1 8 BULLETIN OF THE BUREAU OF FISHERIES. 



Table 12. — Young Chinooks from Clackamas River, Aug. 30 and 31, 1916. 



The check found on these scales, while in some respects similar, can not be con- 

 sidered as identical with the check preceding the intermediate rings, which is a feature 

 of the scale growth of the fish taken on the lower river. The central part of the scales, 

 within the check, is composed of a fewer number of rings, is smaller in size, and the 

 rings succeeding the check are not so wide. (See PI. I, figs. 7 and 8.) While it seems 

 probable that the fundamental causes underlying the formation of these checks are 

 similar (probably a change in the food supply or other environmental conditions), the 

 change in the case of the fish entering the brackish water of the estuary is more pro- 

 found. In order to distinguish these two types of checks in the discussions, the term 

 "primary check" will be used for that formed in the upper parts of the stream and 

 "migratory check" for that formed on entering the estuary. The next collection to be 

 mentioned will throw further light on this question. 



In April and May, 1915, the Oregon Fish and Game Commission planted, from the 

 hatchery at Bonneville, several carloads of chinook fry in a small artificial lake near 

 Seufert, Oreg. The fish were fed daily with offal from Seufert Bros, cannery, which is 

 located at this point. At the time the plant was made the writer measured a small 

 series of the fish. The average length was 44.6 mm. September 2, 191 5, a collection 

 of 55 specimens was made by hook and line from this lake and the outlet which con- 

 nected the lake with the Columbia River. (See Table 13.) The average length was 

 80.9 ram. Twenty-seven were males averaging 81.5 mm. in length and 28 were females 

 averaging 80.3 mm. There were three mature males in the lot, and these averaged 94 

 mm. in length. The most interesting point which appeared in the study of this collec- 

 tion has to do with the formation of the primary check mentioned above. Such a check 

 was apparent on the scales of 84 per cent of the specimens, and an average of 6.7 rings 

 was included within this check. The general appearance of the scales is similar to 

 that of fish reared under typical hatchery conditions; that is, the rings are more or 

 less irregularly spaced and may be broken. (See PI. I, fig. 6.) The central portion 

 was missing from many of the scales examined, so that it was frequently necessary to 

 examine several scales from the same fish before a perfect one was found. Not infre- 

 quently a similar central portion would be dislocated in reference to the scale as a whole, 

 as though it had been loosened and turned within the delicate pocket of the skin in 

 which the scale is formed. This appearance has also been described by Gilbert (1914, p. 

 62), who has found it on the scales of the sockeye salmon. These blank and dislocated 

 centers correspond in size to the area within the check on the perfect scales, and there 

 could be no doubt that the same cause was responsible for all three of these abnor- 

 malities in the scale growth. Nineteen specimens (35 per cent) had begun the slower 



