AGE AND GROWTH OF THE CISCO 
237 
of the other differences between the length distributions of fish of the same age may 
be accounted for by the actual differences in the growth histories of the year classes 
they represent. This appears to be true, for example, in the II groups from Muskel- 
lunge Lake (table 22). The 1931 II-group fish from this lake were much smaller 
in average size than those of the preceding 2 years. The examination of the tabula- 
tion of calculated lengths for these various groups (table 4) likewise shows that the 
1931 II group (1929 year class) actually grew less during the first and second years 
of fife than did the 1929 and 1930 II groups (year classes of 1927 and 1928). 
In table 26 are given the data relative to the longest and the heaviest fish taken 
from each population. (Data concerning the lengths and weights of the oldest fish 
taken may be obtained from tables 3 to 7.) There is sufficient variation in individual 
growth that the largest individual need not necessarily be the oldest. In the Silver 
Lake collections and for both sexes of the Clear Lake samples the largest fish are 
from 1 to 4 years below the observed maximum age. It is true further that the 
largest fish with respect to length is not always the heaviest (for example, see the 
data on the longest and the heaviest fish from Silver Lake). The differences among 
the maximum sizes attained in the different populations are more striking if size is 
considered in terms of weight. The Clear Lake fish reach a weight approximately 
17 times as great as those from Muskellunge Lake, 10 times as great as those from 
Silver Lake, and 7 times as great as those from Trout Lake. 
Table 26. — Data concerning the longest and the heaviest cisco in each of the f lakes 
Trout 
Muskellunge 
Silver 
Clear. 
Year of 
capture 
Age 
Length 
in milli- 
meters 
Weight 
in grams 
Sex 
1931 
XII 
226 
172 
Female. 
f 1932 
IV 
180 
70 
Do. 
\ 1932 
1 188 
Male. 
/ 1930 
V 
206 
110 
Female. 
1 1930 
VI 
204 
120 
Do. 
| 1932 
VIII 
368 
910 
Male. 
( 1931 
X 
> 388 
Female. 
( 1932 
VII 
383 
1,210 
Do. 
* This fish was not weighed before it was preserved. The length recorded includes a correction for shrinkage. 
The maximum size attained depends both upon rate of growth and upon the 
maximum age of survival. The Trout Lake cisco is the slowest growing of the four 
populations, yet a few individuals survive to such an age as to reach a size greater 
than is attained by the fish in either Silver or Muskellunge Lakes. It is probable that 
further collections might change the order of arrangements of the lake with respect 
to the maximum size reached by the cisco, as well as the absolute maximum values for 
length and weight. 
CONDITION AND THE RELATIONSHIP BETWEEN LENGTH AND WEIGHT 
Weight in fishes may be considered a function of the length. If form and 
specific gravity 10 were constant throughout life the relationship could be expressed 
by the equation, 
W=cL\ (1) 
where W= weight, 
L= length, 
and c= constant. 
The above equation is a statement of the well-known cube law. Actually, in 
nature, the value of c is not constant for a species or population but is subject to a 
10 Reibisch (1908) could find no appreciable seasonal variation in the specific gravity of the plaice. Keys (1928) pointed out that 
the hydrostatic equilibrium that exists between the fish and its environment renders great fluctuations in specific gravity unlikely. 
