FISHERY BULLETIN: VOL. 72. NO. 3 



type inclusions (Coe and Turner, 1938). A few 

 primary ovocytes are visible along the alveolar 

 membrane. 



Active (Figure 2d-f) 



As in the male, three stages were identified for 

 this phase: early, middle, and late active. The 

 early active stage (Figure 2d) is characterized by 

 the proliferation of primary ovocytes and their 

 elongation producing stalks which protrude to- 

 ward the center of the alveolus between the follicle 

 cells. In the middle active stage (Figure 2e) the 

 follicle cells and their inclusions have disappeared 

 leaving a central lumen in each alveolus. An in- 

 creasing number of stalked ovocytes attached to 

 the alveolar wall protrude into this lumen. In the 

 late active stage ( Figure 2f) the ovocytes are begin- 

 ning to become spherical with slender stalks, 

 and in many the nucleolus and amphinucleolus 

 are readily visible. 



Ripe (Figure 3a, b) 



In the ripe phase a majority of the ova are free of 

 the alveolar wall and have taken on spherical 

 shape (Figure 3a). In some individuals the ova are 

 quite abundant, and almost all will be free of the 

 alveolar wall (Figure 3b). 



Spawning (Figure 3c) 



The spawning phase is characterized by the 

 emptying of the alveoli of ripe ova, leaving behind 

 a few ovocytes that are still attached to the alveo- 

 lar wall. 



Spent (Figure 3d) 



In the spent clam the alveoli are empty, and 

 follicle cells begin to fill in the alveoli from the 

 basal membrane inward. Inclusions reappear 

 with the follicle cells, and some of the primary 

 ovocytes are visible. 



Iminature 



The immature gonad (Figure 3e) has a much 

 smaller number of alveoli which are filled with 

 follicle cells devoid of any inclusions. 



Each clam was identified as to sex and staged in 

 accordance with the above phases. The percentage 

 of clams in each phase was then calculated. For 

 the purposes of analyzing the reproductive cycle 

 (Figure 4), the three stages of the active phase: 

 early, middle, and late were combined under the 

 single term active phase. In addition, mean 

 monthly percentages were utilized in analyzing 



the reproductive cycle (Figure 4) for those months 

 during which two samples were collected. 



In the presentation of results, the terms 1971 

 and 1972 reproductive cycle refer to the cycle 

 whose spawning phase occurred during that re- 

 spective calendar year. However, the reproductive 

 cycle as a whole does not necessarily coincide with, 

 nor is it restricted to, a particular calendar year. 

 The reproductive cycle was assumed to begin with 

 the active phase and end with the inactive phase. 



RESULTS 



The histological examinations revealed a single 

 yearly spawning period which occurred from late 

 May to early September. This was true for both 

 sexes and for both the 1971 and the 1972 reproduc- 

 tive cycles although the period of peak spawning 

 varied slightly (Figure 4). The sex ratio of the 

 1,739 clams utihzed in the analysis of the repro- 

 ductive cycle was 48% males (837) and 52% 

 females (902). 



1971 Reproductive Cycle 



During the 1971 reproductive cycle (Figure 4) 

 clams in the active phase were encountered from 

 February through July for males and February 

 through June for females. Active clams were un- 

 doubtedly first present in January although no 

 samples were collected that month. Individuals in 

 the early active stage (Figures lb and 2d) first 

 appeared in February for both sexes, while those 

 in the middle active stage (Figures Ic and 2e) first 

 appeared in March and the late active stage (Fig- 

 ures Id and 2f) in early April. 



Ripe clams of both sexes were first observed in 

 late April. Ripe males (35%) were most abundant 

 in May and ripe females (47% ) in June. 



Clams in a spawning condition were first en- 

 countered in the later part of May, peaked in 

 July, and were last observed in the early Septem- 

 ber sample. During July 75% of the males and 

 55% of the females were in a spawning condition. 



Spent clams were present from July to October 

 with the highest percentage occuring in August 

 when 38% of the males and 65% of the females 

 were in this phase. 



There was no observed difference in reproduc- 

 tive cycle with size class, except for clams under 60 

 mm in length. In general the period of peak 

 spawning for those clams was the same as other 

 size classes, but the duration of the spawning 

 period was shorter. It began about 1 mo later than 

 other size classes and ended a month earlier. 



652 



