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Abstract Objective The ayu or sweetfish Plecoglossus altivelis is ray-finned fish that is widely distributed in East Asia. The genome size of ayu was estimated at approximately 420 Mb. Previously, we reported on ayu draft genome assembly by whole-genome shotgun using Illumina short reads and PacBio long reads; however, the assembly was not to chromosome level. Therefore, to improve the draft genome sequence of ayu to chromosome level, we performed in situ Hi-C sequencing as a source of linkage information. Results The ayu genome assembly yielded 28 large scaffolds that corresponded to the karyotype of ayu (n = 28). The resulting ayu genome assembly has a N50 scaffold length of 17.0 Mb, improved from 4.3 Mb. The high-quality reference genome will be helpful for phylogenetic research on bony fishes and for breeding programs in ayu aquaculture.

Background: Ayu or sweetfish, Plecoglossus altivelis, an amphidromous fish ranging in the northwestern Pacific, is economically important inland fisheries and aquaculture resources. Genetic characterization of wild Ayu and derived culture seeds with competent molecular genetic markers is still insufficient for their sustainable use. Microsatellite DNA markers with larger repeat motifs (e.g. tri- and tetra-nucleotide motifs) are convenient and accurate compared with those having mono- and di-nucleotide motifs, but the latter motifs characterized most Ayu microsatellite markers developed previously. Methods and results: Here, we isolated and characterized 17 polymorphic microsatellite DNA markers with tri- and tetra-nucleotide repeat motif using next-generation sequencing. Alleles per locus varied from 6 to 23. The observed and expected heterozygosities ranged from 0.542 to 1.000 and 0.709 to 0.951, respectively. Polymorphic information content (PIC) of 15 out of the 17 loci were high (≧ 0.700), suggesting them to be highly informative. Twelve of the 17 loci were used for preliminary assignment test among three collections, and successfully allocated the examined fish to the original populations. Conclusion: The novel polymorphic microsatellite markers developed herein will be useful to examine the genetic diversity and population structure of wild Ayu and the effect of seed transplantation on native populations, providing a tool for conservation and sustainable adaptive management of this species. [ABSTRACT FROM AUTHOR]

Objective: The ayu or sweetfish Plecoglossus altivelis is ray-finned fish that is widely distributed in East Asia. The genome size of ayu was estimated at approximately 420 Mb. Previously, we reported on ayu draft genome assembly by whole-genome shotgun using Illumina short reads and PacBio long reads; however, the assembly was not to chromosome level. Therefore, to improve the draft genome sequence of ayu to chromosome level, we performed in situ Hi-C sequencing as a source of linkage information. Results: The ayu genome assembly yielded 28 large scaffolds that corresponded to the karyotype of ayu (n = 28). The resulting ayu genome assembly has a N50 scaffold length of 17.0 Mb, improved from 4.3 Mb. The high-quality reference genome will be helpful for phylogenetic research on bony fishes and for breeding programs in ayu aquaculture. [ABSTRACT FROM AUTHOR]

The Ryukyu-ayu population on Okinawa-jima Island went extinct suddenly in the late 1970s, but the cause remains unclear. Reports say that genetic diversity was not responsible, so we investigated food shortage as a probable driver. We examined pre-extinction specimens to look for territorial individuals, which have unique morphological characteristics and occur only in food-affluent conditions. We found that 42.1% (n = 45) of individuals possessed longer dorsal fins than non-territorial fish. Combining this with another key characteristic (blackened membrane at posterior dorsal fin ray), we found that territorial fish probably constituted 35.5% which fell in the range of the expected proportion for territorial fish in the nominotypical subspecies and higher than that observed in the extant population on Amami-oshima Island. These findings imply that the food resources in the riverine environments of Okinawa-jima Island before the extinction event might be sufficient for Ryukyu-ayu to establish feeding territories. Therefore, food shortage did not cause this population extinction. [ABSTRACT FROM AUTHOR]

Abstract Ayu (Plecoglossus altivelis altivelis) is an important freshwater fisheries resource and popular recreational fishing species in Japan that lives for only 1 year, with a single breeding season. To supplement increased recreational fishing demand for this species, more than 13 million wild‐born landlocked juveniles are translocated every year from Lake Biwa into Japanese rivers, and more than 52 million hatchery‐reared juveniles born from captive‐reared parents have been extensively released. The translocation of landlocked juveniles and hatchery release has continued for more than 100 and 30 generations, respectively. Previous studies have reported that landlocked and amphidromous forms of Ayu easily hybridise, leading to concerns that the fitness of hybrid progeny would be reduced in the wild. However, limited information exists regarding the reproductive success of landlocked Ayu in translocated rivers, and to date no studies have evaluated the effects of translocation on population structure. Demonstrating that hybridisation occurs between the two forms is central to future management and conservation of this species. To address this, a literature search to summarise biological knowledge of Ayu and population genetic data screening was undertaken, and published genetic data sets covering a distribution range in Japan were reanalysed. Analyses provide strong evidence for very high gene flow between sampling locations. Genetic diversity is homogeneous in amphidromous samples. Bayesian admixture analysis infers widespread hybridisation in Japanese rivers (24 ± 8%). Maximum likelihood admixture graphs detect two migration events from Lake Biwa to rivers in the northern Sea of Japan and Hokkaido. Analyses consistently indicate that hybridisation between translocated landlocked juveniles and native amphidromous Ayu occurs throughout Japanese rivers. These results are discussed in relation to the management of this species.

For the first time, natural entry of ayu or sweetfish into the river of Peter the Great Bay basin (Japan Sea) and generally into the waters of Russian Federation is registered. This finding extends the list of fish species and families dwelling in the Russian waters.

The present study tested the hypothesis that whether limited genetic diversity was the main factor that led the Ryukyu-ayu population on Okinawa-jima Island to extinction in the late 1970s. The usability of fluctuating asymmetry (FA) in reflecting genetic diversity was tested using two extant populations of Ryukyu-ayu on Amami-oshima Island, then used to estimate genetic diversity for the extinct population which only formalin-preserved specimens are available. The results showed that higher FA indices were associated with lower genetic diversity in the two extant populations, and the extinct population on Okinawa-jima Island had lower FA indices than the two extant populations on Amami-oshima Island. This finding suggests that the genetic diversity of the extinct population was not low enough as to cause its extinction. [ABSTRACT FROM AUTHOR]

With the rapid development of intensive farming, the aquaculture industry uses a great many antibiotics for the prevention and treatment of bacterial diseases. Despite their therapeutic functions, the overuse and accumulation of antibiotics also pose a threat to aquaculture organisms. In the present study, ayu (Plecoglossus altivelis) was used as a fish model to study the impacts of ciprofloxacin (CIP) overuse on intestinal homeostasis and immune response during subsequent Pseudomonas plecoglossicida infection. Based on 16S rRNA gene amplification and Illumina sequencing, we found that CIP pre-exposure caused significant variation in intestinal microbiota, including increased species richness, altered microbiota composition and interaction networks, and increased metabolic dysfunction. Furthermore, immunohistochemical analysis indicated that CIP pre-exposure resulted in severe mucosal layer damage, goblet cell reduction, and epithelial cell necrosis of the intestinal barrier in infected ayu. Quantitative real-time polymerase chain reaction (qRT-PCR) showed that disruption of intestinal homeostasis impaired systemic antiinfection immune responses in the intestine, gill, spleen, and head kidney, while inhibiting IL-1β, TNFα, and IL-10 expression and promoting TGF-β expression. Our findings indicated that CIP administration can directly affect intestinal microbiota composition and intestinal integrity in ayu fish. This perturbation of intestinal homeostasis is likely responsible for the lower survival rate of hosts following subsequent infection as the capacity to mount an effective immune response is compromised. This study also provides preliminary clues for understanding the effects of antibiotic overuse on higher vertebrates through trophic transfer. [ABSTRACT FROM AUTHOR]

Purple nonsulfur bacteria ( PNSB ) reportedly have probiotic effects in fish, but whether they are indigenous in the digestive tract of fish is a question that requires answering. We attempted to isolate PNSB from the digestive tract of ayu ( Plecoglossus altivelis ) from the Kuma River ( Kumamoto, Japan ) and successfully isolated 12 PNSB strains. All the isolated PNSB belonged to the genus Rhodopseudomonas . Five Rhodopseudomonas strains were also isolated from the soil samples collected along the Kuma River. The phylogenetic tree based on the partial sequence of pufLM gene indicated that the PNSB from ayu and soil were similar. The effects of NaCl concentration in growth medium on growth were also compared between the PNSB from ayu and soil. The PNSB from ayu showed a better growth performance at a higher NaCl concentration, suggesting that the intestinal tract of ayu, a euryhaline fish, might provide suitable environment for halophilic microorganisms. [ABSTRACT FROM AUTHOR]

Argulus coregoni Thorell, 1864 was collected from white-spotted char, Salvelinus leucomaenis (Pallas, 1814), redspotted masu salmon, Oncorhynchus masou ishikawae Jordan and McGregor, 1925, masu salmon, O. m. masou (Brevoort, 1856), and a hybrid between white-spotted char and masu salmon in mountain streams, Gifu Prefecture, central Japan. The host’s body surface under and near the pectoral fins was the most common infection site for A. coregoni. The infected white-spotted char were caught at high elevations (461–873m) in the headwater streams. The infected individuals of the two masu salmon subspecies were mostly caught in the upper river reaches, but the elevations where they were caught were lower (237–733m and 660–707m, respectively) than those of the white-spotted char. Since A. coregoni is also known as a parasite of ayu, Plecoglossus altivelis altivelis (Temminck and Schlegel, 1846), in the middle and lower river reaches in the prefecture, this parasite utilizes different fish species as its hosts along a river course: white-spotted char and the two masu salmon subspecies serve as the hosts, respectively, in the headwater and the middle to lower sections of the upper reaches, but in the mid- and lower river reaches, ayu is the important host. [ABSTRACT FROM AUTHOR]

The complete genome sequences of seven Edwardsiella ictaluri strains, isolated from the kidneys of dead ayu ( Plecoglossus altivelis altivelis ) in Kochi's Kagami and Shimanto Rivers, Japan, were determined. Multilocus sequencing typing revealed that their genotypes were sequence-type ST26., Competing Interests: The authors declare no conflict of interest.

We analysed the predisposing factors for Edwardsiella ictaluri infection in the riverine ayu Plecoglossus altivelis on the basis of environmental and epidemiological data obtained in a tributary to and the lower reaches of the Tama River, Japan, in July and August 2011–2015. Mortality of ayu due to E. ictaluri infection was observed only in the tributary in August 2012 and 2013; both periods were unusually hot. During these mortality events, daily average water temperatures rose approximately 3–4°C over 4–8 days, reaching the optimum temperature for E. ictaluri infection (>25°C) and approaching the upper tolerable limit for ayu (30°C). Diurnal water temperature ranges (DWTRs) in the tributary during the mortality events exceeded 6°C, which was 1–2°C greater than in the lower reaches. Experimental infection of ayu with E. ictaluri resulted in higher mortality when exposed to 6°C DWTR than to 4°C DWTR. Furthermore, water levels in the tributary were generally low in August 2012 and 2013 because of low rainfall. From these results, we conclude that unusually high‐water temperatures combined with high DWTRs and low water levels drove riverine ayu mortality from E. ictaluri infection. [ABSTRACT FROM AUTHOR]

• We characterized two PU.1 genes from ayu, Plecoglossus altivelis. • The PU.1 transcripts were altered in ayu upon Vibrio anguillarum infection. • PaPU.1a knockdown decreased inflammatory cytokine expression. • PaPU.1b knockdown attenuated MO/MФ bacterial killing capability. Transcription factor PU.1 is a regulator of macrophage function, however, the specific function of PU.1 in teleost monocytes/macrophages (MO/MФ) remains unknown. We determined the cDNA sequence of two PU.1 genes from ayu (Plecoglossus altivelis ; PaPU.1a and PaPU.1b). Sequence comparisons showed that PaPU.1 were most closely related to the PU.1 of rainbow smelt (Osmerus mordax). The PU.1 transcripts were mainly expressed in the spleen, and their expression was altered in various tissues upon infection with Vibrio anguillarum. PaPU.1a and PaPU.1b proteins were upregulated in MO/MФ, after infection. RNA interference was employed to knockdown PaPU.1a and PaPU.1b to investigate their function in MO/MФ. The expression of inflammatory cytokines was regulated by PaPU.1a, but not PaPU.1b, in ayu MO/MФ upon V. anguillarum infection. Both PaPU.1a and PaPU.1b knockdown lowered the phagocytic activity of MO/MФ. Furthermore, PaPU.1b knockdown attenuated MO/MФ bacterial killing capability. Our results indicate that two PaPU.1 genes differentially modulate the immune response in ayu MO/MФ against bacterial infection. [ABSTRACT FROM AUTHOR]

The Ayu (Plecoglossus altivelis altivelis) population on Yaku-shima Island, Kagoshima Prefecture, Japan represents the southernmost population of the subspecies and is considered to be facing extinction. We investigated the genetic characteristics of Ayu in the Miyanoura River (MYU) in the northeast of the island and the Kurio River (KRO) in the southwest of the island, using partial sequences of mitochondrial (mt) control region and polymorphic microsatellite (simple sequence repeat: SSR) loci. The mtDNA analysis revealed that the Yaku-shima Island population was significantly differentiated from other Ayu populations; additionally, the MYU and KRO populations were significantly different from each other in terms of mtDNA (pairwise ΦST = 0.5826, P < 0.01) and SSR (pairwise ΦST = 0.1598, P < 0.01) analyses, indicating very little or no gene flow between them. The mtDNA haplotype diversity values were minimal for KRO and somewhat lower for MYU (h = 0.8176) than for each population from the mainland of Japan (Honshu–Kyushu) and the Korean Peninsula (h = 0.9905–1.0000). The mean values of expected heterozygosity (He) of SSRs were also lower in KRO (mean He = 0.555) than in MYU (mean He = 0.649). A considerably small effective population size (Ne = 100.1 for MYU, 151.2 for KRO) and a bottleneck effect for Yaku-shima Island population were suggested by SSR analysis. These findings underscore the importance of monitoring the genetic diversity of Ayu on Yaku-shima Island and the necessity of designing conservation policies for each river's population. [ABSTRACT FROM AUTHOR]

Two subspecies of ayu, Plecoglossus altivelis altivelis (nominotypical subspecies) and P. a. ryukyuensis (Ryukyu-ayu), differ morphologically, behaviorally, and genetically. Specimens from nine populations comprising both subspecies were investigated to examine whether their meristic characteristics follow a widely observed geographical tendency known as Jordan's rule. Seven out of the eleven characteristics increased in frequency with latitude, following Jordan's rule. Contrarily to the expectation from Jordan's rule, however, Ryukyu-ayu had more anal fin rays than nominotypical subspecies in the temperate zone, suggesting genetic divergence underlying this characteristic between these two subspecies. The two subtropical populations showed a reversal of the geographic cline in the number of scales and dorsal fin rays, indicating these do not share a gene pool. The present study, without using genetic indicator, remains disputable to consider genetic status within Ryukyu-ayu further. [ABSTRACT FROM AUTHOR]

Ayu sweetfish (Plecoglossus altivelis) is a diurnal freshwater fish that are surface swimmers and active under broad and short wavelength-dominated light. Biochemical analyses have shown that the ayu fish have abundant carotenoids including zeaxanthin in their integuments. Although zeaxanthin plays an important role in the physiological function of the retina, the amount and location of zeaxanthin in the ayu eye have not been accurately determined. In this study, circular dichroism spectral data and chiral highperformance liquid chromatography analysis showed that zeaxanthin was the primary carotenoid in the ayu eye, and the eye had the highest carotenoid content compared to those in the integuments, subcutaneous fat, and digestive tract. Interestingly, zeaxanthin in the ayu eyeball was expressed in the photoreceptor layer and near the retinal pigmented epithelium. In vitro assays showed that zeaxanthin could protect photoreceptors and retinal pigmented epithelial cell lines against the oxidative stress induced by exposure to L-buthionine-(S,R)-sulfoximine/glutamate. These findings indicate that zeaxanthin plays protective roles against oxidative stress in the vision of wild ayu. [ABSTRACT FROM AUTHOR]

Ayurveda is the most ancient holistic science of life which aims at preventing the disease rather than curing it. Dealing with four major components of Hitkar Ayu, Ahitkar Ayu, Sukhkar Ayu and Dukhkar Ayu, it gives immense importance to both community as well as the individual health. In present COVID-19 pandemic, the Ayurvedic approach related to community and individual medicine becomes a significant aid to cope up with this life-threatening pandemic disease. As the renowned health organizations of whole world declared that there is no cure of this disease in mean of vaccine and specific medicines, only symptomatic treatment and boosting of human immune system are only two measures through which we can tackle with this pandemic. For this we have divided the whole population into four groups and different methodologies have been applied in all four with the main emphasis laid on strengthening immune system, doing symptomatic treatment & sterilization by Ayurvedic measures and management of stress. In this way, the Ayurveda system of medicine can play a dynamic and significant role thereby providing a ray of light to whole world against the dimness of this pandemic. [ABSTRACT FROM AUTHOR]

The Ryukyu ayu Plecoglossus altivelis ryukyuensis is an endangered amphidromous fish that inhabits rivers in the Ryukyu Archipelago (Japan). Populations of the species have declined dramatically. Consequently, the Ryukyu ayu has been registered as a natural monument in Japan and monitoring surveys with direct catching are restricted legally. This restriction, unfortunately, makes monitoring of population abundances difficult and creates a barrier to both advancing understanding of the species' status and the development of appropriate conservation plans. We developed a non-invasive monitoring methodology using eDNA analyses. We designed a specific quantitative PCR assay for the Ryukyu ayu using the mitochondrial ND4 region. Using this primer/probe set, we conducted eDNA analyses in three rivers on Amami-Ohshima Island. The DNA fragments were amplified from the eDNA extracted from natural water in each river. The numbers of DNA fragments detected were positively correlated with individual counts of fish obtained by visual snorkelling surveys. Our method does not contravene restrictions and facilitates abundance monitoring of this endangered fish species. [ABSTRACT FROM AUTHOR]

Flavobacterium psychrophilum can be divided into three genotypes, G-C type (ayu type), A-C type (multi-fish type), and A-T type (salmon-trout type), by two single-nucleotide polymorphisms in the DNA gyrase subunit A (gyrA) gene. We isolated F. psychrophilum from various samples collected from the lower basin of a river flowing into Lake Biwa, as a model for bacterial survey, in Shiga Prefecture in June, September, and December from 2010 to 2013 and investigated their gyrA genotypes. All three types of F. psychrophilum were isolated in June when ayu went up the river from the lake. In September, ayu gathered in the lower river basin for spawning and became high in density, almost all of the isolates were of the G-C genotype and the A-T genotype was never isolated. In December, only the A-T type was isolated from the river samples, when Biwa trout Oncorhynchus masou rhodurus came to the river to spawn and were present in the sampling area. In accordance with the seasonal change of the host fish species in the river, the genotype of F. psychrophilum isolated from the environment seems to have changed as well. [ABSTRACT FROM AUTHOR]

Interleukin-6 (IL-6) is one of the most pleiotropic cytokines because of its wide range of effects on cells of the immune and non-immune systems in the body. However, the role of IL-6 in fish monocytes/macrophages (MO/MФ) is poorly understood. In this study, we cloned the cDNA sequence of the IL-6 gene from ayu (Plecoglossus altivelis) and demonstrated using a tissue distribution assay that ayu interleukin-6 (PaIL-6) mRNA is expressed in all tested tissues. Changes in expression were observed in immune tissues as well as in MO/MФ after a Vibrio anguillarum infection; subsequently, PaIL-6 was expressed and purified to prepare anti-PaIL-6 antibodies. Recombinant PaIL-6 protein (rPaIL-6) treatment enhanced pro-inflammatory cytokine expression. Ayu interleukin-6 receptor β (PaIL-6Rβ) knockdown resulted in decreased pro-inflammatory cytokine expression in MO/MФ treated with rPaIL-6, whereas no significant changes were observed after ayu interleukin-6 receptor α (PaIL-6Rα) knockdown in MO/MФ. PaIL-6 and PaIL-6Rβ knockdown in MO/MФ inhibited the phosphorylation of signal transducer and activator of transcription 1. Moreover, PaIL-6Rβ knockdown inhibited the phagocytic and bactericidal ability of ayu MO/MФ treated with rPaIL-6. These data indicate that PaIL-6 may be able to regulate the function of ayu MO/MФ. • We characterized an IL-6 gene from ayu. • IL-6 transcripts were altered in ayu upon Vibrio anguillarum infection. • Infection stimulated IL-6 expression in ayu monocytes/macrophages. • IL-6 regulated the functions of monocyte/macrophage. [ABSTRACT FROM AUTHOR]

The ecology and mortality of larval ayu (Plecoglossus altivelis altivelis) during downstream migration was investigated during three spawning seasons (2008–2010) in the Unosumai River, Iwate Prefecture, Japan. Downstream larval migration occurred from early September to mid-December, peaking from late September to mid-October. Larval drift numbers recorded at the lowest reach spawning ground peaked from 18:00–21:00, twenty-four-hour-surveys in 2008 and 2010 resulting in total daily numbers of drifting larvae of 2,855,660 and 785,880, respectively, with 88.1 and 88.7%, respectively, occurring between 17:00–24:00. A twenty-four-hour-survey at the river mouth in 2010 recorded larvae between 19:00–06:00 (following day), peaking at 21:00 (67.5% of larvae occurred between 21:00–23:00), approximately 2 h later than the peak at the lowest reach spawning ground. The river mouth survey estimated a total larval number of 113,724, corresponding to 14.5% of the number recorded from the lowest reach spawning ground on the same day, indicating a mortality rate of 85.5%. [ABSTRACT FROM AUTHOR]

Classical Fc receptors (FcRs) mediate the binding to and recognition of the Fc portion of antibodies and play an important role during immune responses in mammals. Although proteins similar to soluble FcRs have been identified in fish, little is known about the role of such proteins in fish immunity. Here, we cloned a cDNA sequence encoding a soluble Fc receptor for an immunoglobulin G (FcγR) homolog from ayu (Plecoglossus altivelis) (PaFcγRl). The predicted protein was composed of two immunoglobulin C2-like domains but lacked a transmembrane segment and a cytoplasmic tail. The PaFcγRl transcripts were distributed at low levels in all tested tissues, but significantly increased after Vibrio anguillarum infection. The PaFcγRl protein was expressed in the head kidney, trunk kidney, and neutrophils. Recombinant PaFcγRl (rPaFcγRl) was secreted when transfected into mammalian cells and the native protein was also detected in serum upon infection. rPaFcγRl was also demonstrated to bind to ayu IgM, as assessed by cell transfection. Suppressive activity of the recombinant mature protein of PaFcγRl (rPaFcγRlm) on in vitro antisheep red blood cell (SRBC) responses was detected by a modified hemolytic plaque forming cell assay. In conclusion, our study revealed that PaFcγRl is closely involved in the negative regulation of IgM production in the ayu spleen. [ABSTRACT FROM AUTHOR]

To elucidate spatial and seasonal variations of radiocesium (134Cs and 137Cs) concentrations in ayu Plecoglossus altivelis, amphidromous fish samples were collected both from shallow coastal waters in March 2014 and from seven rivers in Fukushima Prefecture during May–October 2014. Of the rivers, two were located within the designated evacuation zone. After standard length (SL) and body weight measurements, fish were dissected to two parts: body without head and internal organs, BD; head and internal organs, HI. Radiocesium concentrations in these parts were measured using germanium semiconductor detectors. Those in the whole body (WB) were reconstructed using their concentrations and weights. The 137Cs concentrations in BD in oceanic samples (4.3–6.7 cm SL) were below the detection limit, whereas those in riverine samples (6.4–18.8 cm SL) were 0.719–902 Bq kg−1-wet. Statistical analyses indicated a best-fit linear mixed-effects model including "SL" and "sampling site" as explanatory variables. Significant differences in 137Cs concentrations in BD among rivers were detected. Our results indicate that 137Cs concentrations in BD of riverine ayu, which showed lower but site-specifically constant values compared with those in HI or WB, are useful as a good indicator of radiocesium contamination of the respective rivers. [ABSTRACT FROM AUTHOR]

Abstract The glucocorticoid receptor (GR) is an important feedback regulator of the hypothalamic-pituitary-interrenal (HPI) axis. However, there are a limited number of studies focused on host-pathogen interactions in which an association between GR and immune response has been evaluated in monocytes/macrophages (MO/MФ) after being challenged with highly pathogenic bacteria. Here, we cloned the cDNA sequence of the glucocorticoid receptor (PaGR) gene from ayu fish. The PaGR transcript was expressed in all tissues, and changes in expression were observed in immune tissues and MO/MФ after live Vibrio anguillarum infection. Subsequently, PaGR was expressed and purified to prepare anti-PaGR antibodies. We analyzed the subcellular localization of PaGR. PaGR was expressed not only in the intracellular space but also in the plasma membrane. PaGR activation decreased the expression of pro-inflammatory cytokines and increased the expression of anti-inflammatory cytokines. However, PaGR activation suppressed the phagocytosis activity of V. anguillarum -infected ayu MO/MФ via a non-genomic pathway. Interestingly, PaGR activation could enhance MO/MФ bacterial killing capability and apoptosis. Therefore, PaGR may modulate the immune response in ayu MO/MФ by genomic and non-genomic pathways. Highlights • We characterized a GR gene from ayu, Plecoglossus altivelis. • GR transcripts were altered in ayu upon Vibrio anguillarum infection. • GR activation suppressed the phagocytosis of moncytes/macrophages via non-genomic pathway. • GR participated in the regulation of apoptosis in moncytes/macrophages. [ABSTRACT FROM AUTHOR]

A new bio-economic model for managing population of non-renewable inland fishery resource in uncertain environment is presented. Population dynamics of the resource is described with stochastic differential equations (SDEs) having ambiguous growth and mortality rates. The performance index to be maximized by the manager of the resource while minimized by nature is presented in the context of differential game theory. The dynamic programming principle leads to a Hamilton-Jacobi-Bellman-Isaacs (HJBI) equation that governs the optimal resource management strategy under the ambiguity. The main contribution of this paper is a series of theoretical analysis on the reduced HJBI equation for non-renewable fishery resources in a broad sense, indicating that the ambiguity critically affects the resulting optimal controls. Practical implications of the theoretical analysis results are also presented focusing on artificially hatched Plecoglossus altivelis (Ayu), an important inland fishery resource in Japan. [ABSTRACT FROM AUTHOR]

Abstract Adiponectin (ADP), a regulator of the innate immune system, plays a role in the progression of inflammation and metabolic disorders in mammals. However, the role of ADP in fish is poorly understood. Here, we cloned the cDNA sequence of a ADP homolog (PaADP) gene from ayu. Multiple sequence alignment revealed that PaADP presented typical characteristics of ADPs. Phylogenetic tree analysis showed that PaADP was most closely related to that of rainbow trout. In healthy ayu, the transcripts of PaADP were detected in most of the tested tissues and cells, with the highest level in the adipose tissue. Upon V. anguillarum infection, the mRNA expression of PaADP was significantly up-regulated in the tissues and cells except adipose tissue. Subsequently, the full-length mature PaADP (fPaADP) and the globular domain fragment (gPaADP) were prokaryotically expressed in bacteria and purified, and anti-PaADP antibodies were produced. Western blot analysis revealed that three fragments including fPaADP and gPaADP were existed in ayu serum. The recombinant fPaADP (rfPaADP) had an anti-inflammatory effect on ayu MO/MФ by upregulating anti-inflammatory cytokine expressions, downregulating pro-inflammatory cytokine expressions, inhibiting the phagocytosis and subsequent bacterial killing. In contrast, the recombinant gPaADP (rgPaADP) presented a pro-inflammatory effect on ayu MO/MФ by upregulating pro-inflammatory cytokine expression, downregulating anti-inflammatory cytokine expressions, enhancing the phagocytosis and subsequent bacterial killing. These results suggested that fPaADP and gPaADP have opposite roles in the regulation of MO/MФ functions in ayu. Highlights • We characterized an adiponectin (PaADP) gene from ayu. • PaADP existed in ayu serum as multiple forms such as fPaADP and gPaADP. • FPaADP had an anti-inflammatory effect on ayu MO/MФ. • GPaADP had an pro-inflammatory effect on ayu MO/MФ. [ABSTRACT FROM AUTHOR]

Ryukyu-ayu (Plecoglossus altivelis ryukyuensis) is an amphidromous fish species that migrates between the sea and rivers over its one-year life span. Although growth performance during the early marine stage may affect growth in the later riverine stage of this species’ life cycle, no studies have specifically examined this relationship in P. a. ryukyuensis. In the present study, we reconstructed the growth trajectories of P. a. ryukyuensis individuals collected from the Yakugachi River, Amami-Oshima Island, Japan in 2016 (n = 47) throughout their growth period in both the sea and river by using otolith analysis. Using this, we determined the age and body size of individuals at the time of their upstream migration, as well as their growth rates during the marine and riverine stages. Results showed that body size at upstream migration significantly affected body size at the riverine stage, indicating that juveniles with larger body size in the sea had better growth performance in the river. Individuals with higher growth rates during the marine stage tended to enter the river younger and at larger body sizes than those with lower marine growth rates. Our results demonstrated the close linkage between the growth performance in the sea and in rivers of P. a. ryukyuensis. This information will contribute to better understanding variations in growth patterns of this endangered species and potentially aid in its conservation. [ABSTRACT FROM AUTHOR]

Abstract: Riverine systems are inherently dendritic in nature, and turbid water may not necessarily flow equally throughout an entire catchment. Tributaries have the potential to serve as refugia from temporarily turbid water in the main stem. As ayu (Plecoglossus altivelis) are one of the important species for the inland fisheries industry and recreational fishing, their behaviour in a branched river network is a primary concern. We released ayu with radio‐transmitting tags into two experimental streams that joined at a downstream pool. Turbid water was released into one of the streams, and we identified whether avoidance movement of ayu between the two experimental streams was triggered by flowing turbid water. The suspended solid concentration elevated rapidly after adding the turbid water and was maintained at more than 400 mg/L for 3 hr. Avoidance movement of ayu was triggered when the suspended solid concentration exceeded approximately 200 mg/L. Then, most ayu moved from the turbid stream to the nonturbid one, leading to a difference in ayu density between the two streams. Therefore, we demonstrated that turbid water induced interstream movement of a commercially important ayu as refuge behaviour, suggesting that river connectivity is important for the persistence of the ayu. [ABSTRACT FROM AUTHOR]

Tissue factor (TF) plays an important role in the host's immune system as the principal initiator of coagulation. However, the precise function of TF in teleosts remains unclear. We determined the cDNA sequence of TF from ayu Plecoglossus altivelis (PaTF). The PaTF transcript was expressed in all tested tissues, and changes in expression were observed in tissues and monocytes/macrophages (MO/MФ) upon infection with Vibrio anguillarum . PaTF was prokaryotically expressed and purified to prepare anti-PaTF antibodies. Western blot analysis revealed that native PaTF was glycosylated in thrombocytes, but not in ayu MO/MФ. Microparticles could transfer PaTF to thrombocytes. PaTF neutralization or knockdown led to anti-inflammatory status in ayu MO/MФ upon V. anguillarum infection. PaTF neutralization reduced the apoptosis of ayu MO/MФ and improve survival rate in V. anguillarum -infected ayu. Our results indicate that PaTF plays a role in ayu immune response against bacterial infection as a pro-inflammatory mediator. [ABSTRACT FROM AUTHOR]

In this study, we investigated maturation-associated changes in non-specific immune responses of ayu against Flavobacterium psychrophilum . The gonadosomatic index was minimum on 16 June, began to increase on 17 July, and reached the maximum value during August. The highest phagocytic rate (16.3%) was observed on 16 June, which decreased significantly to 5.6% on 26 August. The number of viable bacteria after the serum treatment was highest during August, suggesting that bactericidal activity of the serum decreased along with the sexual maturation. Gene expression levels of interleukin-8, and tumor necrosis factor-α in the spleen did not change significantly during this period, whereas the level of suppressor of cytokine signaling (SOCS)3 was significantly higher on 26 August than that on 16 July ( p  < 0.05). These results suggest that phagocytic activity of trunk kidney leukocytes and serum bactericidal activity against F. psychrophilum decreased with sexual maturation, and that SOCS3 may be related to the decrease in non-specific immune activity in ayu. [ABSTRACT FROM AUTHOR]

The short-chain pentraxins (PTXs), including C-reactive protein (CRP) and serum amyloid P (SAP), are soluble pattern recognition molecules (PRMs) that exhibit calcium-dependent binding to bacterial surface molecules. They opsonize pathogens or other particles by phagocytic clearance. However, the detailed functions of short-chain PTXs in teleosts remained unclear. In this study, we identified a short-chain PTX gene from ayu, Plecoglossus altivelis , and tentatively named as PaCRP/SAP. Sequence analysis revealed that PaCRP/SAP has typical characteristics of fish CRP/SAP and is mostly closely related to rainbow smelt ( Osmerus mordax ) SAP. PaCRP/SAP transcripts were detected in all tested tissues, with the highest level in the liver, and its expression significantly upregulated following Vibrio anguillarum infection. The active recombinant mature PaCRP/SAP (rPaCRP/SAPm) agglutinated Gram-negative bacteria ( Escherichia coli , V. anguillarum , Aeromonas hydrophila , and Vibrio parahaemolyticus ) and Gram-positive bacteria ( Staphylococcus aureus and Listeria monocytogenes ) in a calcium-dependent manner in vitro , and it correspondingly bound peptidoglycan and lipopolysaccharide in a dose-dependent manner. The binding of rPaCRP/SAPm to E. coli and S. aureus resulted in a clear inhibition of the deposition of ayu complement 3 (PaC3) on the bacteria. Furthermore, rPaCRP/SAPm decreased phagocytosis of rPaCRP/SAPm-bound E. coli and S. aureus cells by ayu monocytes/macrophages (MO/MΦ) in a complement-dependent way. However, rPaCRP/SAPm alone had no significant influence on phagocytosis. These results provided the first evidence that PaCRP/SAP might function in ayu immune responses via agglutinating bacteria and inhibiting complement-mediated opsonophagocytosis by MO/MΦ. [ABSTRACT FROM AUTHOR]

Macrophage receptor with collagenous structure (MARCO) plays essential roles in phagocytic cell-mediated innate immune responses. However, studies regarding MARCO, especially its functions, are limited in teleost species. In this study, we identified a MARCO molecule (PaMARCO) from ayu ( Plecoglossus altivelis ). PaMARCO shared conserved functional domains with its mammalian counterparts. Sequence analysis showed that PaMARCO was most closely related to its rainbow trout ( Oncorhynchus mykiss ) counterpart. PaMARCO expression was upregulated in all tested immune tissues and monocytes/macrophages (MO/MΦ) upon Vibrio anguillarum infection, and blocking its function significantly decreased the immune responses of MO/MΦ during infection. PaMARCO could bind to the tested gram-positive and -negative bacteria in a Ca 2+ -dependent manner in vitro . Furthermore, the phagocytosis and bacterial killing activities of MO/MΦ were significantly decreased upon PaMARCO blockade using anti-PaMARCO IgG. PaMARCO was also involved in the polarization processes of ayu MO/MΦ. The upregulated expression of representative cytokines in LPS-induced M1 type (TNF-α, IL-1β) or cAMP-induced M2 type (TGF-β, IL-10) were inhibited in the anti-PaMARCO IgG-treated group, indicating that PaMARCO may be involved in the regulation of both inflammation priming and inflammation resolution of MO/MΦ. In conclusion, our results implicate that PaMARCO has essential regulatory roles for bacterial binding, clearance, and the polarization processes of ayu MO/MΦ. [ABSTRACT FROM AUTHOR]

The CC motif chemokine 19 (CCL19) functions in acute inflammation by recruiting lymphocytes and other cells. However, CCL19 has only been investigated in few fish species. In this study, we characterized a CCL19-like molecule (PaCCL19l) in ayu ( Plecoglossus altivelis ), a teleost fish. Sequence analysis revealed that PaCCL19l was most closely related to Atlantic salmon ( Salmon salar ) CCL19l1, which belonged to the fish CCL19a.1 subcluster. PaCCL19l was constitutively expressed in the tested ayu tissues and peripheral blood mononuclear cells (PBMCs), with the highest transcript level in PBMCs. Upon infection with Vibrio anguillarum , the expressions of PaCCL19l in the head kidney, liver, spleen, PBMCs, and monocytes/macrophages (MO/MΦ) were dramatically up-regulated. Recombinant PaCCL19l (rPaCCL19l) exhibited a significant effect on the chemotaxis of lymphocytes and MO/MΦ in vitro and in vivo . Meanwhile, rPaCCL19l exerted a high chemotaxic activity for lipopolysaccharide (LPS)-stimulated MO/MΦ (M1-type), but not for cyclic adenosine monophosphate (cAMP)-stimulated MO/MΦ (M2-type). When ayu MO/MΦ was treated with rPaCCL19l along with Vibrio anguillarum infection, the mRNA expression of proinflammatory cytokines (IL-1β, TNFα, IL-6, IL-12b, and IFN-γ) was up-regulated, while that of anti-inflammatory cytokines (IL-10, TGFβ, and IL-22) was down-regulated. Ayu MO/MΦ treated with anti-PaCCL19l IgG gave the opposite result. These results implicated that PaCCL19l is involved in the selective chemotaxis of ayu immune cells and promotes the host at a pro-inflammatory state. [ABSTRACT FROM AUTHOR]

The geographic and spatial distribution of ayu Plecoglossus altivelis (Temminck and Schlegel 1846) larvae were determined in the rivers of northern Vietnam. Collections were made with a larval net and a small seine net along the Tien Yen and Kalong Rivers from 2010 to 2015. Thirty individuals were collected in the Tien Yen and 160 from the Kalong. This is the first record of larval and juvenile ayu from the Tien Yen, which constitutes the southernmost range of this species. Collected fish were primarily at the preflexion stage (4.0-59.1 mm body length, BL). Mean temperature, salinity, turbidity and dissolved oxygen where larvae and juveniles were collected ranged from ca. 15.7-20.0 °C, ca. 5.6-20.7 psu, 2.7-14.6 NTU, and 7.7-10.0 mg.L-1, respectively. Larvae began to appear in November for the Kalong and in December for the Tien Yen, primarily occurring at stations far from the river mouth. Larvae <7.0 mm BL were more widely distributed across both estuaries, migrating to shoreline waters after reaching a size of ca. 15.0 mm BL in February. With relatively few larvae being observed in the southernmost region, the Tien Yen estuary may be a focus of conservation efforts of this annual amphidromous fish. [ABSTRACT FROM AUTHOR]

The efficacy of using a bacteriophage (phage) to control Flavobacterium psychrophilum (F. psychrophilum) infection of ayu (Plecoglossus altivelis altivelis) was evaluated in this study. Intramuscular challenge failed to induce sufficient infection levels; therefore, a newly designed net-scratch challenge method was also used to induce bacterial infection. Administration of phage PFpW-3 in F. psychrophilum-infected ayu showed notable protective effects, increased survival rates and mean times to death. Additionally, the fate of inoculated bacteria and phage in ayu were investigated. Our results suggest that the phage PFpW-3 could be considered an alternative biocontrol agent against F. psychrophilum infections in ayu culture. [ABSTRACT FROM AUTHOR]

The word Ayurveda comes from the Sanskrit root Ayu which means span of life. The purpose of examination of Ayu is to obtain knowledge regarding longevity, residual span of life in diseased person and rate of the mortality. The purpose of Dashavidha Pariksha is to obtain knowledge regarding Dosha Bala (Vyadhi Bala), Bala (Rogibala) and Ayu of the patient as described in Charak Samhita. Commonly Ayu and Vaya are regarded as synonyms but they are not similar terms. Hence, description of Vaya and Ayu is separately mentioned in Charaka as well as Sushruta Samhita. Description exclusively on Ayu Pareeksha described in Charaka Viman Sthana, Charaka Chikitsasthana, Charaka Indriya Sthana and Charaka Shareer Sthana. In Indriya Sthana, Ayu Pariksha indicates the residual life-span of the diseased person and where as in Jaatisutriya Adhyaya in Shareer Sthana mentioned the characteristic properties of the child who is going to survive for longer period of time. In Sushruta Samhita, Ayu is classified into three broad headings namely Dhirghayu, Madhyamayu and Alpayu and explained the characteristic properties of all the three.

The ayu Plecoglossus altivelis (Temminck and Schlegel 1846), an annual and amphidromous fish, is generally distributed in the islands of Japan and along the Asian continental coast. Recently, it has been found in two rivers of northern Vietnam and the Tien Yen River is the southernmost distribution range of this species. Morphology of the ayu in Vietnam has been examined; however, its reproductive biology is poorly known. Therefore, this study attempted to describe the fecundity and the egg size of the ayu from this river. Gonadosomatic index (GSI) of the female ayu (160.0-194.7 mm standard length, SL) was 19.7- 25.9 %. The number of eggs ranged from 33,548 to 45,114. Egg size ranged from 0.1 to 1.5 mm, with an average diameter of 0.8-0.9 mm. The GSI of the male ayu (153.3-194.7 mm SL) was 2.5-8.3 %. The present findings indicate that the ayu in its southernmost distribution region could spawn at least twice a year, and the breeding period occurs between November and February. This study provides reproductive data on the ayu species, thus contributing to the conservation of endangered ayu populations in Vietnam. [ABSTRACT FROM AUTHOR]

The ayu ( Plecoglossus altivelis) is an annual, amphidromous, plecoglossid fish, distributed in Vietnam, China, Taiwan, Korea, and Japan. To date, ayu have been found only in two rivers in northern Vietnam, where little is known about their life history. The Tien Yen River is believed to be the most southwestern habitat for this species. To determine whether newly hatched ayu larvae drift and to understand their downstream migration, intensive surveys were conducted in the Tien Yen River from October to March of 2013-2016. In total, 529 drifting ayu larvae were collected from four of six sampling stations along the river. Thus, ayu reproduction has been confirmed in this river for the first time, where only adult fish had been found previously. However, we did not successfully collect larvae in the eastern branch of the river, which has a hydroelectric dam, suggesting that ayu do not inhabit this branch or else do not reproduce there. The presence of drifting larvae in the western branch from mid-December to late January implies that they spawn from late November to mid-January. Drifting larvae were captured primarily at night, but peak occurrences varied depending upon the day and the sampling station. With the range of body sizes and variable diel abundance patterns, ayu in the Tien Yen River probably employ multiple spawning grounds. This study provides fundamental life history data for the vulnerable ayu populations in northern Vietnam. [ABSTRACT FROM AUTHOR]

Gut microbiota plays fundamental roles in protection against pathogen invasion. However, the mechanism and extent of responses of gut microbiota to pathogenic infection are poorly understood. This study investigated the gut bacterial communities and immune responses of ayu ( Plecoglossus altivelis ) upon exposure to Vibrio anguillarum . The succession of V. anguillarum infection was evidenced by increased expression of immune genes and bacterial loads in ayu tissues, which in turn altered the composition and predicted functions of gut bacterial community. The dynamics of gut bacterial diversity and evenness were temporally stable in control ayu but were reduced in infected subjects, particularly at the late stages of infection. Variations in the gut microbiota were significantly associated with the expression levels of TNF-α ( P = 0.019) and IL-1 β ( P = 0.013). The profiles of certain gut bacterial taxa were indicative of V. anguillarum infection. Compared with healthy controls, the ayu infected with V. anguillarum possessed less complex, fewer connected, and lower cooperative gut bacterial interspecies interaction, coinciding with significant shifts in keystone species. These findings imply that V. anguillarum infection substantially disrupted the compositions and interspecies interaction of ayu gut bacterial community, thereby altering gut microbial-mediated functions and inducing host immune responses. This study provides an integrated overview on the interaction between the gut microbiota and host immune responses to pathogen infection from an ecological perspective. [ABSTRACT FROM AUTHOR]