詳細

白樫　正 （シラカシ　ショウ）

  • 水産研究所　准教授/奄美実験場長
Last Updated :2024/05/19

コミュニケーション情報 byコメンテータガイド

  • コメント

    魚類寄生虫の生態解明や、養殖場での防除法開発などを行っています。

  • 報道関連出演・掲載一覧

    ＜報道関連出演・掲載一覧＞ ●2017/5/12 　夕刊フジ 　食中毒アニサキスについて

研究者情報

学位

  • 博士（農学）（2005年03月 東京大学）

ホームページURL

ORCID ID

J-Global ID

研究キーワード

  • 寄生虫生態学   魚病学   寄生虫学   

現在の研究分野（キーワード）

    魚類寄生虫の生態解明や、養殖場での防除法開発などを行っています。

研究分野

  • ライフサイエンス / 水圏生産科学 / 魚病学

経歴

  • 2016年04月 - 現在  近畿大学水産研究所准教授
  • 2012年04月 - 2016年03月  近畿大学水産研究所講師
  • 2009年06月 - 2012年03月  近畿大学水産研究所GCOE博士研究員
  • 2007年04月 - 2009年05月  ミュンヘン大学獣医学部フンボルト財団フェロー
  • 2006年07月 - 2007年03月  東京大学農学生命科学研究科農学特定研究員
  • 2005年12月 - 2006年05月  ブリストル大学理学部生物学科リサーチ・アシスタント
  • 2005年04月 - 2005年11月  東京大学農学生命科学研究科技術補佐員
  • 2003年04月 - 2005年11月  東京大学農学生命科学研究科日本学術振興会特別研究員

学歴

  • 2002年04月 - 2005年03月   東京大学   大学院農学生命科学研究科
  • 1994年09月 - 2001年10月   レスブリッジ大学   Faculty of Art and Science   Department of Biological Science

所属学協会

  • American Society of Parasitologists   日本水産学会   日本魚病学会   

研究活動情報

論文

  • Kazuo Ogawa; Sho Shirakashi; Naoya Sata; Naoki Itoh; Shingo Ito; Eva Lewisch; Stephanie Bornstein
    Systematic Parasitology 101 2 2024年03月
  • Nguyen Ngoc Chinh; Nguyen Thi Hoang Ha; Pham Ngoc Doanh; Jorge C Eiras; Christopher M Whipps; Sho Shirakashi
    Systematic parasitology 100 4 325 - 344 2023年08月 
    This paper provides an updated checklist of species-level identified myxosporeans from marine and freshwater fishes in Vietnam. The list includes 51 nominal species (38 marine and 13 freshwater) belonging to 9 genera: Myxobolus Bütschli, 1882 (26 species); Kudoa Meglitsch, 1947 (6 species); Henneguya Thélohan, 1892 (6 species); Thelohanellus Kudo, 1933 (5 species); Unicapsula Davis, 1924 (2 species); Ceratomyxa Thélohan, 1892 (2 species), Zschokkella Auerbach, 1909 (2 species); Auerbachia Meglitsch, 1960 (1 species), and Meglitschia Kovaleva, 1988 (1 species). For each parasite species, information on myxospore morphology, line drawings, fish hosts, infection sites, and collection locality in Vietnam are reported. Where available, we also provide GenBank accession numbers for nucleotide sequence data. In addition, taxonomic status of several species was discussed and Myxobolus eszterbaueri nom. nov. is proposed as a junior homonym for Myxobolus hakyi Baska, Voronin, Eszterbauer, Müller, Marton & Molnár 2009, which is preoccupied.
  • Kazuo Ogawa; Masaaki Abe; Satoko Hara; Mutsuki Ueno; Sho Shirakashi
    Fish Pathology 58 2 71 - 73 2023年06月
  • Kazuo Ogawa; Naoya Sata; Yukitaka Sugihara; Haruki Miyazaki; Mutsuki Ueno; Sora Kuramochi; Sho Shirakashi
    Fish Pathology 58 1 15 - 21 2023年03月
  • Kiyono Sekii; Soichiro Miyashita; Kentaro Yamaguchi; Ikuma Saito; Yuria Saito; Sayaka Manta; Masaki Ishikawa; Miyu Narita; Taro Watanabe; Riku Ito; Mizuki Taguchi; Ryohei Furukawa; Aoi Ikeuchi; Kayoko Matsuo; Goro Kurita; Takashi Kumagai; Sho Shirakashi; Kazuo Ogawa; Kimitoshi Sakamoto; Ryo Koyanagi; Noriyuki Satoh; Mizuki Sasaki; Takanobu Maezawa; Madoka Ichikawa-Seki; Kazuya Kobayashi
    iScience 26 1 105776 - 105776 2023年01月 
    Various parasitic flatworms infect vertebrates for sexual reproduction, often causing devastating diseases in their hosts. Consequently, flatworms are of great socioeconomic and biomedical importance. Although the cessation of parasitic flatworm sexual reproduction is a major target of anti-parasitic drug design, little is known regarding bioactive compounds controlling flatworm sexual maturation. Using the planarian Dugesia ryukyuensis, we observed that sex-inducing substances found in planarians are also widespread in parasitic flatworms, such as monogeneans and flukes (but not in tapeworms). Reverse-phase HPLC analysis revealed the sex-inducing substance(s) eluting around the tryptophan retention time in the fluke Calicophoron calicophorum, consistent with previous studies on the planarian Bipalium nobile, suggesting that the substance(s) is likely conserved among flatworms. Moreover, six of the 18 ovary-inducing substances identified via transcriptome and metabolome analyses are involved in purine metabolism. Our findings provide a basis for understanding and modifying the life cycles of various parasitic flatworms.
  • Tetsuya Yanagida; Nanami Asai; Michitaka Yamamoto; Kazuhiro Sugahara; Takuto Fujiwara; Sho Shirakashi; Hiroshi Yokoyama
    PARASITOLOGY 150 1 1 - 14 2023年01月 [査読有り]
     
    A new microsporidian disease of cultured rainbow trout Oncorhynchus mykiss was recently confirmed in Japan, and the causative species was tentatively designated as Microsporidium sp. RBT-2021. Involvement of common prawn Palaemon paucidens in its transmission was suggested based on the previous feeding trials, although the microsporidian infection in P. paucidens was not confirmed. In this study, P. paucidens in Lake Biwa, Japan was investigated for microsporidian infection and four types of spores (Type 1-4) were newly found. The nucleotide sequence of the small subunit ribosomal RNA gene was identical between Type 1 and Microsporidium sp. RBT-2021, indicating they are conspecific. However, intriguingly, the spore morphology and the mode of development in fish and prawn were strikingly different. Morphological observations revealed Type 1 in the prawn possesses characteristics of the genus Inodosporus Overstreet and Weidner, 1974, while Microsporidium sp. RBT-2021 in the trout exhibited the characteristics of the genus Kabatana Lom, Dyková and Tonguthai, 2000. In the phylogeny, Type 1 was placed within a clade comprising Kabatana spp. and Inodosporus octosporus. Based on the morphological and molecular analyses, we describe Microsporidium sp. RBT-2021 as Inodosporus fujiokai n. sp. Together with the success of the previous prawn feeding trials, this study strongly suggests I. fujiokai n. sp. has a multi-host life cycle utilizing fish and crustacean hosts and different modes of development in each host. Such polymorphic life cycle has barely been known among fish microsporidians. This study also suggests that the genus Kabatana is a junior synonym of the genus Inodosporus.
  • Nguyen Ngoc Chinh; Nguyen Thi Tham; Violetta M Yurakhno; Pham Ngoc Doanh; Christopher M Whipps; Sho Shirakashi
    Parasitology research 121 9 2495 - 2502 2022年09月 
    During a survey of myxosporean parasites of freshwater fishes in northern Vietnam, myxospores resembling those of the genus Myxobolus (Myxosporea: Myxobolidae) were found in the trunk muscle of 6 out of 35 specimens (17.14%) of wild goldfish Carassius auratus (Cypriniformes: Cyprinidae). The mature spores were 12.0 ± 0.4 (11.4 - 12.6) µm long, 8.5 ± 0.2 (7.9 - 9.0) µm wide and 6.1 ± 0.2 (5.8 - 6.3) µm thick, containing two pyriform-shaped polar capsules unequal in size. The larger polar capsule was 7.6 ± 0.3 (7.1 - 8.4) µm long and 3.5 ± 0.1 (3.3 - 3.8) µm wide, and the smaller polar capsule was 6.2 ± 0.3 (5.5 - 6.7) µm long and 2.9 ± 0.2 (2.6 - 3.4) µm wide. Each polar capsule contained a polar filament with 3-5 coils. A phylogenetic analysis based on the small subunit rDNA (SSU rDNA) sequence revealed that this Myxobolus species forms a distinct branch in the phylogenetic tree sister to Myxobolus artus and Myxobolus cyprini, with DNA sequence similarity at 97.6% to M. artus and 97.5% to M. cyprini. A combination of the morphological characteristics and molecular data suggest that this is an undescribed species, and we propose the name Myxobolus hoabinhensis n. sp.
  • Kazuo Ogawa; Sho Shirakashi; Yutaka Fukuda
    FISH PATHOLOGY 57 2 49 - 55 2022年06月 
    Development of Zeuxapta seriolae (Monogenea: Polyopisthocotylea, Heteraxinidae) collected from Serbia dumerili was described and compared with that of Heteraxine heterocerca, the same heteraxinid species from Seriola quinqueradiata. Based on the morphology of the two monogeneans from very young with a symmetrical body to adult, specimens retrieved from the gills of cultured and wild Seriola spp. (S. quinqueradiata, S. dumerili and S. aureovittata) collected in Japan; and its adjacent areas during 1975-2019 were identified. Heteraxine heterocerca, previously known only from S. quinqueradiata and S. dumerili, was also recorded from S. aureovittata, and Z. seriolae hitherto known only from S. dumerili and S. aureovittata, was recorded from S. quinqueradiata. As a result, both H. heterocerca and Z. seriolae were confirmed from all the three Seriola spp. Cultured. Sc quinqueradiata and S. aureovittata were often infected with both H. heterocerca and Z. seriolae, whereas wild Seriola spp. were infected with a single species of gill monogenean. Culture seeds of foreign origin should be monitored continuously, as information on the polyopisthocotylean monogenean infections of Seriola species known outside Japan is quite limited.
  • Luke J Norbury; Sho Shirakashi; Cecilia Power; Barbara F Nowak; Nathan J Bott
    International journal for parasitology. Drugs and drug resistance 18 87 - 102 2022年04月 
    Parasitic diseases are major constraints in fish mariculture. The anthelmintic praziquantel (PZQ) can effectively treat a range of flatworm parasites in a variety of fish species and has potential for broader application than its current use in the global aquaculture industry. In this review we report on PZQ's current use in the aquaculture industry and discuss its efficacy against various flatworm parasites of fish. Routes of PZQ administration are evaluated, along with issues related to palatability, pharmacokinetics and toxicity in fish, while PZQ's effects on non-target species, environmental impacts, and the development of drug-resistance are discussed.
  • Nicholas Q-X Wee; Thomas H. Cribb; Sho Shirakashi; Scott C. Cutmore
    PARASITOLOGY 149 5 622 - 639 2022年04月 
    We report specimens of monorchiids infecting Haemulidae from the waters off Japan and Australia; these specimens represent five species of Helicometroides Yamaguti, 1934, three of which are unambiguously new. Helicometroides murakamii n. sp. infects Diagramma pictum pictum from off Minabe, Japan; Helicometroides gabrieli n. sp. infects Plectorhinchus chrysotaenia from off Lizard Island, Australia; and Helicometroides wardae n. sp. infects Plectorhinchus flavomaculatus and Plectorhinchus multivittatus from off Heron Island, Australia. Helicometroides murakamii n. sp. and H. gabrieli n. sp. conform to the most recent diagnosis of Helicometroides in lacking a terminal organ, but H. wardae n. sp. possesses a terminal organ with distinct, robust spines; despite this morphological distinction, the three form a strongly-supported clade in phylogenetic analyses. We also report specimens morphologically consistent with Helicometroides longicollis Yamaguti, 1934, from D. pictum pictum from off Minabe, Japan, and Diagramma pictum labiosum on the Great Barrier Reef, Australia. Genetic analyses of ITS2 rDNA, 28S rDNA and cox1 mtDNA sequence data for the Japanese specimens reveal the presence of two distinct genotypes. Specimens of the two genotypes were discovered in mixed infections and are morphologically indistinguishable; neither genotype can be associated definitively with H. longicollis as originally described. We thus identify them as H. longicollis lineage 1 and 2, pending study of further fresh material. Genetic analyses of specimens from the Great Barrier Reef are consistent with the presence of only H. longicollis lineage 1. This species thus has a range that incorporates at least Australia and Japan, localities separated by over 7000 km.
  • Thomas H Cribb; Rodney A Bray; Jean-Lou Justine; James Reimer; Pierre Sasal; Sho Shirakashi; Scott C Cutmore
    Parasitology 149 6 1 - 23 2022年03月 
    The taxonomy of species of Bivesicula Yamaguti, 1934 is analysed for samples from holocentrid, muraenid and serranid fishes from Japan, Ningaloo Reef (Western Australia), the Great Barrier Reef (Queensland), New Caledonia and French Polynesia. Analysis of three genetic markers (cox1 mtDNA, ITS2 and 28S rDNA) identifies three strongly supported clades of species and suggests that Bivesicula as presently recognized is not monophyletic. On the basis of combined morphological, molecular and biological data, 10 species are distinguished of which five are proposed as new. Bivesicula Clade 1 comprises seven species of which three are effectively morphologically cryptic relative to each other; all seven infect serranids and four also infect holocentrids. Bivesicula Clade 2 comprises three species of which two are effectively morphologically cryptic relative to each other; all three infect serranids and one also infects a muraenid. Bivesicula Clade 3 comprises two known species from apogonids and a pomacentrid, and forms a clade with species of Paucivitellosus Coil, Reid & Kuntz, 1965 to the exclusion of other Bivesicula species. Taxonomy in this genus is made challenging by the combination of low resolving power of ribosomal markers, the existence of regional cox1 mtDNA populations, exceptional and unpredictable host-specificity and geographical distribution, and significant host-induced morphological variation.
  • Nguyen Ngoc Chinh; Nguyen Van Ha; Pham Ngoc Doanh; Yurakhno Violetta; Tomoyoshi Yoshinaga; Sho Shirakashi; Sascha L Hallett; Christopher M Whipps
    Parasitology research 121 2 613 - 621 2022年02月 
    A new myxozoan species, Ceratomyxa binhthuanensis n. sp. (Myxosporea: Ceratomyxidae), was found in the gall bladder of blacktip grouper Epinephelus fasciatus (Perciformes: Serranidae) in the East Sea of Vietnam. Myxospores were observed floating free in the gall bladder of 3 out of 20 fish examined (15%). Mature myxospores were elongate and slightly crescent-shaped and measured 12.2 ± 1.3 (10.8-16.0) μm in thickness and 5.8 ± 0.6 (4.8-6.9) μm in length, with two smooth equal shell valves. The two polar capsules were spherical and equal in size, measuring 2.6 ± 0.3 (2.3-2.9) μm in diameter. The posterior angle was slightly concave, 153.7° ± 5.6° (148.9°-166.0°). Molecular analysis of SSU rDNA sequence showed that Ceratomyxa binhthuanensis n. sp. differs from other Ceratomyxa spp. available in GenBank. Phylogenetic analysis indicated that C. binhthuanensis n. sp. was closely related to three species, Ceratomyxa nolani, Ceratomyxa yokoyamai, and Ceratomyxa cutmorei, which also infect fish hosts of the genus Epinephelus.
  • S. C. Cutmore; R. Q. -Y. Yong; J. D. Reimer; S. Shirakashi; M. J. Nolan; T. H. Cribb
    SYSTEMATIC PARASITOLOGY 98 5-6 641 - 664 2021年12月 
    Ankistromeces Nolan & Cribb, 2004 and Phthinomita Nolan & Cribb, 2006 are sister genera of threadlike blood flukes (Trematoda: Aporocotylidae) infecting teleost fishes of the tropical Indo-west Pacific. Here, we report new collections of these genera from Australia, Indonesia, and Japan. A new species of Ankistromeces, Ankistromeces kawamurain. sp., is described from Siganus spinus (Linnaeus) off Okinawa, Japan, and a new species of Phthinomita, Phthinomita abdita n. sp., from Choerodon cephalotes (Castelnau), in Moreton Bay, Australia; the new species are morphologically cryptic within their respective genera and are delineated by molecular and ecological data. Ankistromeces olsoni Nolan & Cribb, 2006 is reported from Siganus fuscescens (Houttuyn) off Heron Island (southern Great Barrier Reef), Lizard Island (northern Great Barrier Reef), and Okinawa and Wakayama Prefectures, Japan and from Siganus spinus (Linnaeus) from off Bali, Indonesia. Ankistromeces mariae Nolan & Cribb, 2004 is re-reported from the type-host, Meuschenia freycineti (Quoy & Gaimard), from a new location, Gypsy Bay, Tasmania. Phthinomita poulini Nolan & Cribb, 2006 is re-reported from its type-locality, Lizard Island, from a range of mullids, including five new host species, and its range is extended to include Moreton Bay. Phthinomita symplocos Nolan & Cribb, 2006 is reported from Bali and P. hallae Nolan & Cribb, 2006, P. jonesi Nolan & Cribb, 2006, P. littlewoodi Nolan & Cribb, 2006, and P. munozae Nolan & Cribb, 2006 are each re-reported from their type-host and type-localities. New cox1 mtDNA data were generated for all known species of these two genera from new and archival material. Analyses of these data enabled an evaluation of all known Phthinomita species; P. robertsthomsoni Nolan & Cribb, 2006 is synonymised with P. adlardi Nolan & Cribb, 2006, and P. brooksi Nolan & Cribb, 2006 is synonymised with P. sasali Nolan & Cribb, 2006. We highlight the failure of ITS2 data to delineate closely related aporocotylid species. In contrast, cox1 sequence data are proving reliable and effective in this context and we recommend their incorporation in future studies of blood fluke taxonomy.
  • S. C. Cutmore; R. Q. -Y. Yong; J. D. Reimer; S. Shirakashi; M. J. Nolan; T. H. Cribb
    SYSTEMATIC PARASITOLOGY 98 5-6 665 - 665 2021年12月
  • Sho Shirakashi; Satoshi Nishikawa; Yuji Ishii; Hidemasa Kawakami; Jun Satoh; Chihaya Nakayasu; Mamoru Ishihara; Tomoko Fukui; Kazuhiko Hirose
    FISH PATHOLOGY 56 4 205 - 211 2021年12月 
    Three experimental trials were conducted to determine the effective dose and administration period of a pro-benzimidazole anthelmintic drug febantel (FBT) against two gill monogenean species on amberjacks; Zeuxapta japonica on Seriola dumerili and Heteraxine heterocerca on Seriola quinqueradiata. The mean Z. japonica intensities were checked at 3 days after given FBT-coated feeds at the doses of 1, 5, 10, or 20 mg/kg body weight (BW)/day (d) for 5 consecutive days (trial 1), and 10 mg/kg BW/d for 1, 3, or 5 days (trial 2). Based on the results of these trials, the efficacy of oral FBT treatment was assessed for H. heterocerca infections at the treatment regime of 10 mg/kg BW/d for 3 or 5 days (trial 3). Over 95% FBT efficacies were achieved for both monogenean species when the fish received the dose of 10 mg/kg/d or higher for 5 consecutive days. Amberjacks showed no apparent avoidance to the FBT-coated feed and no apparent signs of the drug toxicity were detected. Our results demonstrated that the in -feed FBT treatment at the dose of 10 mg/kg BW/d for 5 days is an effective, easy, and practical control measure against gill monogenean infections in aquaculture of Seriola fish.
  • Sho Shirakashi; Satoshi Nishikawa; Yuji Ishii; Hidemasa Kawakami; Yoshiaki Imaoka; Keisuke Yoshii; Jun Satoh; Chihaya Nakayasu; Mamoru Ishihara; Tomoko Fukui; Kazuhiko Hirose
    FISH PATHOLOGY 56 4 212 - 215 2021年12月 
    Field trials were conducted to assess the efficacy of oral febantel (FBT) treatment at the dose of 10 mg/lkg for 5 days against Heteraxine heterocerca and Zeuxapta japonica in Seriola fish. Numbers of gill flukes were checked 1 day before and 3 days after the treatment. In comparison to the control groups, fish given FBT-coated -feed showed deworming efficacies of 99.9% to 100%. No mortality and no signs of drug toxicity were observed. These results indicate that in-feed administration of FBT is an effective and practical treatment for gill fluke infections in Seriola aquaculture.
  • Michitaka Yamamoto; Sho Shirakashi; Nanami Asai; Tetsuya Yanagida; Kazuhiro Sugahara; Hiroshi Yokoyama
    Fish Pathology 56 3 130 - 139 2021年09月 
    A microsporidian disease showing abnormal petechiae-like red spots on the trunk muscle, beneath the skin, occurred among rainbow trout Oncorhynchus mykiss farmed in Shiga Prefecture. Numerous microsporidian spores were detected from the affected area and the causative agent was identified as a microsporidian closely related to Kabatana takedai based on morphology and molecular analyses. Anecdotal information indicated the possible involvement of common prawn Palaemon paucidens for the transmission of the pathogen. Three prawn feeding trials using O. mykiss and Biwa trout Oncorhynchus masou subsp. successfully reproduced the disease in both fish species. The microsporidian infections were confirmed in the fish given fresh and chilled prawns and mortalities occurred in these groups. No infection occurred in the groups fed with frozen prawn. These results strongly suggest that the microsporidian infections can be lethal to Oncorhynchus spp. and that P. paucidens plays important role in the transmission of the pathogen. These findings may lead to the elucidation of the multi-host lifecycle of fish microsporidians.
  • Hirotaka Mizuochi; Yutaro Fujiwara; Sho Shirakashi; Yuji Fujikura; Kazuo Ogawa
    Fish Pathology 56 3 122 - 129 2021年09月 
    Benedenia akajin has recently been described as a new species from cultured coral grouper Plectropomus leopardus. We conducted annual monitoring for the skin monogenean among hatchery -reared P. leopardus juveniles to understand the seasonality of the infections. In addition, growth, development, reproduction, site specificity, and pathogenicity of B. akajin were investigated. The infections were most prominent at a temperature above 25 degrees C and B. akajin was the only capsalid species found in the hatchery-reared P. leopardus juveniles. The parasite took approximately 9 days to reach maturity and had an estimated longevity of approximately 1 month at 26 degrees C. At this temperature, the shortest egg-laying frequency was 131 s, but the oviposition rate was strongly affected by the size of the worm. Most B. akajin individuals were found on the fins of the host. Wounds and lesions were observed on the fins of infected P. leopardus and the host condition factor was negatively correlated with the parasite intensity. These results demonstrated that B. akajin caused decreased growth in cultured P. leopardus juveniles and indicated the needs to control this skin fluke in P. leopardus rearing facilities.
  • Sho Shirakashi; Nanami Asai; Mayuko Miura
    PARASITOLOGY RESEARCH 120 9 3173 - 3180 2021年09月 
    Phototaxis is the common behavioral response exhibited by the oncomiracidia of various monogeneans. However, the changes in the oncomiracidial swimming behavior in response to light cues are not well understood. Here, we investigated the light responses of four monogeneans that are important pathogens in mariculture, namely Benedenia epinepheli, Benedenia seriolae, Neobenedenia girellae, and Heteraxine heterocerca. The swimming trajectory and speed of oncomiracidia of each species were assessed in a glass Petri dish with an LED light placed adjacent to it, based on three different light responses: LED light in the off position (normal swimming), LED light in the on position (phototactic behavior), and immediately (< 5 s) after switching the LED light off (photophobic behavior). The oncomiracidia of all four species exhibited positive phototactic and photophobic responses; however, the change in swimming speed between each response differed among the species. The oncomiracidia of three species (B. epinepheli, N. girellae, and H. heterocerca) exhibited high swimming speed, as a phototactic response; in contrast, the oncomiracidia of B. seriolae exhibited reduced swimming speed when moving toward the light source. Benedenia epinepheli and H. heterocerca exhibited the highest swimming speed during the phototaxis phase, whereas B. seriolae and N. girellae exhibited the highest swimming speed during the photophobic phase. These light responses are considered adaptive traits to increase the chance of encountering and infecting suitable hosts in nature, and such responses could potentially be applied to the control of parasite infections in aquaculture.
  • Soetsu Yanagi; Jun Satoh; Tohru Mekata; Takamitsu Sakai; Hidemasa Kawakami; Shogo Harakawa; Sho Shirakashi; Shogo Hamano; Kei Fukudome; Kazuhiko Wada; Masatoshi Yamasaki; Toyohiro Nishioka; Chihaya Nakayasu; Koh-ichiro Mori
    Fish Pathology 56 2 62 - 70 2021年06月 
    Beko disease, caused by infection of the microsporidian Microsporidium seriolae, results in significant damage to farmed amberjack, Seriola spp., in Japan. Little is known about the disease, including the general biology of the causative agent, and no therapeutic method has been established to treat it. We determine the therapeutic efficacies of various drugs by administering them in -feed to juvenile Seriola spp. naturally infected with M. seriolae. Candidate drugs include commercially available fishery anthelminthic, febantel, and eight other compounds. Fish were given various doses of drugs, and M. seriolae infection in their trunk muscle was then checked by quantitative PCR (qPCR) and macroscopic cyst detection. Fish treated with febantel at an early stage of infection had significantly lower rates of cyst formation and qPCR-positive. However, febantel administered to fish after cyst formation did not reduce cyst numbers. Other drugs showed no apparent efficacy to prevent cyst formation or to promote cyst reduction. Results indicate febantel is a promising therapeutic agent for beko disease when applied at an early stage of infection.
  • Sho Shirakashi; Nanami Asai; Jun Satoh; Chihaya Nakayasu
    FISH PATHOLOGY 56 2 97 - 106 2021年06月 
    Persistence of Febantel (FBT) and its metabolites (FBZ) were assessed in Seriola quinqueradiata after 5 days gavage administration of 20 mg/kg body weight. FBT was not detected in any organs at 1 day post administration (dpa), but traces of FBZ were detected in the liver and kidney at 7 dpa. Neither compound was detected at 14 dpa. While S. quinqueradiata received 20 mg/kg of FBT had higher bilirubin and lower triglyceride values in the blood at 1 dpa, and lower plasma creatinine level at 7 dpa, these were not likely associated with severe damages of organs and physiological functions.
  • Sho Shirakashi; Satoshi Miwa; Takuya Katsuki; Shogo Harakawa; Hidemasa Kawakami; Chihaya Nakayasu; Koh-ichiro Mori
    FISH PATHOLOGY 56 2 79 - 88 2021年06月 
    Recent studies have shown efficacy of febantel (FBT) against Microsporidium seriolae in Seriola fish. This study evaluated the toxicity of FBT in Seriola quinqueradiata. Fish were gavage fed with feed containing various doses of FBT (50 to 1,000 mg/kg/day (d)) for 14 or 28 consecutive days and monitored for growth and survival. Major mortality started at 7 days in fish given 200 and 1,000 mg/kg/d FBT, while the onset of mortality in the 50 and 100 mg/kg/d groups was delayed until 15 days. Doses of 50 rng/kg/d or higher affected fish growth. Histological analyses revealed changes in the distribution and density of Nissl bodies in the brain, and a reduction of vacuolies in hepatocytes. These histological changes were rarely observed after a 9-day drug washout period, suggesting that such changes were reversible. There was no drug-related mortality in fish that received 15 mg/kg/d for 20 days or 20 mg/kg/d for 14 days. These results suggest that, although FBT can have lethal toxicity in S. quinqueradiata when administrated at doses over 50 mg/kg/d for more than 14 days or 200 mg/kg/d for more than 7 days, the drug is considered safe at the normal antiparasitic dose, including the effective dose for M. seriolae treatment (10 mg/kg/d for 5 days).
  • Sho Shirakashi; Takuma Takagi
    AQUACULTURE RESEARCH 52 5 1915 - 1924 2021年05月 
    The use of biological agents to control parasitic diseases in aquaculture is becoming increasingly popular as it is considered safe, effective and economically beneficial strategy for sustainable aquaculture practices. Monogeneans are among the most problematic parasites in fish farms. Their local outbreaks are largely attributed to the accumulation of eggs on farming structures, and the removal of these eggs by biological agents can be a novel solution to control monogenean diseases. We assessed the consumption of monogenean eggs by two amphipod species (a gammarid and a caprellid), the grass shrimp Palaemon pacificus and three fish (two monacanthids and Girella punctata). The ingestion of Neobenedenia girellae and/or Heteraxine heterocerca eggs was directly or indirectly confirmed in all of the tested organisms. The eggs ingested by the crustaceans lost viability, while those eaten by fish hatched after excretion. Monacanthid filefish consumed N. girellae eggs at the highest rate, up to more than 23,000 eggs individual(-1) 24 hr(-1). A cohabitation of Seriola dumerili with a monacanthid, Rudarius ercodes, showed a lower acquisition of N. girellae than those kept without R. ercodes. The results indicated that these crustaceans and fish can be useful biological agents for removing monogenean eggs from culturing facilities.
  • Nguyen Ngoc Chinh; Ha Duy Ngo; Vu Van Tuc; Naoki Itoh; Tomoyoshi Yoshinaga; Sho Shirakashi; Pham Ngoc Doanh
    PARASITOLOGY RESEARCH 120 3 877 - 885 2021年03月 
    During a survey of myxosporean parasites of marine fish in the coastal region of Vietnam, a species of the genus Henneguya (Myxosporea: Bivalvulida) was found in the gill of yellowfin seabream Acanthopagrus latus (Perciformes: Sparidae). White and oval cysts, measuring 145-220 mu m in diameter, were detected in the gill lamellae of 4 of 15 fish examined (26.7%). Mature myxospores were elongate, with smooth valves, two similar polar capsules, and having the following dimensions: spore body length 9.9 +/- 0.5 (8.9-12.5) mu m, body width 6.7 +/- 0.3 (6.1-7.6) mu m, thickness 5.1 +/- 0.2 (4.8-5.4) mu m, caudal appendage length 10.0 +/- 1 (8.3-11.6) mu m, and total myxospore length 19.3 +/- 1.4 (16.5-21.5) mu m. The polar capsules were ovoid, measuring 3.2 +/- 0.2 (2.8-3.9) mu m long and 1.9 +/- 0.2 (1.5-2.3) mu m wide. Each polar capsule has a polar filament with 4-5 coils. Histological analysis revealed plasmodia in the connective tissues of the gill lamellae, but inflammation and deformation of the gills were not observed. In the phylogenetic tree reconstructed from the small subunit ribosomal DNA (SSU rDNA), sequences of the Henneguya specimens found in this study form a distinct branch. Morphological characteristics and molecular data identified a new species, namely Henneguya lata n. sp.
  • Sho Shirakashi; Sang Phil Shin; Tohru Mekata; Ikunari Kiryu
    Fish Pathology 56 3 140 - 148 2021年 
    Kudoa septempunctata is an important myxozoan parasite in culture and capture fisheries as it causes food poisoning in humans. This species is generally considered a parasite of olive flounder Paralichthys olivaceus because K. septempunctata-related food poisoning cases are associated with consumption of raw infected P. olivaceus. However, the host range of K. septempunctata remains unclear. Moreover, there is scarce information on the lifecycle of the parasite, and this hinders the development of a fundamental prophylactic measure in fish farms. During the survey of wild fishes at a K. septempunctata endemic area, kudoid myxospores were detected in the somatic muscle of grass puffer Takifugu alboplumbeus and Japanese whiting, Sillago japonica. Our morphological, molecular, and histological analyses identified them as K. septempunctata. While the infection levels in T. alboplumbeus were higher (up to 92.3% prevalence) than those in S. japonica (23.8%), the maximum spore density in the muscle tissue was about 7×104/g in both fishes, which is far less than the food poisoning risk value of 1 × 106/g. These findings indicate a wide host range of K. septempunctata and further attention is required for its possible infections in fishes other than P. olivaceus.
  • Kazuo Ogawa; Hirotaka Mizuochi; Tomofumi Yamaguchi; Sho Shirakashi; Nanami Asai; Yasuo Agawa
    FISH PATHOLOGY 55 4 117 - 124 2021年01月 
    The grow-out stage of leopard coral grouper Plectropomus leopardus reared in land based tanks in Okinawa Prefecture, Japan, were often heavily infected with capsalid monogeneans, up to a few millimeters in size, on the fins and skin. Morphological investigation revealed that the parasite belongs to Benedenia (Monogenea: Capsalidae). Benedenia akajin n. sp. is proposed here and described morphologically, based on the unique structures in the vaginal duct with a thick-walled distal one-third, the penis with a teat-shaped tip and the testes smaller than the germarium. A positive relationship between the lengths of three haptoral sclerites (anterior sclerites and anterior and posterior hamuli) and body length indicates that these taxonomically important structures keep growing as the parasite ages. Molecular analyses showed that the present species is most closely related to B. epinepheli and B. sargocentron, with the highest 28S rDNA identity of 98.1%, but no identical sequences were found in the database. Both morphological and molecular evidences suggest Benedenia akajin n. sp. as an undescribed species, and this new skin fluke deserves further investigations for the stable aquaculture of P. leopardus.
  • Daniel C. Huston; Kazuo Ogawa; Sho Shirakashi; Barbara F. Nowak
    TRENDS IN PARASITOLOGY 36 12 1002 - 1012 2020年12月 
    Marine fish are a nutritious and high-value food commodity, but many wild-capture fisheries are in decline. Thus, marine fish culture is expected to expand greatly in coming years. Management of disease is a major problem in this industry, and metazoan parasites are among the most significant disease agents in terms of economic loss and animal welfare. Current methods for controlling metazoan parasites are mostly reactionary and rely on chemical treatment. Such methods are ultimately unsustainable. Here, we summarise the life cycles of marine metazoan parasites and how this knowledge can be used for nonchemical management and control. To aid the sustainable growth of marine fish culture, we advocate for a renewed research focus on the basic life history characteristics of parasites.
  • Sho Shirakashi; Tomoya Matsuda; Nanami Asai; Tomoki Honryo; Kazuo Ogawa
    INTERNATIONAL JOURNAL FOR PARASITOLOGY 50 10-11 851 - 857 2020年09月 
    Some fish blood flukes of the genus Cardicola (Aporocotylidae) are considered important pathogens of farmed/ranched tuna, Thunnus spp. Infections with Cardicola spp. might obstruct the blood flow in the gills via massive accumulations of eggs and often lead to mass mortalities in captive tuna. At present, oral administration of an anthelminthic drug, praziquantel is the most effective treatment, but the tuna farming industries are seeking non-drug control measures. Development of prophylactic and holistic measures have been difficult, owing to a lack of basic knowledge about these parasites. Unlike other trematodes which use molluscs, blood flukes of marine actinopterygian fish use terebellid polychaetes as intermediate hosts. However, information about the development of Cardicola spp. within intermediate hosts is very limited. Recent success in Cardicola opisthorchis sporocyst transplantation into the host polychaete has opened possibilities for the cultivation of Cardicola in the laboratory. Here, we conducted several transplantation trials with another tuna blood fluke, Cardicol orientalis, into its natural and surrogate polychaete hosts. Cardicola orientalis sporocysts were injected into a total of 195 Nicolea gracilibranchis, the natural host, and clear sporocyst development and reproduction was observed in 32 recipients (overall success rate 16.4%). The production of daughter sporocysts in the transplanted polychaete occurred within 14 days post injection, and one sporocystogenous cycle took approximately 4 weeks. Serial passage culture via transplantation of in vivo-cultured sporocysts was also achieved, but with limited sporocyst reproduction. In addition, sporocysts were successfully retrieved from six and one individuals of the surrogate hosts, Thelepus setosus (n = 10) and Thelepus japonicas (n = 5), respectively. These results indicate that the in vivo cultivation of C orientalis sporocysts is possible, not only in its natural host but also in other terebellids, although the problems of high mortality and inconsistency in successful transplantation need to be resolved. (C) 2020 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.
  • 白樫, 正; 脇, 司; 小川, 和夫
    魚病研究 54 4 93 - 100 2020年01月 
    アユは両側回遊魚であり，養殖や遊漁の重要対象魚種である。和歌山県の沿岸海域で採取した天然仔魚と近隣河川の遡上稚魚に吸虫のメタセルカリア寄生が高率で見られた。メタセルカリアは主に鰭基部や尾鰭内部に寄生しており，最大で1尾あたり566虫体が確認された。魚体に目立った病変は認められず，宿主に対する病害性は低いと考えられた。遺伝子解析と形態観察の結果，本種は腹口吸虫(Bucephalidae)科Bucephalinae亜科Prosorhynchoides属の一種である可能性が示された。また遺伝子配列が一致するメタセルカリアがマサバとカタクチイワシからも見つかり，この腹口吸虫は海産種であることが明らかとなった。
  • Satoshi Kawato; Keigo Kobayashi; Sho Shirakashi; Soetsu Yanagi; Yutaka Fukuda; Hirofumi Yamashita; Reiko Nozaki; Ikuo Hirono; Hidehiro Kondo
    FISH PATHOLOGY 54 2 27 - 33 2019年06月 [査読有り]
     
    Infection with the skin fluke Benedenia seriolae is a serious threat of yellowtail aquaculture. Development of genomic resources and molecular markers for B. seriolae is an essential infrastructure to develop control strategies against B. seriolae infections. As a seminal study to establish the genomic resources of the Japanese B. seriolae populations, we sequenced the complete mitochondria! genome (mitogenome) sequences of 12 B. seriolae specimens collected from four prefectures in Japan. The Japanese B. seriolae mitogenomes were mutually 99% identical, while the identity was 85% when compared to that of an Australian specimen. Furthermore, the gene arrangement in the Japanese B. seriolae mitogenome was slightly different from that in the Australian specimen. The substantial mitogenomic divergence between the Australian and Japanese specimens indicates that B. seriolae is composed of molecularly divergent populations. Variable sites were dispersed in the mitogenome of the Japanese B. seriolae. Phylogenetic relationships among the Japanese B. seriolae specimens did not reflect the host species or geographic distributions within Japan.
  • Keigo Kobayshi; Germaine Lau Gek Khin; Sho Shirakashi; Yusuke Mukai; Yukitaka Sugihara; Soetsu Yanagi; Ikuo Hirono; Hidehiro Kondo
    FISH PATHOLOGY 53 4 124 - 127 2018年12月 [査読有り]
     
    We developed a PCR-RFLP method to distinguish Benedenia seriolae and Neobenedenia girellae, both infecting amberjacks Seriola spp. more precisely than a morphological method. PCR products of 28S rRNA and COX1 were digested by Cla I and EcoR I, respectively. For all individuals of B. seriolae, the digestions split each of the PCR products into two fragments. On the other hand, although the products of most of the N. girellae samples were digested by neither the enzymes, only PCR products of 28S rRNA gene of three of the individuals were split into three fragments, suggesting they were the hybrid between the two species.
  • Hisashi Chuda; Kazuki Ieda; Sho Shirakashi; Shukei Masuma
    AQUACULTURE 491 346 - 350 2018年04月 [査読有り]
     
    Interspecific hybrids of marine fish are becoming popular for aquaculture. The advantageous characteristics of hybrid fish include high growth rates, enhanced feed conversion rates, better appearance, high tolerance to environmental stress, and increased resistance to certain diseases. A new hybrid grouper Kue-Tama, female Epinephelus bruneus x male E. lanceolatus has recently been established. This hybrid showed significantly higher growth than that by E. bruneus and is considered a promising new species for aquaculture, especially in temperate areas where the slow growth of E. bruneus has prevented stable farming practices. The present study compared the resistance of Kue-Tama, its maternal parent E. bruneus and E. septemfasciatus, another popular grouper for farming, against the skin fluke, Benedenia epinepheli, which is a problematic parasite in grouper farming. The result of the cohabitation experimental infection showed that E. septemfasciatus was the most resistant to the skin fluke, followed by Kue-Tama and then E. bruneus. There appeared to be a negative relationship between the amount of mucus produced and the parasite intensity suggesting a resistance to skin flukes though the dry-weight of mucus collected from a given skin surface area did not differ between the three groupers. These results demonstrated that Kue-Tama has another favorable characteristic for aquaculture, in addition to their higher growth rate.
  • Kazuya Nagasawa; Sho Shirakashi
    CRUSTACEANA 91 2 251 - 255 2018年 [査読有り]
  • Kazuya Nagasawa; Sho Shirakashi; Shinji Yamamoto
    CRUSTACEANA 91 3 375 - 377 2018年 [査読有り]
  • 小川 和夫; 白樫 正
    魚病研究 52 4 186 - 190 日本魚病学会 2017年12月 [査読有り]
     
    Capsalid monogeneans infect the skin of marine fish; among them, Benedenia seriolae and Neobenedenia girellae are most important pathogens of cultured fish. The former infects the skin of amberjacks, Seriola spp., while the latter, being not host specific, has been found from the skin of 15 fishes in Japan. Feeding epithelial cells and mucous of the host results in skin abrasion, causing growth retardation and secondary bacterial infection, even leading to the death of the host fish. Eggs entangle on the culture net, which is prone to heavy infection of fish cultured in net cages. Prevention of infection is practically impossible as its life cycle has been established in fish farms. Chemotherapy with hydrogen peroxide or praziquantel is effective but repeated treatment is required, as immunity is not acquired by infected fish. Development of new control measures such as biological control and selective breeding of a resistant strain against these monogeneans are in progress.
  • Michio Jinnai; Takao Kawai; Tetsuya Harada; Yasutaka Nishiyama; Hiroshi Yokoyama; Sho Shirakashi; Hiroshi Sato; Junko Sakata; Yuko Kumeda; Yutaka Fukuda; Kikuyo Ogata; Kentaro Kawatsu
    INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY 259 59 - 67 2017年10月 [査読有り]
     
    Kudoa septempunctata, a myxosporean parasite of the olive flounder (Paralichthys olivaceus), causes foodbome gastroenteritis after ingestion of contaminated raw flounder. Available methods to detect K. septempunctata require expensive equipment, well-trained personnel, and lengthy procedures. Here we generated a novel monoclonal antibody (MAb 15G11) against K. septempunctata and used it to produce a prototype immunochromatographic assay (prototype Kudoa-ICA). Within 15 min, the prototype Kudoa-ICA detected >= 1.0 x 10(5) spores/mL in a spore suspension and >= 2.0 x 10(4) spores/g of P. olivaceus muscle. The prototype Kudoa-ICA weakly cross-reacted with spores of K. lateolabracis and K. iwatai. cDNA sequence, expression, and western blot analyses revealed that MAb 15G11 detected an approximately 24-kDa protein encoded by a 573 bp mRNA. The cDNA nucleotide and predicted amino acid sequences were not significantly similar to any sequence in the GeneBank database. Immunoelectron microscopy revealed that MAb 15G11 reacted with the sporoplasmic cells and mainly with the capsulogenic cells of the K. septempunctata spore. Although the Kudoa-ICA was weakly cross-reactive with two other Kudoa species, it detected > 1.0 x 10(6) spores/g of K. septempunctata in P. olivaceus muscle, which is the criterion used to indicate a violation of the Food Hygiene Law of Japan. We conclude that MAb 15G11 may be suitable for use in an immunochromatographic assay for screening P. olivaceus muscle contaminated with K. septempunctata at food distribution sites such as food wholesalers, grocery stores, and restaurants.
  • Sho Shirakashi; Kazuki Tani; Katsuya Ishimuru; Tomoki Honryo; Sang Phil Shin; Hiro'omi Uchida; Kazuo Ogawa
    JOURNAL OF PARASITOLOGY 103 5 541 - 546 2017年10月 [査読有り]
     
    Fish blood flukes of the genus Cardicola (Digenea: Aporocotylidae) are important pathogens in tuna aquaculture. Recent advances in marine blood fluke research have led to the elucidation of the lifecycles of 3 Cardicola spp. infecting tuna; all 3 flukes utilize terebellid polychaetes as the intermediate host. In our survey, we obtained large numbers of Nicolea gracilibranchis infected by larval Cardicola orientalis at our tuna farming site. To determine the spatial and temporal changes in the distribution of N. gracilibranchis surrounding tuna culture cages and their infection by C. orientalis, we conducted monthly sampling for a period of 1 yr. Terebellids were most abundant on the floats and ropes of culture cages, but a significantly higher proportion of infected N. gracilibranchis was detected on ropes, particularly up to 4 m in depth. Cardicola orientalis infection in N. gracilibranchis was clearly seasonal, with a higher infection rate between April and July. Our findings indicate that the infected terebellids inhabit specific microhabitats, and both abiotic and biotic factors likely influence blood fluke infection in the intermediate terebellid host. This information is important to better understand the general biology of marine aporocotylids and may be useful to develop a control strategy for blood fluke infection in tuna aquaculture.
  • Sho Shirakashi
    NIPPON SUISAN GAKKAISHI 83 5 829 - 829 2017年09月 [査読有り]
  • S. P. Shin; S. Shirakashi
    JOURNAL OF FISH DISEASES 40 2 287 - 291 2017年02月 [査読有り]
  • Kazuo Ogawa; Sho Shirakashi; Kazuki Tani; Sang Phil Shin; Katsuya Ishimaru; Tomoki Honryo; Yukitaka Sugihara; Hiro'omi Uchida
    PARASITOLOGY INTERNATIONAL 66 1 972 - 977 2017年02月 [査読有り]
     
    Farming of Pacific bluefin tuna (PBT), Thunnus orientalis, is a rapidly growing industry in Japan. Aporocotylid blood flukes of the genus Cardicola comprising C orientalis, C. opisthorchis and C. forsteri are parasites of economic importance for PBT farming. Recently, terebellid polychaetes have been identified as the intermediate hosts for all these parasites. We collected infected polychaetes, Terebella sp., the intermediate host of C. opisthorchis, from ropes and floats attached to tuna cages in Tsushima, Nagasaki Prefecture, Japan. Also, Neoamphitrite vigintipes (formerly as Amphitrite sp. sensu Shirakashi et al., 2016), the intermediate host of C. forsteri, were collected from culture cages in Kushimoto, Wakayama Prefecture, Japan. The terebellid intermediate hosts harbored the sporocysts and cercariae in their body cavity. Developmental stages of these blood flukes were molecularly identified using species specific PCR primers. In this paper, we describe the cercaria and sporocyst stages of C. opisthorchis and C. forsteri and compare their morphological characteristics among three Cardicola blood flukes infecting PBT. We also discuss phylogenetic relations of the six genera of the terebellid intermediate hosts (Artacama, Lanassa, Longicarpus, Terebella, Nicolea and Neoamphitrite) of blood flukes infecting marine fishes, based on their morphological characters. (C) 2016 Elsevier Ireland Ltd. All rights reserved.
  • Nagasawa Kazuya; Shirakashi Sho
    Crustacean Research 46 95 - 101 日本甲殻類学会 2017年 

    Ovigerous females of Nerocila phaiopleura Bleeker, 1857 were collected from the body surface of young Pacific bluefin tuna, Thunnus orientalis (Temminck & Schlegel, 1844), cultured in Japan. This represents the first record of N. phaiopleura in finfish mariculture. The species is the third cymothoid isopod from maricultured fishes in Japan. The infected fish had a large hemorrhagic wound caused by N. phaiopleura at the attachment site. Thunnus orientalis is a new host of the isopod. No cymothoid infection has so far been reported from wild individuals of T. orientalis that swims at high speeds in the oceans, and the observed occurrence of N. phaiopleura on this fish species is regarded as unusual under confined mariculture conditions. The hosts and geographical distribution records of N. phaiopleura in Japan are reviewed.

  • Ylenia Pennacchi; Sho Shirakashi; Barbara F. Nowak; Andrew R. Bridle
    FISH & SHELLFISH IMMUNOLOGY 58 490 - 499 2016年11月 [査読有り]
     
    Pacific bluefin tuna (PBT), Thunnus orientalis, due to its high average price on the market is an economically valuable fish species. Infections by blood flukes from the genus Cardicola (Trematoda: Aporocotylidae) represent a growing concern for the cage culture of bluefin tuna in Japan, Australia and Southern Europe. The accumulation of numerous Cardicola eggs in the fish gills causes severe pathology that has been linked to mortality in PBT juveniles up to one year old. The only effective treatment used to mitigate the infection is the oral administration of the antihelminthic drug praziquantel (PZQ) to the affected fish. However, with the need to minimise therapeutic drug use in aquaculture it is hoped that immunoprophylaxis can provide a future alternative to protect the PBT juveniles against Cardicola infection. Currently, little is known of the host immune response to these parasites and of their infection dynamics. In this study, using real-time qPCR we aimed to quantitatively detect C orientalis and C. opisthorchis DNA within the gills and heart of cultured PBT juveniles and to investigate the host immune response at the transcriptional level in the gills. The research focused mainly during early stages of infection soon after young PBT were transferred to culture cages (from 14 to 77 days post-transfer). An increase (up to 11-fold) of immune-related genes, namely IgM, MHC-I, TCR-beta and IL-1 beta was observed in the PBT gills infected with Cardicola spp. (28-77 days post-transfer). Furthermore, IgM (19 -fold increase) and MHC-I (11.5-fold increase) transcription was strongly up-regulated in gill samples of PBT infected with C orientalis relative to uninfected fish but not in fish infected with C opisthorchis. Cardicola-specific DNA was first detected in the host 14 days post-transfer (DPT) to sea-cages which was 55 days earlier than the first detection of parasite eggs and adults by microscopy. Oral administration of PZQ did not have an immediate effect on parasite DNA presence in the host and the DNA presence started to reduce after 24 days only in the host heart. The results provide evidence of an immune response in early age sea cage cultured juveniles of PBT naturally infected with C. orientalis and C opisthorchis. This response, whilst not protective against primary infection, provides evidence that immunisation at an early age may have potential as a health strategy. (C) 2016 Elsevier Ltd. All rights reserved.
  • Sang Phil Shin; Hiroe Ishitani; Sho Shirakashi
    AQUACULTURE 464 37 - 41 2016年11月 [査読有り]
     
    Since the identification of Kudoa septempunctata as a causative agent of human food poisoning, Kudoa infections have becomea serious concern in the aquaculture of olive flounder (Paralichthys olivaceus). In order to ensure the safety of cultured flounder, various methods have been developed to detect K. septempunctata. However, less attention has been paid for inspection and detection of other Kudoa species. To date, six Kudoa spp. have been reported from olive flounder, 3 species each fromthe trunkmuscle, 2 species fromthe brain, and one species from the heart. During our routine inspection of cultured olive flounder, we isolated several Kudoa species including Kudoa igami and Kudoa ogawai in addition to the list of previously reported species. In the present study, a multiplex PCR (mPCR) was developed to detect all Kudoa spp. known to date fromolive flounder in Japan. ThemPCR also differentiate K. septempunctata among other Kudoa spp. simultaneously. The developed mPCR successfully detected seven Kudoa spp. and differentiated K. septempunctata with a sensitivity of 103 myxospores. Thus, mPCR offers a reliable and relatively simple method to detect Kudoa infection in olive flounder, specifically aiming to identify K. septempunctata infection.Statement of Relevance: Olive flounder Paralichthys olivaceus is one of themost important fish species for commercial aquaculture and fishery trading in Japan and Korea. Infections of microscopic myxozoan parasite of genus Kudoa (Myxozoa: Multivalvulida) has become a serious concern in flounder culture since the recent identification of Kudoa septempunctata as a causative agent of human food poisoning. Although various detection methods have been developed for the inspection of K. septempunctata, relatively little attentions are given to other Kudoa spp. We added K. ogawai and K. igami to the list of Kudoa spp. infecting olive flounder and developed multiplex PCR to simultaneously detect Kudoa spp. and distinguish K. septempunctata. This offers relatively simple and method to inspect Kudoa spp. in cultured flounder. (C) 2016 Elsevier B.V. All rights reserved.
  • 白樫 正; 小川 和夫
    魚病研究 51 3 92 - 98 日本魚病学会 2016年09月 [査読有り]
     
    Fish blood flukes (FBFs) are the most important digenean parasites in marine finfish aqua culture due to their high pathogenicity. Numerous eggs accumulate in gill lamellae and capillary vessels in various organs, interfere the blood flow. This causes fish to suffocate to death or leads to other fatal health problems. In Japan, important culture fish, such as amberjacks, bluefin tuna and tiger puffer are affected by FBFs of different taxa; namely Paradeontacylix spp., Cardicola spp. and Psettarium spp., respectively. FBFs are relatively host specific and utilize a complex two-host lifecycle. To date, the lifecycles have been elucidated for only a handful marine FBF species and all use terebellid polychaetes as the intermediate host. Chemotherapy with the oral treatment of praziquantel is effective and commonly used in fish farms as a sole control measure against FBFs. The development of prevention method is expected with the recent advances in knowledge on the biology of FBFs.
  • 申, 相弼; 西村, 知代; 小川, 和夫; 白樫, 正
    魚病研究 51 3 128 - 131 2016年09月 [査読有り]
     
    海産魚の脳に寄生する粘液胞子虫Kudoa yasunagaiの陸上施設における防除には飼育用水の紫外線処理が有効であることが示されている。防除に必要な最低照射量を検討するため，0，5，15，30mJ/cm2の紫外線処理を施した用水でヒラマサ稚魚を約7週間飼育して，脳における本虫の寄生状況を比較した。無処理区では開始3週目から検鏡，PCRで寄生が確認され，6週目には寄生率45%に達した。一方，5mJ/cm2区では寄生は見られたものの，寄生率は10%を超えず，脳内の胞子数も少ない傾向にあり，ある程度の寄生抑制効果が認められた。照射量15mJ/cm2以上の試験区では寄生は見られず，本虫の防除に必要な最低照射量は5mJ/cm2以上，15mJ/cm2以下であることが示された。
  • Sho Shirakashi; Kazuo Ogawa
    FISH PATHOLOGY 51 3 92 - 98 2016年09月 [査読有り]
     
    Fish blood flukes (FBFs) are the most important digenean parasites in marine finfish aqua culture due to their high pathogenicity. Numerous eggs accumulate in gill lamellae and capillary vessels in various organs, interfere the blood flow. This causes fish to suffocate to death or leads to other fatal health problems. In Japan, important culture fish, such as amberjacks, bluefin tuna and tiger puffer are affected by FBFs of different taxa; namely Paradeontacylix spp., Cardicola spp. and Psettarium spp., respectively. FBFs are relatively host specific and utilize a complex two-host lifecycle. To date, the lifecycles have been elucidated for only a handful marine FBF species and all use terebellid polychaetes as the intermediate host. Chemotherapy with the oral treatment of praziquantel is effective and commonly used in fish farms as a sole control measure against FBFs. The development of prevention method is expected with the recent advances in knowledge on the biology of FBFs.
  • Yasuo Agawa; Kazuki Tani; Syuhei Yamamoto; Chihaya Hirano; Sho Shirakashi
    FISHERIES SCIENCE 82 5 827 - 833 2016年09月 [査読有り]
     
    Skin fluke Neobenedenia girellae infection is a chronic problem in marine finfish aquaculture. Current control measures rely on bath treatments, which are labor intensive and cause significant stress to fish. Although there is an urgent need to develop a strategy to prevent this infection, little is known about the distribution of the larval stage of the skin fluke around culture cages. We aimed to develop a Neobenedenia-specific real-time quantitative polymerase chain reaction (qPCR) assay to detect and quantify N. girellae larvae in environmental water. New PCR primers targeting mitochondrial DNA were designed and showed specificity for N. girellae among five capsalid monogeneans known to occur in Japanese waters. A single N. girellae oncomiracidium is estimated to carry 2.2 million copies of mitochondrial DNA, and the qPCR assay reliably detects DNA equivalent to half of that. We used this qPCR to quantify N. girellae larvae from a fish culture site. Analyses of water samples collected inside shaded culture cages of Seriola dumerili revealed lower larval density than that in the unshaded cage. The results indicate the usefulness of this newly developed qPCR assay for monitoring skin fluke larval density and distribution in fish farms.
  • Sang Phil Shin; Sho Shirakashi; Shogo Hamano; Keitaro Kato; Lissette Trejos Lasso; Hiroshi Yokoyama
    MOLECULAR PHYLOGENETICS AND EVOLUTION 98 337 - 345 2016年05月 [査読有り]
     
    Kudoa rayformis n. sp. (Myxozoa; Multivalvulida) was observed in the trunk muscle of Pacific sierra Scomberomorus sierra caught off the coast of Tonosi, Panama. The species formed pseudocysts in myofibers and infection was subclinical. The myxospores possessed four polar capsules and spore valves, one of which had a distinct filamentous extension. This unique morphological characteristic of the myxospore validated this as a new species of Kudoa. Genetically, K. rayformis n. sp. is closest to K. inornata, with 98% and 91% similarity in 18S and 28S rDNA, respectively, but its spore shape was clearly distinct. The 18S rDNA and concatenated sequences from K. rayformis were used in molecular phylogenetic analyses of kudoids to examine the congruence of phylogeny with infection site tropism, spore morphology and cyst/pseudocyst formation. The results demonstrated that the phenotypic traits were correlated with the phylogeny of Kudoidae, and that the biological features of K. rayformis originated from the ancient Kudoidae as exhibited by the non-specific infection site tropism and the ability to infect muscle and form pseudocysts. (C) 2016 Elsevier Inc. All rights reserved.
  • Sho Shirakashi; Kazuki Tani; Katsuya Ishimaru; Sang Phil Shin; Tomoki Honryo; Hiro'omi Uchida; Kazuo Ogawa
    PARASITOLOGY INTERNATIONAL 65 2 128 - 136 2016年04月 [査読有り]
     
    Fish blood flukes (Aporocotylidae) are important pathogens of farmed finfish around the world. Among them, Cardicola spp. infecting farmed tuna are considered to be serious threats to tuna farming and have received tremendous attention. We conducted periodical samplings at a tuna farming site in Japan between January and May, 2015 to determine the life cycle of Cardicola spp. We collected over 4700 terebellid polychaetes from ropes, floats and frames of tuna culture cages and found nearly 400 infected worms. Sporocysts and cercariae found in Nicolea gracilibranchis were genetically identified as Cardicola orientalis by 28S and ITS2 ribosomal DNA sequences. This was the first discovery of the intermediate host for this parasite species. Infection prevalence and the abundance of N. gracilibranchis significantly varied between sampling points and the highest number of infected terebellids were collected from ropes. We also demonstrated morphologically and molecularly that asexual stages found in a single Amphitrite sp. (Terebellidae) and adult worms isolated from farmed juvenile tuna were Cardicola forsteri. This is the first report of C forsteri in Pacific bluefin tuna (PBT) Thunnus orientalis in Japan. Our results demonstrated that all three species of Cardicola orientalis, C. forsteri and Cardicola opisthorchis exist in Japanese farmed PBTs and that they all use terebellid polychaetes as the intermediate hosts. (C) 2015 Elsevier Ireland Ltd. All rights reserved.
  • Sho Shirakashi
    NIPPON SUISAN GAKKAISHI 81 5 875 - 875 2015年09月 [査読有り]
  • Sho Shirakashi; Chihaya Hirano
    AQUACULTURE 443 1 - 4 2015年06月 [査読有り]
     
    Skin fluke causes chronic problems in marine finfish aquaculture. Their eggs possess a long filamentous appendage that allows them to easily attach to culture cages. Fish farmers periodically change and clean cage nets to remove eggs from the culture sites. However, there is very little information about the accumulation rate and distribution of skin fluke eggs on culture cages. We conducted an experiment at a culture site to assess the accumulation of eggs of the Neobenedenia girellae skin fluke at different culture cage depths. In all three trials, we observed the highest egg accumulation in shallow areas, and the egg number decreased with the depth; however, the second highest accumulation was observed at the deepest depth. These distribution patterns likely reflect the behavior of fish within the cage. The highest accumulation rate was 161.2 eggs/cm(2)/day, with an estimated daily accumulation of more than 10 million eggs on the entire cage ( excluding the cage floor). Such information is useful for optimizing and managing cage net changing and also for the development of a new method of removing/killing parasite eggs. (C) 2015 Elsevier B.V. All rights reserved.
  • Chihaya Hirano; Katsuya Ishimaru; Sho Shirakashi
    FISH PATHOLOGY 50 1 23 - 28 2015年03月 [査読有り]
     
    Diurnal rhythms in egg laying and hatching of the skin fluke Neobenedenia girellae were investigated under different light conditions. Egg production was monitored every 2 h for 3 days under two light conditions (darkness and natural light) using Seriola dumerili infected with multiple Neobenedenia girellae as well as black molly Poecilia sphenops that had been transplanted by a single mature fluke. In any cases, oviposition was continuously observed with no obvious diurnal rhythm. The maximum egg production was approximately 60 eggs/h/worm for both multiple- and single-infection. Such high fecundity emphasizes the importance of the prompt eradication of mature flukes from culture sites to prevent parasite multiplication. The hatching rhythm was monitored under natural light condition and controlled light condition with LED lamp (24L, 12L:12D, 24D). An obvious hatching rhythm with a monomodal peak in the morning was detected under natural light condition. This rhythm was different from that previously reported for Benedenia seriolae whose hatching has bimodal peaks in the early morning and evening. Under controlled light conditions, no such pattern was observed and the overall hatching was considerably less than that under natural light condition.
  • Jimena Balli; Ivona Mladineo; Sho Shirakashi; Barbara F. Nowak
    Advances in Tuna Aquaculture: From Hatchery to Market 253 - 272 2015年01月 [査読有り]
     
    This chapter describes diseases in ranched and farmed bluefin tunas. Blood fluke infection, caused by three different species from genus Cardicola is the main problem in ranching in Australia and farming in Japan. These infections have been managed using praziquantel applied as oral treatment. Swimmer syndrome caused by a scuticociliate Uronema nigricans caused mortalities in southern bluefin tuna (SBFT) but does no longer appear to be an issue. Photobacterium damsela subsp. piscicida caused mortalities in ranched Atlantic bluefin tuna (ABFT) in 2003 and 2004. Closing life cycles for SBFT and ABFT will result in more health issues as naïve fish from hatcheries will be transferred to marine cages, as has been witnessed for hatchery-reared Pacific bluefin tuna (PBFT) in Japan. Intensification of ranching and global challenges may contribute to other health problems. While there are some species-specific and regional differences there are many common issues suggesting effectiveness of international research collaborations.
  • Sho Shirakashi; Tomoyo Nishimura; Nagaharu Kameshima; Hiroshi Yamashita; Hiroe Ishitani; Katsuya Ishimaru; Hiroshi Yokoyama
    FISH PATHOLOGY 49 3 141 - 144 2014年09月 [査読有り]
     
    Kudoa infections have recently become a serious concern in Japanese fisheries. Some species not only cause fish diseases and reduce the commodity value of fish, but also affect human health. We investigated whether the ultraviolet (UV) treatment of culture water prevented infections with two species of Kudoa, K. yasunagai and K. amamiensis, in Seriola lalandi and S. quinqueradiata, respectively. Rearing in untreated filtered seawater resulted in high infection rates, suggesting that the physical filtration systems used in this study did not sufficiently remove the infective stages of these Kudoa species. In contrast, commercially available UV irradiation system effectively prevented the infections with K. yasunagai and K. amamiensis.
  • Shinji Yamamoto; Atsuhiko Fukushima; Katsuya Ishimaru; Sho Shirakashi
    FISHERIES SCIENCE 80 5 1021 - 1026 2014年09月 [査読有り]
     
    The skin fluke Neobenedenia girellae has become a serious problem in Japan since the 1990s. Present control methods focus on the removal of the attached parasite and these post-infection treatments are often labor intensive, time consuming, and/or stressful to fish. Chub mackerel Scomber japonicus are highly susceptible to N. girellae. However, because of their sensitive nature, bath treatments may cause mortality. In this study, we investigated the efficacy of cage shading to reduce skin fluke infection and the frequency of conventional post-infection treatments. Juvenile mackerel were reared in cages with or without shade for 3 months and their skin fluke infections were monitored. We performed either freshwater baths or oral administration of praziquantel if fluke intensity exceeded the given criteria. In unshaded cages, 3 total bath treatments or 6 total drug treatments were conducted. In contrast, no treatment was required for the shaded cage. The overall fluke intensity in the shaded cage was less than half that of the unshaded cages, despite the lack of treatments. This study demonstrated for the first time the practical use of shading in fish farms to reduce skin fluke infection.
  • Hiroshi Yokoyama; Jun Suzuki; Sho Shirakashi
    PARASITOLOGY INTERNATIONAL 63 4 571 - 579 2014年08月 [査読有り]
     
    Since Kudoa septempunctata in olive flounder (Paralichthys olivaceus) was indicated to cause food poisoning in humans, other Kudoa species are suspected to have pathogenic potential. Recently, a myxosporean possibly associated with food poisoning in humans consuming raw Pacific bluefin tuna, Thunnus orientalis, was identified as Kudoa neothunni. This is a known causative myxosporean of post-harvest myoliquefaction in yellowfin tuna Thunnus albacares. Regardless of the significant differences in the 28S rDNA sequence and the pathological character (with/without myoliquefaction) between the two T. orientalis and T. albacares isolates, they were considered intraspecific variants of K. neothunni. However, the light and low-vacuum electron microscopic observations in the present study revealed that there were two morphotypes; pointed- and round-type spores, which were significantly differentiated by the ratio of suture width to spore width. Furthermore, the two morphotypes were genetically distinguishable by the 28S rDNA sequence analysis. This morphological and molecular evidence validates that the two Kudoa types are separate species, and thus the pointed- and round-types are referred to as K. neothunni and Kudoa hexapunctata n. sp., respectively. K. neothunni was detected solely from T. albacares, whereas K. hexapunctata n. sp. was found not only from T. orientalis but also from T. albacares. (C) 2014 Elsevier Ireland Ltd. All rights reserved.
  • Sho Shirakashi; Koji Yamane; Hiroe Ishitani; Tetsuya Yanagida; Hiroshi Yokoyama
    PARASITOLOGY RESEARCH 113 7 2515 - 2524 2014年07月 [査読有り]
     
    Three species of the Kudoid parasite (Myxozoa: Multivalvulida) were observed in the somatic muscle of Japanese parrotfish Calotomus japonicus caught off the coast of western Japan. All three species formed pseudocysts in myofibers and caused subclinical infections. The three Kudoa species were distinguished by spore morphology, as well as their 18S and 28S rDNA sequences. We identified a previously undescribed taxa Kudoa igami n. sp. with spores that were stellate with rounded peripheral edges and five to six polar capsules (prevalence 29.3 %). Kudoa igami n. sp. were morphologically most similar to Kudoa neothunni but were distinguishable by a more rounded shape in the apical view. Molecular analyses demonstrated that the K. igami n. sp. is closely related to Kudoa thalassomi; however, the similarity in the 28S rDNA sequence was <96 % and the spore morphology was different. We found Kudoa thalassomi in one sample (prevalence 2.4 %), which is a new host and geographical record for this species. Kudoa lateolabracis, which causes postmortem myoliquefaction in Chinese sea bass Lateolabrax sp. and olive flounder Paralichthys olivaceus was found in Japanese parrotfish (prevalence 41.5 %) for the first time, but did not cause myoliquefaction. We also expanded the host record for the brain-infecting Kudoa yasunagai (prevalence 94.1 %). In addition, an unidentified microsporidia was observed in the somatic muscle (prevalence 23.3 %).
  • K. Ogawa; S. Shirakashi; H. Ishitani
    PARASITOLOGY INTERNATIONAL 63 2 473 - 478 2014年04月 [査読有り]
     
    In vitro spermatophore formation and insemination of Neobenedenia girellae (Monogenea: Capsalidae, Benedeniinae) were recorded on video and described for the first time. Upon contact of two individuals, the anterior adhesive discs of the donor firmly attached to the dorsal tegument of the recipient and the donor's fore body strongly contracted such that the genital pore region protruded and the penis was pushed anteriorly to protrude through the genital pore. It is hypothesised that the donor penis mechanically damaged the tegument of the recipient. The sperm and spermatophore matrix were released together through the penis, which was placed under the left anterior attachment disc immediately behind the adhesive pad. The spermatophore matrix containing the spermatozoa became solid and attached to the dorsal surface of recipient's body. When observed under scanning electron microscopy, the spermatophores were irregularly shaped, with a diameter of 52-83 mu m. Under light microscopy they consisted of a proximal eosinophilic matrix portion and a distal thin-walled portion containing spermatozoa. Both parts were enclosed with a thin outer casing. Insemination occurred during and after spermatophore formation. Three types of insemination were recorded, unilateral and mutual insemination and self-insemination. The presence of self-insemination indicates that even a single N. girellae on a cultured fish may cause a significant parasite infection in the entire aquaculture system. (C) 2013 Elsevier Ireland Ltd. All rights reserved.
  • Katsuya Ishimaru; Takumi Matsuura; Kazunobu Tsunemoto; Sho Shirakashi
    DISEASES OF AQUATIC ORGANISMS 108 1 45 - 52 2014年02月 [査読有り]
     
    Kudoid myxozoans pose serious chronic problems in marine fisheries by causing pathological damage to host fish, reducing the market value of infected fish and potentially threatening public health. Kudoa yasunagai is a cosmopolitan parasite that infects the brains of various marine fishes, including important aquaculture species. We developed a quantitative PCR assay to detect K. yasunagai in sea water, and we used it to monitor abundance of the parasite in the environment and in culture through spring and winter. Quantitative PCR detected K. yasunagai DNA from sea water, with the lowest reliable threshold of 162 copies 28S rDNA l(-1). Parasite DNA was detected sporadically in sea water throughout the study period of May through December 2012. The highest level of detected DNA occurred in mid-December (winter), at 117 180 copies-equivalent to an estimate of over 200 myxospores l(-1). Parasite DNA was generally not detected in August or September, the period with the highest water temperature. The reason for this observation is unknown, but the timing of parasite development may play a role. The amount of detected DNA was not different between unfiltered culture water and water filtered through a high-speed fiber filtration system. This result and the past incidence of high infection rate of fish reared in filtered water indicate that the mechanical removal of K. yasunagai from culture water is difficult. Detecting the precise onset and time window of infection in host fish will be an important step in the development of measures to control this economically important parasite.
  • Mark Polinski; Sho Shirakashi; Andrew Bridle; Barbara Nowak
    FISH & SHELLFISH IMMUNOLOGY 36 1 61 - 67 2014年01月 [査読有り]
     
    Infections by two blood fluke species, Cardicola orientalis and Cardicola opisthorchis, currently present the greatest disease concern for the sea-cage culture of Pacific bluefln tuna (PBT) - a species of high global economic importance and ecological concern. In this study, we aimed to rapidly, quantitatively, and differentially identify infections by these two parasite species in cultured PBT as well as identify potential host immune responses. Using real-time qPCR, we were successful in quantitatively detecting parasite-specific DNA from within host blood, gill, and heart tissues; positively identifying parasitic infections 44 days earlier than microscopy methods previously employed. Both gill and heart became heavily infected by both parasite species in PBT within two months of sea-cage culture, which was only mitigated by the administration of anthelmintic praziquantel. Nevertheless, fish were observed to mount an organ specific transcriptive immune response during infection that mirrored the relative quantity of pathogenic load. In heart, significant (3-6 fold) increases in IgM, MHC2, TCR beta, and IL-8 transcription was observed in infected fish relative to uninfected controls; whereas in the gills only IgM transcription was observed to be induced (11 fold) by infection. Interestingly, the relative quantity of IgM transcription was highly correlated to the relative abundance of C orientalis but not C opisthorchis DNA in the gill samples, even though this organ showed high prevalence of DNA from both parasite species. Taken together, these findings indicate that although ineffective at combating infection during primary exposure, a cellular immune response is mounted in PBT as a potential rejoinder to future Cardicola exposure, particularly against C. orientalis. Although future investigation into antibody effectiveness will be needed, this work provides valuable preliminary insight into host responsiveness to Cardicola infection as well as additional support for the need of anthelmintic treatment following primary parasite exposure during PBT culture. (C) 2013 Elsevier Ltd. All rights reserved.
  • Katsuya Ishimaru; Ryoma Mine; Sho Shirakashi; Eri Kaneko; Kazushige Kubono; Tokihiko Okada; Yoshifumi Sawada; Kazuo Ogawa
    AQUACULTURE 402 24 - 27 2013年07月 [査読有り]
     
    Blood flukes of the genus Cardicola cause significant problems in the bluefin tuna farming around the world. In Japan, the mortality of the juvenile Pacific bluefin tuna Thunnus orientalis (PBT) caused by C. orientalis and C. opisthorchis has become a serious issue in the tuna farming industry in recent years. Oral treatment with praziquantel (PZQ) is highly effective against blood flukes and is indispensable for sustainable tuna farming. To develop a proper and safe drug treatment procedure, we investigated the minimum effective dose and pharmacokinetics of PZQ in juvenile PBT. Juvenile tuna were orally administered various doses of PZQ (0, 3.75, 7.5, 15 and 30 mg/kg body weight (BW)) once a day for 3 consecutive days, and the occurrence of C. opisthorchis before and after the treatment was compared. A significant decrease in the number of flukes was observed in the 3.75 mg/kg group, and complete eradication of flukes was achieved at dosages of 7.5 mg/kg and greater. This result indicates that the minimal effective dose of PZQ for treating C. opisthorchis is between 3.75 and 7.5 mg/kg, which is less than 1/20 of the treatment dose used for treating the skin fluke Benedenia seriolae in yellowtail culture. We used high-performance liquid chromatography analysis to assess the temporal changes in the concentrations of PZQ in serum, muscle, the liver and the kidney after a single administration of PZQ at 15 mg/kg BW. The PZQ concentration in the tissues peaked between 0.5 and 1.5 h following administration, and PZQ was undetectable after 24 h. The highest serum concentration was 2.0 mu g/mL, which is likely to be the lethal dose for C. opisthorchis. These results suggest that PZQ treatment is a highly effective and relatively safe method to control blood flukes in the tuna farming industry. (c) 2013 Elsevier B.V. All rights reserved.
  • Sho Shirakashi; Chihaya Hirano; Hiroe Ishitani; Katsuya Ishimaru
    AQUACULTURE 402 19 - 23 2013年07月 [査読有り]
     
    Skin fluke infection is a major parasitic problem in the aquaculture industry. Present control measures such as bath treatments are effective for removing flukes from fish but require extensive labour and time. Moreover, bath treatments cause great stress to the fish, and occasionally lead to post-treatment mortality. Our ultimate goal is to develop a culture technique that prevents or lowers the chance of fish encountering larval skin flukes, thus reducing infection. However, little is known about when and where these infections occur on fish farms. We conducted a field experiment at a culture site to determine the diurnal pattern of skin fluke infection at different water depths. Juvenile amberjack, Seriola dumerili, were placed in enclosed mesh cages and exposed to skin flukes at depths of 0, 2 or 4 m for 4 h during different times of the day. A Neobenedenia girellae infection occurred predominantly at the surface during the mid-day. The infection rate declined considerably during the night. The parasite burden was significantly decreased with water depth, and up to an 80% and 95% reduction in intensities was observed when fish were exposed at a depth of 2 and 4 m, respectively. These results suggest that skin fluke infection can be significantly reduced by systematic management strategy and modification of culture techniques. (c) 2013 Elsevier B.V. All rights reserved.
  • Sho Shirakashi; Kazunobu Tsunemoto; Claire Webber; Kirsten Rough; David Ellis; Kazuo Ogawa
    FISH PATHOLOGY 48 1 1 - 4 2013年03月 [査読有り]
     
    We determined the identity of an aporocotylid blood fluke discovered in the gills of southern bluefin tuna Thunnus maccoyii ranched in Australia. Both morphological and molecular data indicate the parasite is Cardicola orientalis, reported previously only from Pacific bluefin tuna T orientalis in Japan. Over 70 C. orientalis adults were retrieved from a single gill arch of an infected southern bluefin tuna and numerous eggs were observed in the gill filaments suggesting possible pathology to the host. In addition, we obtained new information on morphological characteristics and molecular sequences of C. forsteri infecting the heart of T maccoyii. This is the first report of C. orientalis in T maccoyii, which may have a significant impact on the ranching industry of southern bluefin tuna and warrants further investigation.
  • Hiroshi Yokoyama; Shigehiko Urawa; Daniel Grabner; Sho Shirakashi
    PARASITOLOGY INTERNATIONAL 61 4 594 - 598 2012年12月 
    Henneguya cartilaginis n. sp. (Myxozoa: Myxosporea) is described from wild masu salmon Oncorhynchus masou masou in Hokkaido, Japan. H. cartilaginis n. sp. produced white cysts, up to 3 mm in size, in the head of masu salmon. Infected fish exhibited cranial protrusion due to the cysts. Spores (11.4 x 8.6 mu m) of H. cartilaginis n. sp. were egg-shaped with the posterior end more pointed and possessed two caudal appendages (34.2 mu m average length). Histological observations revealed that large plasmodia possessing fine fibrous pseudopodia on the surface developed in the head cartilage. H. cartilaginis n. sp. resembles H. cerebralis, which was described from the cranial cartilage of Kosogol grayling Thymallus nigrescens in Mongolia. However, they were distinguishable by spore morphology. Molecular analysis of the 18S rDNA sequences indicated that H. cartilaginis n. sp. was most closely related to Henneguya zschokkei, H. nuesslini and H. salminicola of salmonid fish, with genetic similarities of 95.3%, 95.1% and 93.9%, respectively. Based on these differences in spore morphology, molecular data, the site of infection and geographical distribution, the present species is considered to be a new species. (C) 2012 Elsevier Ireland Ltd. All rights reserved.
  • Sho Shirakashi; Akinobu Morita; Katsuya Ishimaru; Shigeru Miyashita
    DISEASES OF AQUATIC ORGANISMS 101 2 123 - 130 2012年11月 [査読有り]
     
    We monitored infection by a brain-infecting myxozoan Kudoa yasunagai in hatchery-reared juvenile yellowtail Seriola quinqueradiata at a culturing site in Japan. Infection was detected by PCR and microscopic observation once every 1 to 4 wk during 2010 and 2011. In both years, we detected first infection in mid-July by PCR. Prevalence increased rapidly after the onset of infection, peaking at 100% within 4 wk. Parasites required less than 10 d to reach the brain after invasion. Development of plasmodia and formation of cysts took 4 to 8 wk. Infection did not reach a plateau and number of cysts tended to decline over time, suggesting possible recovery from the infection. A drastic decline in infection prevalence was observed during the season of highest water temperature (>30 degrees C) in 2010. To understand this phenomenon, we conducted a laboratory experiment to compare infection prevalence and cyst formation in fish kept at 25 degrees C and 30 degrees C. However, we could not detect obvious differences between the treatment groups during the 4 wk of the experiment. There was no apparent pathology associated with the infection. These results suggest that pathological effects of K. yasunagai may differ between fish species or that other factors are important in the development of infectious signs.
  • H. Yokoyama; T. Yanagida; S. Shirakashi
    PARASITOLOGY RESEARCH 110 6 2247 - 2254 2012年06月 [査読有り]
     
    Kudoa ogawai n. sp. (Myxozoa; Multivalvulida) is described from the trunk muscle of Pacific barrelfish Hyperoglyphe japonica caught in Japan. Oval to ellipsoidal cysts, white to yellowish in colour, 1-2 mm in size, were filled with numerous spores having four polar capsules. Spores were stellate with rounded peripheral edges in apical view, and garlic shaped with four prominent apical projections in side view. Average (range) spore size was 13.3 (12.0-14.2) mu m in width and 9.0 (8.3-9.7) mu m in length. The spore dimensions and the apical projections of K. ogawai n. sp. were clearly distinguishable from the other muscle-infecting species. Molecular analyses of 18S rDNA and 28S rDNA sequences showed that K. ogawai n. sp. is closely related to Kudo iwatai and Kudoa hemiscylli (95% and 92% genetic similarity, respectively), but the present species is morphologically distinct from the two species. Phylogenetic analysis of 18S and 28S rDNA placed K. ogawai n. sp. sister to all Kudoa spp. available in GenBank.
  • Sho Shirakashi; Yoshiki Kishimoto; Ryuhei Kinami; Hiromitsu Katano; Katsuya Ishimaru; Osamu Murata; Naoki Itoh; Kazuo Ogawa
    PARASITOLOGY INTERNATIONAL 61 2 242 - 249 2012年06月 [査読有り]
     
    Infestations of blood flukes of the genus Cardicola have been observed in juvenile Pacific bluefin tuna (PBT) cultured in Japan. Infected fish harbor large numbers of parasite eggs in their gills. Although the link between blood fluke infection and juvenile mortality is not clear, accumulation of parasite eggs appears to be pathogenic to the fish. We investigated the origins, general morphology/distribution, and histopathology of these eggs in artificially produced 0 yr old PBT. Dead and live fish were sampled on several occasions from two culture facilities in Wakayama prefecture, Japan. The number of eggs in each gill filament was enumerated under a microscope. In addition, we estimated the total number of eggs by dissolving the gills in a weak NaOH solution. We observed two morphologically distinct egg types in the gill filaments, smaller, oval shaped eggs in the gill lamellae and larger, crescent shaped eggs that occurred primarily in the filamentary arteries. Based on the ITS2 sequence, the ovoid and crescent shaped eggs were identified as C on entails and C. opisthorchis, respectively. Eggs of the former species were more abundant (maximum: 6900 per filament) than the latter (maximum: 1400), but the number was highly variable among filaments. The eggs of the latter species were relatively evenly distributed among the filaments. In a heavily infected individual, we estimated a total of >4.5 million eggs were present in the gills on one side of the fish. The number of eggs from the two species was positively correlated to each other and the dead fish tended to harbor more eggs than the live fish. Histological observation revealed host responses around the eggs, including encapsulation by fibroblasts and nodule formation, as seen in response to other aporocotylid eggs. In addition, we observed widespread fusion of gill lamellae and blockage of the filamentary arteries in some instances. Our results provide information that can be used for routine diagnosis of Cardicola blood flukes in cultured tuna and suggest they represent a risk to juvenile PBT. (C) 2011 Elsevier Ireland Ltd. All rights reserved.
  • D. S. Grabner; H. Yokoyama; S. Shirakashi; R. Kinami
    AQUACULTURE 338 36 - 40 2012年03月 [査読有り]
     
    Kudoa infections in muscle tissue can be a serious problem for fisheries and aquaculture of olive flounder (Paralichthys olivaceus) due to post-mortem myoliquefaction that makes the fish unmarketable. Recently, cases of a new food poisoning of human associated with ingestion of raw olive flounder infected with Kudoa septempunctata have increased in Japan. In the present study, diagnostic PCR assays were developed to detect and distinguish Kudoa spp. from olive flounder muscle. Kudoa 18S and 28S rDNA were amplified from infected fish by universal primers and sequenced. Blast searches with the obtained sequences revealed the presence of not only K. septempunctata and K. thyrsites, but also K. lateolabracis which was detected for the first time in olive founder. Comparison of the 28S rDNA sequences obtained from K. thyrsites isolated in the present study with a previous isolate from GenBank indicated the existence of two genetic lineages of this species, both infecting olive flounder. Alignments of partial 28S rDNA sequences were used to design primers for each of the three Kudoa spp. Specificity of each primer pair was tested by PCR with DNA from different myxozoans and host DNA. For sensitivity testing, the target sequence was ligated into a plasmid vector and cloned. PCR was conducted with host DNA spiked with dilution series of the plasmid. Additionally, a practical test of the primers was conducted in comparison to classical diagnostic methods with 10 olive flounders from a fish farm suspected to be infected with Kudoa spp. All three primer pairs were specific for the respective parasite and amplified neither host DNA nor DNA of other tested myxozoans. Primers for K. septempunctata approximately amplified down to 0.06. those for K. thyrsites 0.001 and for K. lateolabracis 0.1 spores per reaction (240, 4 and 400 spores per 1 g of muscle tissue). The diagnostic PCR assay developed in this study was shown to be more effective for detection of K. septempunctata from cultured olive flounder (10 out of 10 fish positive) than microscopic detection of spores in tissue homogenates (5 out of 10 fish positive). K. thyrsites and K. lateolabracis were not detected in the 10 flounders tested. This novel PCR assay will facilitate the screening and monitoring process for Kudoa infections and allow improved disease management in olive flounder aquaculture facilities. It will also improve food safety testing to avoid human consumption of Kudoa infected fillets. (c) 2012 Elsevier B.V. All rights reserved.
  • Development of feeding technology, formula diet, and parasite countermeasures for Pacific bluefin tuna, Thunnus orientalis.
    Y. Ishibashi; K. Takii; O. Murata; K. Ishimaru; A. Biswas; G. Nakase; S. Shirakashi
    Proceedings of the Final Global COE International Symposium of Kinki University, Kushimoto, November 23-24, 2012, Kinki Univ. Press 14 - 25 2012年
  • Sho Shirakashi; Melanie Andrews; Yoshiki Kishimoto; Katsuya Ishimaru; Takahiko Okada; Yoshifumi Sawada; Kazuo Ogawa
    AQUACULTURE 326 15 - 19 2012年01月 [査読有り]
     
    Aquaculture of tuna has shown exponential growth in the recent years. In association with the global development of tuna aquaculture, problems with parasitic infections have arisen. Among the parasites found in cultured tuna, blood flukes are considered to be a significant threat as their eggs accumulate in the gills and interfere with the gas exchange process. To date, two species of blood fluke from the genus Cardicola have been found in Pacific bluefin tuna (Thunnus orientalis, PBT) cultured in Japan. We conducted an experiment to develop a drug treatment against the blood flukes of cultured tuna. Artificially produced juvenile tuna that were naturally infected with blood flukes were orally administered with anthelmintic praziquantel (PZQ) of 150, 15, 1.5 and 0 mg kg(-1) BW for three consecutive days, and differences in the abundance of adults and eggs in the gills were assessed. In the fish given 150 and 15 mg kg(-1) BW PZQ, adult worms in the heart ventricle were eradicated by day 8 post treatment with the number of eggs in the gills gradually declining over time. However, small numbers of adults re-appeared by week 3 or 5 post treatment. The drug does not seem to affect eggs as viable miracidia were observed throughout the experiment. Mortalities in the two lower dose groups were significantly higher than the groups in which PZQ doses were shown to be effective. The study empirically demonstrated the efficacy of PZQ on Cardicola blood flukes and that the parasite significantly affects the survival of juvenile PBT. The oral PZQ treatment may be an essential practice for sustainable aquaculture of PBT. (C) 2011 Elsevier B.V. All rights reserved.
  • Shinji Yamamoto; Sho Shirakashi; Satoshi Morimoto; Katsuya Ishimaru; Osamu Murata
    AQUACULTURE 319 1-2 53 - 57 2011年09月 [査読有り]
     
    Outbreaks of skin flukes and associated mortalities have been observed in cultured chub mackerel, Scomber japonicus. Although freshwater bathing effectively removes the parasites, large post-treatment mortalities are occasionally observed especially under high water temperature conditions due to the stress from handling and confinement. Since outbreaks of the skin fluke infections often occur in high temperature seasons, development of an effective and safe control method is essential for the advancement of mackerel aquaculture. The present study aims to: 1) identify the skin fluke of cultured chub mackerel and 2) develop an alternative control measure using oral drug administration. The skin fluke was identified as Neobenedenia girellae by morphology and molecular data targeting ITS region of rDNA. Two trials of oral administration of praziquantel (PZQ), a common anthelmintic, were conducted and parasite intensity was compared before and after the treatment and between treated and untreated control fish. Fish rejected PZQ-coated commercial pellets, but oral administration was successfully achieved using frozen krill as a basal diet The three-day administration with a dose of 150 mg.kg(-1) BW.day(-1) resulted in over 80% reduction in worm intensity. However, some proportion of the skin flukes survived the drug treatment The resistance to PZQ does not relate to worm's developmental stage. Freshwater bathing was more effective and eradicated the parasite, but some post-treatment mortality of host fish was observed. Moreover, the parasite intensity drastically increased after the freshwater bathing, possibly due to stress and loss of mucus during the bathing. The study indicates the PZQ oral treatment is effective to control N. girellae in chub mackerel aquaculture when the drug is properly administrated with an appropriate feeding technique. (C) 2011 Elsevier B.V. All rights reserved.
  • K. Ogawa; K. Ishimaru; S. Shirakashi; I. Takami; D. Grabner
    PARASITOLOGY INTERNATIONAL 60 3 307 - 312 2011年09月 [査読有り]
     
    A new aporocotylid blood fluke is described, based on specimens from the ventricle of the Pacific bluefin tuna, Thunnus orientalis (Temminck et Schlegel), cultured in Wakayama and Nagasaki Prefectures, Japan. The new species is morphologically similar to the members of the genus Cardicola Short, 1953, but shows distinct differences in the body form, location of the testis and the orientation of the ootype. The body of the new species is long and slender, whereas other Cardicola species are small and generally lanceolate. The testis is mostly located posterior to the caeca and anterior to the ovary, occupying 31-45% of body length, in contrast to the known Cardicola species, whose testis is typically intercaecal. The ootype is oriented anteriorly, while in most congeners, it is directed posteriorly or horizontally. Phylogenetic analyses of this aporocotylid, together with Cardicola orientalis Ogawa, Tanaka, Sugihara et Takami, 2010 from the same host, were conducted based on DNA sequences of the ITS2 rDNA and the 28S region of ribosomal RNA. The analyses revealed that the new blood fluke belongs to the genus Cardicola despite the marked morphological differences. Thus, this aporocotylid is named Cardicola opisthorchis n. sp. and the generic diagnosis is emended in this paper. In addition, 100% identity among the ITS2 sequences from the present species, Cardicola sp. from T. orientalis in Mexico and Cardicola sp. from the northern bluefin tuna, Thunnus thynnus (Linnaeus) in Spain suggests that C. opisthorchis n. sp. has a broad geographical distribution and that it infects both the Pacific and northern bluefin tuna. (C) 2011 Elsevier Ireland Ltd. All rights reserved.
  • F. Meng; H. Yokoyama; S. Shirakashi; D. Grabner; K. Ogawa; K. Ishimaru; Y. Sawada; O. Murata
    PARASITOLOGY INTERNATIONAL 60 1 90 - 96 2011年01月 [査読有り]
     
    Kudoa prunusi n. sp. (Myxozoa; Multivalvulida) is described from the brain of Pacific bluefin tuna Thunnus orientalis cultured in Japan. Numerous white cysts, up to 0.5 mm in size, were found on and in the brain. Spores having typically five spore valves and five polar capsules resembled a five-petal cherry blossom in apical view and were conical shape with a round bottom in side view. Average spore size was 9.63 (8.5-10.3)mu m in width and 7.50 (6.7-8.6)mu m in length. The spore dimensions of K. prunusi overlapped with those of Kudoa yasunagai ex Sillago ciliata having five to six spore valves, but they were clearly distinct in spore shape, 18S rDNA and 28S rDNA sequences (0.3% and 1.7% differences, respectively). Phylogenetic analysis of 18S rDNA revealed that K. prunusi grouped with the brain-infecting multivalvulid species, K. yasunagai, K. chaetodoni, K. lethrini and K. neurophila, rather than five-valved Kudoa spp. Combined with morphological, molecular and biological differences, K. prunusi was proven to be a new species. (C) 2010 Elsevier Ireland Ltd. All rights reserved.
  • Sho Shirakashi; Shuya Nakatsuka; Akihisa Udagawa; Kazuo Ogawa
    FISH PATHOLOGY 45 2 51 - 57 2010年06月 [査読有り]
     
    We conducted a series of experiments to understand the behavioral characteristics of oncomiracidium of the monogenean Heterobothrium okamotoi and compared them with those of two other monogenean species, Heteraxine heterocerca and Neobenedenia girellae. Behavior of H. okamotoi oncomiracidium consisted of two alternate phases: a swimming phase with strong ciliary beatings and a stationary phase with ciliary beatings too weak to generate any movements. The duration of one swimming-stationary cycle considerably varied among individuals but tended to increase with larval age. During the 5-day monitoring, length of the swimming phase decreased while that of the stationary phase tended to increase as the larva became older. The locomotion patterns differed significantly among individuals, but as a whole, larvae showed random horizontal movement and no phototactic reaction. The oncomiracidium tended to move downward because it was heavier than seawater and also swam downward at the start of the swimming phase because its anterior part pointed downward when the larva was not swimming. Those behavioral characteristics of larval H. okamotoi are likely to have evolved in order to maximize the chance of encountering its benthic fish host, tiger puffer Takifugu rubripes.
  • Sho Shirakashi; Mansour El-Matbouli
    DISEASES OF AQUATIC ORGANISMS 89 1 63 - 70 2010年02月 [査読有り]
     
    Environmental pollutants alter a wide range of host-parasite interactions in various ways. In some cases, pollution leads to a significant increase in parasite abundance, causing epidemics of parasitic diseases. In other cases, toxicants restrict the transmission success of parasites, resulting in reduction of their abundance. However, very little is known regarding whether and to what extent aquatic pollution affects myxozoan obligate parasites commonly found in fish. We investigated the effect of cadmium (Cd) on the aquatic oligochaete Tubifex tubifex infected with the myxozoan Myxobolus cerebralis. The oligochaetes were experimentally exposed to M. cerebralis myxospores and kept in various concentrations of Cd for 4 mo. Neither survival nor reproduction of the worms was affected by the metal, but infection prevalence and numbers of triactinosmyxon spores produced by individual worms were higher in the Cd-exposed group than the unexposed control. A comparative assay of a lethal Cd concentration (LC50) on infected and non-infected T tubifex revealed that infected worms are more resistant to the acute toxicity of Cd, probably because uptake of Cd was reduced by the infection. These results suggest that the abundance of M. cerebralis likely increases in polluted waters and escalates the risk of whirling disease in the respective area.
  • Tetsuya Yanagida; Sho Shirakashi; Takashi Iwaki; Noboru Ikushima; Kazuo Ogawa
    PARASITOLOGY INTERNATIONAL 58 3 308 - 310 2009年09月 [査読有り]
     
    To identify the metacercariae of a gymnophallid trematode in the Manila clam Ruditapes philippinarum from the Ariake Sea, experimental infection and molecular analysis were conducted. Based on the morphology of adult worms obtained from experimentally infected mice, the parasite was identified as Parvatrema duboisi. Comparison of internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) sequences for metacercariae and sporocysts from Manila clams and adult worms collected from wild wigeon Anas penelope showed minor differences ranging from 0 to 0.8%. These data strongly suggest that in the Ariake Sea, the parasite has a lifecycle using the Manila clam as the first and second intermediate hosts and wigeon as the definitive host. (C) 2009 Elsevier Ireland Ltd. All rights reserved.
  • S. Shirakashi; M. El-Matbouli
    PARASITOLOGY 136 6 603 - 613 2009年05月 [査読有り]
     
    Myxobolus cerebralis is the causative agent of whirling disease that hats significant economical and ecological impacts oil trout populations. Although intensive studies have been conducted to understand its effects on mid interactions, with its fish host, only limited information is available about hose and to what extent M. cerebralis affects its oligochaete host, Tubifex tubifex. We investigated the effects of M. cerebralis on survival, growth, reproduction, and feeding activity of T. tubifex. Mature, immature and juvenile worms were exposed to myxospores mid their infection prevalence, mortality, sexual development, reproduction and spore production were compared with unexposed worms. The parasite affected neither survival nor growth but inhibited clitellar development and reduced cocoon production by over 80%. Numbers of actinospores released from Mature worms were nearly 9-fold higher than that of immature worms. When non-clitellated infected worms were kept at 30 degrees C for 4 days, spore release ceased and they re-developed a clitellum. These results suggest parasite-induced castration. Comparative monitoring of defecation rate revealed that M. cerebralis reduced feeding activity of T. tubifex by approximately 40%. Low energy intake and impaired energetic allocation may lie the underlying mechanism behind reduced fecundity of infected T. tubifex.
  • Sho Shirakashi; Toyohiro Nishioka; Kazuo Ogawa
    FISHERIES SCIENCE 75 1 121 - 128 2009年02月 [査読有り]
     
    We monitored feeding behavior and survival of starved juvenile olive flounder experimentally infected with the gill monogenean Neoheterobothrium hirame. Infected flounder increased amount of the time spent in the water column by 117% when trying to capture live mysids, Neomysis sp. They also showed different feeding patterns from those of uninfected fish and made fewer attacks towards prey during one feeding attempt. Although the average numbers of mysids captured by individuals were similar between infected and uninfected fish, heavily infected fish tended to catch less prey. These results indicate that N. hirame reduces the feeding efficiency of the host for capturing live prey and possibly makes them more vulnerable to predation during feeding. We could not detect any obvious difference in survival rates between uninfected, lightly and heavily infected fish during 3 months of starvation. There was no evidence that starvation makes fish more susceptible to N. hirame. The present study provides first experimental evidence that N. hirame affects feeding behavior of juvenile olive flounder and supports the idea that this parasite indirectly reducing the host's survival and may be responsible for the recent reduction of the flounder population in Japan.
  • Jianping Fang; Sho Shirakashi; Kazuo Ogawa
    FISH PATHOLOGY 43 4 144 - 151 2008年12月 [査読有り]
     
    Japanese eel Anguilla japonica and European eel A. anguilla, 65 individuals each, were exposed in a tank to 8,600 oncomiracidia of Pseudodactylogyrus bini and P. anguillae, monogeneans originally recorded on Japanese eel from Asia. Infection was monitored weekly for 6 weeks to compare susceptibility to these monogenean infections between the two eel species. Approximately 40% of the oncomiracidia infected the eels. In the six samplings, both P. bini and P. anguillae were always found in greater numbers on the gills of European eel than on Japanese eel. The first generation of parasites matured within 2 weeks, laying eggs in the tank, and the second generation appeared on the gills of the eels on the third week. European eel was more susceptible not only to the first but also to the second and later generations of parasites than Japanese eel. Besides, both parasites grew faster on European eel than on Japanese eel. This is the first experimental evidence that there are substantial differences in the susceptibility to P. spp. infection between European eel, an unnatural host in Japan, and Japanese eel, the natural host in this country.
  • Sho Shirakashi; Kazuhisa Teruya; Kazuo Ogawa
    INTERNATIONAL JOURNAL FOR PARASITOLOGY 38 13 1513 - 1522 2008年11月 [査読有り]
     
    Neoheterobothrium hirame is a blood feeding monogenean of olive flounder Paralichthys olivaceus. The parasite was first reported in the mid-1990s from the Sea of Japan and became epidemic within cultured and wild flounder populations after several years. Infected fish often suffer from severe anaemia and thus the parasite is thought to have played an important role in the recent depletion Of flounder populations in some areas of Japan. However, the causal mechanism underlying the parasite epidemic and decreases in host populations is unclear because apparently A hirame infection is not fatal to the host. Here, we tested the hypothesis that N. hirame indirectly reduces the survival of wild juvenile flounder by altering their behaviour and making them more susceptible to predation. We conducted a series of experiments to compare behaviours and predation susceptibility between experimentally infected juvenile P. olivaceus and uninfected fish. Results showed that X hirame infection increases the activity level, alters diel activity and has negative effects on burrowing performance and swimming endurance. When juvenile flounder cohabitated with predators, the survival rate of infected juveniles was approximately 25% less than that of uninfected fish. We believe this is the first empirical evidence linking N. hirame infection to death of the host through predation. Consequences of N. hirame-induced behavioural change for the survival of juvenile flounder in the wild are discussed. We conclude that recent outbreaks of N. hirame are likely to have been a key factor in the decline of flounder populations in Japan. (C) 2008 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.
  • Koh-Ichiro Mori; Kazuhisa Yamamoto; Kazuhisa Teruya; Satoshi Shiozawa; Kenzo Yoseda; Takuma Sugaya; Sho Shirakashi; Naoki Itoh; Kazuo Ogawa
    FISH PATHOLOGY 42 1 49 - 57 2007年 [査読有り]
     
    Since 1990, mass mortality of fertilized eggs and hatched larvae of the leopard coral grouper Plectropomus leopardus has occurred repeatedly during its seed production in Okinawa Prefecture. A hitherto unknown protozoan parasite multiplied in the yolk sac in great numbers. The yolk sac of fertilized eggs and hatched larvae eventually burst and parasites were released to sea water. The development of the parasite was briefly described, which is very similar to that of the dinoflagellate Ichthyodinium chabelardi, known to infect yolk of several marine fish larvae in Europe. Based on the similarities of, and minor differences in, the mode of infection, development and SSU rDNA sequence, the parasite is tentatively designated as Ichthyodinium sp. PL (= PL for the abbreviated form of the scientific name for the host). Although the life cycle of the parasite is unknown, the disease outbreak was controlled by rearing the broodstock and incubating fertilized eggs in oxidant-treated seawater. The PCR diagnosis using specific primers designed from part of SSU rDNA sequence of the parasite revealed that disease outbreaks in different years were caused by a single species of parasite. This is the first report of Ichthyodinium infection in tropical fish from the Asia-Pacific region.
  • H. Yokoyama; S. Shirakashi
    BULLETIN OF THE EUROPEAN ASSOCIATION OF FISH PATHOLOGISTS 27 2 74 - 78 2007年 [査読有り]
     
    Enteromyxum leei is an enteric myxozoan parasite that causes significant damage to cultured marine fishes in the world. Experimental infections with E. leei, using anemonefish (Amphiprion clarkii and A. ocellaris) as experimental host were conducted. Anemonefish were shown to be as susceptible to E. leei as tiger puffer and Japanese flounder. To evaluate the effects of hyposalinity on infectivity of E. leei, the developmental stages of E. leei collected from the intestinal mucosa of infected fish were exposed to different salinities of seawater or dechlorinated tapwater for 1 h. After the treatment, naive anemonefish were exposed to the parasite and checked for infection at 4 weeks post-exposure. The results indicated that treatment of low salinity below 1/4 seawater (8 parts per thousand) was effective for control of E. leei infection.
  • S. Shirakashi; T. Yamada; T. Yamada; K. Ogawa
    JOURNAL OF FISH DISEASES 29 6 319 - 329 2006年06月 [査読有り]
     
    A recent epidemic of the invasive monogenean Neoheterobothrium hirame is suspected to have caused the significant decline of the commercial catch of olive flounder, Paralichthys olivaceus, in Japan. To clarify the causal link between parasite invasion and host depletion, we monitored the infections of N. hirame on juvenile flounder for 2 years at two widely separate bays, Obama Bay, experiencing a devastating reduction in flounder catches, and Miyako Bay with a stable catch. Prevalence, mean intensity and abundance of developmental stages of N. hirame were compared between the bays and between fish year classes. Fishes captured at Obama Bay harboured three times more worms than those at Miyako Bay and had a significantly higher overall prevalence of infection. In addition, there was a negative correlation between parasite intensity and host condition factor at Obama Bay, suggesting a causal link between the N. hirame epidemic and the reduction of local flounder populations.
  • S Shirakashi; T Yoshinaga; M Oka; K Ogawa
    FISH PATHOLOGY 40 1 33 - 35 2005年03月 [査読有り]
     
    Effects of low water temperature (below 10 degrees C) on the oncomiracidial attachment and its subsequent development of Neoheterobothrium hirame were investigated. The cumulative attached larvae to the gill pieces from olive flounder Paralichthys olivaceus was reduced by 30% at 5 degrees C when compared with 20 degrees C. At 8 degrees C the parasite development on flounder was significantly retarded compared at 20 degrees C, and considerable number of worms disappeared from the host before reaching maturation. These results suggest low water temperature is a factor limiting the population growth of N. hirame in cold temperature regions.
  • S Shirakashi; CP Goater
    PARASITOLOGY 130 177 - 183 2005年02月 [査読有り]
     
    We monitored temporal changes in the magnitude of altered host behaviour in minnows (Pimephales promelas) experimentally infected with metacercariae of a brain-encysting trematode (Ornithodiplostomum ptychocheilus). This parasite develops and then encysts in a region of the brain that mediates the optomotor response (OMR), an innate behaviour that links visual stimuli with motor performance. The OMR of infected and uninfected minnows was evaluated between 0 and 10 weeks post-infection (p.i.), an interval spanning the development period of metacercariae to infectivity in birds. Trials involved monitoring the time an individual minnow spent following a spinning drum that had been painted with alternating black and white stripes. At 2 and 4 weeks p.i., infected minnows followed the drum 40% less often than controls. Differences between controls and infected fish declined thereafter, and were undetectable by 10 weeks p.i. Both control and infected fish habituated equally rapidly to the spinning drum. However, the difference in performance between controls and infected fish was 29% for experienced fish and 48% for fish that: had never experienced the drum. Because maximum parasite induced reduction in OMR coincided with the period of maximum parasite development, the behavioural effects are most likely due to unavoidable pathology in the brain associated with developing larvae.
  • S Shirakashi; CP Goater
    JOURNAL OF PARASITOLOGY 88 6 1071 - 1074 2002年12月 [査読有り]
     
    We examined the relationship between the numbers of brain-encysting trematodes (Omithodiplostomum ptychocheilus) and the magnitude of altered behaviors in fathead minnows (Pimephales promelas). Because cysts develop within a brain region that integrates visual stimuli with motor response, we evaluated the standard optomotor response (OMR). Monitoring this task involved recording the time minnows spent following a spinning drum, on which alternating black and white stripes had been painted. Minnows were exposed to 0, 5, 20, 120, and 300 cercariae and then their OMR was evaluated at 2-wk postinfection. Surprisingly, only minnows that had high numbers of parasites (155 +/- 31 worms/fish) or low numbers of parasites (3 +/- 3 worms/fish) differed significantly in their optomotor performance compared with controls. Reduced OMR of heavily infected minnows was positively correlated with reduction in minnow activity. In contrast, reduced OMR in lightly infected minnows was independent of host activity and was likely associated with the rapid development of parasite larvae within the optic tecta. The nonlinear relationship between parasite intensity and effect on host behavior was consistent with an earlier study, but the underlying mechanisms producing this pattern are unknown.
  • S Shirakashi; CP Goater
    ECOSCIENCE 8 3 289 - 293 2001年 [査読有り]
     
    Many populations of fathead minnows (Pimephales promelas Rafinesque) in northern Alberta, Canada, contain individuals with hundreds of trematode (Ornithodiplostomum ptychocheilus Faust) cysts on the surface of their brains. Most cysts are located on the optic tecta, a region known to play a role in integrating visual and motor stimuli, especially in schooling fish. We determined the effect of infection on visually-mediated behaviours of fathead minnows by evaluating host performance in an optomotor swimming task. Monitoring this task involved recording the time minnows spent following a spinning drum, onto which alternating black and white stripes had been painted. After controlling for host activity and host size, minnows containing an average of 18 (low-intensity) or 98 larvae (high-intensity) reduced their time spent following the spinning drum by 42% and 26%, respectively, compared to uninfected controls. Low-intensity minnows also took longer than controls to respond to a change in the direction of the spinning drum. Reduced optomotor performance has the potential to affect a host's ability to detect and respond to prey, predators and conspecifics.
  • S Shirakashi; CP Goater
    ECOSCIENCE 8 3 289 - 293 2001年 [査読有り]
     
    Many populations of fathead minnows (Pimephales promelas Rafinesque) in northern Alberta, Canada, contain individuals with hundreds of trematode (Ornithodiplostomum ptychocheilus Faust) cysts on the surface of their brains. Most cysts are located on the optic tecta, a region known to play a role in integrating visual and motor stimuli, especially in schooling fish. We determined the effect of infection on visually-mediated behaviours of fathead minnows by evaluating host performance in an optomotor swimming task. Monitoring this task involved recording the time minnows spent following a spinning drum, onto which alternating black and white stripes had been painted. After controlling for host activity and host size, minnows containing an average of 18 (low-intensity) or 98 larvae (high-intensity) reduced their time spent following the spinning drum by 42% and 26%, respectively, compared to uninfected controls. Low-intensity minnows also took longer than controls to respond to a change in the direction of the spinning drum. Reduced optomotor performance has the potential to affect a host's ability to detect and respond to prey, predators and conspecifics.
  • S Shirakashi; N Mutsukura
    PROCEEDINGS OF THE FIFTH INTERNATIONAL SYMPOSIUM ON DIAMOND MATERIALS 97 32 180 - 188 1998年 
    The diamond-like carbon (DLC) films were deposited in CH4/H-2 rf (13.56MHz) plasmas at pressure range of 0.1-1 [Torr] and constant rf power input of 100[W]. Film properties including a Fourier transform infrared (FTIR) absorption spectrum and knoop hardness were examined. Plasma chemistry was studied using the results on mass spectrometry and self-bias voltage measurements. Various carbon films such as DLC, graphitic and polymeric films were obtained in this work, where the film structure considerably depended on the deposition conditions. The film structure indicated a drastic change by the addition of H-2 into CH4 plasma; from DLC to graphitic at 0.1[Torr] and from polymeric films to DLC at 1[Torr].

書籍

  • 農学とはなにか
    小川一夫; 白樫正 (担当:分担執筆範囲:)2018年
  • Health and Environment in Aquaculture, Transmission biology of the Myxozoa
    Yokoyama, H; 白樫 正; Grabner, D (担当:共著範囲:)2012年
  • Tuna Aquaculture
    (担当:分担執筆範囲:)

講演・口頭発表等

  • ブリ類のべこ病治療薬の探索  [通常講演]
    柳宗悦; 福留慶; 和田和彦; 佐藤純; 坂井貴光; 米加田徹; 山崎雅俊; 伊東尚史; 西岡豊弘; 森広一郎; 川上秀昌; 原川翔伍; 白樫正
    平成30年度日本魚病学会春季大会 2018年 東京海洋大学
  • 水産用経口駆虫剤によるべこ病治療効果とフェバンテルのブリ稚魚に対する毒性  [通常講演]
    白樫正; 浜野祥吾; 原川翔伍; 川上秀昌; 柳宗悦; 佐藤純; 三輪理; 森広一郎
    平成30年度日本魚病学会春季大会 2018年 東京海洋大学
  • 新交雑種クエタマ（クエ♀×タマカイ♂）のマハタハダムシBenedenia epinepheli に対する抵抗性  [通常講演]
    中田久; 家田一輝; 白樫正; 村田修; 升間主計
    平成30年度日本水産学会春季大会 2018年 東京海洋大学
  • ブリのべこ病に対するフェバンテルの有効な投与法  [通常講演]
    原川翔伍; 川上秀昌; 柳宗悦; 白樫正; 佐藤純; 森広一郎
    平成30年度日本魚病学会春季大会 2018年 東京海洋大学
  • Light-response larval behavior in three capsalid monogeneans  [通常講演]
    S. Shirakashi; M. Miura
    The 93rd Annual Meeting of the American Society of Parasitologists 2018年 The Marriott Cancun Resort
  • POSSIBILITY FOR NON-DRUG CONTROL OF BLOOD FLUKE INFECTIONS IN FARMED BLUEFIN TUNA  [通常講演]
    S. Shirakashi; T. Honryo; M. Kawahara; K. Ogawa
    AQUA 2018 2018年 Le Corum, Montpellier
  • Cardicola orientalis, the blood fluke of Pacific bluefin tuna, in the polychaete intermediate host  [通常講演]
    K. Ogawa; S. Shirakashi; T. Honryo; H. o. Uchida
    14th International congress of parasitology 2018年 EXCO, Daegu Korea
  • 病原体の生態および感染機構の解明と疾病防除  [通常講演]
    白樫正; 石丸克也
    平成28年度私立大学戦略的研究基盤形成支援事業プロジェクト「魚類の完全養殖の高度化」シンポジウム 2017年 近畿大学農学部
  • 単生類の生存戦略  [通常講演]
    白樫正
    平成29年度日本水産学会春季大会ミニシンポジウム「寄生虫症を宿主の視点から考える」 2017年 東京海洋大学
  • 研究奨励賞受賞講演「養殖種苗の寄生虫病対策に関する研究」  [通常講演]
    白樫正
    平成29年度日本魚病学会春季大会 2017年 日本大学生物資源科学部
  • ハダムシ類のミトコンドリアDNAおよび核ゲノム塩基配列の比較  [通常講演]
    小林圭吾; 白樫正; 杉原志貴; 福田譲; 山下浩史; 廣野育生; 近藤秀裕
    平成29年度日本魚病学会秋季大会 2017年 ホテルメリージュ宮崎
  • 海水中のハダムシNeobenedenia girellae孵化幼生検出法開発  [通常講演]
    阿川泰夫; 谷和樹; 山本修平; 平野千早; 澤田好史; 白樫正
    平成29年度日本水産学会春季大会 2017年 東京海洋大学
  • カンパチにおける種苗サイズによるべこ病発症率の違いとシスト数の長期変化傾向  [通常講演]
    浜野祥吾; 白樫正; 有元操; 森広一郎
    平成28年日本魚病学会秋季大会 2016年 近畿大学農学部
  • ハダムシBenedenia epinepheliふ化幼生の光刺激に対する反応  [通常講演]
    三浦真由子; 石丸克也; 石谷浩江; 白樫正
    平成28年日本魚病学会秋季大会 2016年 近畿大学農学部
  • クロマグロの住血吸虫（Cardicola opisthorchis）に対するプラジクアンテルの臨床試験  [通常講演]
    久保埜和成; 石丸克也; 白樫正; 小川和夫; 小田憲司
    H28年度日本魚病学会春季大会 2016年 日本獣医生命科学大学
  • Temporal and spatial infection patterns of tuna blood flukes Cardicola spp. in polychaete intermediate hosts at a tuna farm in Japan  [通常講演]
    S. Shirakashi; K. Tani; K. Ishimaru; T. Honryo; H. Uchida; K. Ogawa
    91st Annual Meeting, American Society for Parasitologists 2016年 The Westin Edmonton
  • Preventing Kudoa infections in hatchery  [通常講演]
    S. Shirakashi
    Aquaculture Europe 2016年 Edinburgh International COnference Centre
  • ハダムシNeobenedenia girellaeの産卵生態と養殖生簀網における虫卵分布  [通常講演]
    平野千早; 石丸克也; 白樫正
    平成27年度日本水産学会春季大会 2015年 東京海洋大学
  • べこ病に罹患したカンパチ稚魚における体表のべこ症状とシストの関係  [通常講演]
    浜野祥吾; 石谷浩江; 白. 正
    平成27年度日本水産学会春季大会 2015年
  • 養殖クロマグロで見られる住血吸虫とその生活環  [通常講演]
    白樫正; 谷和樹; 石丸克也; 本領智記; 内田紘臣; 小川和夫
    H27年度日本魚病学会秋季大会 2015年 東京大学農学部
  • カナダ・イギリス・ドイツにおける水生動物の寄生虫に関する留学および在外研究  [通常講演]
    白樫正
    平成27年度日本水産学会春季大会ミニシンポジウム「若手が拓く水産学研究：国際舞台で活躍する若手研究者たち」 2015年 東京海洋大学
  • マグロ住血吸虫の中間宿主フサゴカイの分布状況と寄生の季節変動  [通常講演]
    谷和樹; 白樫正; 石丸克也; 本領智記; 内田紘臣; 小川和夫
    H27年度日本魚病学会秋季大会 2015年 東京大学農学部
  • クロマグロ養殖生簀周辺のフサゴカイに寄生していた住血吸虫（予報）  [通常講演]
    谷和樹; 白樫正; 石丸克也; 本領智記; 内田紘臣; 小川和夫
    平成27年度日本魚病学会春期大会 2015年 東京海洋大学
  • 飼育水処理によるKudoa yasunagai防除法の検討および発症軽減に対する効果  [通常講演]
    西村知代; 白樫正; 中務寛; 赤井茜
    H27年度日本魚病学会秋季大会 2015年 東京大学農学部
  • Reproduction and inectious biology of Capsalid Monogenea Neobenedenia gireallae  [通常講演]
    S. Shirakashi; C. Hirano; K. Ogawa
    9th International Symposium of Fish Parasites 2015年 Valencia, Spain
  • Phylogenetic study of the genus Kudoa using Baysian tip-association significance testing (BaTS)  [通常講演]
    S. P. Shin; S. Shirakashi
    平成27年度日本魚病学会秋季大会 2015年 東京大学大学院 農学生命科学研究科
  • Investigation of the immune response during infection with two Cardicola species in farmed Pacific bluefin tuna juveniles  [通常講演]
    Y. Pennacchi; A. Bridle; S. Shirakashi; M. Polinski; B. Nowak
    13th Congress of International Society of Developmental and Comparative Immunology 2015年 Murcia, Spain
  • The life cycle of Cardicola orientalis (Digenea: Aporocotylidae), a blood fluke of Pacific bluefin tuna  [通常講演]
    K. Ogawa; S. Shirakashi; H. Uchida; S. Shin; K. Tani
    9th International Symposium of Fish Parasites 2015年 Valencia, Spain
  • Comparative study of parasites in Pacific bluefin tuna, yellowfin tuna and others Scombrid fishes from Panam?  [通常講演]
    L. Lasso, T; S. Shirakashi; A. Cano
    SATREPS International Symposium 2015年 Smithsonian Tropical Research Institute, Panama City, Panama
  • ハダムシNeobenedenia girellaeの産卵とふ化の日周リズム  [通常講演]
    平野千早; 白樫正; 石丸克也
    平成26年度日本魚病学会春期大会 2014年 函館国際ホテル
  • マサバ養殖におけるハダムシ防除法の比較  [通常講演]
    白樫正; 福島敦彦; 石丸克也; 山本眞司
    平成26年度日本魚病学会春期大会 2014年 函館国際ホテル
  • クロマグロ住血吸虫に対する(特異)抗体価の測定  [通常講演]
    谷和樹; 石丸克也; 白. 正; 小川和夫
    平成26年度日本魚病学会春期大会 2014年 函館国際ホテル
  • 飼育水のUV照射によるクドア寄生防除  [通常講演]
    西村知代; 白樫正; 亀島長治; 山下洋; 石谷浩江; 山博
    平成26年度日本魚病学会春期大会 2014年 函館国際ホテル
  • Kudoa (Myxozoa: multivalvulida) infections in cultured pacific bluerin tuna in Japan  [通常講演]
    S. Shirakashi; J. Suzuki; H. Yokoyama
    World Aquaculture Adelaide 2014 2014年 Adelaide convention centre
  • Shading of culture cage reduces the infection of skin fluke Neobenedenia girellae  [通常講演]
    S. Shirakashi; C. Hirano; A. Fukushima; K. Ogawa
    ICOPAXIII 2014年 Camino Real Hotel, Mexico city, Mexico
  • Transcriptional immune response of cage-cultured Pacific bluefin tuna during infection by two Cardicola blood fluke species  [通常講演]
    M. Polinski; S. Shirakashi; A. Bridle; B. Nowak
    International Symposium on Aquatic Animal Health 2014年 Portland, Oregon
  • 養殖場における水深・時間帯別のネオベネデニア寄生  [通常講演]
    平野千早; 白樫正; 石丸克也
    平成25年度日本魚病学会春期大会 2013年 神奈川県藤沢市日本大学生物資源科学部湘南キャンパス
  • クドア属粘液胞子虫の生態に関する基礎的検討  [通常講演]
    白樫正; 松浦巧; 南裕也; 常本和伸; 石丸克也
    平成25年度日本魚病学会春期大会 2013年 神奈川県藤沢市日本大学生物資源科学部湘南キャンパス
  • ハダムシNeobenedenia girellaeの生態  [通常講演]
    白樫正; 小川和夫
    第73 回日本寄生虫学会東日本支部大会 2013年 国立科学博物館上野本館
  • ハダムシNeobenedenia girellaeの交接行動  [通常講演]
    小川和夫; 白樫正; 石谷浩江
    平成25年度日本魚病学会秋期大会 2013年 三重大学
  • プラジクアンテルを用いたネオベネデニア防除の検討  [通常講演]
    山本眞司; 森本智; 白樫正; 石丸克也; 家戸敬太郎; 村田修; 升間主計; 宮下盛
    第11回 因島種苗生産技術交流会 2013年 広島県尾道市因島
  • ブダイにおけるクドア属粘液胞子虫の寄生  [通常講演]
    山根弘士; 白樫正; 横山博; 石谷浩江; 柳田哲也
    平成25年度日本魚病学会秋期大会 2013年 三重大学
  • Control of parasitic diseases in cultured Pacific bluefin tuna  [通常講演]
    S. Shirakashi; K. Ishimaru; K. Ogawa
    Aquaculture conference: To the Next 40 Years of Sustainable Global Aquaculture 2013年 Palacio de Congresos de Canarias, Las Palmas, Gran Canaria
  • Skin fluke infection in culturing cages-possibilities for ecological control measure-  [通常講演]
    S. Shirakashi; C. Hirano; A. b. Asmara; N. b; Md Noo
    Annual international seminar on marine science and aquaculture 2013 2013年 Kota Kinabaru Sabah, Malaysia
  • Our approach to the Kudoa problems: a case study in hatchery and culture facility  [通常講演]
    S. Shirakashi
    クドア専門家セミナー 2013年 韓国釜山
  • New possibilities of reducing skin fluke infection in net cage mariculture  [通常講演]
    S. Shirakashi
    ASP Parasitic Diseases in Fish Mariculture Workshop 2013年 Launceston, Tasmania, Australia
  • Host-pathogen interaction in blood fluke infection in Pacific bluefin tuna  [通常講演]
    M. Polinski; S. Shirakashi; A. Bridle; B. Nowak
    16th European Association of Fish Pathology Internation Conference on Diseases of Fish and Shellfish 2013年 Tampere, Norway
  • Development of a new method to reduce Neobenedenia girellae infection  [通常講演]
    C. Hirano; S. Shirakashi
    Aquaculture conference: To the Next 40 Years of Sustainable Global Aquaculture 2013年 Palacio de Congresos de Canarias, Las Palmas, Gran Canaria
  • 定量PCRを用いた海水からのKudoa yasunagai検出法の確立  [通常講演]
    白樫正; 松浦巧; 常本和伸; 石丸克也
    H24年日本魚病学会秋季大会 2012年 山口県下関市 水産大学校
  • 水深別のブリハダムシBenedenia seriolae寄生数の変化  [通常講演]
    白樫正; 呉秀賓; 石丸克也; 宮下盛
    平成24年度日本魚病学会春期大会 2012年 東京都品川区 東京海洋大学
  • クロマグロ住血吸虫に対するプラジクアンテルの最低有効量と体内動態  [通常講演]
    石丸克也; 峰龍馬; 白樫正; 宮下盛
    平成24年度日本魚病学会春期大会 2012年 東京都品川区 東京海洋大学
  • オーストラリアの蓄養ミナミマグロにみられた住血吸虫の同定  [通常講演]
    小川和夫; 白樫正; 常本和伸; C. Webber; K. Rough
    H24年日本魚病学会秋季大会 2012年 山口県下関市 水産大学校
  • Control of blood fluke infection in cultured Pacific bluefin tuna, Thunnus orientalis, in Japan  [通常講演]
    S. Shirakashi; K. Ishimaru; T. Okada; Y. Sawada; K. Ogawa
    2012 Australian Society for Parasitology 2012年
  • Parasitic diseases of cultured Pacific bluefin tuna Thunnus orientalis and development of control measure  [通常講演]
    S. Shirakashi; K. Ishimaru; T. Okada; Y. Sawada; S. Miyashita
    World Aquaculture Society 2012年 Las Vegas, USA
  • Effect of water depth and diurnal pattern of skin fluke infection in cultured amberjack  [通常講演]
    S. Shirakashi; C. Hirano; K. Ishimaru
    Internatinal symposium of Kinki University in Kushimoto 2012年 Kushimoto, Wakayama Japan
  • クロマグロに寄生する2種の住血吸虫Cardicola orientalis及びC. sp.虫卵の組織病理学的研究  [通常講演]
    木南竜平; 白樫正; 岸本喜樹; 小川和夫
    平成23年度日本魚病学会春季大会 2011年 東京都文京区 東京大学農学部
  • クロマグロ住血吸虫に対するプラジクアンテルの有効性について  [通常講演]
    白樫正; M. Andrews; 石丸克也; 岡田貴彦; 村田修; 岸本喜樹; 小川和夫
    平成23年度日本魚病学会春季大会 2011年 東京都文京区 東京大学農学部
  • 魚類の住血吸虫に対するプラジクアンテルのin vitroでの殺虫効果  [通常講演]
    孫暁楠; 良永知義; 土井啓行; 白樫正; 石丸克也; 小川和夫
    平成23年度日本魚病学会春季大会 2011年 東京都文京区 東京大学農学部
  • 養殖場における脳クドアの感染動態と病理組織  [通常講演]
    森田明伸; 白樫正; 石丸克也; 村田修
    平成23年度日本水産学会春期大会 2011年 東京都品川区 東京海洋大学
  • PCR法を用いた脳寄生クドアの検出と養殖場における感染動態  [通常講演]
    森田明伸; 白樫正; 石丸克也; 宮下盛
    平成23年度日本水産学会秋季大会 2011年 長崎大学
  • 虫卵を指標としたクロマグロ住血吸虫2種の寄生状況  [通常講演]
    岸本喜樹; 小川和夫; 白樫正; 高見生雄
    平成23年度日本魚病学会春季大会 2011年 東京都文京区 東京大学農学部
  • Kudoa septempunctata (Myxozoa: Multivalvulida) from the trunk muscle of cultured olive flounder (Paralichthys olivaceus) causing the food poisoning of human  [通常講演]
    H. Yokoyama; D. Grabner; S. Shirakashi; R. Kinami
    8th International Symposium on Fish Parasites 2011年 The Gala Hotel, Vi?a del Mar, Chile
  • Control of blood fluke infections in cultured Pacific bluefin tuna, Thunnus orientalis  [通常講演]
    S. Shirakashi; K. Ishimaru; T. Okada; K. Ogawa
    8th International Symposium on Fish Parasites 2011年 The Gala Hotel, Vi?a del Mar, Chile
  • 養殖クロマグロ稚魚に見られた住血吸虫と粘液胞子虫について  [通常講演]
    白樫正; 石丸克也; 岡田貴彦; 澤田好史; 宮下盛; 村田修; 横山博; 小川和夫
    平成22年度日本水産学会春季大会 2010年 神奈川県藤沢市 日本大学生物資源科学部
  • 養殖クロマグロでみられる寄生虫とその防除方法の開発  [通常講演]
    白樫正
    近畿大学グローバルCOE プログラム平成22 年度成果報告シンポジウム 2010年 東大阪市 近畿大学
  • 養殖クロマグロには2種の住血吸虫が寄生する  [通常講演]
    小川和夫; 白樫正; 石丸克也; 村田修
    平成22年度日本魚病学会秋季大会 2010年 三重大学生物資源学部
  • Myxosporean and microsporidian infections in cultured Pacific bluefin tuna Thunnus orientalis in Japan  [通常講演]
    H. Yokoyama; J.-Y. Zhang; F. Meng; K. Ogawa; J. Miyara; I. Takami; S. Shirakashi; K. Ishimaru; Y. Sawada; O. Murata
    The XIIth International Congress of Parasitology 2010年 Exhibition and Convention Centre, Melbourne, Australia
  • Parasitic infections observed in artificially bred Pacific bluefin tuna, Thunnus orientalis  [通常講演]
    S. Shirakashi; K. Ishimaru; Y. Sawada; O. Murata; H. Yokoyama; K. Ogawa
    French-japanese Symposium Kinki Ifremer 2010 2010年 S?te, France
  • Two species of sanguinicolid blood flukes from cultured Pacific bluefin tuna Thunnus orientalis  [通常講演]
    S. Shirakashi; K. Ishimaru; Y. Sawada; O. Murata; N. Itoh; K. Ogawa
    The XIIth International Congress of Parasitology 2010年 Exhibition and Convention Centre, Melbourne, Australia
  • Parasitic infection in cultured Pacific bluefin tuna, Thunnus orientalis  [通常講演]
    S. Shirakashi; K. Ishimaru; T. Okada; Y. Sawada; S. Miyashita; O. Murata; H. Yokoyama; K. Ogawa
    Annual Seminor on Marine Science & Aquaculture 2010年 Universiti Malaysia Sabah
  • Effects of cadmium on Myxobolus cerebralis infection on Tubifex tubifex  [通常講演]
    S. Shirakashi; M. El-Matbouli
    14th European Association of Fish Pathologists International Conference 2009年 Prague Czech Republic
  • アサリ寄生Gymnophallidae 科吸虫は二宿主性生活環を持つ  [通常講演]
    柳田哲矢; 白樫正; 巌城隆; 小川和夫
    第77回日本寄生虫学会大会 2008年
  • Myxobolus cerebralis (Myxozoa) reduces reproduction and feeding rate of its oligochaete host Tubifex tubifex  [通常講演]
    S. Shirakashi; M. El-Matbouli
    5th International Symposium of the Japanese Society for Fish Pathology 2008年 Tokyo, Japan
  • Ribosomal RNA gene sequence indicates the two-host lifecycle of Gymnophallid digenean from Manila clam.  [通常講演]
    T. Yanagida; S. Shirakashi; T. Iwaki; K. Ogawa
    7th International Symposium on Fish Parasitology 2007年 Viterbo, Italy
  • Evaluation of hyposalinity treatment on infection with Enteromyxum leei (Myxozoa), by using anemonefish Amphiprion spp. as an experimental host  [通常講演]
    H. Yokoyama; S. Shirakashi
    The 11th International Congress for Parasitology 2006年 The Scottish Exhibition and Conference Centre (SECC), Glasgow Scotland UK
  • 第７回シンポジウム「水生動物の行動と神経系」  [通常講演]
    Behaviour of fathead minnow; infected with brain-encysting parasite
    2005年
  • 脳内吸虫に感染したFathead minnowの行動  [通常講演]
    白樫正; C. P. Goater
    2005年
  • 日本に侵入した単生類寄生虫によるヒラメ天然資源への影響  [通常講演]
    白樫正
    第20回生態学・疫学談話会in第74回日本寄生虫学会大会ワークショップ 2005年 米子コンベンションセンター,鳥取県米子市
  • 低水温下でのNeoheterobothrium hirameの着定と発育  [通常講演]
    白樫正; 堤信幸; 良永知義; 岡雅一; 小川和夫
    平成16年度日本魚病学会大会 2004年 函館国際ホテル,北海道函館市
  • Effects of Neoheterobothrium hirame on predation of olive flounder, Paralichthys olivaceus  [通常講演]
    S. Shirakashi; K. Teruya; K. Ogawa
    79th Annual Meeting of the American Society of Parasitologists 2004年 DoubleTree Hotel Philadelphia, Pennsylvania, USA
  • Effects of Neoheterobothrium hirame on predation and viral hemorrhagic septicaemia infection of olive flounder, Paralichthys olivaceus  [通常講演]
    S. Shirakashi; K. Mori; T. Sugaya; K. Ogawa
    6th International Symposium on Fish Parasitology 2003年 The University of the Free State, Bloemfontein, South Africa
  • Intensity dependent alteration of minnow behaviour by a brain encysting trematode  [通常講演]
    S. Shirakashi; C. P. Goater
    The 10th International Congress of Parasitology 2002年 The Convention and Exhibition Centre, Vancouver B.C. Canada
  • Behaviour of trematode-infected fathead minnows: a test of the parasite-manipulation hypothesis  [通常講演]
    S. Shirakashi; C. P. Goater
    76th Annual Meeting of the American Society of Parasitologists 2001年 The Sheraton Old Town Hotel, Albuquerque, New Mexico, USA
  • Infection dynamics of Polymorphus paradoxus (Acanthocephala) in Gammarus lacustris collected from a prairie slough  [通常講演]
    S. Shirakashi
    Annual Meeting of the Canadian Society of Zoologists 1998年 Okanagan University College, Kelowna, British Columbia. Canada.

MISC

受賞

  • 2017年03月 日本魚病学会 日本魚病学会研究奨励賞
     
    受賞者: 白樫正
  • 2010年03月 日本水産学会 日本水産学会論文賞
     
    受賞者: 白樫正
  • 2004年07月 American Society of Parasitologists Meritorious Student Paper
     
    受賞者: 白樫正
  • 1998年05月 Canadian Society of Zoology Honorable Mention for Best Undergraduate Student Presentation
     
    受賞者: 白樫正

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2022年04月 -2026年03月 
    代表者 : 白樫 正; 小川 和夫; 服部 亘宏
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2021年04月 -2024年03月 
    代表者 : 小川 和夫; 白樫 正
     
    長崎県産の天然ブリからブリ筋肉線虫Philometroides seriolaeの雌成虫を採集し、そのふ化幼生（第1期幼生）を子宮内から得ることができた。和歌山県白浜町で甲殻類（カイアシ類3種、端脚類2種、十脚類1種）を採集した。これらの甲殻類を小型プラスチック容器内に収容し、P. seriolae雌成虫の子宮内からふ化幼生を取り出して暴露した。幼生を投与直後は実体顕微鏡下で観察して摂食の有無を確認した。その後20℃と25℃で維持して甲殻類体内に幼虫がいるかを解剖、もしくは麻酔をかけて顕微鏡下で確認し、代理宿主としての適性を調べた。その結果、端脚類と十脚類（スジエビの仲間）は幼生を摂食したが、体腔内に虫体は確認できなかった。カイアシ類については、MiraciidaeとTisbiidaeカイアシ類は幼生摂食後、体内に幼虫を確認したが、長期間の維持ができなかった。一方、シオダマリミジンコ（立正大学の岩崎 望先生同定；以下、ミジンコ）は積極的にふ化幼生を摂食し、曝露1時間後には血体腔体内に動く幼虫を確認した。ミジンコ内に最多で3個体の幼虫が確認され、寄生率は最高100％に達した。さらに感染ミジンコの一部を1ヶ月以上生存させることに成功した。ミジンコ内の幼生に脱皮殻を認めたことから、幼生は2期または3期に成長したことも確認された。以上のことから、シオダマリミジンコを代理宿主とする実験系がほぼ確立された。 ブリ筋肉線虫は宿主魚の商品価値を喪失させ、水産業上問題となる。中間宿主が不明であるだけでなく、雄虫も未発見であった。長崎県産の大型天然ブリを2021年4月~9月に計30尾を解剖した。雌成虫をブリ体側筋から取り出す際、寄生部位の洗浄液を検鏡し、雄虫を探索した。その結果、雌成虫140虫を採集したが、同所から2虫の雄成虫を回収することができた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2021年04月 -2024年03月 
    代表者 : 横山 博; 柳田 哲矢; 白樫 正
     
    滋賀県の養殖ニジマスで見られた新しい微胞子虫症について、皮下体側筋に赤斑を呈する症状が特徴的であること、患部から微胞子虫の胞子が検出され、顕微鏡観察と遺伝子解析の結果、武田微胞子虫Kabatana takedaiに近縁であるものの別種であることがわかった。さらに琵琶湖で捕獲されるスジエビを未感染ニジマスに経口投与すると症状が再現されたため、ニジマスおよびビワマスに対して実験的に投与する感染実験を行った結果、いずれも本症が再現され、感染魚の死亡もみられた。なお、ニジマスとビワマスでは死亡率に差異がみられたものの、スジエビの投与量が異なっていた可能性もあり、そのまま感受性が違うと結論付けられなかった。一方、冷凍エビの投与では感染がみられなかった。以上の結果は、琵琶湖産スジエビを介して本微胞子虫がマス類に感染すること、また今回の微胞子虫は新規の疾病であることが示された。これらの成果は、日本魚病学会および日本寄生虫学会で口頭またはポスターで発表され、さらに学術雑誌「魚病研究」においても、"A new microsporidian disease of rainbow trout Oncorhynchus mykiss farmed in Shiga prefecture, Japan and possible involvement of common prawn Palaemon paucidens for transmission of the pathogen" by Yamamoto et al. Fish Pathol., 56(3), 130-139, 2021.という内容で、論文発表された。また、現在、本微胞子虫の新種記載論文についても作成し、海外の学術雑誌に投稿中である。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2019年04月 -2024年03月 
    代表者 : 良永 知義; 伊藤 直樹; 白樫 正; 渡邊 勇歩
     
    研究課題の4つの研究課題(I. 海産白点虫(以下、白点虫）の生態学的特性に基づく発生予測技術の検討、Ⅱ.化学療法剤の探索と有効性・安全性の検討、Ⅲ. 寄生関連タンパク分解酵素を抗原としたワクチンの検討、IV. 新たなin vitro培養法の開発）それぞれについての成果は以下のとおりである。 I. 令和２年度に開発した新たなプライマーとブローブを用いて、植物プランクトンや自由生活性繊毛を混入させた海水中での白点虫セロントの検出を行い、これらの夾雑物の影響が低いことが明らかとなった。また、白点虫病が発生している水槽から採取した海水中のセロントの定量を試みるとともに、蛍光染色による顕微鏡観察で計数したセロント数を経時的に比較したところ、おおむね似た値を示したものの、かなり異なる時間帯もあり、その原因を明らかにしたうえで、改良を加えることが必要となった。シスト期の白点虫（トモント）への12時間の光照射だけ、また、1 lxという極めて低い照度の光照射だけで、トモントからのセロントの放出の概日リズムが形成されることが明らかとなった。 Ⅱ. in vitroで抗白点虫作用が確認されたイオノフォアの効果を、マダイを用いてin vitroでも確認することができた。さらに、比較のために行った実験では、イオノフォアのヒラメの病原せん毛虫Miamiensis avidusに対する抗虫効果がin vitroとin vivoで確認された。 IV.セロントにアポトーシス細胞を与えても、ほとんど取り込まなかった。そこで、改めて、寄生期のトロホントにおける宿主細胞の取り込みについて検討したところ、宿主細胞を大量に取り込むのは宿主に侵入して48時間以降であることが明らかになった。この観察から、アポトーシス細胞の投与時期について再検討が必要と考えている。 III. ワクチンについては令和３年度は研究をおこなわなかった。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 小川 和夫; 脇 司; 白樫 正
     
    2017年6月から毎月、クロマグロ養殖場の生け簀ロープなどに生息する中間宿主フサゴカイ類を調べた結果、寄生は夏に起こり、冬には新たな寄生は起こらないという季節性を確認した。生け簀構造物のフサゴカイ類を駆除したところ、その後は非感染個体のみが見いだされたことから、中間宿主駆除が新たな防除法として有望である可能性が示された。自然感染ゴカイから得たスポロシストを注射することによって、無感染ゴカイ体内でスポロシストを増殖させることに成功した。中間宿主ゴカイのin vivo培養系の確立によって、実験感染系でスポロシスト期の維持や発育・増殖の観察が可能となり、本種の増殖について基礎的知見が得られた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 白樫 正; SHIN SANG PHIL; SHIN Sang Phil
     
    粘液胞子虫の一種であるクドアは様々な海産魚に寄生し、魚体の変形や魚肉の変質を引き起こすため、水産業上の重大な問題となっている。また近年ではクドアがヒトの食中毒原因体で有ることが判明し、公衆衛生上も大きな問題となっている。本研究では養殖魚におけるクドアの防除法開発を最終目的として、それに繋がるクドアの生物学的知見を得ると共に、陸上養殖施設で即時利用可能な防除法を確立した。当初予定してたワクチン開発に繋がるプロテアーゼ解析については、期間内の感染体特定が困難であることが分かったため、研究内容を一部変更した。 クドア属粘液胞子虫の分子系統解析を実施し、パナマ産サワラの筋肉中から得た新種クドアの記載（Kudoa rayformis）含め、学術論文に纏めた。これにより、現在国内外で問題となっているクドアについて包括的に情報を整理し、今後の研究課題の方向性を決定することができた。さらに、国内で食中毒原因体として大きな問題となっているヒラメのナナホシクドアについて、同じくヒラメに寄生する複数のクドアと区別する簡便かつ正確な診断法としてマルチプレックスPCRを確立した。同時に、国内養殖ヒラメに寄生するクドア種リストを更新し、学術論文とした。 当初の予定通り、ヒラマサの脳に寄生するK. yasunagaiの魚体内感染動態を調べ、感染初期には消化管で当該種の遺伝子が多く検出できることを確かめた。これにより、侵入門戸が消化管であることが示され、学術論文としてまとめた。 研究の最終目的であるクドア防除法としては、飼育水を15 mJ/ cm2程度の比較的弱い紫外線殺処理することで、寄生を完全に抑えることを突き止めた。これにより、少なくとも陸上養殖施設でのクドア防除法は確立したと言える。 これらの成果は計4報の学術論文としてまとめた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 白樫 正; 小川 和夫; 津田 裕一
     
    養殖場で問題となっている寄生虫であるハダムシ（ネオベネデニア）の生態を調べたところ、ハダムシは光刺激を受けて午前中にふ化し、幼生は光に集まる性質があるため、主に明るい日中に表層付近で魚に寄生していることがわかった。そこで養殖生簀を遮光し暗くしたところ、寄生の大幅な軽減に成功した。ハダムシ1匹は1日最大700個程度産卵するため、寄生が重篤になると生簀網には1日1千万個以上の虫卵が蓄積し、その多くは生簀網上部に集中していることが分かった。これらの結果から効果的な虫卵除去法や被害軽減に繋がる飼育技術を提案した。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 小川 和夫; 横山 博; 白樫 正; 本領 智記
     
    養殖クロマグロに3種の住血吸虫が寄生し、それぞれに固有のフサゴカイ種が中間宿主となっていた。生活環が養殖場内で完結していることが明らかになった。そのうちの1種ゴカイについては、水深0～4 mで生息密度および寄生率が高く、7月に寄生のピークを示した。ゴカイ1個体が放出する感染期の幼生は最大で100万個体と算出された。粘液胞子虫については、新種を含む2種のクドアの筋肉寄生を明らかにした。寄生はマグロを海面生簀に移動した直後から起きると考えられた。ヒラマサ幼魚に寄生するクドアを用いた試験では，陸上飼育用水の濾過では寄生を防げなかったが、紫外線処理で防除に成功した。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 横山 博; 白樫 正
     
    近年、ヒラメ寄生粘液胞子虫Kudoa septempunctataによる食中毒が問題になっているが、他のクドアについても人への毒性が疑われている。天然海産魚に寄生するKudoa iwataiは宿主によって感受性が異なり、寄生率ではキチヌが高く、シストの成熟度や胞子の生残率ではスズキが高かったが、毒性を証明するには至らなかった。メジマグロ（クロマグロの幼魚）に寄生する種類をKudoa hexapunctataとして新種記載した後、ヒト腸管培養細胞（Caco-2細胞）に対する毒性を確認し、毒性が発現する胞子数、胞子が失活すると考えられる冷凍・冷蔵条件などから、食中毒リスクについて検討した。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2010年 -2012年 
    代表者 : 小川 和夫; 良永 知義; 澤田 好史; 石丸 克也; 白樫 正
     
    第一に,太平洋クロマグロの住血吸虫は,従来,主に鰓血管に寄生するCardicola orientalis1 種と考えられていたが,第2 種として主に心室に寄生するCardicola opisthorchis を見出し, 新種記載した。第二に,鰓に集積した虫卵がどちらの住血吸虫に由来するかを形態によって鑑 別する方法を開発した。さらに,鰓組織をNaOH で融解したのちに,虫卵を計数する方法を開 発した。第三に,沖出し後45 日目に2 種の寄生を確認し,その1 週間後には成虫を、さらに その1 週間後には鰓に虫卵を確認した。第四に,C. opisthorchis はプラジクアンテル(PZQ) 7.5 mg/kg 魚体重以上の用量の3 日間連続投与で完全に駆虫されることを確認した。なお,投 与1 か月後には再寄生が認められた。魚体内の薬剤は投与24 時間後に検出限界以下となった。 第五に,PZQ のin vitro における効果を調べた。SEM 観察によって,2 種ともに外被の損傷 が激しかった。すなわち,C. opisthorchis では体表の膨隆と収縮,および体表に皺形成が顕著 となった。一方,C. orientalis では体表面に小穴の形成が特徴的であった。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2004年 
    代表者 : 白樫 正
     
    ヒラメの寄生虫Neoheterobothrium hirameが天然ヒラメ稚魚の生存に及ぼす影響を調べるため、実験的に感染させたヒラメ稚魚の行動、捕食率、飢餓耐性、ウイルス病(VHSV)に対する感受性等を調べた。 行動実験では感染ヒラメ稚魚で潜砂、遊泳能力の著しい低下がみられ、その活動パターン、摂餌行動が非感染対象区と異なることが分かった。また、捕食実験において、感染ヒラメ稚魚、非感染ヒラメ稚魚、そして捕食者となる大型ヒラメを96時間同居飼育した結果、感染ヒラメ稚魚はより捕食を受けやすいことが明らかになった。さらに、ヒラメ稚魚に寄生虫N.hirameとウイルス性出血性敗血症ウイルス(VHSV)による混合感染実験を行った結果、両者の病原体に感染した魚ではいずれかの病原体に単独感染した魚より著しく高い死亡がみられ、N.hirameによってヒラメのウイルス病に対する感受性が増すことが考えられた。 さらに、2年間におよぶフィールド調査により、ヒラメ漁獲の現象が顕著な海域では感染ヒラメ1尾あたりのN.hirame虫数(寄生虫)が漁獲の安定している海域より著しく多いことが明らかになり、N.hirameとヒラメ資源減少の因果関係が示唆された。このフィールド調査の結果を基に行った実験では、10℃以下の低水温下ではN.hirameの感染力や発育が著しく低下することが分かり、海域間で見られたN.hirame寄生数の差はそれぞれの海域の温度差によるものであると考えられた。 これらの研究で、近年日本沿岸で深刻な問題となっているヒラメ資源の減少に対する新種の移入寄生虫、N.hirameの関与を支持する重要な知見が得られた。

委員歴

  • 2021年03月 - 現在   薬事・食品衛生審議会   薬事・食品衛生審議会委員
  • 2021年03月 - 現在   日本魚病学会   常任編集委員
  • 2015年03月 - 現在   日本魚病学会   評議員

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