Figure 7. — Scale of coho salmon, age 1.1. 



ilii 



Figure 8. — Scale of coho salmon, age 2.1. 



2. The presence of strong radial stria- 

 tions in the posterior field. 



3. The presence of circuli or segments 

 of circuli in the posterior field. 



Coho and Chinook salmon scales are fairly 

 similar, and subtle differences must be eval- 

 uated to distinguish between them: 



1. The fresh- water zone of the coho 

 salmon scale is usually larger and more 

 distinctly marked than that of the chinook 

 salmon. Many chinook salmon migrate 

 seaward at less than 1 year of age, where- 

 as most coho salmon migrate to the 

 ocean after 1 or 2 full years in fresh 

 water. 



2. Usually coho salmon scales have 

 more circuli that are complete below the 

 focus than those of chinook salmon. 



3. Circuli or segments of circuli are 

 usually prominent in the posterior field 

 of the coho salmon scales. On scales of 

 chinook salmon, some of the ridges of 

 the circuli may extend into the posterior 

 field as circular striations. These are 

 weak and unlike true circuli. 



4. Chinook salmon scales also tend to 

 be large for the size of the fish with a 

 large first ocean zone, but mature chinook 

 salmon may have more than one 

 annual mark in the ocean zone, often 

 3 or 4. 



5. Reticulations are seldom present on 

 the scales of either species, but if they do 

 occur, they are netlike and are more likely 

 on the chinook salmon scales than those 

 of the coho salmon. 



Chinook (King or Spring) Salmon 

 (figs 9 and 10) '^ 



Usually nnore than six circuli are complete 

 below the focus of the scales, but often only 7 

 or 8. Radial striations are strong in this 

 species. The circuli seldom invade the clear 

 field from their bases, but some of the first 

 ocean circuli may be followed into this area 

 as weak, irregular markings, the circular 

 striations. Few scales show reticulations, 

 which are usually netlike, if present. The first 

 ocean zone is usually large and has numerous 

 circuli. Mature chinook salmon may have as 

 many as four, or rarely five, annual marks in 

 the ocean zone. 



A substantial percentage of the chinook 

 salmon (ocean-run type), especially in the 

 rivers from California northward to British 

 Columbia, migrate to the sea during their first 

 spring or summer. The scales of these fish 

 may show a small nucleus of fresh-water 

 growth, or none at all. Ocean- run chinook 

 salmon can be distinguished from the ocean- 

 run sockeye and chum salmon by the number 



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. 



