• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.638-642
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• 2001

To investigate the production of $C_{21}$-steroids during the spawning period of spotted sea bass, Lateolabrax maculatus, we have incubated maturing and ovulating follicles with radiolabeled pregnenolone and $17\alpha$-hydroxyprogesterone for 24 hours. The resulting metabolites were analyzed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC), When maturing follicles ($700\sim800{\mu}m$ in diameters) were incubated with radiolabeled precursors, $C_{21}$-metabolites were corticosteroids and $17\alpha$-hydroxy, $20\beta$-dihydroprogesterone ($17\alpha20\beta OHP$). When ovulation follicles ($1,000\sim1,150{\mu}m$ in diameters) were incubated with radiolabeled precursors, the major $C_{21}$-metabolites were $17\alpha20\beta OHP$, $17\alpha$,$20\beta$, 21-trihydroxy-4-pregnen-3-one ($17\alpha20\beta21P$), and corticosterone. Additional chromatography by TLC and HPLC confirmed the presence of radioactive $17\alpha20\beta OHP$ in the maturing follicles, and $17\alpha20\beta OHP$,$17\alpha20\beta21P$ and corticosterone in ovulating follicles. Although $17\alpha20\beta OHP$ was found in a small peak, the synthesis of this steroid suggests that it may play a role in regulating the oocyte maturation process. Whereas ovulation is regulated by both $17\alpha20\beta OHP$ and $17\alpha20\beta21P$ in the spotted sea bass. In addition, an unusual finding was the biosynthesis of corticosterone. Whether this production is responsible for the ovulation, and is an area requiring continued research.

• Korean Journal of Ichthyology
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• v.8 no.2
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• pp.16-22
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• 1996

Age and growth of Epinephelus akaara were determined using samples collected from the south western sea of Korea. Thin - sectioned otoliths showed relatively well defined annuli when examined under dark - field microscope. Because the fish do not feed at the temperature under $10^{\circ}C$, the annuli in otoliths are considered to be formed during the period between December and April. Considering that the peak spawning season is July, the first annulus must have been formed in 0.5 year after birth. The oldest fish examined was 9 years old, and the largest one was 47cm. The body length(L, cm) was linearly related to the otolith radius (R, ${\mu}m$) : L= - 2.84+7.01 R. Back-calculated lengths for each age using the relationship between body and otolith size were well adjusted to the Von Bertalanffy growth curve : $L_t$=55.5[1-exp{-0.162(t+0.128)}]. Using relationship between length and weight ($W_t$=0.00608$L^{3.21}$), growth in weight was expressed by Wt=2409(1-exp{-0.162(t+0.128)}]$^{3.21}$.

• Korean Journal of Ichthyology
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• v.27 no.4
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• pp.284-292
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• 2015

Monthly variation of species composition and abundance of fish eggs were examined to know the spawning time and location of the fishes inhabiting the coastal region of Jejudo Island. Samplings had been performed at the four locations (Jeju port, Seongsanpo, Seogwipo port and Chagwido) with a bongo net which was towed monthly at the sea surface from August 2006 to July 2007. The fish eggs were identified based on phylogenetic analyses with the DNA sequences generated through PCR-amplification and sequencing of the mitochondrial cytochrome b gene. Among a total of 43 taxa classified during the study period, 34 were identified to species, 4 to families, and the remaining 5 were unidentified. Of them, 23 taxa were occurred at Jeju port, 21 at Seongsanpo, 19 at Seogwipo port and 18 at Chagwido, whereas 15 taxa were found in September 2006, 12 in June 2007, 6 to 8 in August 2006 and January~May 2007, 5 in each October and November 2006, 3 in each December 2006 and July 2007. Among 34 species of fish eggs, Engraulis japonicus and Callanthias japonicus most frequently appeared at 16 times out of 48 observations in total. When those eggs were collected, the surface seawater temperature ranged $14.0{\sim}28.6^{\circ}C$ for E. japonicus and $14.9{\sim}20.5^{\circ}C$ for C. japonicus. The success rates of PCR-amplification and species identification in this study were 68.3% and 79.1%, respectively.

• Korean Journal of Environment and Ecology
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• v.30 no.5
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• pp.888-895
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• 2016

The population ecology (Ecological characteristics) of Squalidus chankaensis tsuchigae were investigated at Geum River from March to November, 2013. This species inhabited midstream of the river where was mostly covered with cobble and sand. The depth of the habitat was 30~60 cm and velocity of stream was 2.27~4.88 cm/sec. The sex ratio of female to male was 1 : 0.86. They were sexually mature when they were over two years of age. The spawning period was from June to July with water temperatures from $25^{\circ}C$ to $25^{\circ}C$. Sexually matured individuals appeared over the two year of age. Frequency analysis of total length indicated that the group with 55~70 mm in total length was one year old, the 71~90 mm was two years old, and the group over 91 mm was three years old. The average number of eggs in the ovaries was estimated as 2,219 per matured female. The number of matured eggs size in ovaries was 0.64~0.98 (mean: 0.85) mm. Calulation length-weight relation of S. chankaensis tsuchigae show the value of contant a as 0.0002 and b as 2.81, and condition factor (K) was 1.06 on average. The stomach contents were Cyanophyta, Chlorophyta, Bacillariophyta, Crustaceae, Copepoda, Nematota, Actithocephala, and Ephemeroptera, Hemiptera, Diptera, and Trichoptera that belong to Aquatic insect, and dormant bud of Pectinatella that belongs to Phylactolaemata. The diet of S. chankaensis tsuchigae was omnivorous, mainly vegetable feed on attached algae (filament form), and mainly animality feeded on benthic invertebrates such as Chironomidae larvae.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.5
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• pp.563-567
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• 1999

Changes in proximate composition and meat weight of oysters cultured in shallow-water at Bukman bay of Tongyeong in Korea with Korean and Japanese spats were investigated. Protein content (dry basis) was rich in August and September, accounting for $70\~72\%$ in the oyster (Korean oyster) cultured with Korean spat and $75\~76\%$ in the oyster (Japanese oyster) cultured with Japanese spat. On the contrary to protein content, carbohydrate contents (dry basis) in the both oysters were poor in the both months, There was a negative correlation (r=-0.94, p<0.01) between protein and carbohydrate content during growing of the bath spats. Total lipid (TL) content was the poorest in August, which is known as spawning season, accounting for $1.4\~1.5\%$ in the both oysters. In addition, the korean oyster also showed the lowest level or TL content in october. Meat weights or the Korean and japanese oysterswere 4.2$\~$4.8 g/specimen and 7.5$\~$8.3 g/specimen, respectively, in the harvest season from November to December. Meat weight increased exponentially with TL content, $y=0,2081e^{1.5696x}$ (r=0.8856, p<0.001). These nutritional components per specimen were contained about two times more in the Japanese oyster than in the Korean one in the harvest period.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.5
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• pp.659-663
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• 1999

Gametogenesis, reproductive cycle, condition factor, and meat weight rate of the surf clam, Tresus Keenae were studied by histological observations and morphometric data based on the samples which have been collected from the south coast of Korea, from January 1995 to February 1996. The annual ranges of the mean seawater temperature and specific gravity in habitat of the surf clam were $4.9\~24.9^{\circ}C$ and 1.0210$\~$1.0266, respectively. Monthly changes in the condition factor showed in a wide range from 0.2381 to 0.2827, began to increase in January and reached the first maximum (0.2827) in April. And then the value rapidly decreased in June, thereafter, reached the second peak (0.2812) in August. The condition factor of this species showed the two peaks, and gonadal development reached sexually mature and ripe conditions during the period of these two peaks. The meat weight rate ranged from $38.0\%$ to $46.4\%$, and its change showed a similar tendency with the condition factor. The reproductive cycle of this species can be divided into five successive stages: in both sex, multiplicative (December to January, July to August), growing (January to February, September to October), mature (February to April, September to November), spawning (April to June, September to November), and degenerative and resting stage (May to July, November to January).

• Korean Journal of Remote Sensing
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• v.20 no.4
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• pp.245-252
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• 2004

The mechanism of cold core eddy formation was investigated using boundary conditions between the East China coastal cold water and the Kuroshio Warm Current, wind data related to the monsoon which was measured by QuikSCAT, and the bottom topography of the East China Sea. When winds blow from the southeast at an intensity comparable to that in the winter period in 1999 and 2003, the warm Kuroshio and Tsushima Current became stronger, and temperatures were considerably higher than those of the extended cold water of the coast of the East China. At that time, the cold water was captured by warm water from the Kuroshio and the Tsushima Current. This facilitated the formation of mesoscale cold core eddies with diameter of 150km in the East China Sea in May, 1999 and February, 2003. The cold core eddy which was detected by NOAA, SeaWiFS and QuikSCAT satellites. The East China Sea is considered to be important not only as a good fishing ground but also nursery and spawning area for many kinds of fishes. Therefore, it would be worth studying spatio-temporal variations of the cold core eddy in the environmental conditions of the northwestern East China Sea using systematic remote sensing techniques.

• Korean Journal of Ecology and Environment
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• v.53 no.4
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• pp.445-452
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• 2020

In this study, we carried out a distribution and migration boundary lines of chum salmon (Oncorhynchus keta) in the Milyang River. We measured the total length of dead chum salmons. As a results, 40 chum salmons were found during the study period, 25 dead salmons and 15 alive individuals. The ratio of female was 64%. We verified the migration boundary lines of chum salmons based on a sighting survey until detecting a structure that chum salmons are not able to migrate upstream. We discovered that chum salmons were not able to migrate up to 13 km in a mainstream of the Milyang River and up to 12 km in the Danjang stream (a tributary of the Milayang River) from upstream of the Yerim Bridge. Therefore, our results indicate that Milyang River should improve a river connectivity by demolishing weirs that disturb chum salmon's migration or installing appropriate fishways. Also, effective legislations are needed to retain naturality in spawning ground and micro-habitats to increase the survival rate of parrs and smolts.

• Korean Journal of Ichthyology
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• v.36 no.1
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• pp.10-19
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• 2024

This study investigated the early life history of Hemibarbus labeo from in Wicheon, stream Nakdonggang-River, and compared their characteristics with closely related species. In April 2021, egg formation and development of autonomous fish were observed in fertilized eggs collected at four spawning sites. The size of the fertilized egg was 1.93~2.39 (average 2.22±0.15, n=30) mm. The water temperature was 22.2~24.1°C, and the hatching time took 109~115 hours. Newly after hatching, the total length of the yolk-sac larvae was 7.50~8.80 (average 7.99±0.46) mm, and the mouth and anus did not develop and had difficulty in being yolk. 6 days after hatching, the preflexion larvae were fed with a total length of 9.49~10.2 (9.78±0.23, n=30) mm. 10 days after hatching, the flexion larvae was 9.97~11.9 (10.7±0.72, n=30) mm in total length, and the tail of the vertebrae began to bend. 20 days after hatching, the postflexion larvae was 12.6~15.2 (13.9±0.77, n=30) mm in total length, and the tailbone was completely bent to 45°. 29 days after hatching, the total length of the juvenile was 16.9~19.8 (18.1±0.91, n=30) mm, and the number of fins reached an integer with 10 dorsal fins, 9 anal fins, and 7 ventral fins. The distribution of melanophore, such as the head, the center of the body, and the upper part of the fin, was different from that of the allied species during the postflexion larvae period, so the morphological characteristics could be distinguished.

• Journal of Aquaculture
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• v.7 no.4
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• pp.189-205
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• 1994

Formerly, adult-tiger puffer, Takifugu rubripes with ova caught in the sea, were used for seedling production. But it was difficult to secure naturally-ripened adults. For the purpose of adult tiger puffer in captivity, this study was carried out. To determine the growth 220 tiger puffers hatched in 1990 (3-year-old) and 1991 (2-year-old) were used. For spawning and egg incubation leading to fry development, eggs were stripped from tiger puffers hatched in 1988 (5-year-old) and 1990 (3-year-old) through human chorionic gonadotropin (BCG) treatments. In May, 1993, mean body length and mean body weight of 2-year-old tiger puffer were $30.72\pm1.35cm\;and\;1,048\pm228 g,$ and that of 3-year-old tiger puffers were $36.02\pm1.17cm$ and $1,402\pm66g$ respectively. The relationship between body length (L) and body weight (W) of 2-year-old the tiger puffers during the experiment period was represented as $W\;=\;1.7892L^{31524}\times10^5$ (r= 0.9436) and that of 3-year-old, $W=\;3.2840L^{36099}\times10^6$ (r= 0.9070) respectively. The GSI in female 2-year-old-fish changed from $0.23\times0.l2\;to\;0.74\pm0.08$, during the experiment period, and in male it didn't change remarkably until November, but thereafter it increased and showed a peak of $8.69\pm5.09$. The GSI of 3-year-old-fish showed a peak of $8.05\pm5.58$ in April in female and $12.65\pm4.60$ in May in male. The change of HSI in 3-year-old-fish was correlative to the change of GSI, but in 2-year-old-fish it was little correlative. In female gonad of 2-year-old tiger puffer, the mature oocytes reached $350{\mu}m$ in April, but thereafter they didn't spawn and became atrophied. But in male gonad, a great number of spermatozoa were crowded in the testicular lobuli in April. Female gonad of 3-year-old tiger puffer had the mature oocytes of 650 pm in March and the ripe oocytes, $900{\mu}m$ in April. Male testis development was similar to that of 2-year-old-fish. Egg-stripping after hormone treatments was possible past 139 hours and 142 hours from each of two 5-year-old-fish (500IU/kg, BW), and after 114 hour from a 3-year-old-fish (1,000 IU/kg, BW) under water temperature $16.3\~17.8^{\circ}C$. Eggs stripped amounted was 650 g and 400 g from two 5-year-old-fish and 610 g from the 3-year-old-fish, and fertilization rates were $98.0\%,\;97.4\%\;and\;96.5\%$ respectively. All the hatched larvae devloped into normal fry.