Japanese Eel Anguilla Japonica Research Articles

Daily variation of D2 dopamine receptor transcription in the brain of the Japanese eel Anguilla japonica and its regulation with dopamine and melatonin

Dopamine plays a crucial role in controlling reproduction in eels, and its action is mediated through D2-type dopamine receptors. D2A and D2B receptors in the Japanese eel Anguilla japonica were cloned and characterized in the present study. Attention (daily expression patterns in the brain and endogenous regulation) was paid to D2B receptor because it is considered to play a crucial role in eel reproduction. The cDNAs of D2A and D2B receptors had open reading frames comprising 456 and 454 amino acid residues, respectively, which were phylogenetically clustered with those of other teleost species. Both receptors were highly expressed in the brain. D2B receptor transcript levels exhibited high day/low night variation in the midbrain and pituitary, suggesting that its transcription in these tissues is regulated in a daily manner, possibly under influence of melatonin. Intraperitoneal injection of dopamine downregulated D2B receptor transcription significantly in the midbrain and moderately in the pituitary within 1 h, but upregulated its transcription in the forebrain. Co-injection of dopamine with its antagonist (domperidone) reversed the effect of dopamine in the pituitary and forebrain, but not in the midbrain, suggesting that the effect of dopamine on D2B receptor transcription differs among brain regions. The same treatment with melatonin resulted in decreased D2B receptor transcription in the midbrain. These findings indicate that dopamine and melatonin have key roles in the daily variation in D2B receptor transcription in the brain of Japanese eel, and that they are related to a daily base secretion of hormones in the hypothalamic–pituitary–gonadal axis in this species.

Changes in Sex Steroids and Ovarian Steroidogenic Enzyme mRNA Levels in Artificially Maturing Japanese Eel (Anguilla japonica) and Naturally Maturing New Zealand Longfin Eel (Anguilla dieffenbachii) during Vitellogenesis

Repeated hormone injections are routinely used to induce advanced stages of oogenesis in freshwater eels, but this approach may result in aberrant germ cell development. To investigate the underlying causes, levels of sex steroids (testosterone, T; estradiol-17β, E2) and ovarian steroidogenic enzyme mRNAs were compared between artificially maturing Japanese eels and wild-caught, spontaneously maturing New Zealand longfin eels. The latter were employed as reference, as wild Japanese eels in advanced stages of oogenesis are near-impossible to catch. Serum T levels in artificially maturing Japanese eel changed with stage in a pattern that was comparable to that in longfin eels. Likewise, ovarian mRNA levels of most steroidogenic enzyme genes were not qualitatively dissimilar between both eel species when taking developmental stage into account. However, aromatase (cyp19a) mRNA levels, together with serum E2 levels, rapidly increased in artificially maturing Japanese eels in mid-late stages of oogenesis (gonadosomatic index, GSI = 13.8%), whereas no such increase was evident in longfin eels (GSI ~ 6.9%). In addition, sex steroid and target gene mRNA levels fluctuated drastically with each hormone injection. We contend that expression of most target genes, possibly even that of cyp19a, during induced oogenesis could be “normal”, with the drastic fluctuations due most likely to hormone delivery through repeated injections. The effects of these fluctuations on gamete quality remain unknown and resolving this issue may prove fruitful in the future to further artificial propagation of anguillid eels.

Japanese eel jaw and vertebra ossification occurring respectively during the larval stage and metamorphosis

Morphological deformities of the jaw and vertebrae arise as hindrances to seed production of Japanese eel Anguilla japonica. To obtain basic information related to development in these areas, we analyzed eel larva skeletal system formation by staining with alizarin red S. Results demonstrated that dentary and maxillary ossification at the jaw begins by 10 days after hatching, about 8 mm total length. Subsequent progression of ossification is slow until metamorphosis. For instance, ossification of the angular and quadrate, which are connected to the dentary, begins remarkably later than ossification of the dentary. Ossification of the head develops quickly during metamorphosis and produces a primitive skull in glass eels. Ossification of the vertebral centrum progresses rapidly from the posterior end to the anterior-most during metamorphosis. Our results demonstrate that the process of ossification at the head is shared among some species of Elopomorpha, but that ossification of vertebral centra differed. Furthermore, our results imply consistency of the period between ossification and the occurrence of some morphological deformities around the jaw and vertebrae.

Habitat Partitioning and its Possible Genetic Background Between Two Sympatrically Distributed Eel Species in Taiwan.

The geographical distributions of the Japanese eel (Anguilla japonica) and Giant-mottled eel (A. marmorata) overlap in many regions in East Asia and therefore suffer from interspecific competition in the same rivers. After a long period of adaptation, the Japanese eel and Giant-mottled eel may exhibit habitat partitioning in the rivers to diminish the interspecific competition between them. In this study, we conducted a field investigation in the Fengshan River in Taiwan to survey the habitat distributions of the Japanese eel and Giant-mottled eel throughout a river. Moreover, we investigated whether their habitat distributions are related to their swimming and upstream migration. Thus, the mRNA expression levels of several candidate genes that may be associated with the swimming and upstream migration of eel were examined in the glass eels of the Japanese eel and Giant-mottled eel. Field investigation indicated that the Japanese eel mainly inhabited the lower and middle reaches of the Fengshan River, but the Giant- mottled eel was distributed over the middle to upper reaches. The mRNA expression levels of fMYH, dio2, gria3, and neurod1 were higher in the Giant-mottled eel than in the Japanese eel, implying that Giant- mottled eels might have better swimming bursts and more active upstream migration than Japanese eels. These results suggest that there is a habitat partition at which these two eel species coexist in a river, and their habitat distributions may be linked to their swimming bursts and upstream migration. Determining the habitat distributions of freshwater eels is important for developing applicable plans for eel conservation and resource management.

Anthropogenic impacts on the distribution of wild and cultured Japanese eels in the Tone River watershed, Japan, from otolith oxygen and carbon stable isotopic composition

Effective management decisions are vital for the declining Japanese eel Anguilla japonica. Elucidating the distribution range of wild eels (i.e., naturally recruited individuals) represents the first step in resource management, although stocking of cultured eels throughout the waters of Japan masks the original distribution range of wild eels. Herein, we applied a recently developed discrimination model based on otolith oxygen and carbon stable isotopic ratios (δ18O and δ13C) to determine the distribution range of wild eels throughout the Tone River watershed, which is the largest fisheries ground for this species. The model indicated that eels naturally recruit up to 200 km in the catchment area from the river mouth. Although natural recruitment was confirmed at all sampling sites, the percentages of wild eel occurrence at each site ranged from 56 to 100% of sampled individuals. The presence of wild individuals at sites above river-crossing structures indicates that some individuals successfully navigate through these structures. The operation of sluice gates and fish passes installed on artificial structures might facilitate the recruitment of individuals in areas above the structures and further upstream in the watershed. Difference in the percentages of wild eels among sampling sites might be a product of major variation in the abundance of cultured eels stocked at respective sampling sites and nearby areas.

Trans-omics analyses revealed differences in hormonal and nutritional status between wild and cultured female Japanese eel (Anguilla japonica)

Long-term stock decline in the Japanese eel (Anguilla japonica) is a serious issue. To reduce natural resource utilization in Japan, artificial hormonal induction of maturation and fertilization in the Japanese eel has been intensively studied. Recent experiment on feminized (by feeding a commercial diet containing estradiol-17β for first half year) cultured female eels have shown ovulation problems, which is seldom observed in captured wild female eels. Therefore, the aim of this study is to try to investigate causes of ovulation problem frequently seen in cultured female eels by comparative trans-omics analyses. The omics data showed low growth hormone and luteinizing hormone transcription levels in the brain and low sex hormone–binding globulin transcription levels in the liver of the cultured female eels. In addition, it was found that high accumulation of glucose-6-phosphate and, maltose in the liver of the cultured female eel. It was also found that docosahexaenoic (DHA) acid, eicosapentaenoic acid (EPA) and arachidonic acid (ARA) ratios in cultured female eels were quite different from wild female eels. The data suggested that ovulation problem in cultured female eels was possibly resulted from prolonged intake of a high-carbohydrate diet and/or suboptimal DHA/EPA/ARA ratios in a diet.

Dispersal Characteristics and Pathways of Japanese Glass Eel in the East Asian Continental Shelf

The Japanese eel Anguilla japonica is an important aquaculture fish species in the East Asian countries of Japan, China, Korea, and Taiwan. All glass eel fry are captured from the wild and understanding the recruitment patterns of the glass eel is important. The larvae of A. japonica are passively transported to the East Asian Continental Shelf by the North Equatorial Current, the Kuroshio, the Kuroshio intrusion currents, and coastal currents. In each location, recruitment time is diverse: It is November in Taiwan and April in the Yalu River. How the glass eels reach recruitment areas remains poorly understood. Here, we combine information from larval ages based on otolith increments, simulated drifting paths on the East Asian Continental Shelf, and main fishing seasons in each location of East Asia. We identify five main recruitment blocks: (1) The main Kuroshio, (2) The Taiwan Strait Warm Current, (3) The Taiwan Warm Current, (4) The Yellow Sea Warm Current and (5) The branch of Yellow Sea Warm Current. The counted age of the glass eels is significantly underestimated for the later recruits, possibly due to the cessation of the otolith edge growth under low water temperatures. This study clarifies the eel’s larval characteristics and transport mechanisms in the East Asia Continental Shelf, providing important information for its recruitment dynamics in the marine stage.

Evaluation of optimum temperature for the early larval growth of Japanese eel in captivity

Early larval growth of the Japanese eel Anguilla japonica reared at five different water temperatures (19, 21, 23, 25, and 27 °C) is described for the first month post-hatching, a critical period of time in the culture of these sensitive larvae. After 3 weeks of culture, larvae reared at 27 °C attained the greatest total length and body height of all temperature treatments. Larvae reared at higher temperatures developed rapidly due to active feeding, despite higher metabolic costs. At lower temperatures of 19–21 °C, sudden mortality 12–16 days post-hatching coincides with the transition of larvae from endogenous to exogenous feeding. A linear relationship between water temperature and otolith diameter for cultured eel larvae otoliths suggests that the mean ambient water temperature experienced by wild larvae during their first month after hatching is about 23 °C. This temperature corresponds to mean water temperatures likely experienced by larvae during diel vertical migrations in the North Equatorial Current. We propose rearing early stage Japanese eel larvae at variable temperatures throughout the light/dark cycle to enhance their survival and growth in captivity.

Molecular characterization, expression patterns, and functional analysis of toll-interacting protein (Tollip) in Japanese eel Anguilla japonica

Toll-interacting protein (Tollip) is a key negative regulator of TLR-mediated innate immune responses. The structure and function of Tollip have been well identified in mammals, but the information about Tollip is still limited in teleost fishes. In the present study, the homologue of Tollip was cloned from Japanese eel. It contained an open reading frame encoding a polypeptide of 276 amino acids which shared high identities with other homologues from different species. Multiple alignment of the amino acid sequence showed that the AjTollip protein has the typical conserved domains including an N-terminal Target of Myb1 (Tom1) binding domain (TBD), a central conserved 2 (C2) domain, and a C-terminal coupling of ubiquitin to endoplasmic reticulum degradation (CUE) domain. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed a broad expression for AjTollip in a wide range of tissues, with the highest expression in the liver, a relatively high expression in the spleen, kidney, gills, skin and intestine, and a low expression in the heart and muscle. The AjTollip expressions in the liver and kidney were significantly induced following injection with the bacterial mimic LPS, the viral mimic poly I:C, and Aeromonas hydrophila infection. In vitro, the AjTollip transcripts of Japanese eel liver cells were significantly enhanced by the treatment of LPS, poly I:C, CpG-DNA, and PGN or the stimulation of high concentration of Aeromonas hydrophila (1 × 107 cfu/mL and 1 × 108 cfu/mL). Subcellular localization study showed that AjTollip was mainly distributed in the cytoplasm in a condensed state. When AjTollip was co-transfected with AjMyD88 into HEK293 cells, the luciferase activities of NF-κB were significantly decreased compared with that of AjMyD88 single-transfection groups in natural state or under the stimulation of LPS and poly I:C. These results collectively suggested that AjTollip functions as a negative regulator of MyD88-dependent TLR signaling and plays an important role in fish defense against viral and bacterial infections.

Release of eDNA by different life history stages and during spawning activities of laboratory-reared Japanese eels for interpretation of oceanic survey data

To assist in detection of offshore spawning activities of the Japanese eel Anguilla japonica and facilitate interpretation of results of environmental DNA (eDNA) analysis in their spawning area, we examined the eDNA concentration released by each life history stage of artificially reared Japanese eels in the laboratory using quantitative real-time PCR (qPCR). We also compared eDNA concentrations between before and after artificially induced spawning activities. eDNA was not detected from three 30 L seawater tanks containing each single fertilized egg, but eDNA was found from other tanks each containing single individuals of larval stages (preleptocephalus and leptocephalus), juvenile stages (glass eel, elver and yellow eel) or adult stage (silver eel). The eDNA concentrations increased in the life history stages, showed a significant difference among all stages, and were positively correlated with the total length and wet weight. Moreover, the eDNA concentration after spawning was 10–200 times higher than that before spawning, which indicated that the spawning events in the ocean would produce relatively high eDNA concentration. These results in the laboratory suggested that eDNA analysis appears to be an effective method for assisting oceanic surveys to estimate the presence and spawning events of the Japanese eel in the spawning area.

Evaluation from otolith Sr stable isotope ratios of possible juvenile growth areas of Japanese eels collected from the West Mariana Ridge spawning area

The widely distributed East Asian Japanese eel Anguilla japonica constitutes a single genetically homogeneous population with a single spawning area near the West Mariana Ridge. Otolith 87Sr/86Sr ratios of adults (categorized as “river“, “estuarine” or “sea” eels, according to their habitat use history determined from otolith Sr:Ca ratio analysis) collected from the spawning area in 2008 and 2009 were examined in an attempt to determine their juvenile growth areas. In addition, 87Sr/86Sr ratios of water samples from rivers in China, Taiwan, Korea, and Japan were determined. Otolith 87Sr/86Sr ratios of the “river”, “estuarine” and “sea” eels were 0.707793, 0.708580-0.709944 and 0.709068, respectively, and water sample ratios from China, Korea, Taiwan, and Japan were 0.7104320-0.7141010, 0.7190826-0.7227976, 0.7115523-0.7146914 and 0.706191-0.712484, respectively. “River” and “estuarine” eels, which had otolith 87Sr/86Sr ratios less than 0.7092 (seawater ratio), appeared to have inhabited Japanese rivers and/or estuaries because similarly low isotope ratios were recorded only from Japan. However, the juvenile growth areas of other eels were unknown, as their origins could not be determined from otolith 87Sr/86Sr ratios alone, and required further information regarding otolith elemental and isotope compositions.

Pharmacokinetic study of amoxicillin in Japanese eel Anguilla japonica by high performance liquid chromatography with fluorescence detection

Amoxicillin (AMX) is widely used for the treatment of gastrointestinal and systemic infections. AMX residues above certain levels may pose a threat to human health. Therefore, this study aimed to understand the pharmacokinetics of AMX in Japanese eel, Anguilla japonica, using high-performance liquid chromatography (HPLC) with fluorescence detection. Japanese eels were treated with AMX at concentrations of 40 or 80 mg kg−1 body weight (BW) daily via oral administration. The results revealed that the recoveries of AMX from the muscle, liver, and sera of eels were 84.7–105.1%, 81.8–104.9%, and 88.6–106.3%, respectively. The observed peak retention time was approximately 4.2 min. After administration of 40 mg kg−1 BW per day of AMX, the pharmacokinetic parameters were detected, respectively. The average drug residue concentration in muscles was 180 and 260 ng mL−1 on day 1 and day 2, respectively, and in the liver, it was 70 and 110 ng mL−1 on day 1 and day 2, respectively, after the 40 mg kg−1 BW daily AMX administration. Residue concentrations in the muscle and liver on day 3 after 40 mg kg−1 BW administrations were below the limit of detection (<30 ng mL−1). On the other hand, the average drug residue concentration in muscles was 930 and 1070 ng mL−1 on day 1 and day 3, respectively, and in the liver, it was 35 and 95 ng mL−1 on day 1 and day 3, respectively, after 80 mg kg−1 BW AMX administration. However, the residue concentrations in the muscle and liver on day 5 after 80 mg kg−1 BW administration were below the detection limit (<30 ng mL−1). The pharmacokinetic information derived from Japanese eel can be used to design rational dosing regimens and can also assist the Taiwan government in formulating laws and regulations for AMX residues in Japanese eels. Additionally, this information will provide greater protection to consumers of aquaculture products.

First use of oceanic environmental DNA to study the spawning ecology of the Japanese eel Anguilla japonica

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 609:187-196 (2019) - DOI: https://doi.org/10.3354/meps12828 First use of oceanic environmental DNA to study the spawning ecology of the Japanese eel Anguilla japonica Aya Takeuchi1, Shun Watanabe2,*, Satoshi Yamamoto3, Michael J. Miller4, Tatsuhiro Fukuba5, Tetsuya Miwa5, Tatsufumi Okino6, Toshifumi Minamoto3, Katsumi Tsukamoto1,4 1Graduate School of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa-shi, Kanagawa 252-0880, Japan 2Department of Fisheries, Faculty of Agriculture, Kindai University, Nara 631-8505, Japan 3Graduate School of Human Development and Environment, Kobe University, Hyogo 657-8501, Japan 4Department of Marine Science and Resource, Nihon University, 1866 Kameino, Fujisawa-shi, Kanagawa 252-0880, Japan 5Marine Technology and Engineering Center, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan 6Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan *Corresponding author: swpc@nara.kindai.ac.jp ABSTRACT: Environmental DNA (eDNA) analysis is emerging as an innovative tool to assess the distribution and biomass of species in aquatic environments that enables quick and non-invasive surveys compared to conventional sampling methods such as fishing, hydroacoustics, and diving observations. We applied eDNA analysis to spawning ecology research of the Japanese eel Anguilla japonica in the western North Pacific for the first time. A preliminary laboratory experiment using tank water containing eels confirmed that our specific primers and probe could identify the Japanese eel from a small amount of eDNA (about 0.5 ng per PCR reaction). During a 19-20 May 2015 ocean survey at the southern West Mariana Ridge, seawater samples were collected at 12 water depths at 9 stations in the spawning area of A. japonica. Out of 108 seawater samples, DNA was successfully amplified from 3 samples, which were collected at 250 and 400 m. According to published research on Japanese eel spawning ecology and eDNA dynamics, the eDNA positive signals obtained from the oceanic survey could have been from adult Japanese eels or from larvae from the last spawning events. Thus onboard eDNA analysis proved to be a viable approach for detecting Japanese eels in their spawning area along the southern West Mariana Ridge. KEY WORDS: eDNA · Freshwater eel · Real-time PCR · Spawning ecology · Oceanic survey Full text in pdf format PreviousNextCite this article as: Takeuchi A, Watanabe S, Yamamoto S, Miller MJ and others (2019) First use of oceanic environmental DNA to study the spawning ecology of the Japanese eel Anguilla japonica. Mar Ecol Prog Ser 609:187-196. https://doi.org/10.3354/meps12828 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 609. Online publication date: January 17, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Chinese herbs Epimedium brevicornum Maxim. and Cuscuta chinensis Lam. induced ovary development in Japanese eel Anguilla japonica

PDF HTML阅读 XML下载 导出引用 引用提醒 中草药淫羊藿和菟丝子对日本鳗鲡卵巢发育的影响 DOI: 作者: 作者单位: 1. 集美大学水产学院, 福建 厦门 361021;2. 鳗鲡现代产业技术教育部工程研究中心, 福建 厦门 361021;3. 厦门大学海洋与地球学院, 福建 厦门 361102;4. 厦门出入境检验检疫局检验检疫技术中心, 福建 厦门 361026 作者简介: 赖晓健(1984-),男,博士,硕士生导师,主要从事鱼类生殖生理学研究.E-mail:laixj@jmu.edu.cn 通讯作者: 中图分类号: S965 基金项目: 国家自然科学基金项目（41806193）；厦门市科技局项目（3502Z20133015）；鳗鲡现代产业技术教育部工程研究中心开放基金项目（RE201604，RE201503）. Chinese herbs Epimedium brevicornum Maxim. and Cuscuta chinensis Lam. induced ovary development in Japanese eel Anguilla japonica Author: Affiliation: 1. Fisheries College, Jimei University, Xiamen 361021, China;2. Engineering Research Center of the Modern Industry Technology for Eel, Ministry of Education, Xiamen 361021, China;3. College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China;4. Technical Center of Xiamen Entry-Exit Inspection and Quarantine Bureau, Xiamen 361026, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在水温（21±1）℃下，给体重（592.5±52.5）g的日本鳗鲡（）雌亲鱼投喂每千克体重含0.034 g淫羊藿和0.034 g菟丝子浸膏的饲料90 d，对照组投喂人工配合饲料，研究淫羊藿和菟丝子对卵巢发育的影响。结果显示，饲料中添加淫羊藿和菟丝子的雌鱼卵巢大部分卵母细胞属第Ⅱ时相，性腺指数和肝体比均显著高于对照组（<0.05）；卵母细胞油滴明显增多，部分卵母细胞胞质已充满油滴，核仁变小增多；血清雌二醇（E2）和11-酮基睾酮（11-KT）水平显著升高（cyp19a1仅微量表达，肝脏未检测到的表达；实验组肌肉总脂肪酸、饱和脂肪酸（SFA）、单不饱和脂肪酸（MUFA）和高度不饱和脂肪酸（HUFA）含量均显著高于对照组（<0.05）。本研究表明，在亲鱼培育饲料中添加中草药淫羊藿和菟丝子促进了日本鳗鲡卵母细胞油滴和肝脏卵黄蛋白原增加，提高了肌肉高不饱和脂肪酸的积累，为卵黄生成和卵母细胞进一步发育做好更充分的准备。 Abstract:In the present study, female Japanese eels () with an average body weight of (592.5±52.5) g were fed with a commercial diet supplemented with two Chinese herbs Lam at a water temperature of (21±1)℃ for 90 d. Then, the structure of ovarian development; changes in serum 11-KT and E2 levels; mRNA expression levels of liver vitellogenin (), and ovarian aromatase (tissue section staining, immunoenzymatic assays, semi-quantitative PCR, and gas chromatography, respectively. The results showed that the gonadosomatic indices (GSIs) and the hepatosomatic indices (HISs) in the Japanese eels fed with diets containing Lam. were significantly higher than those in the control group (<0.05); the treated group also showed ovaries filled with advanced perinucleolar follicles and increased numbers of oil droplets, and significantly higher serum 11-KT and E2 levels ( mRNA was elevated in the liver of the treated group; however, mRNA levels were extremely low in the ovaries of both the control group and the treated group, and the expression of mRNA was not detected in the livers of the two groups. Total fatty acid levels, including saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and highly unsaturated fatty acids (HUFA), in muscle were significantly higher in the Japanese eels fed with diets containing Lam than in the control group fish (<0.05); particularly, the levels of arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) were higher in the treated group. These findings indicated that the two Chinese herbs, Lam., induced early ovary development by increasing oil droplets of previtellogenic oocytes and promoted vitellogenin accumulation in the liver of parental female Japanese eels. Moreover, Lam. accelerated absorption of fatty acids, particularly HUFA, from diets, and subsequently their accumulation in the muscle, to prepare for vitellogenesis and further development of oocytes. 参考文献 相似文献 引证文献

Molecular characterization and expression analysis of signal transducer and activator of transcription 1 (STAT1) in Japanese eel Anguilla japonica

Signal transducer and activator of transcription 1 (STAT1) is one of critical signal transduction proteins of interferon (IFN) pathway and the structure and function of this protein have been well identified in mammals, but the information about the STAT1 is still limited in teleost fishes. In the present study, the full-length cDNA sequence of STAT1 (AjSTAT1) in Japanese eel (Anguilla japonica) was identified and characterized. Multiple alignment of the amino acid sequence showed that the AjSTAT1 protein has the typical conserved domains including the amino-terminal, coiled-coil, DNA-binding, linker, Src homology 2 (SH2), transcriptional activation domains (TAD). Quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed a broad expression for AjSTAT1 in a wide range of tissues, with the predominant expression in liver, followed by the spleen, intestine, gills, skin, kidney, and the very low expression in heart and muscle. The AjSTAT1 expressions in liver, spleen and kidney were significantly induced following injection with LPS, the viral mimic poly I:C, and Aeromonas hydrophila infection. In vitro, the AjSTAT1 transcripts of Japanese eel liver cells were significantly enhanced by the treatment of poly I:C or the stimulation of the high concentration of Aeromonas hydrophila (1 × 107 cfu/mL and 1 × 108 cfu/mL). Subcellular localization showed that in the natural state AjSTAT1was uniformly distributed in the cytoplasm, but AjSTAT1 was found to aggregated in the cytoplasm as well as partly in the nucleus after the stimulation of LPS and poly I:C. These results collectively suggested AjSTAT1 is an important transcription factor possibly involved in Japanese eel defense against viral and bacterial infection.

Evaluation of fish meal analogue as partial fish meal replacement in the diet of growing Japanese eel Anguilla japonica

We evaluated the dietary fish meal analogue as a fish meal replacer based on growth, hematology, non-specific immune responses and intestinal integrity in growing Japanese eel, Anguilla japonica. Five experimental diets contained the animal protein sources as 100% FM (FMA0) as control, 90% FM + 10% FMA (FMA10), 80% FM + 20% FMA (FMA20), 70% FM + 30% FMA (FMA30) and 60% FM + 40% FMA (FMA40). Each group of 13 fish with an average initial body weight of 119.60 ± 0.97 g (mean ± SD) were randomly distributed into 15 tanks (250-L each) in triplicates and fish were fed twice a day with one of the 5 experimental diets for 10 weeks. At the end of the feeding trial, weight gain (WG), specific growth rate (SGR), feed intake (FI) and feed efficiency (FE) of fish fed the FMA0, FMA10, and FMA20 diets were significantly higher than those of fish fed the FMA30 and FMA40 diets. Whole body proximate composition and amino acids profile of fish were not affected by dietary treatments. Broken-line regression analysis indicates the optimum dietary FMA replacement level could be 15.39%. Hemato-biochemical parameters such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), and triglycerides (TG) were higher in fish fed the FMA30 and FMA40 diets than those of fish fed the FMA0, FMA10, and FMA20 diets. Non-specific immune responses in terms of serum superoxide dismutase (SOD) and lysozyme activities were unaffected among fish fed the diets. Distal intestinal histology of fish fed the FMA30 and FMA40 diets showed abnormal villi structural arrangements (fold breaks, dilation, and dwarf villi) compared to those of fish fed the FMA0, FMA10, and FMA20 diets. Therefore, the results indicated that the optimum level of dietary FMA could fall between 15.39% and 20% in growing Japanese eel.

Rhabdochona angusticaudata sp. n. (Nematoda: Rhabdochonidae) from the Japanese eel Anguilla japonica, and new records of some other nematodes from inland fishes in Japan.

Collections of parasitic nematodes of fishes from some freshwater and brackish-water localities in Honshu, Shikoku and Hokkaido, Japan, carried out in 1996-2009, yielded the following eight species: Hysterothylacium haze (Machida, Takahashi et Masuuchi, 1978) (Anisakidae), Paraquimperia sp., Pingus sinensis Hsü, 1933 (both Quimperiidae), Heliconema anguillae Yamaguti, 1935 (Physalopteridae), Rhabdochona angusticaudata sp. n., Rhabdochona zacconis Yamaguti, 1935 (both Rhabdochonidae), Ascarophis arctica Polyanskiy, 1952 (Cystidicolidae) and Eustrongylides sp. larvae (Dioctophymatidae). The new species, R. angusticaudata sp. n., described from the intestine of the Japanese eel Anguilla japonica Temminck et Schlegel in the Renjoji River, Shikoku, is mainly characterised by the presence of 14-16 anterior prostomal teeth, non-bifurcated deirids with rounded ends, the length of the left spicule (300-384 µm long), the right spicule with a dorsal barb and non-filamented eggs. The species of Paraquimperia Baylis, 1934 and A. arctica are reported from Japan for the first time. Based on light and scanning electron microscopical examinations, some new morphological data on H. haze, H. anguillae, R. zacconis and A. arctica are provided.

Correction to: Predation on glass eels of Japanese eel Anguilla japonica in the Tone River Estuary, Japan

Correction to: Predation on glass eels of Japanese eel Anguilla japonica in the Tone River Estuary, Japan

Accumulation of hyaluronan in reared Japanese eel Anguilla japonica during early ontogeny

Hyaluronan (HA) is a main component of the highly hydrated extracellular body matrix of the larval stage of eels (leptocephalus). To determine the physiological and nutritional significance of HA in artificially reared larvae of the Japanese eel Anguilla japonica, HA and water content were measured at various larval stages in captivity. HA accumulated in the larval body with growth and water content also increased in parallel with HA. Almost all the accumulated HA was consumed during metamorphosis, suggesting HA plays a significant role in eel growth and metamorphosis. However, the amounts of HA and water were significantly lower in reared than in wild-caught larvae at the young stage, indicating a poorer nutritional condition of reared larvae, probably due to the deficient performance of currently used artificial diets. HA accumulation in reared larvae, however, eventually attained a level sufficient for metamorphosis by 250 days or more, and the glass eels of reared larvae had the same nutritional condition as that of wild glass eels. These findings are discussed with respect to the development of more effective artificial diets for rearing eel larvae.

Predation on glass eels of Japanese eel Anguilla japonica in the Tone River Estuary, Japan

Aquaculture of Japanese eel Anguilla japonica relies upon the natural recruitment of their glass eels (juveniles); however, predation that could influence glass eel recruitment remains unknown. In the present study, we aimed to elucidate the proportion of predation on A. japonica glass eels through stomach content analysis of predatory fishes collected in the estuary region of the Tone River system and its vicinity in Japan. Species of the predated glass eels were identified by DNA barcoding. A total of 270 predatory fishes of 15 taxa was collected over 2 years. The overall proportion of predation on glass eels, genetically identified as Japanese eel, was 0.7%, but this rose to 2.0% when data were limited to fishes caught during the peak months of glass eel recruitment. A glass eel was found in the stomach contents of a channel catfish Ictalurus punctatus, an invasive species in this river system, and a blackfin sea bass Lateolabrax latus. These fishes are therefore considered potential predators of A. japonica glass eels. However, as the proportion of predation was low, and the glass eels represented only small proportions of predator stomach contents, further investigation is needed for a better understanding of predation on A. japonica glass eels, and its effects on the early life stages of this endangered species.