PORTER: REPRODUCTIVE CYCLE OF MYA ARENARIA 



in surface water temperature at Strawberry Point 

 was 4°C. 



METHODS AND MATERIALS 



The study began in November 1970 and was 

 completed in November 1972. Samples were col- 

 lected once a month from November thru Feb- 

 ruary and twice a month from April thru October 

 in 1971 and March thru October in 1972. The 

 bimonthly samples were taken at 2-wk intervals: 

 generally during the first and third weeks of the 

 month. No sample was collected in January 1971 

 because river flooding prevented access to the 

 study area. Each sample consisted of 50 clams 

 which was separated from a larger random sample 

 to represent five size classes: clams less than 60 

 mm in length, those in the 60-, 70-, and 80-mm 

 length ranges, and those larger than 90 mm. As 

 far as possible the 50 clams selected for each sam- 

 ple were equally distributed between the five size 

 classes. The samples taken during the first 3 mo of 

 the study consisted of only 10, 10, and 15 clams 

 respectively. A total of 1,785 clams were collected 

 which ranged from 22 to 105.5 mm in length. Of 

 this total 2.6% were immature, leaving a total of 

 1,739 mature clams that were utilized in the 

 analysis of the reproductive cycle. 



The samples were returned to the laboratory 

 where they were measured and weighed and the 

 gonadal mass removed and preserved in 

 Davidson's acetic acid fixative (Shaw and Battle, 

 1957). In smaller clams the entire visceral mass 

 was preserved and sectioned; for larger clams a 

 cube of gonadal tissue was removed from the 

 mid-lateral portion of the visceral mass. Usually 

 dissection and preservation were accomplished 

 the day of collection. Clams not dissected until the 

 following day were held in a refrigerated saltwa- 

 ter system overnight. 



Slides were prepared by standard histological 

 techniques: tissues were dehydrated in alcohol, 

 cleared in xylene, embedded in paraffin, sectioned 

 at 5-8 microns, and stained with Mayer's 

 hematoxylin and alcoholic eosin (Galigher and 

 Kozloff, 1971). 



The number of gonadal stages used to describe 

 bivalve reproductive cycles varies widely. Lam- 

 mens (1967) distinguished 11 stages and meas- 

 ured the nuclear-cytoplasmic ratio. Previous in- 

 vestigations on Mya reproductive biology gener- 

 ally have recognized five phases of development 

 (Shaw, 1962, 1965; Ropes and Stickney, 1965); 

 therefore the following five phases were used: in- 



active, active, ripe, spawning, and spent. These 

 five phases were distinguished by the following 

 characteristics. 



Males 



Inactive (Figure la) 



During this phase the alveoli are filled with 

 follicle cells which contain the typical male type 

 inclusions as described by Coe and Turner ( 1938). 

 Primary spermatocytes may be visible along the 

 alveolar wall, but are not abundant. 



Active (Figure Ib-d) 



This phase is typified by the proliferation and 

 maturing of the spermatocytes. In staging the 

 slides, an early active, middle active, and late 

 active stage were identified. The early active stage 

 (Figure lb) is characterized by the proliferation of 

 primary spermatocytes at the basal membrane of 

 the alveoli and the appearance of some sper- 

 matids. The middle active stage (Figure Ic) is 

 characterized by the disappearance of the follicle 

 cells and the migration of spermatids toward the 

 center of the alveoli where they begin aligning in 

 radial columns. The late active stage (Figure Id) is 

 characterized by the greatly increased number of 

 radially aligned spermatids and the formation of a 

 central lumen in the alveoli. 



Ripe (Figure le) 



In the ripe male clam, the sperm are distinctly 

 bunched in radial columns around the alveoli with 

 their tails, which stain pink with eosin, projecting 

 into the central lumen. 



Spawning (Figures If and 2a) 



When spawning commences a single row of fol- 

 licle cells form at the alveolar membrane (Figure 

 If). These follicle cells contain the typical inclu- 

 sions of the male, and the number of rows in- 

 creases as spawning proceeds (Figure 2a). 



Spent (Figure 2b) 



In the spent clam most all sperm have been 

 discharged, but a few may remain. The alveoli are 

 almost completely filled with follicle cells. 



Females 



Inactive (Figure 2c) 



In the inactive phase the alveoli are filled with 

 follicle cells which contain the distinctive female 



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