This study was carried out to obtain information on the developmental biology and the management of biological resources of the abalone Haliotis gigantea in Korea. The sex ratio (female:male) in the present study was 1:1.7 and the proportion of females was 36.6% (n=106/290). Their gonadal structures displayed definitive seasonal changes which were similar in pattern to the changes in the gonad index (GI). The GI showed a pattern of definitive seasonal changes in both males and females it was high in the fall and low in the spring. The reproductive cycle could be categorized into the following six stages: inactive, early active, late active, ripe, spent, and degenerative stage. Based on the monthly changes in GI and stages of gonadal development, October to November was determined to be the main spawning period for H. gigantea on Jeju Island, Korea.

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Samples were collected from the subtidal region of Jumunjin on the eastern coast of Korea in July 2020. A total of 338 mussels of shell height (SH) 20.8–149.8 mm were used for sex ratio analysis. The sex ratio (F:M) in the same population of mussel Mytilus coruscus was approximately 1:0.7. The sex ratio according to the class of SH was different. The sex reversal pattern of M. coruscus appears to go from male → female → male → female, and as such is determined to be sequential hermaphrodites.

This study was performed to obtain information on the basic reproductive ecology and biological resource management of Buccinum osagawai. Samples were collected from August 2018 to October 2019 with a drum-shaped net at a depth of 150–250 m along the continental shelf in Jumunjin, on the east coast of Korea. The species showed gonochorism and a lack of external sexual dimorphism. The overall sex ratio (F:M) was 1:1.2 (n = 549, F = 250, M = 299); as the size of the individuals increased, the proportion of males tended to decrease. The development pattern of the oocyte was synchronous, in which a dominant group of oocytes was identified within the same ovary. The size of the ripe oocyte was 82.3 (±22.6) × 125.5 (±22.0) μm. The spermatocyte development pattern was group-synchronous, in which multiple stages of germ cell populations were simultaneously identified within the same spermatogenic acinus. The gonad index (GI) for both males and females showed the highest value during June, after which it decreased sharply, and after August it was below 2.0. The main spawning season was from June to July, and the GI and stages of gonadal development did not show a pattern of seasonal changes. The main gonadal active season was from May to July, and both male and female gonadal development and maturation took place over a short period, whereas the recovery period after spawning was longer. At least 60.5% of the group, considering both males and females, showed maturity at 50.1 mm SH or more. Furthermore, the size of 50% group maturity was shown at approximately 50.0 mm SH.

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