• The Korean Journal of Ecology
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• v.19 no.3
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• pp.217-222
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• 1996

For the ecological study on the gobioid (Favonigobius gymnauchen), samples were collected in the Korean coasts from 1983 to 1995, and the process of ovarian maturation, spawning season, settling period of young individuals and growth were investigated with the specimens collected from Kunsan coast. The ovarian egg development of this species underwent three stages; growth stage from March to April, maturity stage from May to June and spawning stage in July. All the adults died after spawning in late July. Young individuals of total length 10 mm began to live a bottom life in the tide pool of shallow waters in early and middle August. The total length of these individuals reached about 42.1 mm (mean 36.7 mm) in late November. The largest specimen examined in this study was 85.0mm of male. After that time, individuals of this species inhabited in subtidal zone from December to May of the next year. The Favonigobius gymnauchen is distributed at 17 areas of shallow waters and estuaries in the western and southern coasts of Korea.

• Animal cells and systems
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• v.11 no.2
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• pp.227-234
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• 2007

Spermatogenesis, the reproductive cycle, and the size at first sexual maturity in male Mactra chinensis were investigated by cytological and histological observations. The spermatozoon exhibits a primitive type morphology and is similar to those of other bivalves in that it contains a short midpiece with four mitochondria surrounding the centrioles. The morphologies of the sperm nucleus type and the acrosome shape of this species are cylindrical and modified cap-like, respectively. The spermatozoon is approximately $40-45\;{\mu}m$ in length including the sperm nucleus (about $1.46\;{\mu}m$), acrosome (about $1.20\;{\mu}m$) and tail flagellum. The axoneme of the sperm tail flagellum consists of nine pairs of microtubules at the periphery and a pair at the center. The axoneme of the sperm tail shows a 9+2 structure. The spawning period of this species lasts from June to September, and the main spawning occurs in July and August, when the seawater temperature is greater than $20^{\circ}C$. The percentage of individual male clams at first sexual maturity was 56.5% for those whose shell lengths were 35.1-40.0 mm, and 100% for over 45.1 mm. Accordingly, harvesting clams <35.1 mm in shell length could potentially cause a drastic reduction in recruitment, and a measure indicating a prohibitory fishing size should be taken for adequate fisheries management.

• The Korean Journal of Malacology
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• v.22 no.1 s.35
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• pp.51-61
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• 2006

Oogenesis and the reproductive cycle in female Ruditapes philippinarum were investigated by cytological and histological observations. R. philippinarum is dioecious and oviparous. During vitellogenesis, the Golgi complex, glycogen particles and mitochondria were involved in the formation of lipid droplets and lipid granules in the cytoplasm of the early vitellogenic oocyte. In the late vitellogenic oocyte, cortical granules, the endoplasmic reticulum, and mitochondria were involved in the formation of proteid yolk granules in the cytoplasm. At this time, exogenous lipid granular substance and glycogen particles in the germinal epithelium passed into the oocyte through the microvilli of the vitelline envelope. The spawning period was once a year between early June and early October, and the main spawning occurred between July and August when seawater temperature was approximately $20^{\circ}C$. The reproductive cycle of this species can be categorized into five successive stages: early active stage (January to March), late active stage (February to May), ripe stage (April to August), partially spawned stage (May to October), and spent/inactive stage (August to February). Percentages of female clams at frst sexual maturity of 15.1-20.0 mm in shell length were 52.6% (50% of the rate of group maturity was 17.83 mm in length), and 100% for the clams > 25.1 mm.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.6
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• pp.646-653
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• 2003

Investigations were made on the population structure, sex ratio, growth, and recruitment patterns of Leptochela sydniensis in the southwestern coastal areas of Korea, between May 2000 and December 2001. Spawning period, fecundity, brood loss, reproductive output, and size at sexual maturity also were examined. The results of the sex ratio showed that females were more numerous than males during the overall study period. Parameters of growth were estimated using the modified von Bertalanffy growth function (VBGF) model incorporating seasonal variation into growth. Females grew somewhat faster and reached a larger size than males $(L\infty=12.80\;mm\;CL\;and\;K=0.70\;yr^{-1}\;or\;females,\and\;L\infty=12.08\;mm\;CL\;and\;K=0.69\;yr^{-1}$ for males). The structure of recruitment patterns obtained by the FiSAT program indicated one normally distributed group. Based on the occurrence of ovigerous females and the gonadosomatic index (GSI), the main spawning season was from June to August. Analysis of covariance indicated that brood loss was not observed during the incubation period. The size at which $50\%$ of females are mature is estimated as 5.48 mm CL.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.57 no.4
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• pp.459-466
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• 2024

Digital color analysis was used to determine the gonadal maturity stages and levels of robust tonguefish Cynoglossus robustus specimens collected from the South Sea of Korea. Maturity stages were determined using photomicrographs depicting ovarian developmental phases and compared with digital color values. Speciments of C. robustus ranged in total length from 21 to 40 cm, with mature ovaries predominantly observed in specimens exceeding 30 cm in length. Monthly color values of the ovaries were primarily concentrated in the 1st and 4th quadrants of the color space, with a^* and b^* values ranging within ±20 and ±15, respectively. The color values of the testes were predominantly located in the 1^st and 4^sth quadrants, with a^* and b^* values ranging from -10 to 10 and -5 to 10, respectively. Although the color values of the mature and spawning stages overlap within a narrow range, distinguishing between them requires consideration of both color values and their monthly distribution. This study underscores the effectiveness of using digital color measurements over subjective visual assessments to evaluate the maturity of C. robustus gonads, thereby providing more quantitative insights into their reproductive biology.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.57 no.3
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• pp.253-261
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• 2024

This study investigated the digital color profiles corresponding to different maturity stages and levels of brown croaker Miichthys miiuy specimens collected from the Southern Sea of South Korea. Maturity stages were determined using photomicrographs of ovarian developmental phases, which were compared with digital color values. Brown croaker specimens ranged from 24 to 81 cm in standard length; mature ovaries were predominantly observed in specimens that exceed 40 cm in length. Monthly ovary color values were primarily concentrated in the 1st and 4th quadrants, with both a^* and b^* values falling within a range of ±15 centered on the origin. Similarly, the testes color values were predominantly situated in the 4th quadrant, with a^* and b^* values ranging from -5 to 15 and 10 to 14, respectively. While the color values of the mature and spawning stages overlapped within a narrow range, distinguishing between them required both the color value and monthly color value distribution to be considered. Thus, this study underscores the efficacy of digital color measurements for assessing brown croaker gonad maturity, and provides more quantitative insights compared to subjective visual assessments by humans.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.39 no.5
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• pp.391-397
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• 2006

This study correlated changes in estradiol-l7$\beta$ ($E_2$), testosterone (T), 17$\alpha$,20-dihydroxy-4-pregnen-3-one (DHP), and vitellogenin (VTG) levels with changes in the gonadosomatic index (GSI) and ovarian histology during the annual reproductive cycle of the wild marbled sole, Limanda yokohamae. Synchronous oocyte development occurs in this fish. Ovary maturity was classified into four periods, based on histological observations: the spawning (December to February), post-spawning (February to April), recovery (May to August), and vitellogenic (September to November) periods. Seasonal changes in the GSI were inversely correlated with water temperatures and reflected the degree of ovarian maturity. Plasma VTG levels were correlated with changes in the GSI, which increased from September to a peak in January, and levels remained comparatively high until February. Estradiol-17$\beta$ was at baseline levels (<0.11 ng/mL) during the spring and summer, and peaked rapidly (1.55$\pm$0.445 ng/mL) from October to January. Plasma T and DHP levels had a similar profile; they rose markedly during the spawning period and remained low (or were not detectable) from spring through autumn. These data indicate that changes in plsama steroid hormones and VTG levels are correlated with the annual ovarian activity of the marbled sole. Based on these results and published reports, it appears that in this species DHP is the most important maturation-inducing steroid and that T is also related to final maturation.

• The Korean Journal of Malacology
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• v.25 no.2
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• pp.173-178
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• 2009

The bigfin reef squid, Sepioteuthis lessoniana is commercially important species in Korea. Korean fishing vessels have actively caught it. However, the reproductive Biology of this species has been poorly known. Therefore, the purpose of this study is to provide information on the reproductive biology of Sepioteuthis lessoniana in Jeju Island, Korea. The bigfin reef squid caught by set net, from June to November 2006. Monthly changes in maturity stages, gonad weight, mantle length at 50% group maturity and sex ratio were investigated. The mantle length of the bigfin reef squid was between 10.6 and 32.1 cm. Maturation and spawning occur all year around, with more intensity from July to September, with peak July. The spawning period was June. The mantle length at 50% group maturity was estimated to be 18.01 cm. Sex ratio was 1:1.4 (male:female). The proportion of female was significantly higher than male ($x^2$-test, p > 0.01).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.1
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• pp.27-35
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• 2020

Filefish Thamnaconus modestus has seen a sharp decline in their catch, we must strive for continuous resource management. We investigated the maturation and spawning of T. modestus by trawl net and set net from January 2018 to November 2019, off Jeju Is. and in coastal waters of North Gyeongsang Province's Korea. We analyzed monthly change total length (cm), gonadosomatic index (GSI) and maturity stages, egg diameter (mm), the relations fecundity and total length. GSI for Jeju Is. was the highest in April (3.17, 2.43), and decreased from July to 1.73 in August and GyeongBuk's GSI was the highest in Apri l (1.86, 2.58), followed by the high in May and the sharp decline in September, which is 0.23. Using a histological method, the annual reproductive cycle of T. modestus can be divided into 5stage in females; the early growing stage (Jan.-Mar.), late growing stage (Apr.-May), Mature stage, spent stage (Oct.), Recover and resting stage (Nov.-Jan.).We estimate the TL at 50% maturity as 24.1cm for female, fecundity ranged from 560,044 eggs at 23.4cm total length to 1,580,387 eggs at 36.6.cm TL.

• The Korean Journal of Malacology
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• v.26 no.4
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• pp.261-265
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• 2010

Reproductive biology of the purplish Washington clam, Saxidomus purpuratus was investigated based on the samples captured in Jinhae Bay, the East China Sea from January to December 2002. The gonad index (GI) began to increase in January, reached the maximum value in March. The reproductive cycle of this species can be divided into five successive stages: the early active stage (from November to January), the late active stage (from December to February), the ripe stage (from February to May and October), the spawned stage (from May to December), and inactive stage (from November to December). The spawning period was from April to December, and the main spawning occurred between June and August. The shell length at 50% group maturity was estimated to be 71.85 mm. The Sex ratio of this species was not significantly different a 1:1 sex ratio (P > 0.05).