spring spawning of the soft- shell clam for the 

 years 1957, 1958, and 1959 at Solomons, Md., 

 but, except for the five Mya caught in the 

 bottle collector, I had no evidence of spring 

 spawning in the Tred Avon River either in 

 1962 or 1963. 



In the spring of 1963, to compare the condi- 

 tion of Tred Avon River clams with clams of 

 other areas, I made collections from a salt- 

 water tank at the Chesapeake Biological Labo- 

 ratory, Solomons, Md. (April 16), and in the 

 Patuxent River (April 2 5 and May 22), Potomac 

 River (May 22), and Chester River (May 22). 

 All samples from the Patuxent, Potomac, and 

 Chester Rivers were in a similar gonadal 

 stage as those collected from our local waters 

 at the corresponding time. None showed signs 

 of spawning or preparing to spawn. The cjams 

 from Chesapeake Biological Laboratory were 

 in all stages of gametogenesis. Many were 

 approaching ripeness, several were ripe, while 

 others were entering the summer or inactive 

 stage. These differences in gonadal develop- 

 ment could be caused by the unnatural condi- 

 tions existing in the salt-water tanks. Un- 

 fortunately, the source of these clams and 

 how long they had been in the tanks were not 

 known. 



No hernnaphrodites were found in more than 

 800 clams. Coe and Turner (1938) found only 

 3 hernnaphrodites in 1,000 individuals. The 

 possibility of sex change from male to female 

 in the soft- shell clam seems doubtful. Except 

 in instances where the clams were in very 

 poor condition, the sex was never in doubt. 

 Each sex is easily recognizable throughout 

 the year by their inclusions (only multinucleated 

 in males) and sex cells. The indifferent stage, 

 found in oysters (Loosanoff, 1942), was not 

 present in Mya . 



CONCLUSIONS 



Histological examination of the male soft- 

 shell clam from the Tred Avon River revealed, 

 as in the female, two cycles of gonadal 

 development each year, one that begins in 

 August, and a second initiated shortly after 

 fall spawning is completed. Evidence that 

 spring setting of limited nature can take 

 place in the Tred Avon River was observed 

 when five Mya were found in our bottle 

 collectors. Where this spawning took place 

 is not known, since the clams collected in 

 front of the laboratory showed no signs of 

 spawning. 



The formation of sperm-balls derived from 

 the unspent sperm in Mya has not been found 

 in Mercenaria ( Venus ) mercenaria (Loosanoff, 

 1937) or Crassostrea virginica (Loosanoff, 

 1942). In these two species the unspawned 

 sperm undergo cytolysis. The sperm-balls 

 in Mya were found after fall spawning and in 

 summer. Present evidence indicates that the 



major source of spernn found in the gonad 

 during the spring is derived from these balls, 

 while in the fall sperm is derived both from 

 normal spermatogenesis and from sperm- 

 balls. 



Future ecological research may reveal the 

 limiting factors in spring spawning. In order 

 to interpret age, growth, mortality, and sur- 

 vival data, it wll be necessary to watch closely 

 the spawning cycle of Mya each year in the 

 Chesapeake Bay area. 



ACKNOWLEDGMENTS 



A similar investigation was carried out by 

 the U.S. Bureau of Commercial Fisheries 

 Biological Laboratory, Boothbay Harbor, 

 Maine. Dr. Victor Loosanoff, John Ropes, 

 and Alden Stickney gave their advice, and 

 William Brey, Fishery Reporting Specialist 

 in the Bureau's Branch of Statistics, provided 

 clam samples collected in spring 1963. 



LITERATURE CITED 



COE, WESLEY ROSWELL, and HARRY J. 

 TURNER, Jr. 

 1938. Development of the gonads and ga- 

 metes in the soft-shell clam ( Mya 

 arenaria ). J. Morphol. 62(9):91- 1 1 1 . 

 GUYER, MICHAEL F, 



1953. Animal micrology. 5th ed. University 

 of Chicago Press, Chicago, 327 p. 



LANDERS, WARREN S. 



1954. Seasonal abundance of clam larvae in 

 Rhode Island waters, 1950-1952. U.S. 

 Fish Wildl. Serv., Spec. Sci. Rep. - 

 Fish. 117, 29 p. 



LOOSANOFF, VICTOR L. 



1937. Seasonal gonadal changes of adult 

 clams, Venus mercenaria (L). Biol. 

 Bull. 72:406-416. 

 1942. Seasonal gonadal changes in the adult 

 oyster, Ostrea virginica, of Long Island 

 Sound. Biol. Bull. 82:195-206. 

 PFITZENMEYER, HAYES T. 



1962. Periods of spawning and setting of 

 the soft- shell clam, Mya arenaria, at 

 Solomons, Maryland. Chesapeake Sci. 

 3(2):114-120. 

 ROGERS, W. E. 



1959. Gonad development and spawning of 

 soft-clam. Maryland Tidewater News 

 15:9-10. 

 SHAW, WILLIAM N. 



1964. Seasonal gonadal changes in the fe- 

 male soft- shell clam, Mya arenaria , in 

 the Tred Avon River, Maryland. Proc. 

 Nat. Shellfish. Ass. 53:121-132. 

 THORSON, GUNNAR. 



1946. Reproduction and larval development 

 of Danish marine bottom invertebrates, 

 Medd. Komm. Dan. Fish. Havunder sog., 

 Ser. Plankton 4(l):l-523. 



