AGE AND GROWTH OF THE CISCO 
223 
selection by gear could have taken place. Some other explanation must be sought, 
therefore, for the high growth values of this age group. 
Since disagreements in the calculated growth data of fish are generally attributed 
in part to changes with age in the growth relation between body and scale, it was 
deemed advisable to study this relationship in the Silver Lake cisco. The 1931 collec- 
tion was selected as best suited for this purpose. As was mentioned previously 
(p. 216) the scale samples used in this entire investigation were all taken from the same 
region of the body. Selections of scales for mounting anti for measuring were made on 
the basis of distinctness of the annuli and symmetry of form rather than on size. As a 
consequence of this procedure the relationship between the length of body and the 
diameters of the scales measured should be comparable in the different age groups of a 
single sample. 
As may be seen in table 8 the average ratio between the body length and the 
magnified diameters of the scales does not vary greatly from one age group to another. 
The generally made assumption of a linear relationship between scale size and body 
size tends to the determination for the Silver Lake cisco of the equation: 7 
L=10.7 mm + 1.078 D, 
where £=length of body in millimeters, 
and Zl=the (magnified) diameter of the scale in millimeters. 
Table 8. — The body-scale ratio for the different age groups of the Silver Lake cisco collected in 1931, 
and the average diameters of scales as measured at the magnification X 40.5 
[Dt is total diameter. The diameters within the different growth areas of the scales are indicated by the subscript figure] 
Age 
Number 
of speci- 
mens 
Body- 
scale 
ratio 
Dt 
D! 
Da 
Dj 
D ( 
Dj 
D« 
D 7 
VII... 
1 
21 
108 
102 
01 
19 
66 
1. 16 
1. 16 
1. 13 
1.13 
1. 15 
1. 18 
1. 17 
174.0 
168.3 
167.9 
161.9 
155.7 
145.8 
121. 3 
67.0 
67.5 
70.9 
71.0 
72.6 
88.0 
90. 2 
96.0 
104.0 
112.6 
117.5 
119.5 
128.7 
117.0 
123.7 
133.8 
140.8 
145.7 
137.0 
139.5 
150. 5 
155.7 
149.0 
153.6 
162.6 
161.0 
164.5 
170.0 
VI 
V 
IV 
III 
II 
I 
Table 9 gives a comparison of the calculated growths of the 1931 Silver Lake 
collection first as they were determined on the assumption of a constant body scale 
ratio at all ages and second as they appear after correction for the changing body- 
scale relationship indicated by the above equation. It will be noticed that while the 
"correction” produced changes in the actual values of the individual average cal- 
culated lengths, it did little toward the elimination of the discrepancies between 
the calculated growths of the different age groups. For example, it may be seen 
that the maximum discrepancy in the calculated growth for the first year of life 
(between the calculations for the I group and the VI group) was reduced from 28 
millimeters in the uncorrected to 24 millimeters in the corrected data — an improve- 
ment in agreement of only 4 millimeters. Similarly, the improvements in the agree- 
ment in the calculated lengths for the later years of life are unimportant when they 
; It is realized that a more precise evaluation of the body-scale relationship might have been obtained through the use of “key ” 
scales selected from exactly the same location in each fish. However, the complete failure of the “correction " equation to eliminate 
the discrepancies in the calculated growths of the Silver Lake cisco together with the fact that no corrections are needed in 
the other three populations made any detailed study of the body-scale relationship in these cisco populations unnecessary 
