• Korean Journal of Fisheries and Aquatic Sciences
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• v.44 no.6
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• pp.701-708
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• 2011

The aim of the present study was to analyze the reductive cycle of the red marbled rockfish Sebastiscus tertius. The analysis was based on annual changes in the gonadosomatic index (GSI), the hepatosomatic index (HSI), histology of the gonadal structure, and plasma sex steroid hormone levels of adult fish from April 1997 to April 1998. GSI of females began to increase in February and peaked ($10.8{\pm}2.72$) in May. HIS levels ($3.41{\pm}0.49$) peaked in February and elevated plasma steroid hormones ($1.47{\pm}0.75$ ng/mL for estradiol-$17{\beta}$ ($E_2$) and $230.7{\pm}27.6$ pg/mL for testosterone (T)) were observed in April. However, in male fish, GSI levels started to increase in August and remained high until November ($0.21{\pm}0.05$). T levels were was also elevated in August and peaked in October ($188.1{\pm}43.5$ pg/mL) and November ($186.8{\pm}28.0$ pg/mL), but started to decline 1 month than the GSI. These results suggest that female ovoviviparious periods span from April to June and amle mating periods occur from November to February.

• Korean Journal of Environmental Biology
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• v.33 no.4
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• pp.419-424
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• 2015

In order to determine the ovarian cycle of Asian Toad, Bufo gargarizans, the developmental stage based on the gonadosomatic index (GSI), size of follicle oocytes in ovary and vitellogenesis for adult females were investigated all around the year. The weight of ovary and GSI were the lowest from April, and all follicle oocytes exist in the pre-vitellogenic form, indicating that the vitellogenesis was suspended. The follicle oocytes in early-vitellogenic stage appeared in ovary during may when the weight of ovary and GSI start to increased, and the follicle oocytes in mid-vitellogenic and pre-vitellogenic stages existed during June and the weight of ovary and GSI also increased. This indicates that vitellogenesis has been carried out actively during this period. The follicle oocytes in mid-vitellogenic stage and late-vitellogenic stage when the vitellogenesis was also completed existed on September. Post-vitellogenic follicle oocytes after vitellogenesis started to appear from October and rapidly increased from December in hibernation. The full grown follicle oocytes existed during February, indicating the ovarian cycle that all follicle oocytes in ovary are developed separately, not synchronized, during the growing period of follicle oocytes and the post-vitellogenic follicle oocytes are maintained the ovulation period.

• Korean Journal of Environment and Ecology
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• v.28 no.3
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• pp.287-292
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• 2014

In order to determine the ovarian cycle of Korean brown frog, Rana coreana, the developmental stage based on the gonadosomatic index (GSI), size of follicle oocytes in ovary and vitellogenesis for adult females were investigated all around the year. The weight of ovary and GSI were the lowest from March to May, and all follicle oocytes existed in the pre-vitellogenic form, indicating that the vitellogenesis was suspended. The follicle oocytes in early-vitellogenic stage appeared in ovary during June when the weight of ovary and GSI started to increase, and the follicle oocytes in mid-vitellogenic and pre-vitellogenic stages existed during August and the weight of ovary and GSI also increased. This indicates that vitellogenesis has been carried out actively during this period. The follicle oocytes in mid-vitellogenic stage and late-vitellogenic stage when the vitellogenesis was also completed existed between September and November. Post-vitellogenic follicle oocytes after vitellogenesis started to appear from December in hibernation, and the full grown follicle oocytes existed during February, indicating the ovarian cycle that all follicle oocytes in ovary are developed separately, not synchronized, during the growing period of follicle oocytes and the post-vitellogenic follicle oocytes are maintained the ovulation period.

• Fisheries and Aquatic Sciences
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• v.1 no.1
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• pp.82-93
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• 1998

Monthly changes of the gonad follicle index (GFI), reproductive cycle, egg-diameter composition, first sexual maturity of the Pacific oyster, Crassostrea gigas, were studied based on the samples which have been collected from the intertidal zone of Poryong west coast of Korea, from January to December, 1996. C. gigas, is dioecious, while a few individuals are alternatively hermaphroditic. Monthly variation of gonad follicle index (GFI) used for determination of spawning period, coincided with the reproductive cycle. GFI increased from April when seawater temperatures gradually increased and reached the maximum in May. And then, GFI sharply decreased from June to September due to spawning. Reproductive cycle of this species can be divided into five successive stages: in females, early active stage (March to April), late active stage (April to May), ripe stage (May to August), partially spawned stage (June to September) and spent/inactive stage (September to February); in males, early active stage (February to March), late active stage (April to May), ripe stage (May to September), partially spawned stage (June to September) and spent/ inactive stage (September to February). The diameter of fully mature eggs are approximately 50um. Spawning occurred from June to September, and two spawning peaks were observed in June and August when the seawater temperature was above $20^{\circ}C$. Percentages of the first sexual maturity of males of 20.1-25.0 mm in shell height were over $50\%$, while those of females of 25.1-30.0 mm in shell height were over $50\%$. All the males of > 30.1 mm and all the females of ^gt; 35.1 mm completed their first sexual maturity. The results suggest that C. gigas has a protandry phenomenon. Sex ratios of 919 oysters observed were 453 females $(49.29\%)$, 429 males $(46.68\%)$, 16 hermaphrodites $(1.74\%)$, and 21 indeterminate individuals $(2.29\%)$. In age class I, sex ratio of males were $64.00\%$, thus, a higher percentage than that of females. It was noted that $64.00\%$ of the young males (age class I) were more functional than females in age class I, but 2-3 year-old oysters showed higher percentage of females. Percentages of hemaphrodites in 2-3 year classes were relatively higher than those in other year classes. Histological pattern of hermaphrodites can be divided into two types: Type I (hermaphrodite having a number of newly formed developing oocytes on the oogenic tissues within a degenerating spermatogenic follicle after discharge of numerous spermatozoa) and Type II (hermaphrodite having two separate follicles in the same gonad).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.4
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• pp.489-499
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• 1998

Gonadal development, reproductive cycle and embryonic development of the marbled rockfish, Sebastiscus marmoratus were investigated histologically. A total of 1,035 specimens were collected from the Cheju Island from July of 1992 to May of 1996. Gonadosomatic index (GSI) in female reached the maximum during October to March, thereafter, the values decreased from Norvember to April. GSI in male reached the maximum in September (before one to three months of the female's maximum), thereafter, the values rapidly decreased from October to December. The annual reproductive cycle can be divided into five stages in female and four stages in male: females, Growing(June to September), Mature(September to February), Ripe and copulation(October to March), Gestation and parturition(November to April), Degenerative and resting(December to May); in males, Growing(April to July), Mature(August to November), Ripe and copulation(September to December), and Degenerstive and resting(November to March). Size frequency distribution of eggs and larvae showed non-synchrony. Maternal larvae parturition occurred one or two time during November to April. Mean length of the larvae parturition was 3.5 mm. Mean number of eggs and maternal larvae for the 15 cm minimum class of female was 58,377, and fecundity increased with the increase of total length and body weight.

• The Korean Journal of Malacology
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• v.22 no.1 s.35
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• pp.13-22
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• 2006

Gonadosomatic index (GSI), oogenesis and reproductive cycle of Glossaulax didyma were investigated by the cytological histological obserbations and morphometric data. Samples were collected monthly from the intertidal zone of Biin Bay, Seocheon, Korea, for one year. Monthly variations in the GSI showed similar patterns with gonadal development. In the early vitellogenic oocyte, the Golgi complex and mitochondria were invovled in the formation of lipid droplet and yolk precursor. In the late vitellogenic oocytes, the rough endoplasmic reticulum and multivesicular bodies were involved in the formation of profeid yolk granules in the cytoplasm. A mature yolk granule was composed of three components: main body (central core), superficial layer, and the limiting membrane. The spawning season was from early June to late August, and the main spawning occurred between July and August when the seawater temperature was above $19^{\circ}C$. The female reproductive cycle can be classified into five successive stages: early active stage (December to February), late active stage (February to March), ripe stage (April to July), spawning stage (June to August), recovery stage (August to November). Fully mature oocytes were approximately $250-270{\mu}m$ in diameter.

• The Korean Journal of Malacology
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• v.30 no.2
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• pp.107-116
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• 2014

Gonadal development and maturation mechanism were studied on the freshwater marsh clam Corbicula papyracea (Heude), which is the endangered species in Korea. The specimens were collected in the rearing ponds and waterway of NFRDI in Gapyeong-gun, Gyeonggi-do from January to December 2004, and then investigated by condition factor, relative growth, gonadal development phases and gonad histological characters based on 30-50 individuals every month. Comparing with the freshwater marsh clam, C. papyracea is small, light olive brown shell and violet interior. The hermaphrodite individuals of C. papyracea take an internal fertilization and fertilized eggs are stored in the foster-sack in the gills, then the hatched juveniles are released outside after an ovoviviparous process. The average water temperature of inhabit area was in range of $1.8-27.0^{\circ}C$ and usually took great effects on the gonad maturation of C. papyracea. The condition factor ranged from 0.14 to 0.21 throughout the year, which was the lowest during winter season (December-February), and gradually increased to the highest value of 0.21 in May. The ratio of meat weight to total weight was 25.9-38.7%, indicating the similar trend with condition factor. The highest values of condition factor and the ratio of meat weight appeared 1-2 months later than gonadosomatic index reached the peak value, it was probably because that the ovoviviparous eggs would spend a long period before hatching from the foster-sack in the gills. To synthesize the characters of meat weight, condition factor and gonad development by histological study, reproductive cycle of C. papyracea could be divided into five successive stages: multiplicative stage (December to February), growing stage (February to May), mature stage (June to August), spawning stage (August to November), recovery stage (November to December). The smallest shell length of matured C. papyracea was 12.6 mm, and individuals, larger than 16 mm, was formed the nursery in the gills.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.3
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• pp.345-352
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• 1999

The sand dollar, Astriclypeus manni is commonly encountered on a subtidal sand bottom along the coast of Cheju Island. limited information has been reported on their ecology despite their natural abundance. This study reports ecology and an annual reproductive cycle of the sand dollars present at Hamdock, northern coast of Cheju Island. A. manni collected from Hamdock revealed that they are 80 to 200 mm in test diameter. Sediment Brain size analysis indicated that A. manni mostly occurs on medium (particle diameter of 500 $\mu$m) to very find sand (particle diameter of 125 $\mu$m), particularly on fine sand (particle diameter of 250 $\mu$m). Internal morphology and in situ observations on their feeding habit indicated that A. manni is a deposit feeder, feeding on organic debris contained in the sediment around its habitat. A. manni were more frequently observed near Zostrea marina bed where content of organic matter in the sediment is considered to be higher. Gonadal tissues of the male were yellow in color while female gonads appeared to be purple. Fully mature eggs, with a mean diameter of 381 $\mu$m, and sperm were observed from the histological slides of the sand dollars collected in late July to August, suggesting that A. manni spawn during July to August when water temperature reaches 20 to $25^{\circ}C$.

• Korean Journal of Ichthyology
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• v.23 no.3
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• pp.179-186
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• 2011

Slime flounder, Microstomus achne is distributed in the coastal waters of Korea, west sea of Japan, BoHai, Yellow sea and East china sea. They are mainly caught by bottom trawl net during winter, from December to March. Sexual maturation of slime flounder were investigated using samples collected from commercial catch in the southern coast of Korea from November, 2006 to March, 2007. The ovary of the slime flounder is a conical bag in shape and is bilateral structure develops lengthily from the posterior of the abdomen to the end of the anal fin. The testis also is bilateral in structure, usually located in small size in the abdomen. In females, the gonadosomatic index (GSI) were peaked in January (12.46), then decreased rapidly thereafter. Female GSI values plummeted to 2.72 in March just after spawning. Male GSI values were peaked in December (2.46) before in the spawning season, then decreased slowly thereafter. The reproductive cycle would be classified into three successive developmental stages : maturation stage (November to January), ripe and spawning stage (December to February), degenerative and resting stage (February to March). Relationships between the fish sizes in total length (TL) and the number of ovarian eggs (F), the body weights (BW) and the number of ovarian eggs were indicated by the exponential equation respectively: F=29.027TL-767.8 (r$^2$=0.7686), F=0.3998BW+24.288 (r$^2$=0.8919).

• Asian-Australasian Journal of Animal Sciences
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• v.14 no.2
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• pp.174-183
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• 2001

During the rapid phase of gonadal development of the freshwater teleost, the catfish (Silurus asotus), the influence of hCG upon the inducement of final oocyte maturation and spawning was investigated electrophoretically and ultrastructurally. The electrophoretic patterns obtained were different in the presence and absence of some of the major or minor zones, because of the hormone level in catfish. The vitellogenin of hormone-treated fish was stained more intensively than that of sham-treated fish. These proteins showed some minor or main bands of egg extracts which migrated at positions corresponding to molecular weights of approximately 90,000. However, the thickness of electrophoretic band in molecular weight for hCG-treated fish was slightly lower than that for saline control. It seemed the plasma protein with molecular weight of approximately 45,000 in hCG-treated fish disappeared. In contrast to the control fish, the ovaries in the catfish treated with hCG shows a marked ultrastructural change under the electron microscope. No dilated profiles were seen in the granulosa cells of the mature oocyte before ovulation. After germinal vesicle breakdown (GVBD), the zona radiata interna (ZRI) becomes more compact, and there is a loss of all the processes from the pore canals. There is a wide space between the vitelline membrane and zona radiata. Also, during final maturation, the microvillar processes from the oocyte are seen no longer to penetrate deeply into the extracellular spaces of the overlying granulosa cells, and the reticulate patterns of the zona radiata interna becomes occluded, giving the zona radiata a more solid appearance. It has been possible to initiate 100% oocyte maturation in yolk granules and follicles in vivo by treatment with hCG and a high water temperature ($27^{\circ}C$). In hCG-treated fish, the percentages of successful artificial fertilization and hatching were maximal at 15 h after a single injection. It seems clear that a long acting preparation containing hCG can be successfully used in prespawning fish to advance the final events of gonadal maturation and initiate spawning. Further studies are necessary to evaluate the potential of hCG to either stimulate or inhibit the reproductive development of fish at other stages of the seasonal reproductive cycle.