• Journal of Life Science
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• v.23 no.8
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• pp.998-1003
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• 2013

The effects of oral administration of estradiol-$17{\beta}$ (E2) on glass eels (Body weight: $0.16{\pm}0.05g$, Total length: $6.2{\pm}0.9cm$) and young eels (Body weight: $2.6{\pm}0.6g$, Total length: $13.2{\pm}0.6cm$) on gonadal sex and growth were examined, respectively. Glass eels were fed a diet containing E2 at a dose of 10 mg/kg or 25 mg/kg, respectively, for five months. The female ratio significantly increased in all E2-treated groups (10 mg/kg diet group: 70%; 25 mg/kg diet group: 90%) when compared to the control group (10%). Young eels were fed a diet containing E2 at a dose of 25 mg/kg for four months. The female ratio also significantly increased in the E2-treated groups (60%) compared to the control group (20%). The highest female ratio was observed in the stage of glass eels rather than young eels. In all experiments, however, the growth of eels treated with E2 was similar to that of controls to the end of the experiment. Thus, oral administration of E2 could be a good approach to controlling sex differentiation.

• Journal of fish pathology
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• v.9 no.2
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• pp.147-155
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• 1996

This study was carried out to examine the acute toxic effects of ammonia to the eel, Anguilla japonica in high temperature and pH levels by histopathological observations. The eels of 40 g average body weight were exposed to 4 different concentrations of total ammonia (0, 10, 20, 30 mg/$\ell$) for 24~120 hours. Each concentration was treated under 4 different levels of pH (7.5, 8.0, 8.5, 9.0) and each of these treatments was tested at 2 different temperatures ($27^{\circ}C$, $32^{\circ}C$). Histopathological changes in gill tissues were observed by hematoxylin-eosin stain. As increasing of pH (from 7.5 to 9.0), water temperature (from $27^{\circ}C$ to $32^{\circ}C$), total ammonia concentration (from 0 mg/$\ell$ to 30 mg/$\ell$) and exposure time (from 24 hours to 120 hours), gill discolorated to dark brown with the naked eye and gill tissues showed hypertrophy of gill lamellae, winding of the secondary gill lamellae, epitherial separation and necrosis histopathologically. When gill lamellae epithelium was separated from the blood vessels, gill discolorated to dark brown with the naked eye.

• Journal of Life Science
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• v.23 no.10
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• pp.1288-1294
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• 2013

Knowledge of morphological changes in eel larvae is very important for artificial rearing of eel larvae. In this study, we investigated the morphological structure of the head region and histological changes of the eye retina in artificially reared larvae at various stages and in glass eel just after metamorphosis. Structural changes were observed in the upper jaw (maxilla) and the lower jaw (mandible) after 100 dah (day after hatchery) and after metamorphosis. Teeth had degenerated by the time of completion of metamorphosis. Major histological changes observed in the eye retina were the formation of the outer plexiform layer and the outer nuclear layer from 100 dah larva and a change in the rod cell layer after metamorphosis. The cornea was not observed at 10 dah in the eel larva. More information is needed on the early developmental stages of eel larvae to enable mass production of glass eels. The results obtained in the present research will be useful when developing novel rearing programs for eel larvae.

• Journal of Aquaculture
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• v.16 no.4
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• pp.267-272
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• 2003

This study investigated sex determination through serum steroid hormone level and compared hematological characteristics of one-year old cultured eels, Anguilla japonica. Four different groups were divided with total length at 40∼45, 45∼50, 50∼55, and 55∼60 cm. Males dominated eels of 40∼50 cm in total length group, while females dominated eels of more than 50 cm. All females and males were immature. Hematocrit levels of males (total length: 40∼50 cm) were higher than those of females (total length: 50∼60 cm). Hemoglobin content also differed between males and females. Glutamate oxaloacetate transaminase (GOT) levels of 40∼45 cm males tended to be higher (157$\pm$3.46 IU/L) than that of other sized males, but there were no significant differences between groups (P<0.05). The highest GOT levels were found in of 55∼60 cm females (148$\pm$3.46 IU/L) compared with that of other female groups (P<0.05). Glutamate pyruvate transaminase (GPT) levels of males and females in the 55∼60 cm size range was significantly higher thanothers (P<0.05). The result of this study indicated steroid hormone content of males and females were very low, but testosterone (T) and estradiol-17$\beta$, (E2) contents of females were higher than those of males. For further research of sex determination in cultured eels, it needs to investigate in more defined body length.

• Journal of Aquaculture
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• v.16 no.4
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• pp.273-278
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• 2003

The present study provides nutritional characteristics of body composition based on the different collected locations and body sizes in wild eels, Anguilla japonica. Eels were collected in Kyungho river, near the Sachun bay (Gyeongnam) and Inchun river, near Gochang, Jeonnam. Eels were divided by size into the following groups: less than 100 g (Gochang: 75.8$\pm$17.6 g, Sachun: 89.3$\pm$6.42 g) and more than 200 g group (Gochang: 215$\pm$8.95 g, Sachun: 236$\pm$11.7 g). The moisture content of individuals in Gochang area (Gw) was higher than that in Sacheon area (Sw). In the results of proximate analysis, the ranges of moisture, crude protein, crude fat, and crude ash were 63∼72, 16∼20, 6.1∼15.4 and 2.2∼2.8%, respectively. Moisture and crude fat were significantly different (P<0.05) based on the captured locations. In fatty acid composition, the ranges of saturates, monoenes, polyenes, and n-3 PUFA content were 38.0∼48.0, 51.5∼58.5, 1.95∼4.12 and 0.68∼1.53%, respectively. It was significantly different (P<0.05) based on the captured locations. In the amino acid composition, the ranges of essential and non-essential amino acids were 7.11∼12.5 and 8.34∼ 12.9%, respectively. These values were not significantly different (P>0.05) based on the captured locations, however these were significant different (P<0.05) based on their body weight. Therefore, these results indicated that the different body composition depends on the different captured locations and body sizes. Furthermore, it is necessary to examine more varied locations and body sizes for their body composition in eels.

• Journal of fish pathology
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• v.23 no.3
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• pp.293-302
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• 2010

Effects of formalin on removal of Pseudodactylogyrus spp. were examined against naturally infected eel, Anguilla japonica (weight 89.9~96g) at a water temperature of $28^{\circ}$. Prior to experiments for removal of the parasite, the hematological toxicity of formalin bath at 0~500 ppm for 30 min~24 h was assessed by hematocrit values (Ht). Based on the results of Ht, appropriate methods of treatment, concentrations and durations, were examined in the main study. There was no significant (P>0.05) change of Ht in 100 to 200 ppm for 24 h. In contrast, Ht increased significantly (P<0.05) at above 300 ppm. This suggests that physiological damage was caused by formalin bath treating with 300 to 500 ppm. Formalin bath with 100 and 200 ppm for 24 h caused significant decreases (P<0.05) in the infection of the parasite. In conclusion, the 100 ppm formalin for 24 hour-bath was found most recommendable for the effective treatment of Pseudodactylogyrus spp. for the gills of the infected eel because of the median lethal concentration ($LC_{50}$) of formalin to eel; cumulative mortalities were found to be 0 and 13.3%, respectively, following 24 h bathing.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.5
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• pp.557-566
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• 2022

The Japanese eel Anguilla japonica is a highly valued research object that is important for aquaculture in Asia, including the Republic of Korea. However, few studies have been conducted analyzing parentage using microsatellite markers derived from the Japanese eel. We acquired Japanese eel genome data using next generation sequencing technology, and constructed a draft genome comprising 1,087 Mbp. Using the Simple Sequence Repeat Identification Tool program, 444,724 microsatellites were identified. Of these, 1,842 microsatellites located in the 3' untranslated region, which are stably inherited, were finally selected. Ninety-six primers were selected to validate polymorphism at these microsatellites, and 9 primers were finally identified for multiplex analysis. Using multiplex polymerase chain reaction with three different fluorescence chemistries, we performed parentage analysis of an artificial Japanese eel population. CERVUS software was used to calculate the logarithm of the odds (LOD) scores and the confidence of the parentage assignments. The results presented here show that 83 out of 85 paternity cases were assigned at 95% confidence to a candidate father and mother with LOD scores ranging from 4.79 to 28.2. This study provided a microsatellite marker-based assay for parentage analysis of Japanese eels, which will be useful for selective breeding and genetic diversity studies.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2002.05a
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• pp.517-518
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• 2002

• Proceedings of the Korean Aquaculture Society Conference
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• 2005.05a
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• pp.126-127
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• 2005

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2000.05a
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• pp.440-441
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• 2000

1990년대에 들면서, 온수 양어장에서 버나바이러스(Birnavirus)성 아가미 질병인 2차새변 벽주세포 괴사증(일명: 아가미 점상출혈증)과는 그 증상에서 차이를 보이는 아가미 질병이 발생되었다. 새변의 울혈과 괴사 병변을 주로 나타내는 본 질병은 경우에 따라 가슴지느러미와 아가미 근접복부에 출혈상을 나타내기도 한다. 병어의 병리조직학적 관찰, 분리 바이러스의 생화학적 또는 전자현미경 관찰 및 감염실험을 통해 아가미 질병의 원인 바이러스로도 H. anguillae가 인정되었으므로 이에 그 연구내용을 보고한다. (중략)