228 BULLETIN OF THE BUREAU OF FISHERIES 



or less distinct baud of intermediate rings, whicli in turn is surrounded by the wider 

 rings of ocean growth formed during the second year. Although the scales are all 

 similar, there is considerable variation, which it is important to consider in some 

 detail. 



The true stream growth is relatively small, as compared with the usual size of 

 stream nuclei, and is often poorly defined with marginal winter rings that are not as 

 typical as those on the scales of wild fish. An incidental check was found on the 

 scales of 13 individuals. The number of rings within the incidental check ranges 

 from 4 to 9 and averages 5.8. The general appearance of the stream growth in these 

 adult scales corresponds exactly with that of typical scales from the yoimg fish 

 preserved at the time of marking. (Compare figs. 20 and 21 with the stream growths 

 in figs. 23, 25, 27, 29, 30, and 31 .) The average number of rings in the stream growth 

 of the adult scales (see Table 6) is 11, as compared ^\^th an average of 9.2 on the 

 scales of the young fish. The average length of the anterior radius to the edge of the 



QA 1 31 8 



trae stream growth is y^ millimeters, as compared with ^r~ millimeters for the 



young fish. It is apparent from these figures that the check considered here as 

 terminating the true stream growth was formed at approximately the time when 

 the fish were liberated at the hatchery. Immediately outside of this true stream 

 growth is usually found a band of distinctly wider rings forming the intermediate 

 growth. The term "intermediate" has been applied by Gilbert and others to the 

 band of rings frequently encountered between the true stream and the undoubted 

 ocean growth, the rings of which are intermediate in width between the stream and 

 ocean rings. It frequently, though not always, is developed during the time spent 

 in the brackish water of the estuaries during the seaward migration. The inter- 

 mediate growth shown on the scales of the marked fish of this lot is usually fairly 

 wide, averagLag 9 rings and ranging from none (fig. 29) to 15 rings (fig. 27). Not 

 infrequently the outer rings of the intermediate band widen gradually and merge 

 into the ocean growth, so that it is difficult to set a definite boundar}^ between the 

 two (fig. 23). In extreme cases, where both the stream and the intermediate bands 

 are poorly defined, the true character of the nucleus is so obscured that were the 

 scales presented without additional data the nuclei might be mistaken for the ocean 

 type. Figures 29 and 31 show such nuclei. These scales show considerable grada- 

 tion from a pure stream type of nucleus to what we have designated a "composite 

 nucleus." This type will be discussed in more detail later in this report in connection 

 with another experiment, which throws light on the interpretation of these scales. 



EXPERIMENT NO. 5. LITTLE WHITE SALMON RIVER HATCHERY, JUNE AND JULY, 1917 



Eggs from: McKenzie River, 1916. 



Reared and marked at: Little White Salmon River hatchery. 



Mark used: Removal of adipose fin and dorsal fin. 



Number marked: 44,500. 



Liberated: In Little White Salmon River during June and July, 1917. 



Age: Approximately 10 months. 



The average length of 45 unselected specimens of young fish preserved on July 

 18, 1917, is 47.4 millimeters (1. 9 inches). The scales have an average of 4.4 rings. 



