• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.5
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• pp.668-675
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• 2021

The infection status of domestic farmed eels Anguilla japonica, Anguilla bicolor and Anguilla marmorata with Japanese eel endothelial cell-infecting virus (JEECV) and anguillid herpesvirus 1 (AnHV) was examined at the major eel farming areas in Korea. These viruses were detected in all areas examined, regardless of the eel species or age. Any farm with a history of viral infection in adult fish confirmed the infection to be transmitted to stocked fry within 3 to 5 months. It is proposed that both viruses are horizontally transmitted within a given farm. The primary symptoms and histopathological lesions produced by the two viral infections are similar, making it difficult to distinguish the two diseases through clinical symptoms. Both viruses displayed 100% detection in the gills, suggesting that the gills are an optimal tissue for JEECV and AnHV monitoring. This study concluded that JEECV and AnHV were prevalent on eel farms across the country and caused very high mortality when the two viruses co-infected fry. Additional studies, including experimental infections, are needed to clearly understand the pathogenicity of each virus and the risk of co-infection.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.6
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• pp.860-868
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• 2014

The study was performed to investigate changes in hematological responses and antioxidative enzyme activities (superoxide dismutase, SOD; catalase, CAT) of Japanese eel Anguilla japonica following exposure to 0 (control), 2.33, 4.60, 6,64 and 8.78 mM nitrite-N in fresh water for 48 h. Hematological parameters such as plasma nitrite, electrolytes, cortisol, glucose, glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), hemoglobin (Hb), methemoglobin (metHb) and NADH-methemoglobin reductase (NMR) were measured. Plasma nitrite, cortisol, metHb and NMR increased directly with increasing ambient nitrite concentration, while Hb content showed a progressive decline. Levels of plasma potassium, GOT and GPT of the eel exposed to 6.64 mM ambient nitrite were significantly higher than the control fish. The activity of SOD and CAT in plasma, gill and liver of the eel following exposure to nitrite were augmented by increasing ambient nitrite. Levels of plasma nitrite, metHb, NMR, cortisol, glucose and antioxidative enzyme activities of the eel exposed to 2.33 mM ambient nitrite were significantly higher than the control fish. This study suggested that the eel acutely exposed to elevated ambient nitrite causes nitrite-induced stress responses, changes in antioxidative enzyme activities and hematological parameters.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.40 no.4
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• pp.193-200
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• 2007

Ion-exchange chromatography and ultra-filtration permeation were used to extract carnosine from the eel Anguilla japonica. In an investigation of its antioxidant properties, the eel carnosine prevented lipid peroxidation in linoleic acid systems, scavenged free radicals, and exhibited superoxide dismutase-like activity. These activities increased as the carnosine concentration increased. The nitrite scavenging effects (NSEs) of commercial carnosine and the eel carnosine were measured at various acidic pHs (1.2, 3.0, and 4.2). For both types of carnosine, the maximum NSE was observed at pH 1.2. At this pH, the NSE of the eel carnosine was 65.3%. Both types of carnosine were effective at maintaining reasonably good color of ground beef patties over 5 days of storage at $4^{\circ}C$ and inhibited metmyoglobin formation as well as lipid peroxidation. These data suggest that the eel carnosine might be useful as a "natural" antioxidant in commercial production and storage of muscle foodstuffs.

• Development and Reproduction
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• v.19 no.3
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• pp.163-166
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• 2015

Genomic DNAs were extracted from the muscle of twenty-one specimens of three eel species collected in Anguilla japonica (AJ), Muraenesox cinereus (MC) and Conger myriaster (CM) from the Yellow Sea, respectively. In the present study, 7 oligonucleotides primers generated 191 specific loci in the AJ species, 226 in the (MC) species and 181 in the CM species, respectively. The primer BION-02 generated the most loci (a total of 83), with an average of 11.86 in the AJ species. The specific loci generated by oligonucleotides primers exhibited inter-individual-specific characteristics, thus revealing DNA polymorphisms. With regard to average bandsharing value (BS) results, individuals from Conger myriaster species (0.808) exhibited higher bandsharing values than did individuals from Muraenesox cinereus species (0.729) (P<0.05). The longest genetic distance (0.430) displaying significant molecular difference was also between individual no. 01 within Anguilla japonica eel species and individual no. 04 within Anguilla japonica species. In this study, the dendrogram resulted from reliable seven oligonucleotides primers, indicating three genetic clusters composed of group I (ANGUILLA 01~ANGUILLA 07), group II (MURAENESOX 08~MURAENESOX 14) and group III (CONGER 15~CONGER 21). The existence of species differentiation and DNA polymorphisms among three eel species were detected by PCR analysis. As mentioned above, a dendrogram revealed close relationships between individual identities within three eel species. High levels of a significant genetic distance among three eel species showed this PCR approach is one of the most suitable tools for individuals and/or species biological DNA studies.

• Korean Journal of Ichthyology
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• v.29 no.2
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• pp.94-100
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• 2017

Three pseudo-silver eels (PS1~PS3) were found by analysis of silvering index and biological characteristics of 454 eels, Anguilla japonica, collected from the 9 sites of Korean fresh and brackish waters from September 2014 to August 2015. Two specimens (PS1~PS2) from Lake Soyang and one (PS3) from Geum river estuary were identified as pseudo-silver eel showing a large difference between silvering index and GSI. The external morphology of the pseudo-silver eels were in S2 (late silver eel) stage, but they were classified into Y1 (yellow eel) and Y2 (late yellow eel) stage in GSI, Gut index, Eye index and Y2 stage in gonadal development and mean egg diameter.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.48 no.1
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• pp.44-50
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• 2015

The basic and main nutritive ingredients of two temperature (Anguilla japonica and A. rostrata) and two tropical (A. bicolor pacifica and A. marmorata) fresh water eel species that are farmed domestically were evaluated. With exception of A. rostrata, eels cultured at the same farm were used for analysis. The contents of crude protein were in the order A. marmorata (17.7%)>A. rostrata (17.5%)>A. bicolor pacifica (17.4%)>A. japonica (15.8%) and the contents of crude lipids were A. japonica (21.5%)>A. rostrata (15.4%)>A. bicolor pacifica (10.5%)>A. marmorata (8.9%). These values differed significantly even among the three species of eel farmed under identical culture conditions. In comparison, all four species of eel showed similar pattern in overall amino acid composition, although slight differences in the compositions of some amino acids were observed. The fatty acid compositions of muscle tissues were notably different among four species of eel, especially between the tropical and temperature eels. In a taste-test of the meat of the four eel species, which considered taste, flavor and texture, the overall preference was in the order A. japonica, A. marmorata, A. bicolor pacifica and A. rostrata.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.5
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• pp.520-526
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• 2017

Carnosine was recently reported to protect against the DNA damage induced by oxidative stress. In this study, we investigated the protective effect of eel Anguilla japonica carnosine extracts prepared using different methods (heat treatment extracts, HTEs; ion exchange chromatography, IEC; ultrafiltration permeation, UFP) on leukocyte DNA damage using the comet assay. Human leukocytes were incubated with extracts of eel carnosine at concentrations (of 10, 50, $100{\mu}g/mL$), and then subjected to an oxidative stimulus [$200{\mu}M$ hydrogen peroxide ($H_2O_2$)]. Pretreatment of the cells for 30 min with carnosine significantly reduced the genotoxicity of $H_2O_2$ measured as DNA strand breaks. The protective effects of the three types of extract (HTE, IEC, and UFP) increased with concentration. At the highest concentration (100 g/mL). there were no statistical differences in oxidative damage between each extract treatment and PBS-treated negative controls. When leukocytes were incubated with carnosine for 30 min after exposure to $H_2O_2$. the protective ability of each extract changed. Therefore, eel carnosine inhibits the $H_2O_2$ induced damage to cellular DNA in human leukocytes, supporting the protective effect of this compound against oxidative damage.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.39 no.5
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• pp.384-390
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• 2006

To improve the extractability of carnosine and the levels of pro-oxidants such as iron in eel (Anguilla japonica) extracts, we examined the effects of extraction time, temperature, ion exchange chromatography and ultrafiltration (UF). The respective protein and total iron were reduced approximately 55 and 60% at 60$^{\circ}C$, 63 and 70% at 80$^{\circ}C$, 68 and 76% at 100$^{\circ}C$ and 82 and 48% with ion exchange chromatography, respectively, compared to the untreated extract. However, there was no significant difference in the carnosine levels in the eel extracts. Ultrafiltration reduced the protein content of the extract by 52% compared with the untreated extract. UF reduced the protein contents of the samples from 60, 80, and 100% heat treatment and ion exchange chromatography treatment by 27, 50, 46 and 47%, respectively. UF reduced the total iron contents of the identical four treatments by 14, 22, 23, and 43%, respectively, while UF increased the carnosine by 23, 17, 20, and 6%, respectively.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.6
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• pp.1573-1580
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• 2016

The disease occurred in cultured eel (Anguilla japonica) in a recirculatory culture system without any separated filtration apparatus. As the pond had a high level of nitrite with $60mg/{\ell}$, 1% NaCl was added to reduce nitrite toxicity to eel. The first outbreak was observed a week after the NaCl treatment and continued for 10 days. Accumulated mortality was about 0.2-0.5%. Affected fish ranged from 150-350 g were usually anorexic and exhibited yellow colour in the skin of the abdominal region and at the base of pectoral fins, as well as in the eyes. In a few individuals with severe symptoms, the lateral skin was also yellowish. The spleen, kidney, muscle and gall bladder were yellowish and the liver was pale-yellow colour but green on the posterior part. The gall bladder was shrunken without bile. Some abnormal erythrocytes such as "tear drop" cells (dacrocyte) were observed in peripheral blood smears stained with May-Grunwald Giemsa. Hematocrit values and hemoglobin contents in the jaundiced eel were significantly lower compared with apparently heathy eel. Severe haemosiderosis accompanied by erythrophagocytosis was found in the kidney and spleen. Haemosiderin deposits were observed in macrophages of the haematopoietic tissue of the kidney and in the splenocytes. But no significant alterations were found in the hepatic cells. In this study we report the first outbreak of jaundice in cultured eel in Korea. Pathological and hematological investigations suggested that severe hemolysis may resulted in jaundice in eel although the cause of hemolytic jaundice was not identified in this study.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.2
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• pp.104-108
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• 2009

Glycation and oxidation induce formation of carbonyl (CO) groups in proteins, which can be used to develop an index of cellular aging. Methyl glyoxal (MG) and hypochlorite anions are deleterious products of oxygen free-radical reaction. The effects of eel carnosine on protein modification mediated by MG and hypochlorite were studied. MG and hypochlorite induced formation of carbonyl groups with high molecular weight and cross-linked forms of ovalbumin. The presence of eel carnosine effectively inhibited these modifications in a concentration-dependent manner. Imidazole ring in eel carnosine might have a primary role in inhibition of protein glycation. Our data suggests that the eel carnosine may be useful as a "natural" anti-glycating agents.