The Iceland scallop, Chlamys islandica (O.F. Müller), in Breidafjördur, West Iceland : II. Gamete development and spawning

Abstract

Annual cycles of gamete development in male and female Chlamys islandica (O.F. Müller), in Breidafjördur, west Iceland, were investigated for 2 years (August 1988–August 1990) by histological and stereological techniques. Spermatogenesis proceeded rapidly after spawning in July and continued while food was available. During winter a resting phase was observed and at that time mature sperm were present in small follicles. Spermatogenesis continued in early spring when the follicles became larger and in May 80–85% of the males had fully matured. Oogenesis started immediately after spawning and continued throughout the autumn with a resting phase during the winter. The follicles in overwintering females contained no mature ova. In early spring the follicles became larger and oocytes developed further. The first fully developed ova were detected in April–May but females were not fully mature until June. During both years spawning occurred at the beginning of July. In 1989 this coincided with both maximum chlorophyll- a level and highest temperature while in 1990 the maximum temperature and chlorophyll- a were observed approximately 1 month after spawning.