Plecoglossus Research Articles

久慈川河口周辺海域におけるアユ仔稚魚の分布

久慈川河口周辺海域におけるアユ仔稚魚の分布

2011 年 3 月の福島原発事故によってアユ漁場に流出したセシウム137

2011 年 3 月の福島原発事故によってアユ漁場に流出したセシウム137

アユのエドワジエラ・イクタルリ感染症に対する薬剤の有効性

アユのエドワジエラ・イクタルリ（Edwardsiella ictaluri）感染症に対する有効な薬剤を明らかにすることを目的として，アユに対して使用が認められている水産用医薬品（6薬剤）の抗菌活性を調べた結果，本菌はスルフィソゾールとスルファモノメトキシンには感受性が低く，フロルフェニコール，オキソリン酸，オリメトプリムおよびスルファモノメトキシン・オリメトプリム配合剤に高い感受性を示した。このうちの3薬剤（フロルフェニコール，オキソリン酸，スルフィソゾール）について，実験感染させたアユに対する経口投与による薬剤治療試験をおこなった結果，フロルフェニコールとオキソリン酸では優れた治療成績が得られ，またスルフィソゾールでは延命効果が認められた。

Epizootic ulcerative syndrome (EUS) in fish: history and current status of understanding

Epizootic ulcerative syndrome (EUS) is one of the most important diseases affecting more than 100 species of wild and cultured finfish. EUS was first reported in farmed ayu (Plecoglossus altivelis) from Japan in 1971 and has since then spread across different countries of four continents including Asia, Australia, North America and Africa. The spread of the disease, especially in Asia–Pacific region and Africa has led to substantial damage to the fish resources and livelihood of the fish farmers. No reports are available confirming the outbreak of the disease from Europe and South America. The latest outbreak of EUS has been reported from Canada in a new susceptible species brown bullhead, Ameiurus nebulosus. It seems that the disease has potential to spread further, owing to the epizootic nature of the disease and broad susceptible host range. Considering the global importance of this disease, this review provides the current status of understanding about the etiology, process of diseases development, species affected, diagnostic methods as well as control and preventive measures, in light of the historical developments in those areas.

A simulation-optimization method for ecohydraulic design of fish habitat in a canal

A decision-support method for ecohydraulic design of a canal in rural engineering is developed using a GA (Genetic Algorithm)-based simulation-optimization technique. In order to demonstrate the ability of the method, a simple problem is presented aiming at searching for best configuration of blocks located for creating valuable fish habitat in a canal. The habitat condition is evaluated using a habitat suitability index (HSI) considering hydraulic factors such as water depth and velocity. The study area, a section of canal, is discretized into triangular finite elements with nodes, and the two-dimensional simulation of flow is conducted by the finite element method applied to the steady-state shallow water equations. The computed water depth and velocity at each node are then used to evaluate the weighted average HSI (AHSI) for the canal. In order to develop a robust method insensitive to uncertainty in these hydraulic parameters, a scenario-based stochastic optimization framework is adopted. The simulation part of the developed method comprises the numerical computation of canal flow at every scenario aiming at evaluation of the expected AHSI, whereas the optimization part includes rearrangement of blocks conducted by GA operators. The simulation and optimization process is iterated to maximize the expected AHSI in the canal section. The performance of the presented simulation-optimization method is demonstrated for a hypothetical ecohydraulic design of spawning area of Ayu (Plecoglossus altivelis) in a canal. The demonstrative example shows that the presented method can successfully specify the best block configuration in the canal section with the largest expected AHSI value.

Cesium-137 discharge into the freshwater fishery ground of grazing fish, ayu Plecoglossus altivelis after the March 2011 Fukushima nuclear accident

The Fukushima nuclear accident led to deposition of radionuclides into the freshwater fishery ground of ayu Plecoglossus altivelis. For the purpose of more comprehensive understanding of the radioactive contamination, cesium-137 (137Cs) was analyzed in running water, muddy sediment, attached algae, and ayu using samples from three river systems with different levels of contamination within Fukushima Prefecture in summer and autumn 2011. The amount of 137Cs contained in water as well as in sediment declined over an interval of two months, although the concentration in sediment samples was up to 10,000-fold higher than that in water samples. The changes in 137Cs concentration of algae showed different courses among the three river systems, the concentration being greater in autumn in the river systems with high and moderate radioactive contamination. 137Cs detected within a single stock of ayu appeared to be excreted rather rapidly with a calculated half-life of approximately 39 days, while the concentration ratio ranged from 103 to 104 l/kg, attaining higher levels than previously reported. These findings indicate that the most important pathway of 137Cs into ayu is via intake of algae as food but that the retention time of 137Cs inside ayu is relatively short.

Cloning and expression analysis of the NFκB inhibitor IκBα of ayu (Plecoglossus altivelis)

The NFκB inhibitor (IκBα) is an integral part of NFκB/IκB signaling pathways, which plays roles in a variety of immune responses, such as bacterial infection resistance. By interacting with nuclear transcription factor NFκB, IκBα controls a variety of biological immune gene expressions. In this study, full-length cDNA (1341 bp) of the NFκB inhibitor IκBα (PaIκBα, GenBank Accession No. JN801027) of Plecoglossus altivelis was obtained by RACE and PCR, and included a 5' untranslated region (UTR) (64 bp), a 3' untranslated region (UTR) (341 bp) and an open reading frame (ORF) (936 bp) encoding a polypeptide of 311 amino acids. PaIκBα had high homology with other IκBαs, containing a conserved ankyrin repeat domain, which was required for interacting with NFκB, a PEST sequence in the C-terminus and a signal responsive domain in the N-terminus. The deduced amino acid sequence of PaIκBα shared 95% homology with Osmerus mordax, and 76%, 75%, 70%, and 68% homology with Salmo salar, Oncorhynchus mykiss, Nile tilapia, and Siniperca chuatsi, respectively. Phylogenetic analysis revealed that IκBα of ayu and Osmerus mordax, Salmo salar, Oncorhynchus mykiss, Nile tilapia, and Siniperca chuatsi were in the same phylogenetic tree. RT-PCR analysis showed that PaIκBα mRNA expression was highest in the liver, kidney, intestine, and gills, then followed by the spleen, brain and muscle, and was lowly expressed in the heart. Likewise, after Aeromonas hydrophila infection, the mRNA level of ayu PaIκBα in the liver was also up-regulated.

Tropical and temperate freshwater amphidromy: a comparison between life history characteristics of Sicydiinae, ayu, sculpins and galaxiids

Amphidromy is a distinctive form of diadromy, but differences in the life histories of tropical and temperate amphidromous fishes suggest that there are two types of freshwater amphidromy. The life histories of Sicydiinae gobies, ayu (Plecoglossus altivelis), Japanese sculpins (Cottus) and galaxiids (Galaxiidae), suggest that the Sicydiinae are representatives of tropical freshwater amphidromy, whereas ayu, sculpins and galaxiids are representatives of temperate freshwater amphidromy. The Sicydiine larval stage may be required to occur in the ocean for all species, but ayu, sculpins and galaxiids have landlocked or fluvial forms with larvae that do not need to enter the ocean for larval feeding and growth. This suggests that Sicydiine larvae have a high oceanic dependency whereas ayu, sculpins and galaxiid larvae have a low oceanic dependency. Freshwater amphidromous fish in tropical and temperate zones appear to have developed two different strategies in the evolution of their life histories. It is likely that the evolutionary direction of the larval stage of tropical amphidromy is to remain in the sea and that of temperate amphidromy is towards having the ability to remain in freshwater if needed. Tropical and temperate amphidromy appear to be biologically informative categories and evaluations of this hypothesis will facilitate better understanding of the various forms of amphidromy in the future.

Overview of active cesium contamination of freshwater fish in Fukushima and Eastern Japan

This paper focuses on an overview of radioactive cesium 137 (quasi-Cs137 included Cs134) contamination of freshwater fish in Fukushima and eastern Japan based on the data published by the Fisheries Agency of the Japanese Government in 2011. In the area north and west of the Fukushima Nuclear plant, freshwater fish have been highly contaminated. For example, the mean of active cesium (quasi-Cs137) contamination of Ayu (Plecoglossus altivelis) is 2,657 Bq/kg at Mano River, 20–40 km north-west from the plant. Bioaccumulation is observed in the Agano river basin in Aizu sub-region, 70–150 km west from the plant. The active cesium (quasi-Cs137) contamination of carnivorous Salmondae is around 2 times higher than herbivorous Ayu. The extent of active cesium (quasi-Cs137) contamination of Ayu is observed in the entire eastern Japan. The some level of the contamination is recognized even in Shizuoka prefecture, 400 km south-west from the plant.

Molecular cloning, characterization and expression analysis of a novel wap65-1 gene from Plecoglossus altivelis

Warm temperature acclimation associated 65-kDa protein 1 (WAP65-1) is a specific fish plasma glycoprotein that is possibly involved in various physiological or pathological processes. In this study, we obtained the cDNA and genomic DNA sequences of the Plecoglossus altivelis wap65-1 (Pawap65-1) gene. Multiple sequence alignment showed that Pawap65-1 is similar in structure to wap65-1 in fish. Phylogenetic analysis revealed that Pawap65-1 is most closely related to that of a rainbow trout. Pawap65-1 transcripts are present in various tissues and are most abundant in the liver. We expressed recombinant PaWAP65-1 in Escherichia coli and raised antiserum against it in mouse. Western blot analysis revealed that the higher molecular mass of PaWAP65-1 in blood plasma was caused by post-translational N-glycosylation. Quantitative real-time quantitative PCR (qPCR) and Western blot analysis data showed that the hepatic mRNA and blood plasma levels of PaWAP65-1 were both influenced by warm temperature acclimation and cadmium exposure, but not by Listonella anguillarum infection, hypo-osmotic, or cold temperature acclimation. In conclusion, our data reveals that PaWAP65-1 is a stress-related protein, and may play a role in fish acclimation to warm temperature and cadmium exposure.

Characterization of P2X7R and Its Function in the Macrophages of ayu, Plecoglossus altivelis

P2X purinoceptor 7 (P2X7R), an ATP-gated ion channel, plays an important role during the innate immune response in mammals. However, relatively little is known about the role of P2X7R in the fish immune system. Here, we cloned a cDNA sequence encoding ayu (Plecoglossus altivelis) P2X7R (aP2X7R). The predicted protein was composed of 574 amino acid residues with a P2X family signature, two transmembrane domains, and a long C-terminal. aP2X7R transcripts were mainly distributed in ayu immune tissues and significantly increased in all tested tissues and in macrophages after Listonella anguillarum infection. The aP2X7R protein was upregulated significantly in macrophages upon bacterial challenge. An antibody against the ectodomain of aP2X7R (aEPAb) and an antagonist (oATP) were used to block aP2X7R. aP2X7R siRNA was also used to knockdown the receptor expression in ayu macrophages. Cell death induced by ATP was significantly inhibited in ayu macrophages after aEPAb, oATP, or siRNA treatment. Moreover, aP2X7R ablation also resulted in suppression of phagocytic activity and ATP-induced bacterial killing in ayu macrophages. Our results indicated that aP2X7R was upregulated after infection and mediated cell death, phagocytosis, and bacterial killing of ayu macrophages.

Molecular characterization of an IL-1β gene from ayu, Plecoglossus altivelis

IL-1β plays a crucial role as a prototypical proinflammatory cytokine in immune responses and has been shown to affect macrophage functions. However, the effects of putative IL-1β homologs on fish macrophages are still less known. Here, we cloned the full-length cDNA sequence of IL-1β (aIL-1β) gene from ayu, Plecoglossus altivelis. Phylogenetic analysis indicated that aIL-1β was closest to that of Atlantic salmon (Salmo salar). Real-time quantitative PCR (RT-qPCR) revealed that aIL-1β transcript was mainly expressed in spleen, head kidney and gill, and dramatically increased in various tissues after Listonella anguillarum infection. Subsequently, aIL-1β was prokaryotic expressed and purified to prepare anti-aIL-1β antibody. After L. anguillarum challenge, the aIL-1β mRNA and protein levels were significantly up-regulated in ayu monocytes/macrophages. Moreover, aIL-1β neutralization did not change phagocytic capability, but reduced bacterial killing capability in ayu head kidney-derived monocytes/macrophages. Therefore, aIL-1β may play an important role in immune response of ayu, especially, contributing to bacterial killing of monocytes/macrophages.

Stress hormone responses in ayu Plecoglossus altivelis in reaction to different catching methods: comparisons between electrofishing and cast netting

It is important to select the most appropriate method for fish sampling in streams and rivers; the sampling efficiency as well as any negative effect of the method of fish sampling on fishes such as stress, injury, and mortality must be considered. This study aimed to investigate stress hormone responses in ayu Plecoglossus altivelis in reaction to direct current (DC) electrofishing, alternating current (AC) electrofishing, and cast netting in artificial streams. The mortality, injury rate, and catch efficiency of these catching methods were also compared. It was found that immediately after capture, fish caught using a cast net exhibited significantly higher cortisol levels than did control fish that were caught rapidly by a hand net. Cortisol levels did not differ between electroshocked fish and the controls. Time required to catch 12 fish was shorter when DC was used (20 s) than when AC was used (45 s). The time required to catch fish greatly increased when a cast net was used (840 s). Cortisol levels in DC electroshocked and control treatment groups were at resting levels 24 and 48 h after capture. However, higher cortisol levels were found in fish captured using a cast net at both these time points. Cortisol levels in AC electroshocked fish returned to lower levels at 24 h, but increased again at 48 h. Furthermore, 48 h following capture, the fish caught by AC electrofishing exhibited higher mortality (7.5 %) than those captured by other methods (0 %). Spinal injury was also detected in one of the fish in this group. Considering these findings, DC electrofishing is the most effective and least damaging method for collecting P. altivelis in streams with respect to stress, physical damage, and efficiency.

Molecular cloning, sequence analysis and expression of ayu complement component <I>C9</I> gene

C9, a component of the membrane attack complex, participates in the final stage of the complement cascade which lyses foreign organisms by disrupting the integrity of their cell membranes. In the present study, a full-length ayu C9 (aC9) cDNA was cloned which contains 2,125 nucleotides and encodes a protein of 592 amino acids. A signal peptide was deposited in the N-terminal 22 residues. The deduced amino acid sequence of aC9 showed 56.8% identity to the C9 of rainbow trout, and 40.9% to 53.8% identity to the C9 of other teleosts. RT-PCR analysis demonstrated that the mRNA of aC9 was expressed in the liver, spleen, intestine, gill and muscle of healthy ayu fish with the highest level in the liver. Quantitative RT-PCR analysis showed that aC9 transcripts were significantly up-regulated in the liver at 4 h post Listonella anguillarum infection, peaked at 16 h post injection. Western blotting analysis revealed that serum aC9 significantly increased in Listonella anguillarum infected ayu fish. Our results suggested that aC9 may play an important role in fish immune response of anti-bacteria.

Moderate turbidity enhances schooling behaviour in fish larvae in coastal waters

AbstractWe evaluated the effects of turbidity on school formation in ayu (Plecoglossus altivelis) [24.5 ± 2.2 mm standard length (Ls)], Japanese anchovy (Engraulis japonicus) (29.1 ± 3.1 mm Ls) larvae, which often live in turbid coastal waters, and yellowtail (Seriola quinqueradiata) juveniles (37.1 ± 2.5 mm Ls), which live in clear offshore waters. Fish were introduced into experimental tanks at one of five turbidity levels obtained by dissolving 0, 5, 20, 50, or 300 mg l−1 of kaolin in seawater. Their behaviour was video recorded, and the nearest neighbour distance (DNN) and separation angle (AS) were compared among turbidity levels. Mean DNN of ayu was significantly smaller at 20 and 50 mg l−1 than any other level of turbidity, as was AS at 20 mg l−1 compared with 0 mg l−1. Mean AS of anchovy was smaller at 50 mg l−1 of turbidity than any others. In contrast, mean DNN of yellowtail was larger at 300 mg l−1 than any others. These results suggest that moderate turbidities enhance schooling behaviour in ayu and Japanese anchovy larvae, whereas turbidity has an inhibitive effect on schooling of yellowtail juveniles, corresponding well to the habitat characteristics of each species.

広島県成羽川におけるアユの個体別系統判別とその組成

広島県成羽川におけるアユの個体別系統判別とその組成

養殖アユの胸部の穴あき症状を伴う死亡事例

2012年6月に滋賀県下のアユ養殖場で，胸部に潰瘍から穴あき症状を呈して死亡する症例が見られた。細菌学的検査により，胸部体表患部と腎臓から Flavobacterium psychrophilum が分離されたことから，本事例は冷水病と判断されたが，これまでに胸部にのみ穴あき症状を呈する冷水病の死亡事例についての報告はない。そこで，予め微細な傷を胸部体表に付けて F. psychrophilum に浸漬感染させた結果，胸部に穴あき症状が再現され，累積死亡率は胸部に傷を付けた区の方が無処理区よりも有意に高くなった。一方，F. psychrophilum に浸漬感染させた後に，研磨シートを敷き詰めた水槽内で高密度飼育した場合には穴あき症状は再現されなかった。よって，胸部の傷がこの病徴につながることは明らかであるが，養殖場での飼育条件でこの病徴を起こす要因を確定し得なかった。

Comparisons of Internal Behavior after Exposure to <i>Flavobacterium psychrophilum</i> between Two Ayu (<i>Plecoglossus altivelis altivelis</i>) Strains Showing Different Cumulative Mortality to Bacterial Cold Water Disease

ABSTRACT Bacterial cold water disease (BCWD) in ayu (Plecoglossus altivelis altivelis) has a serious impact on aquaculture and fisheries. There is known to be a significant difference among ayu strains with regard to mortality caused by BCWD. In this study, the immune response of different ayu strains against Flavobacterium psychrophilum infection was observed. One strain was resistant to infection by F. psychrophilum, and the other was susceptible to infection by the same bacteria. The number of bacteria in the body was observed in each ayu strain, and the change in bacterial counts was similar. However, there was a significant difference in bacterial count in the spleen between the two strains on days 6, 9, 12 and 15 after exposure. To observe the immune response against F. psychrophilum, agglutination assay using serum was performed. An agglutination reaction in the resistant ayu strain was observed in 4 out of 6 ayu on day 6 after exposure, while no reactions in the susceptible ayu strain were observed in any sampled fish until day 12. However, some reactions in the susceptible ayu strain were observed in surviving ayu. These results indicate that there is a correlation between the presence of bacterial multiplication and agglutination reaction against F. psychrophilum.

Sequencing of the first ayu (Plecoglossus altivelis) macrophage transcriptome and microarray development for investigation the effect of LECT2 on macrophages

Macrophages play an important role in first-line host defense of innate immune in fishes. However, it is difficult to investigate cellular mechanism of immune response in fish species with little genomic information available. Here we present the first use of RNA-Sequencing to study the macrophage transcriptome of ayu, Plecoglossus altivelis, which is an economically important fish in East Asia. De novo assembly generated 49,808 non-redundant consensus sequences, among which 23,490 transcripts found respective coding sequences. 15,707 transcripts are predicted to be involved in known metabolic or signaling pathways. The sequences were then used to develop a microarray for measurement the effect of recombinant LECT2 on ayu macrophages. LECT2 altered expression of a variety of genes mainly implicated in actin cytoskeleton, pattern recognition receptors and cytokines. Meanwhile, LECT2 enhanced phagocytosis, bacterial killing, and respiratory burst in ayu macrophages, which supported the thought derived from the microarray data that LECT2 activates macrophages. In conclusion, our results contribute to understanding the specific regulation mechanism of LECT2 in macrophage activation, and the combination of transcriptome analysis and microarray assay is a good method for screening a special tissue or cell response to a stimulus or pathogen in non-model fish species.

Population Genetic Structure and Evidence of Demographic Expansion of the Ayu (Plecoglossus altivelis) in East Asia

Plecoglossus altivelis (ayu) is an amphidromous fish widely distributed in Northeastern Asia from the East China Sea to the northern Japanese coastal waters, encompassing the Korean Peninsula within its range. The shore lines of northeastern region in Asia have severely fluctuated following glaciations in the Quaternary. In the present study, we investigate the population genetic structure and historical demographic change of P. altivelis at a population level in East Asia. Analysis of molecular variance (AMOVA) based on 244 mitochondrial control region DNA sequences clearly showed that as the sampling scope extended to a larger geographic area, genetic differentiation began to become significant, particularly among Northeastern populations. A series of hierarchical AMOVA could detect the genetic relationship of three closely located islands between Korea and Japan that might have been tightly connected by the regional Tsushima current. Neutrality and mismatch distribution analyses revealed a strong signature of a recent population expansion of P. altivelis in East Asia, estimated at 126 to 391 thousand years ago during the late Pleistocene. Therefore it suggests that the present population of P. altivelis traces back to its approximate demographic change long before the last glacial maximum. This contrasts our a priori expectation that the most recent glacial event might have the most crucial effect on the present day demography of marine organisms through bottleneck and subsequent increase of effective population size in this region.