CAIN: REPRODUCTION AND RECRUITMENT OF RANGIA CUNEATA 



stations were collected about 0.3 m below the sur- 

 face. Temperature measurements were taken im- 

 mediately with a stem thermometer. Bottom 

 temperatures recorded at VEPCO instrument 

 towers 1 and 6 (near stations A and B, respec- 

 tively) were also used in this study. Salinity 

 samples were analyzed in the laboratory with a 

 Beckman RS7B induction salinometer. Dissolved 

 oxygen samples were fixed immediately after 

 collection and analyzed in the laboratory by a 

 modified Winkler method. 



Freshwater input was compiled from records 

 taken at gauging stations on the James River near 

 Richmond, the Appomattox River near Matoaca, 

 and the Chickahominy River near Providence 

 Forge. Combined, these three rivers are the major 

 sources of freshwater for the James River in the 

 study region. 



RESULTS 



Histological Study of 

 the Reproductive Cycle 



A histological basis for classifying the gonadal 

 condition was used because the external ap- 

 pearance of gonads did not accurately reflect 

 phase of development. The appearance of gonads 

 of both sexes is superficially the same during each 

 phase. 



No evidence of gonadal parasitism was found in 

 any of the tissue sections, nor were hermaphrodi- 

 tic individuals found. 



There was little difference in the time of initia- 

 tion of gametogenesis and ripening between the 

 sexes so the number of males and females in each 

 stage was combined for analyses. Figures 3 to 6 

 show the phases in the development of the female 

 and male gonads. 



Station A 



The reproductive cycle of clams at station A 

 (Figure 7) was more complex than at the other 

 stations. From early February to late March 1970 

 most clams were in the spent phase, although a 

 few male clams contained ripe sperm with sperm 

 balls. In early April 1970, 40% of the sample were 

 in the early active phase. By May, 40% were ripe, 

 with 10% partially spawned. From May through 

 September clams were found in all gonadal phases. 



Evidently some spawning and rematuration oc- 

 curred during the summer months. In early Oc- 

 tober 1970, all clams examined were ripe. The 

 volume of eggs and sperm at the second ripening 

 was much greater than that in the early spring and 

 summer. Partially spawned clams were numerous 

 at the end of October and by mid-November 85% of 

 the sample were partially spawned or spent. 

 Throughout the rest of the winter most clams were 

 in the spent stage, although some males retained 

 sperm and slight gonadal activity was noted in 

 some females. 



The reproductive cycle for 1971 was basically the 

 same as the previous year. In early June 1971, 65% 

 of the clams were ripe. Spawning was indicated 

 during the next 2-wk period because 60% were 

 spent or partially spent. The fall spawning season 

 was very similar to that of 1970, with 95% ripe by 

 late September. Spawning was completed by early 

 November and, again, some ripe males were ob- 

 served during the winter. 



Station B 



Clams in the spent or inactive phase were found 

 from February to early April 1970 (Figure 8). 

 Some males still contained sperm in various stages 

 of cytolysis. By late April 1970, half of those 

 collected had begun gametogenesis, resulting in 

 80% being ripe by early June 1970. Clams remained 

 in the ripe phase throughout the summer with 

 some spawning occurring during July. During 

 August there was a second development, resulting 

 in all clams observed being ripe in early Sep- 

 tember 1970. Spawning commenced in early Oc- 

 tober and was completed by mid-November 1970. 

 Immediately after spawning some clams were in 

 the early active phase, but development did not 

 proceed further during the winter. 



The reproductive cycle for 1971 was similar to 

 that of 1970. Gametogenesis commenced in early 

 May. Fewer ripe clams were observed during the 

 summer months than in 1970. The second cycle 

 began in early July and by early September all 

 clams were ripe. Spawning began in late October 

 and was completed by late November. As found at 

 station A, the second seasonal cycle for station B 

 was more intensive; more ripe clams were found 

 and their gonads contained far more sperm and 

 eggs. Spawning was more intensive during the 

 fall, with gonads progressing from ripe to spent in 

 a month. 



415 



