Scales of Atlantic Salmon. 
As Indicative of the Life History of the Fish. 
In 1907 W. L. Calderwood published his splen¬ 
did work “The Life of the Salmon.” In this 
book he advanced the theory that the age and 
a good deal of the history of any individual 
salmon could be deducted by a microscopical ex¬ 
amination of its scales. The late Lord B'yths- 
wood) H. W. Johnston and J. A. Hutton have 
all done considerable work with salmon scales, 
and are firm believers in the above theory. 
If one examines a salmon scale with a power- 
such rings are added during a year, about one 
every two weeks, as the fish increases in size 
and as no new scales are formed, the individual 
scales naturally increase in size. As a conse¬ 
quence of this the rings formed during the 
winter will be placed much closer together than 
those which are formed during the warmer 
months when the growth of the fish is very 
rapid. 
Further information may be obtained from 
the so-called spawning marks or kelt marks. 
Ihese are roughened, scar-like ridges found on 
the upper and lower portions of the scale, pro¬ 
duced by the shrinkage in depth and girth of 
most perfect of these placed on a slide and 
covered with a cover glass. The cover glass 
may be held in place by gummed slips of paper, 
as recommended by Hutton, or a drop of Canada 
balsam may be used to hold the cover glass in 
place, lhe balsam should not be allowed to 
come in contact with the scale. Balsam, cover 
glasses and slides can be obtained from any 
drug store. A label should be placed on the 
slide and the sex, weight, length and girth of 
the fish recorded, together with the date of cap¬ 
ture, and the river from which the fish was 
taken. A low power microscope is the best in¬ 
strument with which to study the scales, a'l- 
HEN KELT, ABOUT SEVEN POUNDS, TAKEN IN A NEWFOUNDLAND 
RIVER ABOUT THE MIDDLE OF JUNE. 
The Scale presents a generally shrunken, ragged appearance. 
A represents the primordial center. B, smolt growth. C, first winter 
in the sea. D, summer growth in the sea, during the latter part of 
which the fish returned to the river and spawned in the fall, spending 
the winter, E, in the river. F represents the summer’s growth in the 
sea as a 4%-year-old fish. As a 4%-year-old the fish again returned to 
i the river, probably weighing about 9 or 10 pounds, and spawned. The 
scale was secured the following spring. SM are spawning marks. 
H, the exposed portion of the scale, was covered by a dark membrane. 
SCALE OF A SMOLT CAUGHT IN TIDAL POOL OF A NEWFOUNDLAND RIVER, 
The fish measured 5.25 inches, a is the exposed portion of the 
scale, b is the part of the scale which is enclosed in an envelope of 
skin. Highly magnified. 
ful magnifying glass, or better, under a low 
power microscope, it will be seen that the scale 
is covered by concentric rings surrounding a 
small opaque spot in the center of the scale. 
The theory is based upon the fact that as the 
fish grows rapidly, the rings are further apart, 
and during periods in the life of the fish when 
it grows slowly the rings are close together. It 
may be taken as an accepted fact that salmon 
retain their scales throughout life. It has also 
been observed by ichthyologists and others who 
have attempted to raise fish that the growth of 
the fish is quite rapid during the summer and 
-is comparatively slow during the winter months. 
This applies to both fresh and salt water fish. 
The scale reading, as far as the age of the fish 
is concerned, is based upon these two facts. It 
is somewhat similar to the rings seen in the 
cross section of a tree trunk, only that in the 
case of a salmon there are a number of rings 
added each year. If for example twenty-five 
the fish after spawning. According to Calder¬ 
wood the hen salmon loses 23 per cent, of her 
weight after spawning. This necessitates great 
shrinkage of the skin, and as she loses nothing 
in length, the scales are forced together laterally, 
each movement of the fish rubbing the edges 
of the scales together, producing a roughened 
frayed surface on the upper and lower border 
of the scale, which, although the fish may run 
to the sea and regain its condition, are still 
detectable with the microscope. 
This theory of reading the life history of a 
salmon by its scales has received ample con¬ 
firmation in Scotland, where for years large 
numbers of parr, grilse and salmon have been 
marked annually. Many of these marked fish 
have been recaptured and their scales examined 
and the correctness of the scale reading ratified. 
The method of examination of the scales is 
extremely simple. A few scales should be taken 
from the shoulder of the fish and some of the 
though considerable information may be re¬ 
ceived by the use of a powerful magnifying 
glass. In examining the scales from fish which 
have been in fresh water for some time, a thin 
dark membrane will often be found covering the 
scale. Jf the scale is soaked in water for twenty- 
four hours this can easily be removed. The 
part of the scale which is most satisfactory for 
purposes of study is that which is not exposed 
when in situ. This represents about three- 
fourths of the scale. The small central portion 
of the scale represents the parrhood of the fish. 
The microscope shows that most smolts are 
about two years of age. This has been con¬ 
firmed by the examination of the scales of 
numerous parr which have been artificially 
propagated. 
In 1908 I fished a Newfoundland stream 
where something over two-thirds of the fish 
caught were grilse. These ran a very even size, 
averaging about 3^4 pounds. Practically all 
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