Ryusuke Sudo

• Ph.D.
• Group leader at Japan Fisheries Research and Education Agency

Background Anguillid eels spend their larval period as leptocephalus larvae that have a unique and specialized body form with leaf-like and transparent features, and they undergo drastic metamorphosis to juvenile glass eels. Less is known about the transition of leptocephali to the glass eel stage, because it is difficult to catch the metamorphosin...

The only diet that has been capable of rearing eel larvae to the glass eel stage in captivity is the shark egg (SE)-based diet (SE). This study investigated the potential of alternative dietary components, namely hen egg yolk (HEY), milk proteins, and fish protein hydrolysate (FPH), on the growth and survival of eel larvae. In the first experiment,...

A novel filamentous eel-leptocephalus pathogenic marine bacterium, designated strain EL160426T, was isolated from Japanese eel, Anguilla japonica, leptocephali reared at a laboratory in Mie, Japan. In experimental infection studies on eel larvae, the strain EL160426T caused massive larval mortality and was reisolated from moribund leptocephali. Cha...

Anguillid eels undergo 2 major external changes during their life cycle: metamorphosis, which occurs when they shift their lifestyle from planktonic life in the ocean to sedentary life in inland water, and silvering, which occurs when they begin their spawning migration to the oceanic spawning area. Both metamorphosis and silvering occur synchronou...

Temporal changes of feeding incidences, digestive organ tissues, and mRNA expression of digestive enzymes were investigated in artificially reared Anguilla japonica glass eels. Incidences of daily feeding and cumulative first feeding exceeded 50% at day 40 and 33, respectively, but tended to increase gradually. Time until first feeding varied from...

Simple Summary Endocrine regulation has been thought to play a major role in the onset of migration. Anguillid eels provide a good model for studying the onset mechanisms of migrations to breeding areas, because the process of the onset of migration occurs in inland waters. In this review, we summarize information about the silvering process in ang...

Growth hormone (Gh) regulates somatic growth in fishes, particularly through the Gh - insulin-like growth factor-I (Igf-I) axis. In this study, recombinant Japanese eel Ghs with or without C-terminal peptides of human chorionic gonadotropin (CTP), which are known to prolong the half-life, were produced using the HEK 293 and CHO expression system. T...

Organogenesis of Japanese eels (Anguilla japonica) was investigated histologically from the late leptocephalus to the yellow eel stages. Early organogenesis, such as the formation of inner ears and the appearance of round blood cells that might be larval erythrocytes, had already begun at the late leptocephalus stage. During the first developmental...

The Japanese eel (Anguilla japonica) is one of the most important aquaculture fish species in Eastern Asia. A major bottleneck in the mass production of glass eels is the long larval period that they undergo in captivity. In the present study, 1689 glass eels, originating from a partly factorial cross (43 sires × 32 dams), were used to investigate...

Whole-genome duplication and genome compaction are thought to have played important roles in teleost fish evolution. Ayu (or sweetfish), Plecoglossus altivelis, belongs to the superorder Stomiati, order Osmeriformes. Stomiati is phylogenetically classified as sister taxa of Neoteleostei. Thus, ayu holds an important position in the fish tree of lif...

Downstream‐migrating (n = 64) and non‐migrating (n = 21) female Celebes eels Anguilla celebesensis were captured from the Poso Lake–River system on Sulawesi Island, Indonesia, and their reproductive physiological characteristics were examined. A histological observation of the ovaries revealed that most non‐migrating eels were at the perinucleolus...

The Japanese eel (Anguilla japonica) is among the most important aquaculture fish species in Eastern Asia. The present study aimed to identify the genetic parameters underlying body size and the timing at metamorphosis from leptocephali to glass eels in captive-bred Japanese eels, with the intent to foster sustainable development. Larvae from a par...

Phenotype and pedigree data for the estimation of genetic parameters by ASReml. (XLSX)

Summary statistics of the integration for each of the three component maps of the Japanese eel (female map, male map, consensus map with equal weights) and the final consensus anchoring (“anchored”). (XLSX)

List of SNP markers and anchored draft genome. (XLSX)

Pseudochromosome 1–19 from the Japanese eel genome, reconstructed from three input maps by ALLMAPS. (PDF)

List of the short tandem repeat (STR) markers used for parentage assignment. (XLSX)

Next-generation sequencing (NGS) information. (XLSX)

Phenotype data used for quantitative trait locus (QTL) mapping. (XLSX)

Completeness assessment results by CEGMA and BUSCO. (XLSX)

Single nucleotide polymorphism (SNP) genotype data used for linkage mapping. (XLSX)

Many diadromous fishes such as salmon and eels that move between freshwater and the ocean have evolved semelparous reproductive strategies, but both groups display considerable plasticity in characteristics. Factors such as population density and growth, predation risk or reproduction cost have been found to influence timing of maturation. We inves...

Hatchery produced leptocephalus larvae of the Japanese eel (Anguilla japonica) were reared on a research vessel and fed natural particulate organic matter (POM) collected in the Western North Pacific. A small net (36 cm diameter, 60 μm mesh) was vertically towed from 200 m depth to surface in 2013, and POM-enriched water (POMEW) filtered through 35...

Anguillid eels are a high value species for aquaculture in East Asian countries, but natural stocks of eels have been decreasing. Mass production of glass eels is one of the most effective ways to solve this problem. Genetic improvements will become important to establish mass production of glass eels in the near future. However, there is a lack of...

The timing of downstream migrations of anguillid silver eels in relation to environmental factors in rivers has been examined using various types of data. Less is known about the factors that affect when silver eels leave estuaries and enter the sea or about the onset of the spawning migrations of eels living in brackish-water coastal areas. The ti...

Migratory restlessness refers to a type of locomotor activity observed just before the onset of a migration. This behavior is primarily known in birds, where it is considered to be an indicator of the urge for migration. In contrast, little is known about migratory restlessness in fishes. To confirm migratory restlessness in a fish, we measured the...

To understand the roles of thyroid hormones in downstream migration of anguillid eels, we examined the profiles of serum thyroid hormones (thyroxine, T4 and triiodothyronine, T3) and thyroid stimulating hormone β-subunit (TSHβ) mRNA expression in relation to habitat use, silvering, and seasonal changes. Female Japanese eels, Anguillajaponica, were...

To clarify the role of thyroid function during metamorphosis from leptocephalus to glass eel in the Japanese eel, we examined the histology of the thyroid gland and measured whole-body concentrations of thyroid hormones, thyroxine (T4) and triiodothyronine (T3), and thyroid stimulating hormone β-subunit TSH (TSHβ) mRNA expression levels in five sta...

Lunar periodicity has been thought to influence the onset of the spawning migration of anguillid eels. In this study, we measured daily locomotor activity of 8 silver-phase Japanese eels Anguilla japonica in outdoor tanks to examine the effect of lunar periodicity on their activity and the following seaward migration. The activity of silver eels wa...

The Japanese coastlines along the Sea of Japan (Japan Sea) have been thought to be one of the margins of the distribution range of the Japanese eel Anguilla japonica, and there is evidence that eels had naturally recruited into these areas several hundred years ago. However, recruitment there is uncertain recently, because there seems to be no stud...

Effects of salinity-different habitats on growth rate, age and body size of Japanese eels at the silver-stage were investigated. Fish were sampled in one drainage system, that includes the brackish Hamana Lake and its inlet freshwater rivers, and were evaluated using otolith strontium:calcium (Sr : Ca) analysis to determine whether the eels had bee...

For understanding the functions of the growth hormone (GH)/prolactin (PRL)/somatolactin (SL) family of hormones, we examined pituitary mRNA expression of these hormones in anguillid eels in relation to salinity difference, silvering, and seasonal change. Female Japanese eels (Anguilla japonica) were collected in the brackish Hamana Lake and its fre...

To evaluate the effects of sex steroids on silvering in the Japanese eel, Anguilla japonica, the development of oocytes, eye size, digestive tract, and swim bladder were studied in relation to observations of the profiles of plasma levels of sex steroids (estradiol 17β, E2; testosterone, T; 11-ketotestosterone; 11-KT) during silvering for each sex...

Eggs of the Japanese eel Anguilla japonica collected in the western North Pacific were identified by onboard species-specific polymerase chain reaction (PCR) and DNA nucleotide sequencing after the cruise. Fish eggs of various species were collected by large plankton net tows at 12 stations along the southern part of the West Mariana Ridge on 19–25...

The distribution of all larval stages of the Japanese eel, Anguilla japonica, were examined using historical catch records and original data in the western North Pacific (WNP) to evaluate existing information about the larval distribution and migration of this species. A total of 148 preleptocephali, 2547 leptocephali, 6 metamorphosing larvae, and...

To improve understanding of the mechanism of early ovarian development in eels, the effects of water temperature decrease on oocyte development, plasma levels of sex steroids [estradiol 17β (E2), testosterone (T), 11-ketotestosterone (11-KT)], and gonadotropin β-subunit [follicle-stimulating hormone (FSHβ), luteinizing hormone (LHβ)] messenger RNA...

The profiles of sex steroids (estradiol-17β, testosterone and 11-ketotestosterone) and the mRNA levels of gonadotropins (luteinizing hormone and follicle-stimulating hormone) were investigated before and after downstream migration in females of the Japanese eel species Anguilla japonica, which were collected in the brackish Hamana Lake and its inle...

The biological characteristics of 259 silver-phase Japanese eels, Anguilla japonica, were investigated in Hamana Lake, Japan from 2003 to 2007, to obtain basic data for this species at the downstream migration. Their silvering stage, condition factor, three internal (gonad-somatic index: GSI, hepato-somatic index and gut index) and two morphometric...

We verified whether telomere length shortens with age in the loggerhead sea turtle (Caretta caretta) by measuring telomere lengths (relative telomere to single copy gene [T/S] ratios) in whole blood and epidermis from 20 captive individuals with a real-time PCR method. There was no significant correlation between age and relative T/S ratios in bloo...

津軽海峡の鯨類に関する知見は極めて乏しい。本研究では津軽海峡の鯨類の鯨種，それらの出現頻度を明らかにするため，2003年4月から2004年11月まで函館・青森間を運行するフェリーからの目視調査を実施した。58日6,102kmの目視調査により，合計415群3,010 個体の鯨類の発見があった。発見はカマイルカが優占し，マイルカ，イシイルカ，ハンドウイルカ、ネズミイルカ、コビレゴンドウ等が発見された。カマイルカの来遊のピークは5～6月の年一回であった。