Temporal variation in the reproduction and tissue biochemical composition in the Gray mussel, Crenomytilus grayanus (Dunker 1853) on the east coast of Korea

Abstract

The Gray Mussel Crenomytilus grayanus occurs in high density in the shallow, rocky, subtidal zone on the east coast of Korea, where this mussel is commercially exploited by the local shellfish industries. Despite its commercial and ecological importance, little is known about its reproductive physiology, which is crucial to the management and the future aquaculture development of this species. In this study, we first examined the annual reproductive cycle and temporal changes in the tissue composition of C. grayanus during September 2012 to August 2013 from the east coast of Korea. Histology revealed that oogenesis and spermatogenesis commenced in September, as the small oogonia (16.67 ± 4.87µm) and spermatogonia could be observed in the follicles, respectively. Mature oocytes (46.55 ± 9.91 µm) and mature spermatozoa were observed in March, and most of the males and females spawned during May and June, when the surface seawater temperature (SST) increased from 15.5 to 22.3oC. The total carbohydrate level in the tissue increased dramatically from April to May, which coincided with the chlorophyll a maximum occurring in April. Condition index, as a ratio of tissue weight to shell weight, also increased from February to May, and then declined in June, indicating that most mussels spawned during May and June. Our data suggests that C. grayanus is a spring spawner, and the onset of gametogenesis and subsequent spawning is closely linked to the seasonal changes in water temperature and food availability in the water column.