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Ex-situ conservation, which is important to protect critically endangered species, requires special artificial breeding and rearing techniques during the early life stages of a species. This study describes the artificial breeding and larval rearing techniques to conserve ayu (Plecoglossus altivelis), an important fish that is endangered in some locations. Fish eggs and milt were acquired from mature fish by gently pressing the fish abdomen; subsequently, artificial insemination was performed by gentle mixing. The fertilized eggs were then incubated in running freshwater (for approximately 14 days). After hatching, the larvae were placed in brackish water (ca. 10‰ salinity; 7-8 mg L-1 dissolved oxygen) to maintain live food to the larvae. From the 1st to 35th day after hatching (DAH), the larvae were fed with live rotifers. Subsequently, from the 15th DAH onwards, the larvae were fed with brine shrimp nauplii along with rotifers and were familiarized with artificial food. After the fish gained a body length of 4-5 cm and started consuming 0.5-0.8 mm formulated food grain, they were transferred to a fingerling nursery with freshwater for further cultivation. This study also noticed that the susceptible stages of ayu larvae were at approximately 14-16th and 40-45th DAH. This work provides necessary information to design a conservation plan for the ayu population in the southern distribution range of this species where it is currently facing threats of extinction, such as in Vietnam. Additionally, the study describes the rotifer culturing technique that can assist in conducting larviculture., AACL Bioflux, 15(6), pp.2763-2774; 2022

The present study describes a fish individual of Plecoglossus altivelis ryukyuensis with three pelvic fins collected from a hatchery-reared population in Amami-oshima Island, Japan. The additional pelvic fin had the same number of rays as the neighboring pelvic fins (eight fin rays), and its girdle was fused with that of the neighbor. The comparison of morphometric measurements and meristic counts of the abnormal specimen with those of the normal specimens revealed that this abnormality was not a syndrome when all other characteristics were in the expected ranges. The condition factor of abnormal fish was close to the ideal value, suggesting that this abnormality did not severely affect the activities of the fish under rearing conditions. Well-managed rearing conditions might contribute significantly to the survival and growth of abnormal fish. The cause of this abnormality is unclear, but the limited diversity in the genome of the subspecies is assumed to be a probable factor., Aquaculture, Aquarium, Conservation & Legislation - International Journal of the Bioflux Society, 15(3), pp. 1302-1307; 2022

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 life. Although ayu is economically important for the food industry and recreational fishing in Japan, few genomic resources are available for this species. To address this problem, we produced a draft genome sequence of ayu by whole-genome shotgun sequencing and constructed linkage maps using a genotyping-by-sequencing approach. Syntenic analyses of ayu and other teleost fish provided information about chromosomal rearrangements during the divergence of Stomiati, Protacanthopterygii and Neoteleostei. The size of the ayu genome indicates that genome compaction occurred after the divergence of the family Osmeridae. Ayu has an XX/XY sex-determination system for which we identified sex-associated loci by a genome-wide association study by genotyping-by-sequencing and whole-genome resequencing using wild populations. Genome-wide association mapping using wild ayu populations revealed three sex-linked scaffolds (total, 2.03 Mb). Comparison of whole-genome resequencing mapping coverage between males and females identified male-specific regions in sex-linked scaffolds. A duplicate copy of the anti-Müllerian hormone type-II receptor gene (amhr2bY) was found within these male-specific regions, distinct from the autosomal copy of amhr2. Expression of the Y-linked amhr2 gene was male-specific in sox9b-positive somatic cells surrounding germ cells in undifferentiated gonads, whereas autosomal amhr2 transcripts were detected in somatic cells in sexually undifferentiated gonads of both genetic males and females. Loss-of-function mutation for amhr2bY induced male to female sex reversal. Taken together with the known role of Amh and Amhr2 in sex differentiation, these results indicate that the paralog of amhr2 on the ayu Y chromosome determines genetic sex, and the male-specific amh-amhr2 pathway is critical for testicular differentiation in ayu., この研究のプレスリリース版はこちら: http://id.nii.ac.jp/1342/00002272/

Plecoglossus altivelis (ayu) is one of the most important fish species in the Japanese islands and in internal fish hatcheries. Living in open aquatic environments exposes fish to many pathogens. Therefore, they require rapid and strong immune defenses. We investigated in vivo the direct association between the ayu innate immune response, represented by the relative transcription of genes encoding the cathelicidin and hepcidin antimicrobial peptides, and lipopolysaccharide (LPS), a conventional pathogen-associated molecular patterns (PAMPs) of Gram-negative bacteria. Different concentrations of LPS (1, 10 and 100 µg/fish) were injected intraperitoneally into young (sexually immature) and adult (fully sexually mature) ayu. The relative expression of the antimicrobial peptide genes was measured 6 hr, 24 hr and 1 week after stimulation with LPS. We found a direct association between the expression of the antimicrobial peptide genes investigated and LPS stimulation. This relationship was time-, dose- and age-dependent. Further research is required to determine the cell-specific transcriptional regulation and posttranscriptional regulation of these antimicrobial peptides.

An adult male of Argulus coregoni Thorell, 1864, was collected from the body surface of an ayu, Plecoglossus altivelis altivelis (Temminck & Schlegel, 1846), in the middle reaches of the Ani River, a tributary of the Yoneshiro River, Akita Prefecture, northern Honshu, Japan. The previous northernmost record of A. coregoni in Japan is from Fukushima Prefecture, and the present collection extends its geographical distribution from Fukushima Prefecture northward to Akita Prefecture in Japan.

Argulus coregoni Thorell, 1864 was collected from the body surface of ayu, Plecoglossus altivelis altivelis (Temminck & Schlegel, 1846), from six rivers in Gifu, Achi, Mie, and Shiga prefectures, central Honshu, Japan. The collection of A. coregoni from Mie Prefecture represents its new prefectural record. Salmonids have been regarded as the major hosts of A. coregoni in Japanese rivers, but the present collections suggest that ayu is also important as a riverine host of the parasite.

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To investigate the utility of soybean meal in ayu, four isoenergetic diets were formulated: fish meal 65% (FM, control), fish meal 47% + soybean meal 20% (SM20), fish meal 30% + soybean meal 40% (SM40) and fish meal 13% + soybean meal 58% (SM58). Thirty fish with mean body weight ca. 17.3g were randomly distributed into each of 12 tanks (300 L) in triplicate for each treatment. Fish were fed twice daily at 09:00 and 16:00, 6 days per week for 9 weeks. There were no significant differences in final mean body weight, specific growth rate, daily feeding rate and feed conversion efficiency between FM and SM20; however, SM40 and SM58 showed significantly lower values of those parameters. Retention efficiencies of protein and energy were significantly higher in FM and SM20 than those of SM40 and SM58. Phosphorus retention and discharge were significantly higher and lower, respectively in diet SM20 than others. The results suggested that 20% soybean meal can be included in ayu diet (around 30% fish meal replacement), which will help to achieve both economical and ecological benefits as it will reduce diet cost and phosphorus discharge to the environment. アユの大豆粕に対する利用能を, 等エネルギーの65％魚粉（FM, 対照）, 47％魚粉+20％大豆粕（SM20）, 30％魚粉+40％大豆粕（SM40）および13％魚粉+58％大豆粕（SM58）飼料を用いて調べた. 平均体重17.3ｇのアユ稚魚を30尾ずつ収容した3反復試験区に, 1日２回, 1週間に6日所定の飼料を与えて9週間飼育したところ, 終了時平均体重, 成長率, 日間摂餌率, 飼料効率, タンパク質・エネルギー蓄積率などは, FMおよびSM20に区間差はなく, SM40とSM58ではいずれも有意に低下した. 一方, SM20は他区に比べてリン蓄積率は有意に高く, リン排泄量は有意に低かった. アユ稚魚に20％大豆粕飼料（魚粉代替率 30％）を給与することで, 生産コストや環境負荷の低減につながることが示された.

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.

Peripheral blood cells from ayu, Plecoglossus altivelis altivelis, were separated using a density gradient. Blood cells were then smeared using Shandon Cytospin and subjected to cytochemical staining. Blood cells were categorized based on morphological and cytochemical characteristics, and the density fractionation range and nucleus area/cell area ratio were observed. Lymphocytes are distinguished from neutrophils by their basophilic cytoplasm and Golgi-like field. The features of chromatin in thrombocytes are different from those of lymphocytes or neutrophils, but some small neutrophils have similar chromatin. Therefore, it is necessary to perform peroxidase staining to distinguish small neutrophils from thrombocytes. Basophils have large basophilic granules in cytoplasm. Based on density fractionation of blood cells, thrombocytes in the low-density area were separated from other blood cells. Identification of peripheral blood cells from ayu was possible with these staining methods. Monocytes/macrophages from spleen are specifically positive for esterase staining by α-naphthyl butyrate. As a result, thrombocytes, lymphocytes, neutrophils, basophils and monocytes/macrophages were identified in smears from peripheral blood or spleen tissue. In this paper, we confirmed that the peripheral blood corpuscles of ayu are able to be identified using the present staining methods.

高知県を流れる仁淀川の支流，土居川で採捕されたアユPlecoglossus altivelis altivelisの体表からエラオ類のチョウモドキArgulus coregoni Thorell, 1864を採集した。これは，四国におけるチョウモドキの初記録である。, A male specimen of Argulus coregoni Thorell, 1864 was collected from the body surface of an ayu (Plecoglossus altivelis altivelis) (Salmoniformes: Plecoglossidae) collected in the Doi River, a tributary of the Niyodo River, Kochi Prefecture, Shikoku, Japan, on August 14, 2010. This collection represents the first locality record for A. coregoni in Shikoku, one of the four major islands of Japan.

Ayu Plecoglossus altivelis altivelis is a common fish that is composed by two major forms, amphidrDmOuS and landlocked forms, based on itsannual1ife history. Althoughrecent decline in the reserves of amphidromous stocks in rivers has prompted frequent transplantations from landlocked stocks, a low survival rate of larvae of the landlocked fbm occllrS during periods of high water temperature in seawater. In brackish water environment, however, non-native landlocked form may survive and show sympatric distribution with mother populations. This study was conducted to verifythe genetic status of ayll 0cclmed in Nakaumi Lagoon, which is the second largest brackish lake in Japan. Nucleotide sequence polymoIPhism of the first 300 bp of themitochondrial DNA control region Was analyzed for 30 individuals including each 15 Specimens collected from 2 locales ofNakaumi Lagoon in May 2009, along with each 15 reference specimens oftheamphidromous and landlocked stocks. Comparatively high1evels of nucleotide substitution were observedwith 35 polymoIPhic sites from Nakatlm population and 40 sites from the amphidromous stock, as contrasted with24 sites from the landlocked stock. Based on nucleotide sequences at 5 hypervariable sites, 2 haplotypes occured in only the amphidromousstock were obtained at a high frequency in Nakaumi Population These results suggest that the amphidromous form forms the majority of Nakaum population., Article, 信州大学山地水環境教育研究センター研究報告 6: 125-132(2010)

6～8月にかけて主に沼田川中流域で採集したアユ30尾の耳石Sr/Ca比を調べ，由来判別を行った。その結果，30尾中12尾が天然遡上アユであることが判明した。また，支流の椋梨ダム湖（白竜湖）より上流の椋梨川で採集した13尾は，全ての個体で耳石Sr/Ca比の変動が認められなかったことから，これらはダム湖で再生産した陸封アユと考えられた。, Ayu, Plecoglossus altivelis altivelis, is a commercially important species of amphidromous fish. Thus it is being targeted for stock replenishment to sustain harvest numbers. Stock identification between amphidromous and hatchery fish was conducted using the otolith Sr/Ca concentration ratio on fish taken from the Nuta River in Hiroshima Prefecture, where 170,000 hatchery ayu had been previously released. Of 30 fish sampled from the middle-reaches, 12 were identified as an amphidromous form. Of the 13 fish sampled from the Mukunashi River, a branch of the Nuta River, all were identified as landlocked fish that would have completed their life cycle between the Mukunashi River and the artificial lakes formed by the Mukunashi Dam., 本研究は平成19年度広島大学地域貢献研究において，東広島市沼田川漁業協同組合より課題提案された「東広島市沼田川におけるアユの資源保全と有効利用」の一環として行った。

The Yoneshiro river has very good and many spawning grounds for ayu. The river experiences snowmelting flood every year from begin of March to end of May. After 2006 snow-melting flood, the river form is extremely changed and the good spawning around 22km from the mouth disappear. We think that that main reason is that the duration of 2006 flood is longer than normal year. Recently, the river researcher indicate that sandbar deformation process is affected the duration time of flood with flume experimental study and theoretic analysis. In this study, the deformation process is reproduced with 2d numerical model for river bed fluctuation to investigate the deference of the duration of flood in natural river. The results of long flood shows that river bed fluctuation is larger than the short flood like normal year., application/pdf

1912～2007年の96年間に出版された文献に基づき, 日本産アユPlecoglossus altivelis altivelisの寄生虫に関する情報を寄生虫-宿主リストに整理して目録を作成した。本目録には, 29種の寄生虫(微胞子虫類1種, ミクソゾア類1種, 吸虫類13種, 単生類3種, 条虫類1種, 線虫類1種, 鉤頭動物3種, カイアシ類4種, エラオ類2種)に加えて, 学名がまだ決定していない寄生虫の情報が含まれる。寄生虫-宿主リストでは, 各寄生虫は高位分類群ごとに配列され, 最新の学名, シノニム, 寄生部位, 地理的分布および報告者の情報が示されている。アユの亜種, リュウキュウアユPlecoglossus altivelis ryukyuensisからは寄生虫の記録はない。ミクソゾア類のMitraspora plecoglossiをHoferellus属に移すとともに, ハスコウトウチュウAcanthocephalus opsariichthydis Yamaguti, 1935の学名が動物命名規約に則って正しい綴りと命名年であることを確定した。また鉤頭動物のEchinorhynchus oblitusをカジカコウトウチュウEchinorhynchus cottiのシノニムとした。, The ayu or sweetfish Plecoglossus altivelis altivelis is distributed in many rivers and some lakes in Japan and also occurs in rivers of the Korean Peninsula and along the east coast of China and northern Vietnam. In Japan, this species is one of the most important freshwater fishes for commercial fisheries, aquaculture, and recreational fishing. In the present paper, information on the protistan and metazoan parasites of ayu in Japan is compiled based on the literature published for 96 years between 1912 and 2007, and the parasites, including 29 named species and those not identified to species level, are listed by higher taxon as follows: Ciliophora (no named species), Microspora (1), Myxozoa (1), Trematoda (13), Monogenea (3), Cestoda (1), Nematoda (1), Acanthocephala (3), Copepoda (4), and Branchiura (2). For each taxon of parasite, the following information is given: its currently recognized scientific name, any original combination, synonym(s), or other previous identification used for the parasite occurring in ayu; habitat (freshwater, brackish, or marine); site(s) of infection within or on the host; known geographical distribution in Japanese waters; and the published source of each locality record. There has been no record of parasites from a subspecies of ayu, the ryukyu-ayu Plecoglossus altivelis ryukyuensis. The myxozoan Mitraspora plecoglossi Fujita is transferred to the genus Hoferellus (as H. plecoglossi n. comb.), Acanthocephalus opsariichthydis Yamaguti, 1935 is determined to be the nomenclaturally correct spelling and date of that acanthocephalan species, and synonymy of the acanthocephalan Echinorhynchus oblitus Golvan with E. cotti Yamaguti is formally accepted.

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The maintenance flow discharge of the Ohyama River, which is located in the upper Chikugo River, had been restricted to 1.5m3/s by a hydroelectric dam. To improve the river environment, the river administrator has changed the maintenance flow discharge to 4.5m3/s in summer and to 1.8m3/s in winter. In this study, we aim at proposing an optimal control of the maintenance flow discharge for the river environment. Firstly, we carried out field surveys before and after reducing the river discharge in order to figure out effects on hydraulic conditions and attached algae. The results of the surveys show that hydraulic conditions become worse for ayu (plecoglossus altivelis) and attached algae. Also, there is a tendency to stagnate at the pool when the maintenance flow discharge decreases. Secondly, because it was reported that the length of ayu became larger than before changing the maintenance flow discharge, we attempted to analyze carbon and nitrogen stable isotope ratio of ayu and attached algae. We confirmed an obvious difference in food web structure between natural and cultured ayu.

The ayu, Plecoglossus altivelis altivelis Temminck et Schlegel, an amphidromous osmerid fish with an annual life cycle, is distributed throughout the Japanese Archipelago. This fish is one of the most important species for fresh water fisheries and recreational fishing. It spawns in the lower reaches of rivers in late autumn. Newly hatched larvae drift downstream tothe sea, where they spend the winter months until ascending rivers as juveniles in spring. In the 1980's, Senta & Kinoshita (1985) found that ayu larvae and juveniles occurred abundantly in the surf zones of sandy beaches in western Japan. This discovery spurred the research on surf zones of sandy beaches as nurseries of ayu in various parts of Japan. In these studies, the nursery ground of ayu was confirmed to be shallow waters such as surf zones of sandy beaches, but the migration pattern of ayu larvae and juveniles between surf zones and offshore waters has not been revealed, Moreover little information has been gathered on the annual fluctuations of larval distribution in the sea. Such information is essential to encourage the propagation of ayu resources in the river.The present thesis deals with, 1) seasonal and annual changes of occurrence and developmental processes of ayu collected in surf zones of sandy beaches, 2) the larval migration of ayu in the sea (inshore migration to surf zone, diel movement in the surf zone, migration from surf zone to shallow waters, 3) annual changes of larval occurrence and stock fluctuation, and 4) the survival of released landlocked ayu in the sea using a biochemical genetic marker and the character of otolith daily ring.

The ayu Plecoglossus altivelis altivelis, is an amphidromous fish with a life span of only one year. This is one of the most important species for both commercial fisheries and sport fishing in Japan. Hatching occurs about two weeks after spawning in thelower reaches of rivers in autumn and yolk-sac larvae drift down into the coastal waters, where they remain throughout the larval and early juvenile stages. In spring, juveniles ascend the rivers, where they feed attached algae on rocks and grow over the summer. They mature the following autumn, and spawn in the lower reaches of rivers after a downstream migration by adult.Much works has been on the ecology of the ayu in a river, but little is done about the early life history of ayu before 1980s. Studies on the early life history of ayu have progressed since the 1980s when the main nursery ground of the ayu was found to be in the shallow waters such as the surf zone. In recent years, some studies on larval and juvenile ayu proved us the information on growth, migration and so on forth in the coastal waters. However, the habitat, development, mortality and so forth in the early stages are not yet fully understood. Since 1985, I have conducted the survey of larval and juvenile ayu in the Shimanto Estuary, and found that a number of the larvae and juveniles of ayu remain in the estuary, and achieve higher growth rates. This indicates the importance of the estuary as a nursery ground for ayu.In the present study, I try to detail the early life history of ayu, especially for migration, mortality and development, which are still unknown, in the Shimanto Estuary, and clear the significance of the estuary for ayu.

視覚情報は魚の行動特性に影響を及ぼす一因であるため，光を用いた魚の行動制御が試みられてきた．光に対する反応は魚種によって異なると推定されている．井上らは海洋魚より河川魚の方が視覚を利用して定位する傾向が強いことを指摘した．しかし，光と各魚種の行動特性との関係は十分には解明されていない．本研究では矩形プール内外において白色光の配置を変化させ，静水中を遊泳するアユの遊泳挙動に及ぼす影響の解明を試みた．その結果，白色光の配置を変化させてもアユの魚群半径にほとんど影響を与えないが，プール内で白色光が底面に接近するとアユの遊泳速度が増加することやアユが白色光から遠ざかることが判明した．, 環境工学研究論文集 第54巻

Peripheral blood cells from ayu, Plecoglossus altivelis altivelis, were separated using a density gradient. Blood cells were then smeared using Shandon Cytospin and subjected to cytochemical staining. Blood cells were categorized based on morphological and cytochemical characteristics, and the density fractionation range and nucleus area/cell area ratio were observed. Lymphocytes are distinguished from neutrophils by their basophilic cytoplasm and Golgi-like field. The features of chromatin in thrombocytes are different from those of lymphocytes or neutrophils, but some small neutrophils have similar chromatin. Therefore, it is necessary to perform peroxidase staining to distinguish small neutrophils from thrombocytes. Basophils have large basophilic granules in cytoplasm. Based on density fractionation of blood cells, thrombocytes in the low-density area were separated from other blood cells. Identification of peripheral blood cells from ayu was possible with these staining methods. Monocytes/macrophages from spleen are specifically positive for esterase staining by α-naphthyl butyrate. As a result, thrombocytes, lymphocytes, neutrophils, basophils and monocytes/macrophages were identified in smears from peripheral blood or spleen tissue. In this paper, we confirmed that the peripheral blood corpuscles of ayu are able to be identified using the present staining methods.

In order to evaluate the genetic variability of the causative agent of cold water disease (CWD), plasmid profiling was used to characterize Flavobacterium (F.) psychrophilum isolates (n = 169). Size analysis of plasmids in F. psychrophilum isolates (n = 128) from several fish species demonstrated that six kinds of plasmids were harbored, and ayu isolates had different profiles compared to other isolates. Moreover, multiple isolates (n = 41) from CWD outbreaks in 2002 to 2003 at a single ayu farm were examined to determine differences between isolates from successive outbreaks and showed different profiles by the sources of seedlings.

広島県沼田川下流域でスズキに捕食された稚アユの由来判別を，耳石結晶化および耳石Sr/Ca比を指標に行った。稚アユ7個体のうち，3個体は耳石の結晶化が認められたことから人工放流種苗とした。正常な耳石を有していた4個体の耳石Sr/Ca比分析を行ったところ，3個体が人工放流種苗で，天然遡上は1個体となった。結局，稚アユ7個体の由来は，天然遡上が1個体で，6個体は放流された人工放流種苗と考えられた。耳石形状やSr/Ca比分析は，外敵に捕食された稚アユの由来判別に有効であると考えられた。, Stock discrimination study for juvenile ayu, Plecoglossus altivelis altivelis from stomach of Japanese seabass, Lateolabrax japonicus in the Nuta River estuary was conducted using prey otolith morphology and Sr/Ca profiling. Out of 7 individuals, 3 individuals identified as hatchery-stock ayu that had crystallized otolith. Based on the Sr/Ca profiling for 4 individuals that have normal otolith, 1 individual was identified as an amohidromous form and 3 individuals were identified as hatchery-stock ayu. The results showed that otolith-based approches could provide insight into stock discrimination for even highly digested ayu that have lost all phenotypic characteristics.

The circulus formation was observed in scales of two geographical races of ayu Plecoglossus altivelis altivelis; amphidromous and landlocked forms, and the ryukyu subspecies Plecoglossus altivelis ryukyuensis. The depth and length of the scales and the first circulus, and the distance between the first and second circuli (DFSC) were measured in twelve spots of each individual. Although the circulus formation was different between spots within an individual, it was similar at the same spot among different individuals in each group. The circulus formation of the amphidromous and the ryukyu ayu was similar while distinct difference was observed between these two groups and the landlocked ayu particularly those on the middle part of the caudal peduncle region. Ratio of depth and length in diameter of the first circulus (DDFC / LDFC) and the DFSC in the amphidromous and the ryukyu ayu were over 1.3 and 24μm respectively, and those values in the landlocked ayu were less than 1.3 and 24μm respectively.

脂質代謝を比較する目的で天然と養殖アユの脂肪組織の性状を生化学的、形態学的に観察した。養殖アユより腹腔内脂肪組織(IPF)をとり、ホモジェネート、脂肪細胞、スライスで in vitro で脂肪分解活性を比較した。活性は IPF を含む反応液に脂質動員ホルモン、牛血清アルブミンを添加して孵置して遊離した脂肪酸量で示した。Cyclic-AMP の添加は脂肪分解の活性化に無効であったが、di-butyryl-AMP は有効であった。これらの結果から、脂肪分解反応系にホルモン感受性リパーゼの存在と protein-kinase によるリン酸化への cyclic-AMP の関与が示唆された。In vitro 脂肪分解では、天然、養殖アユ共 IPF ホモジェネートからC20:6の脂肪酸が選択的に遊離したが、スライスでは遊離脂肪酸に選択性はなく均等に遊離した。養殖アユは天然アユと比較して脂肪分解能が著しく低い。IPF の走査電顕像は天然と養殖アユでは形状に差異はなかったが、養殖アユの脂肪細胞が有意に大きかった。, Intraperitoneal fat body (IPF) was biochemically and morphologically compared between wild and cultured ayu in relation to lipid mobilization. In vitro lipolysis activity was preliminarily determined using IPF obtained from cultured ayu. IPF preparations (homogenates, fat cells, and slices) were incubated with bovine serum albumin with lipolytic hormones. Lipolytic hormones induced marked fatty acid release from IPF. Although cyclic AMP (c-AMP) did not stimulate the activity, dibutyryl-AMP induced fatty acid liberation. These results suggest the presence of a hormone-sensitive lipase and a possible role of c-AMP in phosphorylation by protein-kinase in lipolysis. In the in vitro lipolytic system, incubation with IPF homogenates from both wild and cultured ayu liberated preferentially C22:6. However, incubation with IPF slices liberated all fatty acids non-selectively. In vitro lipolysis activity of cultured ayu was markedly lower than that of wild ayu. Scanning electronic microscopic observation of IPF of cultured ayu showed significantly larger cell diameter than in that of wild ayu.

An undescribed virus was isolated from the brain of coho salmon (Oncorhynchus kisutch), iwana (Salvelinus pluvius), rainbow trout (O. mykiss) and ayu (Plecoglossus altivelis), and ovarian fluid of masu salmon (O. masou) cultured in the northern part of Japan. The virus was isolated from both juveniles and adult fishes. Diseased fish showed abnormal swimming movement and were lethargic. The virus replicated, inducing cytopathic effects and lysis in susceptible cell lines at temperatures of 5 to 25°C. Persistent infection was observed in several fish cell lines. The virus particles were enveloped, and were icosahedral in shape with about 80 nm in diameter with a central electron-dense core. The virus was replicated with IUdR and BVdU, and inclusion bodies in the infected cells were stained with acridine orange. The virus density was 1.155g/ml and the viral RNA was 7.3kb in length. The virus was stable to pH, diethyl ether and chloroform. The virus was not neutralized by antisera against known 6 fish viruses.

6～8月にかけて主に沼田川中流域で採集したアユ30尾の耳石Sr/Ca比を調べ，由来判別を行った。その結果，30尾中12尾が天然遡上アユであることが判明した。また，支流の椋梨ダム湖（白竜湖）より上流の椋梨川で採集した13尾は，全ての個体で耳石Sr/Ca比の変動が認められなかったことから，これらはダム湖で再生産した陸封アユと考えられた。 Ayu, Plecoglossus altivelis altivelis, is a commercially important species of amphidromous fish. Thus it is being targeted for stock replenishment to sustain harvest numbers. Stock identification between amphidromous and hatchery fish was conducted using the otolith Sr/Ca concentration ratio on fish taken from the Nuta River in Hiroshima Prefecture, where 170,000 hatchery ayu had been previously released. Of 30 fish sampled from the middle-reaches, 12 were identified as an amphidromous form. Of the 13 fish sampled from the Mukunashi River, a branch of the Nuta River, all were identified as landlocked fish that would have completed their life cycle between the Mukunashi River and the artificial lakes formed by the Mukunashi Dam. 本研究は平成19年度広島大学地域貢献研究において，東広島市沼田川漁業協同組合より課題提案された「東広島市沼田川におけるアユの資源保全と有効利用」の一環として行った。

広島県芦田川中流・上流域で捕獲したアユ成魚10個体の耳石Sr/Ca比を調べ由来判別を行った。その結果, 9個体の耳石Sr/Ca比に変動がなく, 終始低レベルに推移したため, それらは仔稚魚期に海洋生活を送らなかった陸封アユと判断された。これら陸封アユは, 芦田川に建設された八田原ダムや三川ダムによって形成された人造湖(芦田湖, 神農湖)で再生産したものと考えられた。, Ayu Plecoglossus altivelis is one of the most important freshwater fishes in Japan and usually amphidromous. Stock identification was conducted using otolith Sr/Ca analysis for ayu from the Ashida River, Hiroshima Prefecture. In nine of 10 adults sampled from the upper and middle-reaches in August-October 2006, the ratio did not fluctuate and remained at a low level, indicating that these ayu were landlocked fish without staying as larvae and juveniles in coastal marine waters. The landlocked ayu likely reproduce in two artificial lakes (Lake Ashida and Lake Jin-no formed by Hattabara Dam and Mikawa Dam, respectirely) in the Ashida River.

島根県江の川において産卵期のアユ42個体の由来判別を耳石Sr/Ca比を用いておこなった。放流実績からすれば江の川水系には天然アユの他,琵琶湖産,人工海産アユが生息している。産卵群42個体の由来を判別した結果,天然アユは13個体,人工海産が26個体となり,湖産アユは皆無であった。したがって,江の川においては湖産アユが海産系アユの産卵行動に関与している可能性は低いと考えられた。, Stock separation for spawning population of ayu Plecoglossus altivelis in the Gouno River was conducted using otolith Sr/Ca concentration ratio. Based on stock enhancement record, coexistence of amphidromus, hatchery-reared and landlocked ayu can be expected in the spawning population. In case of stock separation in the spawning population carrying out the otolith Sr/Ca ratio, 29 and 13 out of 42 individuals were categorized as the hatchery-reared and amphidromus ayu, respectively. The result of no landlocked ayu in the spawning population suggests that the contribution of the landlocked ayu to spawning and reproduction can be neglected at the Gouno River.

Fishermen are embarrassed upon the population reduction of larval fish by the sluice gate which is constructed with dams and weirs. The terror by the falling object from the upward may be valid to make fish avoid from the sluice gate. In this study, the small object was dropped from the upward toward the water surface of a pool, and the fish trajectories were recorded by a digital video camera. It was found that the ayu avoid from the object very quickly during about 1s, and after that ayu make a school of fish gradually. The swimming speed and also the swimming distance during avoiding decreases with an increase of the fish population due to the crowding., 水工学論文集 第57巻

1999年4月に徳島県下のアユ養殖場で出血性の腹水症状を呈する病魚から、水溶性の褐色色素を産生するグラム陰性、好気性、非運動性の桿菌が分離された。形態学的、生化学的性状および抗 -P. plecoglossicida 血清との凝集試験結果に基づいて、分離株は細菌性出血性腹水病の原因菌である P. plecoglossicida に同定された。分離株のアユに対する病原性は強く、そのLD50値は 7×100 CFU (筋肉内注射)であった。本病の原因菌に褐色色素産生株も存在することが判明した。

Responses of eggs of the ayu Plecoglossus altivelis to series of temperature and salinity combinations were measured for percents of total and viable hatch and time to 50% hatch.Hatch occurred at almost all tested combinations of temperature range of 11.0 to 26.0℃ and chlorinity range of 0 to 8.0‰. Response surface analysis suggests that the maximum percents of total and viable hatch (i.e.,optimum) may be found at 19.0℃ combined with 0.9-1.1‰.Time required to 50% hatch varied 6.5 and 26.2 days after fertilization,and was inversely and exponentially related to temperature. The Q₁₀ value was higher at the lower temperature. The effect of chlorinity on the time was satistically insignificant within the hatchable range of eggs.

Ego-ryo, a unique way of catching ayu fry fish on Amori-river system, Kagoshima prefecture, was studied on the structure of fishing devices used, the actual operation, and the catches. The fish were caught from the 1 st of March to the end of April at the nine fishing grounds established between 5.2-9.9km upstream of the river mouth. Each fishing ground was constructed from a flat floor (150m long, 20m wide), an embankment hemmed on each side, and a wooden weir of the upper end and fence nets with traps of the lower end surrounded. Once fish schools came in the fishing grounds, the weir was shut to keep out the inflow of water causing drainage of water in the ground. The drainage stimulated the fish to rush into the trap. This draining technique which leads them into the trap has not been known in any other ayu fry fishery in Japan. The Ego-ryo fishery might be settled in the way that ayu fly are caught in the lower river and released in the upper river, where they will find it difficult to ascend.