Relationship between the vitellin concentration in the hemolymph and oocyte necroses during the annual reproduction cycle in the Japanese scallop, Mizuhopecten yessoensis

Summary

A specific and sensitive enzyme-linked immunosorbent assay (ELISA) was developed for measurement of vitellin in the hemolymph and ovary of the Japanese scallop, Mizuhopecten yessoensis. We observed two peaks of vitellin concentration in the hemolymph during the annual reproductive cycle. The peaks corresponded with the occurrence of two types of oocyte necrosis, type I and type II. Type I necrosis occurs in the early phase of vitellogenesis and is characterized by necrotic oocytes that do not have a germinal vesicle. Type II necrosis occurs during the mid-to late-phase of vitellogenesis and peaks just before spawning. It is characterized by necrotic oocytes whose germinal vesicle is strongly stained by eosin, i.e., the germinal vesicle has lost basophilic properties. In immunohistochemical examinations, oocytes and auxiliary cells (which are in contact with oocytes), reacted with anti-vitellin serum; mid-gut gland, adductor muscles, intestine, gonoduct, kidney, and gill do not. These results suggest that the presence of vitellin in the hemolymph is a result of leakage of yolk protein from necrotic oocytes.

Key words:

• Oocyte necrosis
• vitellin
• hemolymph
• Japanese scallop