• Korean Journal of Environmental Biology
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• v.32 no.4
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• pp.382-388
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• 2014

Shortfin eel (Anguilla bicolor pacifica) is a species of commercial importance and its production is greatly affected due to the infection by Heterosporis anguillarum. In this study, we evaluated the effect of H. anguillarum infection on the growth of Shortfin eel. A disease that trunk muscle of cultured shortfin eel, Anguilla bicolor pacifica, were irregular and resulted in death, breakout of the commercial eel culture farm. We observed that the trunk muscle of infected eels were irregular and represented white or yellowish externally. Histopathologically, a great numbers of large or small spores and sporophorocysts were also observed in degenerated muscle layer. The cloning of specific gene of H. anguillarum, encoding small subunit ribosomal RNA (SSU-rRNA) was amplified by the polymerase chain reaction(PCR) from the muscle lesion of diseased eel. The size of clone gene is well matched with the size of small subunit ribosomal RNA of H. anguillarum and thus confirming the infection by H. anguillarum.

• Journal of Life Science
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• v.27 no.10
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• pp.1097-1103
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• 2017

For the artificial induction of the sexual maturation of Anguilla japonica, salmon pituitary extract (SPE) is continuously injected into females, and the eggs obtained from artificial sexual maturation are artificially fertilized with sperms and hatched. However, repeated injection of SPE in the abdominal cavity causes tremendous stress in females, which may prevent their complete sexual maturation and reduce the immune system function, ultimately resulting in death. In addition, the poor quality of the ovulated eggs can reduce the hatching and survival rate of larvae. In the present study, sexual maturation of females was induced by inserting an osmotic (OS) pump containing hormone analogs known to effectively induce sexual maturation into the abdominal cavity of female eels, and the effect of the OS pump on the induced sexual maturation was investigated. Our study results showed that the gonadosomatic index (GSI) was significantly higher in the fish subjected to SPE injection than those subjected to human chorionic gonadotropin (hCG), gonadotropin-releasing hormone analog (GnRHa), and methyl testosterone (MT) injections, either separately or in combination. In addition, a histological analysis showed that the oocytes in the SPE OS pump groups were more mature (entered the nuclear shift stage) than those in the other groups. These results suggest that an osmotic pump containing hormone analogs can be used to induce sexual maturation in female A. japonica artificially.

• Journal of Fisheries and Marine Sciences Education
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• v.27 no.3
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• pp.672-681
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• 2015

Edwardsiellosis has become a serious diseases problem in cultured eels for many years. This study was performed to investigate possibility of vaccination against edwardsiellosis caused by Edwardsiella tarda. We conducted a immersion and/or oral vaccination using formalin-killed E. tarda in eel Anguilla japonica. Three groups of fish ($26.8{\pm}1.2g$, $7.1{\pm}0.7g$ and $2.2{\pm}0.4g$) were used in this study. The protection (relative percentage survival, RPS) and serum antibody response (agglutination titer) were evaluated in the vaccinated fish. No correlation between agglutination titer and survival rate was observed in vaccinated fish. However, there was a satisfactory protective (RPS>50%) in vaccinated fish. Immersion (10 mg/mL, 1 hr) and immersion (10 mg/mL, 1 hr) plus oral (10 mg/g, 10 days) of $26.8{\pm}1.2g$, immersion (10 mg/mL, 1 hr) plus oral (10 mg/g, 10 days) of $7.1{\pm}0.7g$ showed RPS of 62.6%, 52.2% and 56.8%, respectively.

• Development and Reproduction
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• v.10 no.3
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• pp.177-184
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• 2006

Retinol-binding protein(RBP) plays an important role in the specific transport of retinol to target cells through the blood stream in higher vertebrates. In order to clarify the effects of 4-nonylphenol(4-NP) on RBP mRNA expression in the rockfish, Sebastes schlegeli which is common in coastal waters of Korea and commercially important species, the cDNA library was constructed from the liver, and a partial fragment of the RBP gene was cloned. The deduced amino acid sequence from the RBP mRNA showed a high homology to the amino acid sequence from Sparus aurata(80%), Oncorhynchus mykiss(72%) or Anguilla anguilla(78%). Effects of 4-NP on RBP and vitellogenin(VTG) mRNA expression level in rockfish were examined by the northern blot analysis. In female and male rockfish injected with 4-NP(10 mg/kg BW, lower dose), there was no changes in the levels of VTG mRNA expression in the liver. The RBP mRNA levels, however, decreased at 48 hours after the injection in male. In the rockfish injected with 4-NP(25 mg/kg BW, higher dose), the level of VTG mRNA expression increased after 24 hours, regardless of sex. The level of RBP mRNA expression decreased at 48 hours after the injection in both sexes. These data indicate that estrogenic mimics such as 4-NP exhibit a contrasting effect on RBP and VTG gene expression in rockfish.

• Development and Reproduction
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• v.13 no.1
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• pp.35-41
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• 2009

In the present study, we investigated the effects of rearing condition during the winter period on artificial maturation and reproduction of cultured female eel, Anguilla japonica. The female eel was adapted by combination of environmental conditions (seawater/low temperature, $10^{\circ}C$; seawater/high temperature, $20^{\circ}C$; freshwater/low temperature, $10^{\circ}C$; freshwater/high temperature, $20^{\circ}C$) during 8 weeks of the winter period. Then, the female eel cultivated by different conditions during the winter were transferred to seawater at $20^{\circ}C$ for induction of artificial maturation by salmon pituitary extraction (SPE) injection. The results shown that gonadosomatic index (GSI) and plasma levels of estradiol-$17{\beta}$ (E2) were significantly higher in female eel were reared in seawater than in freshwater, and were the highest at eel adapted by seawater/low temperature. Also, reproduction coefficient were higher in seawater/low temperature than in the other groups. These results will provide valuable information for elevation of the artificial maturation and reproduction coefficient in the cultured female eel.

• Korean Journal of Ichthyology
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• v.30 no.4
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• pp.185-193
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• 2018

From 2017 to 2018, the disease has been monitored at four culturing eel farms in Incheon and Gyeonggi region in Korea. As a result, diseases with gill congestion frequently occurred. This disease occurred regardless of size of eel, but the frequency and cumulative mortality were high in eels within 3 months after stocking. The infected fish showed pathological histopathological features such as intense congestion and dilation in the central venous sinus (CVS) of gill filaments and hemorrhages in liver and kidney. Hexagonal viral particles measuring about 70 nm in diameter was observed in nuclei and cytoplasm of gill vascular endothelial cells. Molecular biologic diagnosis by both PCR and genetic analysis has been revealed that the causative agent of this disease is Japanese eel endothelial cells-infecting virus (JEECV), the cause of viral endothelial cell necrosis of eel (VECNE), which is mainly reported in Japan. This study is the first report on the characteristics of JEECV and VECNE infection in domestic eel farms.

• Journal of Life Science
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• v.28 no.12
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• pp.1424-1431
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• 2018

We prepared flocculated detritus-like organic marine snow originating from various organisms by fermentation using microorganisms; this fermented organic material was fed to the leptocephali of the eel (Anguilla japonica) to investigate whether or not such organic matter was an appropriate food source for the larvae. A strain was isolated from a biofloc technology system used to culture fish, and seven types of organic material from hen's egg, eel muscle, tuna muscle, lugworm, shrimp, manila clam, mussel, and sea squirt were fermented using isolated bacteria (Bacillus sp.). The fermented matter did not show any specific form and was larger than $10-20{\mu}m$ but no more than $100{\mu}m$ in size. Four diets (A-D) were prepared using the various fermented products, and the larvae were fed the prepared food from 20 days after hatching. The leptocephali fed the A, B, and C diets survived until 37, 39, and 37 days after hatching, respectively. However, the leptocephali fed the D diet survived for 60 days after hatching. The protein content of each diet was very similar, but the n-3 HUFA concentration in the D diet was approximately twice as high as that of the others.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.5
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• pp.697-704
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• 2022

This study was investigated to evaluate the level of acute TAN (total ammonia nitrogen) and NO₂^--N concentrations at pH levels of 6.0, 7.0 and 8.0 for 96 h in juvenile marbled eel Anguilla marmorata (total length 209.0±22.02 mm and body weight 13.0±5.01 g). The result of the present study showed that the survival rate of juvenile eel at TAN concentrations 0, 100, 200, 300, 400, and 500 ppm at pH 6.0, pH 7.0, and pH 8.0 were 100, 100, 96.7, 74.4, 31.1, and 0%; 100, 82.2, 61.1, 36.7, 0, and 0%; and 98.9, 55.6, 8.9, 0, 0, and 0%, respectively. In addition, the survival rate of juvenile eel at NO₂^--N concentrations 0, 100, 200, 300, 400, and 500 ppm at pH 6.0, pH 7.0, and pH 8.0 were 100, 43.3, 21.7, 0, 0, and 0%; 100, 76.7, 65.0, 43.3, 21.7, and 13.3%; and 100, 100, 100, 88.3, 78.3; and 58.3% respectively. The 96h-LC₅₀ at pH 6.0, 7.0, and 8.0 were 332, 235, and 167 mg/L for TAN, and 188, 296, and 711 mg/L for NO₂^--N, respectively. The acute toxicity of TAN to juvenile eel increased exponentially with increase in pH, whereas the acute toxicity of NO₂^--N to juvenile ell increased with low levels of pH and lengthening of exposure time to NO₂^--N.

• Development and Reproduction
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• v.12 no.3
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• pp.261-266
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• 2008

In the present study, we investigated in vivo effects of Manchurian trout recombinant gonadotrophin hormone (mt-rGTH) on the induction of maturation in female eel, Anguilla japonica. The brood stock, female eel (450$\pm$50 g) were weekly injected intramuscularly with different doses of 0.1, 1, 10 ${\mu}g\m{\ell}$/fish (mt-rFSH or mt-rLH) for 10 week. The effects of r-mtGTH were analyzed by gonadosomatic index (GSI), ovarian follicle diameter and sex steroid levels. All groups did not exhibit significant differences in the GSI values. Whereas plasma testosterone (T) and estradiol-17$\beta$ (E2) levels did not change significantly in control group, plasma levels of T and E2 by injection of the r-mtFSH or r-mtLH were increased at 2 or 4 week after injection. In addition, injection of the mt-rFSH (1, 10 ${\mu}g/m{\ell}$/fish) or mt-rLH (0.1, 1, 10 ${\mu}g/m{\ell}$/fish) significantly increased follicle diameters comparing to the control group. These results demonstrate that the recombinant hormone may affect early ovary development and maturation in female eel. Taken together, these results suggest that the recombinant Manchurian trout FSH and LH are effective for reproductive activities in female eel.

• Proceedings of the Korean Aquaculture Society Conference
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• 2004.05a
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• pp.415-416
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• 2004