. A 

 few of the ocean circuli may continue into the 

 clear field as weak circular striations, but 

 radial striations do not occur . Granular reticu- 

 lations are usually present. Steelhead trout 

 scales are usually large and may show one 

 or more spawning checks (fig. 17). 



KEY TO IDENTIFICATION OF 

 POSTJUVENILE FISH 



lA. Nucleus (fresh-water zone) absent. 

 2A. Scales small relative to size of fish. 



.... Pink salmon Oncorhynchus gor - 

 buscha (page 4 and figure 3). 

 2B. Scales large relative to size of fish. 



3A. Seven or more circuli complete 



below the focus. 

 .... Ocean- run chinook salmon On - 

 corhynchus tshawytscha (page 6 and 

 figure 11). 



3B. Less than seven circuli complete 

 below the focus . 

 4A. Radial striations strong. 



. . . Chum salmon Oncorhyn - 

 chus keta (page 4 and figure 

 4). 



Radial striations absent, (If 

 any markings are present in 

 the posterior field, they are 



4B. 







-J<*^v 



Figure 17.— Section of a steelhead trout scale showing a 

 spawning check, 3 winters in the ocean. The spawning 

 check Is In the second ocean winter. 



