224 
BULLETIN OF THE BUEEAU OF FISHEEIES 
MATURITY 
AGE AT MATURITY 
During the sxunmer of 1924 a large amount of fresh material was examined to 
determine the age and size at maturity. In some localities the specimens were 
taken from boxes on the cannery floors soon after they arrived from the beds; at 
other times they were dug especially for this purpose and examined on the beach. 
As the length of the clams used for this study varied from 7 to 12 centimeters (2^2 
to 41/) inches) the shells were vers^ thin. The mantle was split along the mid- 
ventral line, and the shell broken back to expose the interior. When the mantle is 
234Se234S 
J 1 I I I _J I I 1_ 
A^e in Years Age in Years 
Cordova Swickshak 
Leyen</:^ immature, II 2"° stage of imwaturify, [j mature. 
Fig. 16. — Showing the coining into maturity of small clams from Swickshak and Cordova, with 
reference to age. All are immature at 2 years of age and change gradually, to become com- 
pletely mature at 5 and 6 years of age, respectively. Some pass through an intermediate 
stage the year prior to full maturity 
opened, the larger part of the body is seen to be composed of the foot, or " digger," 
which contains the gonads and in mature specimens before spawning is distended 
with a great mass of x-eproductive material. In immature clams the posterior part 
of the foot appears translucent, and through its walls the outline of the digestive 
tract can be seen. After a number of examinations a marked difference, apart from 
size, can be noticed between clams that have spawned out and those that have never 
formed reproductive material. The mature clams never regain the translucent 
appearance and some become very dark soon after spawning. 
In localities where maturity comes on at from 3 to 5 or even 6 years of age, there 
is a gradual changing over from the immature to the mature state. This makes a 
class between the obviously immature and the mature that can be distinguished 
