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Germ cell development, sexual maturation, and fecundity of female Rapana venosa (Valencihave been examined by light and electron microscope observations. The Golgi apparatus, vacuoles and mitochondria were involved in the formation of glycogen particles, lipid droplets and yolk granules in early vitellogenic oocytes. The modified mitochondria and endoplasmic reticulum in late vitellogenic oocytes were involved in the formation of proteid yolk granules near the cortical layer. A mature yolk granule was composed of three components: main body (central core), superficial layer, and limiting membrane. Monthly changes in the gonadosomatic index were closely associated with ovarian developmental phases. Spawning occurred between May and early August, when the seawater temperature rose to 18-26°C. The female reproductive cycle of this species was divided into five successive stages: early active stage (September to February), late active stage (October to April), ripe stage (March to July). partially spawned stage (May to August), and recovery stage (June to September). The rate of individuals reaching the first sexual maturity was 51.6% in females of 7.1-8.0 cm in shell height, and 100% in those> 10.1 cm. The total number of egg capsules per individual and the mean number of eggs in an egg capsule were 184 to 410 and 976, respectively. Fecundity ranged approximately from 179,000 to 400,000 eggs/individual with two to four broods (spawning frequencies) during the spawning season. The duration of development in egg capsules was 15-17 days at about 20°C. Rapana venosa is a species with embryos that hatch as veliger larvae. The sex ratio of female: male was not significantly different from 1 :1.

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