• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.3
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• pp.298-310
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• 2021

Freshwater eel Anguilla japonica is a commercially important species in East Asia. However, given the continuously decreasing resources due to many problems as climate change, habitat destruction and overfishing, mass seed production is crucial. In particular, the eel larvae present a unique life history, spending prolonged periods in the Pacific Ocean. Therefore, finding suitable feed that lasts through the long larval stages is rather difficult. In the present study, we histologically observed the development of digestive organs for 50 days after hatching (DAH). The endogenous reserves were completely absorbed at 7 DAH, and the first exogenous feeding started thereafter. The teeth appeared at 4 DAH and dramatically changed from needle-like to broad-based types by 50 DAH. The intestine remained as straight gut until 50 DAH. The intestinal cilia appeared first at 6 DAH and their density continuously increased thereafter. Interestingly, goblet cells appeared in the intestine, but not in the esophagus, where these cells are commonly observed in other teleosts. In addition, high amounts of eosinophil substances, assumed to be zymogen granules, accumulated in the pancreas, suggesting a specific digestive strategy of this species. Overall, these observations largely update the previous reports and can be useful to improve A. japonica seed production.

• Journal of fish pathology
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• v.33 no.2
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• pp.153-161
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• 2020

Cytochrome P450(CYP) gene is involved in the biotransformation of drugs and environmental pollutants. In this study, we analyzed the nucleotide sequence of the Anguilla japonica CYP1(AjCYP1) family gene and examined the relative expression of AjCYP1A, AjCYP1B and AjCYP1C1 in response to the exposure to environmental pollutants. After exposure to B[a]P 20mg/kg bw, the expression of AjCYP1 family gene increased over time. Among four tissues examined (liver, spleen, gill and kidney), AjCYP1 family gene was expressed significantly in the kidney. Compared with the control group, AjCYP1A was expressed about 5-fold at 48 hr, AjCYP1B about 6-fold at 24 hr, and AjCYP1C1 about 4-fold at 24 hr. However, after exposure to B[a]P 200mg/kg bw, AjCYP1A did not change in all tissues. On the other hand, AjCYP1B was expressed at about 4-fold at 24 hr in the spleen and 4-fold at 48 hr in the gill. Finally AjCYP1C1 was expressed 3.7-fold and 4.3-fold in the spleen and kidneys at 48 hr, respectively. Taken together, our results suggest that the expression of AjCYP1 gene in eel tissues might be used as a useful tool to assess the exposure to environmental pollutants in aquaculture system.

• 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.

• Fisheries and Aquatic Sciences
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• v.18 no.4
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• pp.387-393
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• 2015

Biotyping of Vibrio vulnificus strains isolated from marine environments along the south coast of Korea showed that the majority of the isolates (94.7%) belonged to biotype 1 and the remaining isolates (5.3%) belonged to biotype 2. Analysis of 16S rRNA V. vulnificus strains isolated from marine environments using a multiplex polymerase chain reaction (PCR) revealed that 78.7% were type A and 21.3% were type B. Random amplified polymorphic DNA (RAPD) was used to analyze the genomic differences in V. vulnificus among the biotype 2 strains isolated from marine environments (newly isolated strains group) and reference strains obtained from infected eels (reference strains group). The two groups had distinctly different profiles of the amplicons produced from RAPD. Additionally, biochemical comparison of these strains revealed that all four strains isolated from marine environments differed from the strains isolated from eels in their ability to promote D-mannitol fermentation. Two (NH 1 and NH 2) out of four isolates of biotype 2 from marine environments showed pathogenicity in eels Anguilla japonica in a challenge test. These isolates did not agglutinate with antisera against V. vulnificus NCIMB 2137 (serovar E), ATCC 27562 (non-serovar E), and ATCC 33816 (atypical serovar E).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.4
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• pp.551-556
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• 2020

Eel Anguilla japonica is an economically important inland culture fish species in East Asian countries, particularly in Korea, Japan, China, and Taiwan. In this study, the effects of feeding frequency on larval growth and survival rate were investigated. Eel larvae (average length, 6 mm) were fed a slurry-type diet containing shark eggs three, five, seven, or nine times per day. Survival rates differed significantly among the four experimental groups. Feeding frequencies of at least five and seven times a day were required until 15 and 30 days after hatching, respectively, to maintain an acceptable survival rate. Leptocephalus growth improved with increased feeding frequency until 15 days after hatching. The results suggest that providing an opportunity for early food intake enhances eel survival and growth in the early leptocephalus stage.

• Journal of fish pathology
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• v.13 no.2
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• pp.75-86
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• 2000

Monogeneans(Phylum Platyhelminthes) have been known as common parasites onto the skin and gills of cultured freshwater fishes. Infestation with these parasites result in a great loss in aquaculture industry. Some classification studies on these parasites have mostly been conducted in Japan but rarely in Korea. For the purpose of classifying monogenean parasites infesting two Korean freshwater fishes, eel (Anguilla japonica) and catfish(Parasilurus asotus), samples captured from March 1998 to April 2000 were examined. Here we report for the first time in Korea that four different species of monogeneans are identified: Pseudodactylogyrus bini and P. anguillae in eels; Ancylodiscoides infundibulovagina and Ancylodiscoides sp. in catfish.

• Journal of fish pathology
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• v.14 no.1
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• pp.31-36
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• 2001

A novel clonidine binding sites were characterized in the intestinal membrane isolated from seawater eels, Anguilla japonica. The specific clonidine binding sites consisted of at least two classes, high affinity ($K_d=1.4{\pm}0.3$ nM n = 5) and low affinity ($K_d=175{\pm}34$ nM n = 5) sites. The specific binding of 2 nM [$^3H$]clonidine was most enhanced at $20^{\circ}C$ and pH 7.5, and reversed by unlabelled clonidine. Such binding was hardly inhibited by adrenaline, yohimbine or rauwolscine, indicating that most binding sites are distinct from $\alpha_2$-adrenoceptor. The specific clonidine binding sites was inhibited by various imidazoline/guanidinium drugs, indicating existence of imidazoline/guanidinium receptive sites (IGRS) or imidazoline receptors in the eel intestine. Competition experiments revealed that rank order to displace 2 nM [$^3H$]clonidine from their binding sites was as follows : guanabenz > cirazoline = naphazoline = UK14,304 = ST587 $\geq$ clonidine $\geq$ idazoxan = RX821002 = tolazoline > ST93 = oxymetazoline = amiloride = ST91 > yohimbine = efaroxan = rauwolscine $\geq$ adrenaline = ST567 = histamine = agmatine. Although physiological role of IGRS is not clear yet even in mammalian cell/tissues, eel intestine may be a good model to elucidate how the IGRS act in the cell and to decide what is the endogenous ligand for the IGRS.

• Journal of Aquaculture
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• v.21 no.3
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• pp.176-180
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• 2008

This study clarified biochemical overripeness characterization of ovulated eggs of Anguilla japonica and suggested a method maintained overripeness after ovulation for high hatching rates. In maturated Japanese eel eggs, the relationships between fertilization rate and hatching rate, and fertilization and survival rates were measured. DNA contents showed the significantly low 0.653 pg/ug protein in 20% downward hatching rate trial with decrease of hatching rate(P<0.05), whereas RNA/DNA ratio showed the significantly high 1.058 in 20% downward hatching rate trial(P<0.05). And activities of total alkaline protease and ACPase according to the hatching rate groups did not show the significant difference(P>0.05). The protein contents were assayed the significantly high 186.16 ug/mg protein in 20% downward hatching rate trial(P<0.05). However, the overripened eggs had lowed hatching rate, because of stimulate the overripening of normal maturated eggs due to the continuous supplement of protein (vitellogenin). We suggested that need to reduce supplement speed or interception of vitellogenin produced in live for prevent overripeness of maturated eggs after ovulation

• Korean Journal of Ichthyology
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• v.27 no.4
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• pp.263-274
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• 2015

Change in morphological and biological characteristics of Japanese eel, Anguilla japonica, by maturation were determined by examination of 182 individuals collected in Korea waters from September to December 2014. Eels were classified into four stages based on the silvering index. The proportion of silver eels collected from streams and estuaries (34.6%) was higher than that from the freshwater reservoirs (3.8%). The sex ratio between female and male was 1:0.11 (n=182). Mean total length and weight were positively related to the silvering process. The ratios of head and pectoral lengths to total length and the ratio of horizontal and vertical orbital diameters to head length were significantly different between the maturation stages. However the ratio of pre-dorsal and pre-anal lengths to total length were not significantly different between the maturation stages. The gonado-somatic index was the single character that could identify the whole four stages among the indices examined: gonado-somatic index (GSI), condition factor (K), gut index (GI) and eye index (EI) but hepato-somatic index (HSI). One pseudo-silver eel collected. looked like a late silver eel in the S2 stage according to its external body color and morphology, but most of other characteristics suggested that it might be in Y1 (yellow eel) or Y2 stage (late yellow eel).

• Journal of fish pathology
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• v.25 no.3
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• pp.151-158
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• 2012

Diseased eel (Anguilla bicolor) displayed severe hemorrhages in the gills, and congestion and swelling in the liver. During the epizootic, the water temperature was $28^{\circ}C$ and the morality rates were about 5%. No parasites were found on the gills and skin. Bacteria were not cultured from any internal organs using TSA or SS agar at $28^{\circ}C$ for 48 hrs. Histopathologically, the gills showed epithelial hyperplasia in the base of secondary gill lamellae and hemorrhages in the capillaries. Some cells in the proliferated interlamellar epithelia exhibited marginal hyperchromatosis. And severe vacuolated changes in the parenchymal cells and congestion in the central veins were observed in the liver. The specific amplicon (396 bp) was detected from gills and opercula of affected eel PCR using Anguillid herpesvirus-1 (AngHV-1) -specific primer sets HVAPOLVPSD (5-'GTG TCG GGC TTT GTG GTG C-3') and HVAPOLOOSN (5'-CAT GCC GGG AGT CTT TTT GAT-3'). Sequencing analysis of the amplicon demonstrated that this gene was 99% homologous to the AngHV-1 sequence deposited in GenBank. This is the first report of AngHV-1 outbreak in the farmed shortfin eels (A. bicolor) in Korea. When diseased fish were maintained for 10 days at water temperatures of $32^{\circ}C$ and $35^{\circ}C$, the cumulative mortalities were 100% and 10%, respectively. Even though the AngHV-1 genome in the gills from the eel kept at $35^{\circ}C$ was detected using PCR, the structure of gill filaments was similar with that of normal fish. Increasing the water temperature to $35^{\circ}C$ was an effective way to diminish the mortality of AngHV-1 affected eel.