• Development and Reproduction
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• v.25 no.4
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• pp.225-234
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• 2021

The present study aimed to investigate the mechanism of cell surface receptor loss by two constitutively activating mutants (designated L469R, and D590Y) and two inactivating mutants (D417N and Y558F) of the luteinizing hormone receptor (LHR) in the Japanese eel Anguilla japonica, known to naturally occur in human LHR transmembrane domains. We investigated cell surface receptor loss using an enzyme-linked immunosorbent assay in HEK 293 cells. The expression level of wild-type eel LHR was considered to be 100%, and the expression levels of L469R and D417N were 97% and 101%, respectively, whereas the expression levels of D590Y and Y558F slightly increased to approximately 110% and 106%, respectively. The constitutively activating mutants L469R and D590Y exhibited a decrease in cell surface loss in a manner similar to that of wild-type eel LHR. The rates of loss of cell surface agonist-receptor complexes were observed to be very rapid (2.6-6.2 min) in both the wild-type eel LHR and activating mutants. However, cell surface receptor loss in the cells expressing inactivating mutants D417N and Y558F was slightly observed in the cells expressing inactivating mutants D417N and Y558F, despite treatment with a high concentration of agonist. These results provide important information on LHR function in fish and the regulation of mutations of highly conserved amino acids in glycoprotein hormone receptors.

• Korean Journal of Ecology and Environment
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• v.55 no.2
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• pp.167-174
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• 2022

The Ministry of Oceans and Fisheries promoted the installation of eel-ladder for the purpose of creating inland water resources. Currently, eel-ladder have been installed and operated at the Geumgang Estuary Bank (2018), Yeongam Embankment (2019), and Asanman Embankment (2020). In this study, the number of glass eels in eel-ladder in 2021 was monitored and factors affecting the rise that from ocean to river of eels were investigated. Glass eels in eel-ladder were found when the salinity was relatively low, and they started when the freshwater and seawater temperatures were above 20℃. Comparing the number of occurrences by year, the largest number of glass eels was observed in 2021, but it is judged that this is not according to the distribution of glass eels in sea, but rather as a result of the investigator's eel-ladder repair and guidance on illegal fishing.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.21 no.1
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• pp.36-43
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• 2016

Wild glass eels found in the Korean peninsula are thought to migrate along the North Equatorial Current and undergo the processes of spawning and incubation in the Mariana Trench. Juveniles of the wild glass eels are collected from the southern and western coasts of the Korean peninsula and used as seeds for aquaculture. To investigate the feeding behavior of wild glass eels, we collected glass eels from the Nakdong River estuary during March and April 2014 and analyzed the total length, wet weight, dry weight, carbon and nitrogen contents, and stable isotope ratio of eels as well as water temperature and salinity. Water temperature in the Nakdong River estuary was $13.2{\pm}1.0$ (mean ${\pm}$ 1SE; range, $10.1{\sim}15.7)^{\circ}C$ and salinity was $24.8{\pm}2.4$ (13.2~34.0), showed a lower range from 13.2 to 30.0 (a mean of 21.2) when the floodgates were opened. The total length of glass eels was $56.5{\pm}0.2$ (51.0~63.6) mm, wet weight was $70.9{\pm}1.4$ (33.6~133.2) mg, and dry weight was $16.5{\pm}0.3$ (10.1~29.1) mg. Carbon and nitrogen contents of glass eels were $51.0{\pm}0.8%$ and $13.9{\pm}0.1%$, respectively. Mean ${\delta}^{13}C$ and ${\delta}^{15}N$ values of glass eels collected from the Nakdong River estuary were -20.9±0.2‰ and 6.1±0.1‰, displaying similar values to those of leptocephalus, glass eel larvae collected from the North Equatorial Current. Therefore, this result suggest that the glass eels collected from the Nakdong River estuary do not feed on prey after metamorphosis from eel larvae to glass eels their migration.

• Journal of fish pathology
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• v.9 no.2
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• pp.185-193
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• 1996

Extensive acquirement of drug resistance to traditional antibacterial agents poses a serious problem to eel aquaculturists. To collect the basic information for new drug development in the future, we assessed the in vitro antibacterial efficacy of 14 new quinolones with 75 isolates of Edwardsiella tarda from local aquaculture tanks of Anguilla japonica. Of all tested quinolones under development or marketed for human use, DU-6859 was most potent with its $MIC_{50}$ value of $0.05{\mu}g$/ml in broth microdilution assay. The drugs whose $MIC_{50}$ values ranged from 0.2 to $0.78{\mu}g$/ml were T-3762, Bay-y3118, ciprofloxacin, norfloxacin, ofloxcin and tosufloxacin. The weakest group of drugs, with their $MIC_{50}$ being 1.56-$3.13{\mu}g$/ml, were difloxacin, sparfloxacin, fleroxacin, Q-35, amifloxacin, lomefloxacin and enoxacin. The number of resistant strains, when arbitrarily defined with their MICs of $\geq6.25{\mu}g$/ml, was : 3 to T-3762, 3 to Bay-y3118, 44 to difloxacin, 16 to sparfloxacin, 13 to ciprofloxacin, 19 to fleroxacin, 36 to Q-35). 31 to amifloxacin, 5 to norfloxacin, 13 to ofloxacin, 31 to lomefloxacin, 41 to enoxacin, 12 to tosufloxacin and 0% to DU-6859, respectively. This information can be taken into consideration for the future development of fisheries antibacterial quinolones.

• Journal of Aquaculture
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• v.17 no.4
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• pp.275-281
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• 2004

The present study was conducted to evaluate dietary requirements for essential fatty acids (EFAs) such as linoleic acid (LA, l8:2n-6), -lenolenic acid (LNA, 18:3n-3), or docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (ARA, 20:4n-6) in juvenile eel Anguilla japonica cultured in a recirculating system for 16 weeks. The experimental diets contained 50% crude protein, 10% crude lipid and 3800 kcal/kg energy.Brown fish meal and blood meal were used as the main protein sources, while coconut oil, com oil and linseed oil were used as the lipid source to yield target fatty acids ratios. At the end of the trial, the effects of essential fatty acids supplementation on weight gain (WG), specific growth rate (SGR), feeding efficiency (FE), proximate composition andwhole body fatty acids contents were examined. WG, SGR, and FEof eels fed diet D2, D3, was significantly higher (P<0.05) than those of fish fed the other diets. Whole body HUFA concentration of eels fed D 1 was significantly lower (P<0.05) than those fed the other diets. HUFA/SFA (saturated fatty acids) ratio of whole body in eels fed diets D2, D3 and D6 were significantly higher than that of eels fed diet D1 (P<0.05).DHA/EPA ratio of whole body in eels fed diet D7was significantly higher than those fed the other diets; and eels fed diet D5 showed the lowest DHA/EPA ratio among all the dietary treatments (P<0.05).Based on the experimental results, we concluded that LNA (n-3) and LA (n-6) were necessary for optimum growth of juvenile eel, and the dietary requirement of LNA and LA were 0.35∼0.5% and 0.5∼0.65%, respectively.

• Korean Journal of Ecology and Environment
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• v.35 no.3 s.99
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• pp.237-246
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• 2002

Tamjin Dam is built in the upper reaches of the Tamjin River which flows through the Janghung-gun and Gangjin-gun of the Jeollanamdo, Korea. In order to map out a preservation strategy of the fish community from dam construction, We studied the distribution of fish distribution and changes of the habitat environment. we found 49 fish species inhabiting in the downstream and upstream of the Tamjin Dam. Among them, migratory fish were two species sweet smelt, Plecoglossus altivelis and freshwater eel, Anguilla japonica. The Coreoperca kawamebari which designated as a species to be protected by The Ministry of Environment of Korea was also observed. After the dam construction, reservoir would be filled with water and running water system will change to standing water system. Then the habitat and spawning space for mountain torrent fish will be reduced and the migration of migratory fish to upstream will be blocked. Through our study, we proposed several ways to protect fish community. In order to preserve the reduced habitat and spawning area of mountain torrent fish, a fishway has been diagnosed to be built in the shallow reservoir in the entrance of the upriver. The establishment of artificial spawning ground on the riverside has been recommended. In addition, We propose a creation of a shelter for fresh water eel, Anguilla japonica in areas where the depth of the water is about l0m by laying rocks. Since it is difficult for a spawning ground to be formed naturally in the reservoir due to the year-round changes in water level, We suggested a floating spawning facility using an artificial fixture. In the downstream of the dam, a waterway-style habitat and spawning ground in the river and increasing the diversity and abundance of fish fauna in the Tamjin River. A low-cost and highly efficient operational fishway has been recommended so that migratory fish such as Plecoglossus altivelis (sweetfish) can migrate from the lower reaches to the upper reaches of the river.

• Korean Journal of Ecology and Environment
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• v.34 no.3 s.95
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• pp.251-258
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• 2001

The ichthyofauna and passing efficiency of fish ways were surveyed in the lower and upper regions of the river mouth dam in the lower reaches of the Nakdong river from June to December in 20()0. As the dam built in the river mouth, the brackish area in the estuary disappeared completely and the transitional area did not formed. The fishes collected from survey were classified into 49 species, 45 genera belonging to 29 families. Among them, the fresh water fishes composed of 10 species, peripheral freshwater fishes 11 species and sea water fishes 28 species respectively. Because of the ecological difference between the fresh and sea water, dominant species in the Myeong-ji of sea water area was Acanthogobius flavimanus (39.1%) and in the Sa-sang of fresh water area was Achanthorhodeus macropterus (44.4%). By the video camera records, fishes were identified nine species like as Coilia ectenes, Cyprinus carpio, Hemibarbus labeo, Squalidus gracilis majimae, Plecoglosus altivelis, Lateolabrax japonicus, Anguilla japonica, Mugil cephalus and Pholis nebulosa. Based on total species collected, the efficiency of the fish way for the anadromous fish was 10.1%. Therefore, efficiency evaluation of the fish way in the Nakdong River Mouth Dam was low.

• Korean Journal of Environment and Ecology
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• v.27 no.4
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• pp.437-448
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• 2013

The ichthyofauna and fish community were studied in Daecheon Stream from April to October 2012. During the survey period a total of 42 species belonging to 13 families were collected. Dominant species by number was Zacco platypus(32.3%) and Tridentiger brevispinis(12.8%). In biomass, the dominant species was Z. platypus(27.7%) and Chelon haematocheilus(11.9%). Also, eight Korean endemic fish species and one endangered species (Rhodeus pseudosericeus) were collected. In addition, two exotic species(Carassius cuvieri and Micropterus salmoides) and migration fish species(Anguila japonica) were observed. Based on the length-weight relationship of Z. platypus, the b value was 3.21~3.29, and the condition factor(K) was 0.89 on average with stable condition. According to similarity analysis, fish communities in Daecheon Stream were divided into three groups; the upper reaches near a reservoir(St. 1), the middle reaches (St. 2 to 4) and the lower reaches near a weir(St. 5). Dominant species at each group were Zacco koreanus(St. 1), Z. platypus(St. 2 to 4) and T. brevispinis(St. 5). This result suggested that artificial structures such as dam and a weir have a marked effect on the distribution of fish communities in Daecheon Stream.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.17 no.6
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• pp.477-484
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• 1984

The crude lipid contents in meat, skin and viscera of eel were 24.94, 20.00 and 14.96, respectively, and higher than the other fresh water fishes. The free lipid was consisted in order of neutral lipid(86.71~94.94), phospholipid(4.13~12.74) and glycolipid(0.63~1.22), and the bound lipid in order of phospholipid(51.74~75.21), neutral lipid(14.41~36.82) and glycolipid(5.12~7.51). The neutral lipid in free lipid was mainly consisted of TG(68.51~95.22), and that in bound lipid TG(36.54~39.94), ES & HC(17.20~18.01), and MG(15.81~18.11). The phospholipid in free lipid was mainly consisted of PC (32.40~56.08) and PE(18.71~31.09), while that in bound lipid PC (<42.51~67.90) and PS (23.37~34.49). The contents of major fatty acid of polar lipid in free and bound lipids were $C_{16:0}$(16.58, 14.10, $C_{18:0}$(12.44, 7.36), $C_{18:1}$(16.01, 15.78), $C_{20:4}$(10.01, 6.11) $C_{20:5}$(4.20, 8.67) and $C_{22:6}$(10.26, 18.32) and those of nonpolar lipid in free and bound lipids were $C_{16:0}$(22.31, 18.61), $C_{18:0}$(4.36, 5.69, $C_{18:1}$(36.30, 27.20) $C_{20:5}$(2.88, 2.38) $C_{22:5}$(6.38, 5.11) and $C_{22:6}$(1.20, 5.11). The total essential fatty acid(TEFA) content of polar lipid in meat was ranged from 17.33 to 22.88, and 2.0~3.0 times higher than that of nonpolar lipid, and the TEFA content of bound lipid in meat was ranged from 11.54 to 22.88, and 1.5~2.0 times higher than that of free lipid. The w3 highly unsaturated fatty acid(w3-HUFA) content of polar lipid in meat was ranged from 8.63 to 42.85, and higer than 11.48 to 14.42 of nonpolar lipid. Also the w3-HUFA content of bound lipid in meat was ranged from 13.35 to 42.85, and higher than 11.48 to 18.63 of free lipid. The w3-HUFA content in meat was higher than that in skin and/or viscera

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.5
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• pp.439-446
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• 1985

This study was designed to compare the lipid components among wild and cultured eel, Anguilla japonica, and conger eel, Astroconger myriaster. The lipid components of cultured eel were analyzed and compared with those of wild and conger eel. In the content of total lipid, the lipid content in cultured eel was slightly higher than that in wild one, but 2 times higher than that in conger eel. The lipid contents in edible portion of wild and cultured eel were 5 times higher than those in viscera, but the lipid content in edible portion of conger eel showed a similar trend to that in viscera. In the fatty acid composition of neutral lipid in edible portion, percentages of $C_{14:0},\;C_{16:0}\;and\;C_{18:1}$ in cultured eel were higher than those in wild one, while percentages of $C_{16:1},\;C_{18:2},\;C_{18:3},\;C_{20:4},\;C_{20:5},\;C_{22:5}\;and\;C_{22:6}$ lower, and percentages of $C_{18:0},\;C_{20:4}\;and\;C_{22:6}$ in conger eel were noticeably higher than those in wild and cultured eels. In the case of phospholipid in edible portion, percentages of $C_{18:0}\;and\;C_{18:2}$ in cultured eel were higher than those in wild one, while percentages of $C_{16:0},\;C_{16:1},\;C_{18:1},\;C_{18:3},\;C_{20:4},\;C_{20:5},\;C_{22:5}\;and\;C_{22:6}$ lower. The unsaturation (TUFA/TSFA) of neutral lipid was no significant difference among wild and cultured eel, and conger eel, but that of phospholipid in wild eel was higher than that in cultured eel and conger eel. The essential fatty acid content(TEFA) of neutral lipid in edible portion of wild eel was 3 times higher than that of cultured one. but the TEFA of phospholipid in edible portion was no significant difference among wild and cultured eels, and conger eel. The w3 highly unsaturated fatty acid content (w3 HUFA) of neutral lipid in edible portion of wild eel was 2.0 to 2.5 times higher than that of cultured eel and conger eel, but the w3 HUFA of phospholipid in edible portion of wild eel was noticeably higher than that of cultured eel and conger eel. In the ratio (A/B) of fatty acid content (A) in cultured eel to that (B) in diet, the A/B ratios of $C_{18:2}\;w6,\;C_{18:3}\;w3,\;C_{20:5}\;w3\;and\;C_{22:6}\;w3$ were 0.23 to 0.48 much lower than the other fatty acid. Consequently, it is considered that the ratios of w3 HUFA is related to the biosynthesis of polyenoic acid and growth rate of cultured eel.