Okamejei Kenojei Research Articles

Bacterial community of kimchi added with seafood based on culture-dependent investigations

Previously, microbial communities of five commercial kimchi added with seafood and one kimchi without seafood were analyzed using a culture-independent (CI) method. In the current study, microbial communities of the same samples were analyzed using a culture-dependent (CD) method with two media: tryptic soy agar (TSA) and Lactobacilli de Man, Rogosa and Sharpe (MRS) agar. MRS agar showed a higher proportion of lactic acid bacteria, while TSA showed a higher proportion of Bacillus species. Leuconostoc mesenteroides became dominant over time except in kimchi added with hongeu (HBK, okamejei kenojei). In the case of HBK, Bacillus was dominant. The low pH of HBK was confirmed by cell size and heat treatment under pH 4–7 conditions that Bacillus could be present in the form of spores. With the CD method, only Lactococcus lactis, Leu. citreum, and Weissella cibaria were detected. With the CI method, only Pediococcus inopinatus was detected. A notable finding was that Leu. mesenteroides was more abundant than Latilactobacillus sakei with the CD method, whereas it was similar or lower with the CI method. This discrepancy was confirmed to be due to different rates of DNA recovered from the two strains. This shows that the assay method may influence the detection of these two strains.

Distribution of Food Resources for Two Species of the Skate Family (Beringraja pulchra and Okamejei kenojei) in the South Sea of Korea

Distribution of Food Resources for Two Species of the Skate Family (Beringraja pulchra and Okamejei kenojei) in the South Sea of Korea

Genomic Characteristics of Okamejei kenojei and the Implications to Its Evolutionary Biology Study.

Okamejei kenojei is an important economic species widely distributed in shallow coastal waters of the western North Pacific. In this study, the whole-genome survey analysis of O. kenojei was conducted to reveal its genomic characteristics. The genome size was estimated to be 2027.44Mb, the repeat sequence content was 44.90%, and the heterozygous ratio was 1.04%. The mitochondrial genome excavated from the sequencing data was 16,974bp, and it can form the closed circular molecule. The phylogenetic tree based on 13 protein-coding gene sequences supported the validity of Okamejei and assisted the conclusion that Raja porosa was the junior synonym of O. kenojei. Plenty of potential microsatellite loci were identified, and the distribution frequency was estimated to be approximately 236.3 SSRs per Mb. Among all motif types of microsatellites, the dinucleotide repeats were dominant (82.59%), followed by the trinucleotide repeats (8.05%), tetranucleotide repeats (5.80%), pentanucleotide repeats (2.83%), and hexanucleotide repeats (0.72%). The results of the present study could not only provide useful information for understanding the genome structure and functional characteristics of O. kenojei, but also lay the foundation for the subsequent mapping of the whole genome.

Identification and characterization of IgNAR and VNAR repertoire from the ocellate spot skate (Okamejei kenojei)

Elasmobranchs are crucial for comparative studies of evolution, as they belong to the most ancient vertebrate lineages that survived numerous extinction events and persist until today. The immunoglobulin new antigen receptor (IgNAR) found in sharks and heavy-chain-only antibody (HCAb) found in camelidae are products of convergent evolution. Although it was previously believed that IgNAR emerged 220 million years ago, before the divergence of sharks and skates, there is limited evidence to support this. In this study, we provide data supporting the existence of IgNAR in the ocellate spot skate (Okamejei kenojei) mononuclear cell transcriptome and peripheral blood serum. Additionally, we characterize the germline gene configuration of the ocellate spot skate IgNAR V domain. The ocellate spot skate IgNAR structure prediction and VNAR crystal structure exhibit high similarity to their shark counterparts. These data strongly suggest that IgNAR in both sharks and skates share a common ancestor. Sequencing of the ocellate spot skate VNAR repertoire provided crucial data for further understanding of the IgNAR generation. Notably, we discovered that approximately 99% of the ocellate spot skate VNARs belonged to type IV. This represents an exceptionally high proportion of type IV within the VNAR repertoire, which has not been documented in previously studied elasmobranchs. This unique characteristic of the ocellate spot skate VNAR adds essential structural diversity to the naïve VNAR library from elasmobranchs and could potentially benefit the development of pharmaceutical drugs.

Spatial distributions of and species differences in 90Sr accumulation in marine fishes from the Fukushima coastal region

Large amounts of radionuclides were released into the ocean during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. One of the released radionuclides, 90Sr, tends to accumulate in bone, and could conceivably have long-term negative impacts on fishes. Here, we investigated 90Sr radioactivity concentrations in the vertebrae of demersal fishes collected off the coast of Fukushima Prefecture in January and July 2014. High 90Sr radioactivity concentrations were detected in fish collected from central Fukushima (offshore of the FDNPP) and southern Fukushima (offshore of Iwaki City), but were almost hardly detected in northern Fukushima (offshore of Soma City). Additionally, 90Sr radioactivity concentrations were higher among rays (Okamejei kenojei and Hemitrygon akajei: from 1.1 ± 0.5 to 103.3 ± 15.1 mBq/g Ca) and soles (Cynoglossus joyneri and Paraplagusia japonica: from 18.5 ± 2.8 to 52.8 ± 11.3 mBq/g Ca) than among other species. Vertebral stable Sr/Ca ratios also differed by fish species. Ca concentrations were relatively constant among species, but Sr concentrations were higher among elasmobranchs and soles, indicating that differences in Sr/Ca might be related to differences in 90Sr accumulation in fish vertebrae.

First observation of the mating, egg-laying and hatching behaviour of a captive female Kong skate, Okamejei kenojei (Müller & Henle, 1841).

This study provides a novel record of the reproductive behaviour of the Kong skate (Okamejei kenojei) in captivity. These skates were found to mate and deposit eggs at a temperature of 16.5 ± 0.5°C. The results showed that 76.13% of the eggs possessed one yolk, 0.77% of the eggs possessed two yolks and 23.11% of the eggs had no yolk (N=1043). The deposition of non-yolk and double-yolk eggs was random. A total of 100 eggs were collected. After nearly 92 ± 5 days of incubation, 28 eggs failed to hatch, and 72 skates were successfully hatched with a female-to-male ratio of 1:1 (P > 0.05). The results enrich our knowledge of the reproduction in cartilaginous fishes and can inform management and conservation strategies for this species.

Spawning Period and Size at Maturity of the Ocellate Spot Skate Okamejei kenojei in the West Sea of Korea

This study aimed to investigate the gonadal development process and size at maturity of the ocellate spot skate Okamejei kenojei (Müller and Henle, 1841). In total, 1234 specimens were collected from the center of the Korean West Sea between January 2019 and December 2020. The maturity stage of the gonads of each individual was determined visually based on size, color, and egg size. To estimate the spawning period, each specimen was measured for disc width, body weight, and gonad weight, and the monthly gonadosomatic index (GSI) was derived. The GSI of the specimens peaked in April and May, and the main spawning period occurred during June and July. Egg capsules were first observed in specimens collected in March and were most commonly observed in specimens collected in July (56.8%). The maturity ogives for disc widths of female specimens at 50%, 75%, and 97.5% maturity were 26.6, 27.9, and 30.8 cm, respectively, whereas those of male specimens were 26.2, 27.5, and 30.7 cm. The findings of this study provide basic information on reproductive ecology related to the fertility of the ocellate spot skate.

How the Skate Embryo Develops: A Fine Developmental Timeline of Kong Skate Okamejei kenojei (Müller & Henle, 1841)

Cartilaginous fishes, as an important group of jawed vertebrates, hold great promise for improving our understanding of vertebrate evolution. Previous studies have established a good staging scheme for shark embryos. However, to date, little attention has been paid to the development of skate embryos. In this study, we established a fine developmental timeline for the Kong skate. We hatched eggs of the Kong skate (Okamejei kenojei) at fixed temperatures (16.5°C ± 0.5°C) while observing three samples every day and recorded the complete embryonic development. The embryo weight and development time were found to have a quadratic relationship. The weight-at-day curve was fitted by y = 0.0005x2 - 0.0109x + 0.0882 (R² = 0.9406). In addition, complete embryonic development from gastrula to skate larvae took 92 ± 5 days. Here, we divided the entire development process into 39 stages. This shows that the jaw of O. kenojei is developed from the first pair of pharyngeal arches, and its body disc is formed by the fusion of the pectoral fin and head. The eyespots began to form from stage 36 and then became thicker and bigger until the young skate broke out of the egg. Notably, we found that males and females develop differently from stage 31; the end of the male pelvic fins expands inward, which develop into copulatory organ-claspers, whereas in the females, they do not expand. To the best of our knowledge, this is the first study to record the embryonic development of eyes, body discs, eyespots, and other organs of O. kenojei in detail. We hope that our work will provide valuable information for researchers to identify specific time points for developing skate embryos.

서해 5도 주변해역에서 출현하는 홍어(Okamejei kenojei)의 식성

서해 5도 주변해역에서 출현하는 홍어(Okamejei kenojei)의 식성

Population structure of the ocellate spot skate (Okamejei kenojei) inferred from variations in mitochondrial DNA (mtDNA) sequences and from morphological characters of regional populations: suppl. table

Population structure of the ocellate spot skate (Okamejei kenojei) inferred from variations in mitochondrial DNA (mtDNA) sequences and from morphological characters of regional populations: suppl. table

Population structure of the ocellate spot skate (Okamejei kenojei) inferred from variations in mitochondrial DNA (mtDNA) sequences and from morphological characters of regional populations

Population structure of the ocellate spot skate (Okamejei kenojei) inferred from variations in mitochondrial DNA (mtDNA) sequences and from morphological characters of regional populations

Embryonic transcriptome sequencing of the ocellate spot skate Okamejei kenojei

Chondrichthyans (cartilaginous fishes) exhibit highly variable reproductive styles, categorized as viviparity and oviparity. Among these, species with oviparity provide an enormous potential of molecular experimentation with stable sample supply which does not demand the sacrifices of live mothers. Cartilaginous fishes are divided into two subclasses, chimaeras (Holocephali) and elasmobranchs (Elasmobranchii), and the latter consists of two monophyletic groups, Batoidea (rays, skates and torpedoes) and Selachimorpha (sharks). Here we report transcriptome assemblies of the ocellate spot skate Okamejei kenojei, produced by strand-specific RNA-seq of its embryonic tissues. We obtained a total of 325 million illumina short reads from libraries prepared using four different tissue domains and assembled them all together. Our assembly result confirmed the species authenticity and high continuity of contig sequences. Also, assessment of its coverage of pre-selected one-to-one orthologs supported high diversity of transcripts in the assemblies. Our products are expected to provide a basis of comparative molecular studies encompassing other chondrichthyan species with emerging genomic and transcriptomic sequence information.

Radiocesium in seawater, sediments, and marine megabenthic species in coastal waters off Fukushima in 2012–2016, after the 2011 nuclear disaster

In bottom-sediment samples collected in 2012 from a coastal strip (∼30 km × 120 km) off the Fukushima Daiichi Nuclear Power Plant (FDNPP), radiocesium activity concentrations were generally higher south of the FDNPP, with high activity concentration patches in the north. In periodic surveys conducted at nearshore sites during 2012–2016, no clear temporal trends were observed in radiocesium activity concentrations in seawater or bottom sediment, and activity concentrations were higher in fish than in invertebrates. During 2012–2014, radiocesium activity concentrations tended to decrease in fish, but during 2012–2013 in the south, some increases were observed. Radiocesium activity concentrations were significantly higher in some fish (e.g., Okamejei kenojei) directly offshore and south of the FDNPP than in the north. Activity concentrations in fish stomach contents were significantly correlated with those in muscle tissue, suggesting that the consumption of contaminated prey contributed greatly to radiocesium contamination in demersal fish.

서해 군산 연안에서 새우조망으로 어획된 저서생물의 종조성 및 군집구조

Abstract Species composition of aquatic organism in the marine ranching area of Gunsan, Korea were investigated using shrimp beam trawl from May to December in 2010. A total of 91 species, 98,127 ind./ ㎢ and 877.6 ㎏/㎢ of aquatic organism were collected. Among them, species were included 60 species in Pisces, 21 in Crustacea and 10 in Mollusca. The individual dominant species, occupying over 10% of total individuals, were Latreutes anoplonyx(47,327 ind/㎢, 48.23%), Crangon hakodatei(11,578 ind./㎢, 11.80%) and Trachysalambria curvirostris(10,237 ind./㎢, 10.40%). And the biomass dominant species, occupying over 9% of total biomass, were Paralichthys olivaceus(135 ㎏/㎢, 15.4%), Okamejei kenojei(98.2 ㎏/㎢, 11.2%) and Portunus tribuberculatus(84.8 ㎏/㎢, 9.6%). From the cluster and MDS analysis based on Bray-Curtis similarity matrix of fourth root transformed data of number of species and individuals per unit area collected more than two times during this survey by each month and station was divided into three different groups. Group A showed seasonal similarity of characteristic of distribution in August and November, Group B in December and Group C in May. Key words : Species composition, Community structure, Dermersal organisms, Gunsan, Shrimp beam trawlCorresponding author : 051-626-9895, bluejuve@gmail.com 2016 (R2016051) .

Angiotensin-I converting enzyme inhibitory peptides from antihypertensive skate (Okamejei kenojei) skin gelatin hydrolysate in spontaneously hypertensive rats

The aim of this study was to investigate antihypertensive effect of bioactive peptides from skate (Okamejei kenojei) skin gelatin. The Alcalase/protease gelatin hydrolysate below 1kDa (SAP) exhibited the highest angiotensin-I converting enzyme (ACE) inhibition compared to other hydrolysates. SAP can decrease systolic blood pressure significantly in spontaneously hypertensive rats. SAP inhibited vasoconstriction via PPAR-γ expression, activation and phosphorylation of eNOS in lungs. Moreover, the expression levels of endothelin-1, RhoA, α-smooth muscle actin, cleaved caspase 3 and MAPK were decreased by SAP in lungs. Vascularity, muscularization and cellular proliferation in lungs were detected by immunohistochemical staining. Finally, two purified peptides (LGPLGHQ, 720Da and MVGSAPGVL, 829Da) showed potent ACE inhibition with IC50 values of 4.22 and 3.09μM, respectively. These results indicate that bioactive peptides isolated from skate skin gelatin may serve as candidates against hypertension and could be used as functional food ingredients.

Protective effects of peptides from skate (Okamejei kenojei) skin gelatin against endothelial dysfunction

Seafood processing by-product, skate (Okamejei kenojei) skin, was utilized to isolate active peptides with antihypertensive effect. Two peptides (MVGSAPGVL, 829 Da and LGPLGHQ, 720 Da) were purified from skate skin gelatin. In human endothelial cells, nitric oxide (NO) synthesis was found to be increased and eNOS phosphorylation was upregulated by the peptides. The peptides exhibited inhibitory activities on the production and expression of IL-6. Furthermore, the peptides down-regulated the expression levels of endothelin-1. The peptides inhibited the NF-κB and the phosphorylation of MAPK pathways. In addition, the activation of the PI3K/Akt pathway by the peptides was confirmed. The present study demonstrated that the purified peptides had vasorelaxant effects via endothelium-dependent NO signaling through activation of the PI3K/Akt-eNOS pathway and inhibition of the NF-κB and MAPK pathways. The purified peptides could be used in the food industry as functional ingredients with potent benefits in reducing the risk of cardiovascular diseases.

한국 남해 가덕도 주변해역에 출현하는 어류의 종조성과 계절변동

Seasonal variations in species composition and abundance of the fish assemblages in the coastal waters off Gadeok-do were determined using monthly sample collection by a small otter trawl in 2010-2011. Of a total of 65 fishes collected, the dominant species were Leiognathus nuchalis, Clupea pallasii, Thryssa kammalensis, Engraulis japonicus, Repomucenus valenciennei, Sillago japonica, Trachurus japonicus, Pennahia argentatus, Okamejei kenojei, Cynoglossus joyneri, Pholis fangi, Pleuronectes yokohamae, and Zoarces gillii. These 13 fishes accounted for 92.8% of the total number of individuals collected. The number of fish species, number of individuals, biomass, and species diversity indices fluctuated with the seasons. The peak number of fishes occurred in April, whereas the biomass of fishes was highest in August. The numbers and biomass of fishes were lower in February corresponding with the low temperatures, and diversity indices were lower in January than in any other month.

자망에 의한 홍어의 망목선택성

To estimate the mesh selectivity of gillnet for ocellate spot skate (Okamejei kenojei), the field tests were carried out 12 times with six different mesh sizes (121.2mm, 137.7mm, 151.5mm, 168.3mm, 178.2mm, 189.4mm) in the coastal waters of Taean, Chungcheongnamdo of Korea, 2010~2011. In the field tests, the total number of species was 31, and that of catch was 1,410 and the total weight was 618,006g. The number and weight of ocellate spot skate which is main target in this study were 1,004 and 434,592g, respectively. The catch in number of ocellate spot skate occupied about 71.2% in total catch. The others of catch species were marbled sole (8.4%), sea raven (4.4%), japanese swimming crab (4.2%) and flatfish (4.1%) and so on. The range of body disk width (DW) of ocellate spot skates which were caught in this study was 15.2~35cm and the mode was 27~29cm. The estimation equation of mesh selectivity using the extended Kitahara`s method was expressed as s $(R)

2007-2009년 매물도에서 새우조망에 의한 어류 종조성의 연변동

We investigated yearly fluctuation of the fish species composition of beam trawls off Maemuldo in the east southern sea of Korea, from March 2007 to November 2009. A total of 75 fish species were collected during the period. The number of fish species accumulated amounted to 54, 64 and 75 species in 2007, 2008 and 2009, respectively. The number of newly occurring species increased with time. The number of expected resident species in Maemuldo was estimated as 9 species including Conger myrister, Okamejei kenojei and Pholis nebulosa, each of which appeared more than 14 out of a total 27 times. Cluster analysis showed that the years 2007 and 2008 were closely clustered, while the year 2009 was distantly clustered with 2007 and 2008. This may be due to the high catch ratio of Clidoderma asperrimum in 2009 alone, when a low water temperature phenomenon was observed unlike the situation in 2007 and 2008.

Active peptides from skate (Okamejei kenojei) skin gelatin diminish angiotensin-I converting enzyme activity and intracellular free radical-mediated oxidation

Skin gelatin of skate (Okamejei kenojei) was hydrolyzed using Alcalase, flavourzyme, Neutrase and protamex. It was found that the Alcalase hydrolysate exhibited the highest angiotensin-I converting enzyme (ACE) inhibitory activity. Then, Alcalase hydrolysate was further hydrolyzed with protease and separated by an ultrafiltration membrane system. Finally, two peptides responsible for ACE inhibitory activity were identified to be MVGSAPGVL (829Da) and LGPLGHQ (720Da), with IC50 values of 3.09 and 4.22μM, respectively. Moreover, the free radical-scavenging activity of the purified peptides was determined in human endothelial cells. In addition, the antioxidative mechanism of the purified peptides was evaluated by protein and gene expression levels of antioxidant enzymes. The current study demonstrated that the peptides derived from skate skin gelatin could be used in the food industry as functional ingredients with potent antihypertensive and antioxidant benefits.