28 THE ROYAL SOCIETY OF CANADA 



varying in length from 63cm. to 104.5 cm., the measurement in each 

 case being from the tip of the snout to tlic base of the caudal fin. Ac- 

 cording to their scale markings these fish may be classified into three 

 groups, and since there is a marked correlation between the differences 

 in the scale-markings and the sizes of the fish, the former may justly 

 be regarded as indicative of the age of the fish. 



The smallest and presumably tlie youngest fish obtained ranged from 

 63 to 68 cm. in length, and of these I had four examples for study. 

 The scale markings are practically identical in all and presented the 

 arrangement shown in fig. 2. On comparing such a scale with one 

 from one of the Oncorhynchi, a Coho for example (Fig. 1), a striking 

 difference is to be noticed in the extent and number of the fine lines 

 which indicate the period spent in fresh-water. Indeed the measure- 

 ment of the radii of the fresh-water areas of a number of scales showed 

 that those of the Steelhead were on the average approximately twice as 

 long as those of the Oncorhynchus. While my experience especially 

 with the Spring Salmon, does not lead me to place any great reliance 

 upon the number of lines on a scale as an index of the age of the fish and 

 still less upon the theory that a definite number of lines are formed 

 annually, (Malloch),* nevertheless it must be admitted that the number 

 of lines indicate the amount of growth of the fish. A comparison of 

 the fresh-water lines of the Steelhead and Coho would accordingly 

 indicate one of two things, either (1) that both species spend the same 

 length of time in fresh water, but that during that period of their lives 

 the Steelhead grow twice as rapidly as the Coho; or, (2) that the rate 

 of growth of the two species is essentially the same, but the time spent 

 by the Steelhead in fresh water is twice as long as that spent by the 

 Coho. That the second supposition is the correct one is shown by the 

 fact that in many Steelhead scales one can clearly recognize a division 

 of the fresh-water area into two distinct zones (Fig. 3). The lines 

 formed during that portion of the life of the fish that is spent in fresh 

 water are always very close together, and it is consequently somewhat 

 difficult to distinguish in some cases the slightly greater concentration 

 of those formed in winter as compared with those formed in summer. 

 But in the majoiity of cases the the diffe ence can be made out, and 

 one then finds that a band of lines, closer together than usual, and 



*P. D. Malloch. — The History and Habits of the Salmon, Sea-trout and other 

 Fresh-water Fish. London, 1910. 



Miss Esdaile (Mem. and Proc. Manchester Lit. antl Phil. 8oc. Vol. L\l, 1912) 

 has recently shown that the absolute number of rings upon different scales of the 

 same fish may vary considerably, so that the application of Malloch's method of 

 determining the age, by dividing the number of rings by a definite number, supposed 

 to represent the annual increment, would give the anomalous result of different ages 

 for different portions of the body of a fish. 



