Changes in Biochemical Composition of the Digestive Gland of the Female Purple Shell, Rapana venosa, in Relation to the Ovarian Developmental Phases

The Ovarian developmental phases of the reproductive cycle of Rapana venosa can be classified into five successive stages by histological study: early active stage (September to February), late active stage (December to April), ripe stage (March to July), partially spawned stage (May to August), and recovery stage (June to September). To understand the characteristics of nutrient storage and utilization in the digestive gland cells with ovarian developmental phases, we examined the digestive gland - which is the major nutrient supply organ associated with ovarian development of the female purple shell - by biochemical methods. Total protein contents in the digestive gland tissues increased in March (late active stage) and reached the maximum in May (ripe and partially spawned stages), and then their levels sharply decreased in July (partially spawned and recovery stages). Total lipid contents in the digestive gland tissues reached the maximum in January (early active stage). Thereafter, their levels rapidly decreased from May (ripe and partially spawned stages) and reached a minimum in July (partially spawned and recovery stages). The total DNA contents did not significantly change regardless of the different developmental stages of the ovary. However, it was also found from biochemical analysis that changes in total RNA content follow the same seasonal cycling to protein. These results indicate that the digestive gland is an important energy storage and supply organ in purple shells, and that the nutrient contents of the digestive gland change in response to gonadal energy needs.