Seasonal Gonadal Cycle of the Male Soft Shell 

 Clam, Mya arenaria , in Maryland 



By 



WILLIAM N. SHAW, Fishery Biologist (Research) 



Bureau of Commercial Fisheries Biological Laboratory 

 Oxford, Md. 



ABSTRACT 



Seasonal changes in the gonad of the male soft-shell clann, Mya arenaria , were 

 observed histologically in sannples collected from May 1961 to June 1963 in the 

 Tred Avon River, located on the eastern shore of Chesapeake Bay, Md, In the summer 

 no active spermatogenesis was found. The aveoli contained nnany atypical cell 

 inclusions with 1 to 16 nuclei. In about 50 percent of the male clams, the aveoli 

 also contained sperm-balls, a grouping of unspawned sperm. 



Spermatogenesis started in August. Spawning began about mid-October and was 

 completed early in November 1961, while in 1962 spawning was first observed about 

 mid-September and was completed about mid-October. 



A second cycle of spermatogenesis followed shortly after the completion of fall 

 spawning. In April many clams were entering the inactive stage and spermatogenesis 

 was not completed. In others, spermatozoa occupied the center of each alveolus. 

 These sperm were surrounded by follicle cells containing inclusions. No spring 

 spawning was observed in clams in the Tred Avon River; instead, those sperm pres- 

 ent were grouped into balls and held until fall. 



No hermaphrodites were found, and possible sex change from male to female 

 seems doubtful. 



INTRODUCTION 



An understanding of the seasonal sperma- 

 togenic cycle of the soft- shell clam, Mya 

 arenaria , in Chesapeake Bay is essential 

 before the fishery for this commercially 

 important species can be properly managed. 

 Coe and Turner (1938) described the develop- 

 ment of the gonad in M . arenaria at New Haven, 

 Conn., and stated that there was one repro- 

 ductive cycle each year. Ropes and Stickney 

 (personal communication) found a single annual 

 spawning cycle for the soft- shell clam in the 

 Gulf of Maine. Further south in Wickford 

 Harbor, Narragansett Bay, R.I., Landers 

 (1954) found Mya larvae from May to mid- 

 July and a smaller second wave from mid- 

 August to November. A lack of larvae between 

 the two waves indicated that spawning occurred 

 biannually in that region. Rogers (1959), work- 

 ing at Solomons Island on the western shore 

 of Chesapeake Bay, reported that the soft- 

 shell clam spawned in the fall, and he believed 

 a second period of spawning was thought to 

 have occurred in the spring. Pfitzenmeyer 

 (1962) showed from clam larvae counts and 

 set traps that the Maryland soft- shell clam 



in the Patuxent River spawned twice a year; 

 he mentioned only briefly his findings from 

 histological examination of Mya collected in 

 the area. From histological examination 

 Shaw (1964) demonstrated that there were 

 two reproductive cycles each year in the 

 female soft-shell clam on the eastern shore 

 of Chesapeake Bay, but the second or spring 

 cycle was not completed. Apparently Mya in 

 Maryland waters, with two seasonal repro- 

 ductive cycles, must differ from its more 

 northern relative in Maine and Long Island 

 Sound, Conn., which has only one spawning 

 cycle each year. 



The purpose of this paper is to describe 

 the seasonal gonadal cycle of the male M. 

 arenaria observed in histological sections 

 from samples collected from May 1961 to 

 June 1963 in the Tred Avon River, Md. Infor- 

 mation collected on the seasonal occurrence of 

 Mya larvae, seasonal setting records in bottle 

 collectors, and results from histological ex- 

 amination of M. arenaria fronn other areas of 

 Chesapeake Bay are also given. 



NOTE: A paper read July 24, 1963, Annual Meeting of 

 the National Shellflsheries Association, Washington, D.C. 



