BULLETIN OP THB bureau OF FISHERIES. 

 Table i. — Fry From Lower Columbia River, Mar. 31 to Apr. 2, 1916. 



Length. 



Number. 



Number of speci- 

 mens with — 



Plate- 

 lets only. 



Scales 

 with 

 rings. 



Scale record. « 



Average 

 number of 



Average 

 length of 

 anterior 

 radius. « 



46 to 50 mm . . 

 41 to 45 mm. . 

 36 to 40 mm. . 

 31 to 35 mm.. 



Total 



3-0 



2.0 

 1-3 

 I-S 



20.5 

 8-5 

 5-1 



Av. 3S.7 mm. 



I 



6.3 



a For units of measurement used in the scale records in this and all succeeding tables see explanation on p. 6. 

 ft Estimated from those specimens only which have scales with rings, 

 c Estimated from all specimens with either scales or platelets. 



It is apparent from this table that the scales are usually formed by the time the 

 fish reach a length of 40 mm. It is not surprising that this condition is subject to a 

 considerable amount of variation, especially when so few individuals are involved. 

 The increase in the number of rings and in the size of the scales parallels the increase 

 in total length of the fish. 



Owing to the difficulty in sexing these small fry, no information is avaUdble regarding 

 either sex proportions or variations due to sex. 



A collection of 62 fry from the Clackamas hatchery, maintained near Oregon City, 

 Oreg., by the U. S. Bureau of Fisheries, was made April 11, 1916. (See Table 2.) It 

 will be interesting to compare this with the wild fish taken in the Columbia River. 

 These hatchery fish average considerably larger than the wUd individuals. This is 

 presumably due, at least in part, to the warmer water in which they were hatched and 

 reared. At the time this collection was made the water supply at the hatchery came 

 from a spring, and the temperature was uniformly 50° F. throughout the year. None 

 of the specimens are less than 40 mm. in length. The average is 46.5 mm., wth the 

 mode at 43 mm. 



Table 2. — Data for 62 Fry from Clackamas Hatchery, Apr. ii, 1916. 



Length. 



Number. 



Scale record. 



Average 



number of 



rings. 



Average 

 length of 

 anterior 

 radius. 



61 to 65 mm., 

 56 to 60 mm., 

 51 to 55 mm. 

 46 to so mm. 

 41 to 45 mm., 

 36 to 40 mm. . 



Av. 46.5 mm. 



8.0 

 7-s 



7-5 

 5-5 

 4-7 

 3-2 



jS.o 

 25-5 

 25-8 

 20.3 

 17.2 

 13.7 



18.8 



The obvious skewing of the curve of length toward the smaller sizes is probably due 

 to constant additions to the smaller fish as a result of the hatching of the eggs spawned 

 later in the season. The data at hand are not suflScient to prove this, however. Almost 

 all the collections of small fry show such skewing which is apparently due to some such 

 fundamental cause as the one suggested. The scales show a progressive increase in 



