MANN: CONAOAL DEVELOPMENT IN ARCTICA ISLANDICA 



1978 1979 



1980 



□ EARLY ACTIVE □ LATE ACTIVE  RIPE 



□ SPENT 



El PARTIALLY SPENT 



Figure 6.— Seasonal changes in gonadal development by sex in Arctica island ica for the period September 1978- 



May 1980; all stations pooled. 



due to shrinkage during fixation and subsequent 

 dehydration in alcohol. Both values are consider- 

 ably lower than the diameter of 85-90 ju reported 

 by Loosanoff (1953); however, these latter values 

 were for fertilized eggs. Individual spermatozoa 

 measured 6 n in length in both fixed and live 

 preparations. 



Table 1 summarizes observed gonadal condi- 

 tions in midventral sections taken from A. islan- 

 dica at all stations during the study. Data are 

 pooled for shallow (A and B) and deep (C and D) 

 stations, respectively, due to the similarity of 

 annual bottom temperature changes at these 

 sites (Figs. 1, 2). Gonadal condition data are 

 pooled for all stations and are presented graphic- 

 ally in Figure 6. Several major features were evi- 

 dent. Early active development in the male 

 clams first occurred in early February and con- 

 tinued through May. Late active male develop- 

 ment began in late February and remained evi- 

 dent until June. Most ripe males occurred from 

 May through September and partially spent 

 male clams were found from May through No- 

 vember and during January 1979. Eight percent 

 of the female clams were in early active stage in 

 May 1979. Two percent of the female clams were 

 in late active stage in June and August 1979. 



Gametogenesis in the female clams began earlier 

 in the year of 1980 than in 1979, with 12% of the 

 females in early or late active stage in February 

 1980, and 10% in late active stage in both March 

 and April 1980. Ripe females were present from 

 May through October. The small proportion of 

 early and late active females recorded during 

 February to June in comparison to the larger 

 equivalent proportion (31-93%) of males sug- 

 gested that the duration of the period required to 

 attain ripeness is shorter in the female clams. 



The onset of spawning activity in both sexes 

 was marked by a substantial increase in the pro- 

 portion (to over 30% of total in both males and 

 females) of partially spent animals and contin- 

 ued during the spawning period. Completely 

 spent individuals were greatest from August 

 through November, although some were found 

 as early as May and June. In the female clams 

 only partially spent and spent individuals were 

 present year-round, the former being particu- 

 larly abundant during August and September, 

 and the latter being most abundant from Novem- 

 ber through March. A prolonged spawning per- 

 iod from May through November was indicated 

 even though levels were low during the period 

 May through July. 



321 



