• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.4
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• pp.599-607
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• 1998

To clarify annual reproductive cycle of Korean dark sleeper, Odontobutis platycephala (Iwata et Jeon), we examined the seasonal changes of gonadosomatic index (GSI), the proportional frequency of oocyte development stages in the ovary and the changes of sex steroid hormone levels in blood from December 1995 to November 1997. In July and August, GSI was 0.35 to 0.72 and most oocytes in the ovary were chromatin-nucleolus stage and perinucleolar stage (proportional frequency: $87\%\~96\%$). In September, GSI was 1.20 $\pm$ 0.12, some oocytes in the ovary were yolk vesifle stage (proportional frequency: $22.8\%$) and vitellogenic stage which appeared very rarely(proportional frequency: $2.2\%$). GSI increased gradually from October and reached 4.59± 0.61 to December. During this period, oocytes of vitellogenic stage increased slightly (proportional frequency in December: $22.1\%$). In January, GSI was 4.32 $\pm$ 0.72 but the proportional frequency of oocytes in vitellogenic stage increased (proportional frequency: $51.2\%$). from February, GSI was increased sharply and reached to 10.51 $\pm$ 1.04 in March, the highest value throughout the year and the proportional frequency of oocytes in vitellogenic stage also reached the highest levels (proportional frequency: $60\%$). From April, GSI was gradually decreased and fell down to 1.11 $\pm$ 0.35 in June. During this period, the proportional frequency of mature oocytes was the highest in April (proportional frequency of mature oocyte stage: $40\%$ in April, $12\%$ May, $5\%$ June) throughout the year, and atretic ovarian follicles were appeared. The blood level of estradiol-17$\beta$ ($E_2$), which stimulates the hepatic synthesis and secretion of vitellogenin, was $0.84{\pm}0.20\;ng/m{\ell}$ in August, and thereafter was not changed until December. from January, it increased sharply and reached the highest level of $ 2.85{\pm}0.35\;ng/m{\ell}$ in March throughout the year, but fell to $0.14{\pm}0.02\;ng/m{\ell}$ in July(P<0.05), 17$\alpha$-hydroxprogesterone(17$\alpha$-OHP) was the peak $13.37{\pm}0.52ng/m{\ell}$ in March, but no significant changes in other period(below $3ng/m{\ell}$, P<0.05). 17$\alpha$, 20$\beta$-dihydroxy-4-pregnen-3-one(17$\alpha$, 20$\beta$-P), which was known as the final maturation inducing hormone in teleost, was $0.74{\pm}0.09ng/m{\ell}$ in April and $0.54{\pm}0.07ng/m{\ell}$ in May, but no significant changes in other period (below $0.26\;ng/m{\ell}$, p<0.05). Taken together these results, the annual reproductive cycle of O. platycephala divided into 4 periods as follows: 1) ripe and spawning period from April to June, main spawning period was from April to May, 2) Resting period from July to August, 3) Growing period from September to December, 4) Maturing period from January to March. Moreover, It was showed that the changes of sex steroid hormone in blood played a important roles in the annual reproductive cycle of O. platycephala.

• Development and Reproduction
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• v.4 no.2
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• pp.187-193
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• 2000

Gonad and blood samples were taken from the cultured female Korean sea bass, Lateolabrax japonicus from October to February between 1997 and 1999. Gonadosomatic index began to increase in November and reached the highest value in December (12.8$\pm$1.5) and January (14.8$\pm$3.5), and then decreased sharply in February (2.6$\pm$1.5, p<0.05). The ovarian oocytes developed to tertiary yolk stage and reached fully-Brown stage in December and January, and then underwent atresia without maturation and ovulation in February. The plasma estradio3-17 $\beta$ level increased from November, and reached the highest value in December (1,152.3$\pm$107.2 pg/ml) and January (1,315.4$\pm$99.5 pg/ml), after then decreased in February (P<0.05). The concentration of plasma 17 $\alpha$ ,20 $\beta$-dihydroxy-4-pregnen-3-one was not significantly changed at low levels (86.6$\pm$6.5∼93.8$\pm$2.8 pg/ml) during the experimental period (P<0.05). All the fish with fully-grown oocytes in the ovary were matured and ovulated by HCG injection. The number of floating eggs were 325,000$\pm$26,000 at HCG 1,000 luhg and 195,000$\pm$35,000 at 2,000 lUikg. There was no difference in fertilization rate and hatching rate of the eggs (P<0.05). Considering these results, we could infer that the ovarian oocyte of the cultured Korean sea bass were not matured and ovulated because of the lack of gonadotropin surge. Moreover, HCG injection could induce oocyte maturation and ovulation in the cultured fish, and the effective dose was 1,000 IU/kg.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.3
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• pp.253-261
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• 2012

We investigated the reproductive capacity of starry flounder Platichthys stellatus from the Uljin (UJ) marine ranching area and compared it to that of P. stellatus from the coastal waters of Pohang (PH). In UJ, female gonadosomatic index (GSI) peaked in October ($3.14{\pm}0.87$) and male GSI was high in October and December. In PH, female GSI peaked in January ($18.64{\pm}2.15$) while male GSI began to increase in October and remained high until March. Most ovaries of UJ females were immature with perinucleus oocytes, although the testes of UJ males were ripe in January. Both the ovaries and testes of PH starry flounders were ripe from January to March. The plasma estradiol-$17{\beta}$ ($E_2$) levels of UJ females were highest in October ($4.09{\pm}1.90$ ng/mL) although the testosterone (T) levels of UJ males were highest in December ($3.81{\pm}0.78$ ng/mL) and decreased gradually until April. The $17{\alpha}$,$20{\beta}$-dihydroxy-4-pregnen-3-one ($17{\alpha}20{\beta}P$) levels of UJ females were not detected. The E2 levels of PH females were highest in December ($36.25{\pm}33.07$ ng/mL) and $17{\alpha}20{\beta}P$ levels were highest in March ($5.51{\pm}0.95$5 ng/mL). The T levels of PH males were highest in December ($4.03{\pm}1.34$ ng/mL) and decreased gradually until October. Taken together, these results suggest that most females from UJ did not reach maturation with a spawning period that was considered to be between December and January.