• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.5
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• pp.464-470
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• 1985

Some eels Anguilla japonica, ranging from 16 to 23 g in their weight(average: 20 g), were sampled at the private eel farming company equipped with water recycling system, located at Kimhae city, Kyungnam Province, Korea. Three kinds of vaccine were prepared with Vibrio anguillarum (EPM-8406) isolated at National Fisheries University in Korea for the immune response experiment against eels; those vaccines were made by inactivating the strain with $0.3\%$ formalin for 24 hrs at $25^{\circ}C$, heating for 3 mins or for 15 mins at $121^{\circ}C$, respectively. The various optimal vaccination conditions for the control of vibriosis in the fish were investigated based on the cultivation temperature, vaccination concentration and booster effect. The maximum titer rapidly increased with higher temperature up to $23^{\circ}C$, but there were little differences between $23^{\circ}C\;and\;28^{\circ}C$. The formalin-killed vaccine showed good efficacy at the injection concentration of above $10^8$ cells per fish and little effect at the below $10^7$ cells. The booster effect on the vaccination showed good efficacy above twice-injections with little difference between the numbers of injection.

• 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.

• Journal of fish pathology
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• v.35 no.1
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• pp.93-102
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• 2022

This study performed a trichlorfon (TCF) residue and pharmacokinetic analysis with Japanese eels, Anguilla japonica, to obtain baseline data to establish the maximum residue level (MRL) of TCF in A. japonica. After dipping A. japonica in 30 ppm and 150 ppm of TCF at 28℃ and 18℃, drug residue in the body was analyzed with LC-MS/MS, and these results were further analyzed with the PK solver program to obtain the pharmacokinetic parameters of TCF in the serum, muscles, and liver. The maximum concentrations (C_max) in the serum, muscles, and liver were 25.87-357.42, 129.91-1043.73, and 40.47-375.20, respectively, and the time to maximum concentration (T_max) was 0.13-1.32h, 1.17-3.34h, and 0.14-5.40h, respectively. The terminal elimination half-life (T_1/2) was 2.13-3.92h, 5.30-10.35h, and 0.65-13.81h, respectively. In the 30 mg/L concentration group, TCF was not detected in the serum of eels 96 hours after bathing, and was below the detection limit after 336 hours in muscle and liver. On the other hand, in the 150 mg/L concentration group, TCF was not detected in the serum of eels 336 hours after bathing, but was detected in muscle and liver at 336 hours. In conclusion, the results of this study would be useful in establishing the MRL of TCF in farmed A. japonica.

• Journal of Marine Life Science
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• v.3 no.2
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• pp.81-86
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• 2018

The purpose of this study is to determine the effects of vibration on primary (e.g. plasma cortisol), secondary (e.g. plasma glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT), Na⁺, K⁺ and Cl^- and tertiary (e.g. mortality) stress responses in cultured eel, Anguilla japonica. For this purpose, three groups (including one control group and two stress groups) were set up. The control group was made exposed to vibration corresponding to 48 decibel (dB, V) (produced using electric vibrators) for 15 minutes per hour every day, and the two stress groups was made exposed to vibration corresponding to 58 and 68 dB (V) (produced using the same electric vibrators), equally, for 15 minutes per hour every day. Blood was sampled at day 0 (before starting vibration stress tests, BS), and days 1, 3, 5, 7, 9 and 11 (after starting vibration stress tests). As a result, plasma cortisol showed trend to continuously rise by consecutive stress from 4.1±0.1 ng/ml in BS. In 48 dB group (control), cortisol showed the highest level with 7.6±0.9 ng/ml after 7 days (p<0.05), but at 9 and 11 days was not significantly compared with BS level. In 58 dB group, the cortisol showed the highest level with 43.1±4.8 ng/ml after 1st day. Cortisol of 68 dB group increased significantly during the experimental period (14.4±2.3~32.0±5.7 ng/ml) (p<0.05). In 58, and 68 dB groups during the experimental period differed significantly compared to 48 group (p<0.05). Glucose in 48 dB were increased from 42.0 ±5.7 (BS) to 52.5±2.1 (1 day), the level was not significantly from 1 to 11 days. Glucose in 58 and 68 dB groups was increased significantly than BS during experimental period (p<0.05). K⁺ in 68 dB increased significantly (p<0.05) from 2.3±0.2 mE/ql (BS) to 3.3±0.5 mE/ql at 5 days. In 48 and 58 dB groups during the experimental period differed significantly (p<0.05). Na⁺ and Cl^- levels were not differed significantly during the experimental period. AST and ALT in 58 and 68 dB groups showed trend to continuously rise by consecutive stress. At 7 and 9 days in AST, between 48, 58 and 68 dB groups differed significantly (p<0.05). In 48, 58 and 68 dB groups at 1 day, blood hematocrit increased significantly higher than BS. The 11 days after vibration stress, the mortality in 48, 58 and 68 dB groups was 1.1, 5.1 and 5.8%, respectively. The present results have shown that A. japonica exhibited ''typical'' physiological responses when exposed to chronic vibration stress. These data suggested that chronic vibration stress caused substantial stress in the fish; especially the persisting elevated plasma AST and ALT levels observed would be expected to adverse effect. In conclusion, chronic vibration stress could greatly affects the hematological characteristics in A. japonica.