First report of Gyrodactylus teuchis (Monopisthocotyla: Gyrodactylidae) in farmed rainbow trout Oncorhynchus mykiss from Eastern Europe

First report of Gyrodactylus teuchis (Monopisthocotyla: Gyrodactylidae) in farmed rainbow trout Oncorhynchus mykiss from Eastern Europe | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article First report of Gyrodactylus teuchis (Monopisthocotyla: Gyrodactylidae) in farmed rainbow trout Oncorhynchus mykiss from Eastern Europe Aleksey Parshukov, Evgeny Ieshko, Sergey Sokolov, Lubov Mugue, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5433938/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Gyrodactylus teuchis is a widespread in Western and Central Europe parasite of wild and farmed salmonid fishes. We recorded this parasite species on one-year-old caged rainbow trout Oncorhynchus mykiss from Lake Kalmozero (White Sea drainage system, Republic of Karelia, Russia) in May and October 2023. The infection prevalence was 100% and 75%, and the mean abundance was 20.8 and 18.1 ind., respectively. Morphological identification of these specimens was confirmed by molecular data on the mitochondrial cox1 gene. This is the first report on G. teuchis finding in the White Sea drainage basin as well as in cage-reared rainbow trout in Russia. aquaculture salmonids Russia White Sea cox1 gene Figures Figure 1 Introduction The development of the freshwater aquaculture of the rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), brings about risks of alien parasite introductions and transfer from farmed fish to native salmonid species. A pressing parasitological problem of trout farming in the north of European Russia is the infection of farmed fish with Gyrodactylus spp. (Ziętara et al. 2006 ; Kuusela et al. 2008 ; Evseeva et al. 2009 ; Ieshko et al. 2016 ; Hansen et al. 2022 ). Gyrodactylus teuchis Lautraite, Blanc, Thiery, Daniel & Vigneulle, 1999 is a widespread in Central and Western Europe parasite of wild and farmed salmonid fishes, namely O. mykiss, Salmo trutta Linnaeus, 1758, and Salmo salar Linnaeus, 1758 (Johnston et al. 1996; Lautraite et al. 1999 ; Cunningham et al. 2001 ; Harris et al. 2004 ; Rokicka et al. 2007 ; Paladini et al. 2009 ; Hahn et al. 2011 , 2015 ). Thus far, G. teuchis was encountered in European Russia only once, in June 2013, on cage-reared brown trout ( Salmo trutta lacustris Linnaeus, 1758) from a farm in Lake Jänisjärvi (Lake Ladoga catchment, Baltic Sea drainage system) (Ieshko et al. 2015). Originally, these worms were identified based on the sequence of mitochondrial and nuclear DNA fragments as Gyrodactylus cf. teuchis (a hybrid between G. teuchis and Gyrodactylus sp. maternally and paternally, respectively) (Ieshko et al. 2015). The ideas about the hybrid status of Gyrodactylus cf. teuchis found in fish from Lake Jänisjärvi were based on the limited data on ITS region polymorphism available to the authors. Simultaneously, Hahn et al. ( 2015 ) published new data on the ITS-marker haplotypic diversity in G. teuchis . Relying on these data, Leis et al. ( 2021 ) later identified worms from Lake Jänisjärvi as true G. teuchis. During parasitological studies of farmed rainbow trout from Lake Kalmozero (White Sea drainage system) in Russian Karelia, we discovered G. teuchis . Our data represent the first record of this parasite species in the White Sea drainage system supported by molecular and morphological evidence. Materials and Methods Cage-reared trout were sampled in one of the farms situated within Lake Kalmozero (catchment of the Kemʹ River, draining to the White Sea), Russian Karelia. In total, 18 one-year-old (age 1) rainbow trout individuals were sampled in May 2023 and 12 yearlings (1+) were collected in October 2023. The fish were immobilized, measured, fixed in 96° ethanol, and transported to the laboratory. In the laboratory, all fins of the fixed fish were cut off and were examined under LOMO MSP–2 stereomicroscope with magnification ranging from ×7 to ×45. Gyrodactylus specimens were transferred for storage to 5 ml Eppendorf tubes with 96° ethanol. The infection rates were quantified by standard metrics: prevalence (%) and mean abundance (ind.) (Bush et al. 1997 ). The parasite specimens were identified based on morphological and molecular characteristics. The morphological study of G. teuchis mainly focused on marginal hooks as the most significant structures in the traditional taxonomy of Gyrodactylus spp. (e.g., Ergens 1985 ; Shinn et al. 2001 , 2004 ). The haptoral disc of the worms picked out of 96° ethanol was cut off by a micro-scalpel and transferred with a mounting needle to micro-volume vessels with fresh water for 1–2 minutes, from where it was moved into a droplet of Proteinase K (60 µg/ml) on a glass slide for several minutes to digest the soft tissues (Ziętara et al. 2006 ). After that, the region of the glass slide containing the separated hard parts of the disc was rinsed with fresh water, a single drop of liquefied glycerol gelatin was added, and a coverslip was placed over it. The slides were then observed through a light microscope Olympus BX-53 (Nagano, Japan) equipped with the differential interference contrast at the Core Facility of the Karelian Research Centre of the Russian Academy of Sciences, Petrozavodsk, Russia. The morphometric parameters of the haptoral hard parts were measured as suggested by Shinn et al. ( 2004 ). DNA was extracted separately from body parts (anterior body remaining after haptoral disc severance) of three G. teuchis specimens according to the methods described elsewhere (Ziętara et al. 2000 , 2006 , 2010 ). The G. teuchis body parts were transferred from tubes with 96% ethanol into individual 0.2 ml tubes containing 10 µl of lysis buffer. The buffer consisted of 2.5x PCR buffer, 0.5% Tween 20, 0.5% Igepal, and 60 µg/ml Proteinase K. The tubes were incubated for 25 min at 65°C and denatured for 10 min at 94°C. The process was stopped at 4–6°C. Aliquots of 2 µl of this lysate were used as templates for PCR amplification. To amplify a 413-bp region of the mitochondrial DNA gene belonging to subunit I of cytochrome c oxidase (cox1), we designed and used primers based on sequences available in GenBank (G_teu_COIF (5ʹ-AGTAG GTGTA TGAGC CGGGT-3ʹ) and G_teu_COIR (5ʹ-GGATG CCCRA AGAAC CAGAA-3ʹ)). These primers were also used for sequencing. The amplification reaction contained 8 µl 2.5˟PCR Buffer (DIALAT Ltd., Russia), 0.6 mM dNTPs (Evrogen, Russia), 1 µM of each primer, 1 U of HF-fuzz DNA polymerase (DIALAT Ltd., Russia), 2 µl of template and nuclease-free water, making the final volume of 20 µl. The cox1 gene was amplified as in Ziętara et al. ( 2006 ). PCR products were electrophoresed on 2% agarose gels containing 0.5 µg ml − 1 ethidium bromide and visualized under UV light. Sequencing was performed on an ABI 3500 sequencer with BigDye v3.1 kit, followed by analysis and alignment of the obtained sequences using the LaserGene 17.2.1 bioinformatics software package. Results and Discussion Gyrodactylus teuchis (Fig. 1) was recorded when studying two cage-reared rainbow trout samples from May (n=18; mean weight 21.1±1.3 g) and October (n=12; mean weight 240.4±57.1 g) 2023. The prevalence of the parasite in the spring (May 2023) sample of the host was somewhat higher than in the fall (October 2023) – 100% vs 75%. Also, mean abundance was higher in May compared to October (20.8 vs 18.1). The infection intensity (min–max) varied from 1 to 126 ind. in May 2023 and from 2 to 86 ind. in October 2023. All host individuals appeared healthy, without any visible clinical signs of disease. The morphometric characteristics (min-max (mean±SD), μm) of marginal hooks in the studied G. teuchis specimens (n=20) were the following: marginal hook sickle length (MHSL) 7.3–8.2 (7.7±0.3), marginal hook sickle proximal width (MHSPW) 4.7–5.5 (5.1±0.2), marginal hook toe length (MHSTL) 1.5–2.3 (2.0±0.2), marginal hook sickle distal width (MHSDW) 6.6–7.9 (7.3±0.3), marginal hook aperture (MHAD) 6.1–6.9 (6.5±0.2), marginal hook total length (MHTL) 33.7–37.6 (35.2±1.1), and marginal hook shaft length (MHSHL) 26.6–30.2 (28.0±1.0). Pressing down of the coverslip into a strictly lateral position often deformed the hamuli and the ventral bar. As a result, their dimensions could be measured only in a few individuals (μm): hamulus total length (HTL) – 60.2, hamulus aperture distance (HAD) – 25.0, hamulus point length (HPL) – 37.7, ventral bar total width (VBTW) – 30.0, ventral bar total length (VBTL) – 27.8, ventral bar membrane length (VBMBL) – 14.7. We obtained partial sequences of the cox1 gene (373bp) for three specimens of G. teuchis collected in May 2023 on farmed rainbow trout from Lake Kalmozero. These sequences were identical both among themselves and with those obtained for G. teuchis specimens from aquacultured brook trout from River Bistrica, Slovenia (GenBank accession number KJ748454) and Lake Jänisjärvi, Karelia, Russia (GenBank accession number KR080723). This is the first report on G. teuchis finding in the White Sea drainage basin as well as in cage-reared rainbow trout in Russia. Data on the rates of infection of farmed rainbow trout by this parasite in different European localities are scarcely intercomparable because the literature provides no data on G. teuchis abundance (Lautraite et al. 1999). Such data are available only for cage-reared and wild brown trout sampled in the same cold (for northern latitudes) seasons. Compared to our results, G. teuchis in brown trout exhibited similar prevalence but lower mean abundance: prevalence 75%, mean intensity 5.9 ind. (Ieshko et al. 2015); prevalence 100%, mean intensity 14.0 ind. (Hahn et al. 2011). The morphometric features of haptoral hard parts in G. teuchis specimens collected from farmed rainbow trout in Lake Kalmozero are the most similar to those of conspecific individuals on the same host from France (Cunningham et al. 2001). This finding adds to the list of Gyrodactylus species recorded on cage-reared rainbow trout in Northwestern Russia. To date, the total list of identified helminths includes Gyrodactylus salaris RBT and the Ossetian strain of G. salaris , Gyrodactylus lavareti Malmberg, 1957 , as well as one interspecific hybrid Gyrodactylus pomeraniae ´ Gyrodactylus lavareti (e. g., Karasev et al. 1997; Evseeva et al. 2009; Ieshko et al. 2016). Meanwhile, G. lavareti and G. pomeraniae x G. lavareti has only been found once in Northwestern Russia (Karasev et al. 1997; Ieshko et al. 2016). It is difficult to say, for now, whether G. teuchis is a native species in the White Sea drainage basin or, otherwise, it is an alien species introduced together with its farmed trout host. To further our understanding of G. teuchis range and distributions more research is needed. The new data consistently demonstrate the importance of monitoring fish health in order to prevent the transfer of parasites between water bodies. Declarations Acknowledgements The authors thank Olga Kislova for language editing. Author contributions Aleksey Parshukov: writing – original draft preparation, conceptualization, collecting samples, methodology, morphological analysis, funding acquisition, resources, supervision. Evgeny Ieshko: writing – review and editing, collecting samples, conceptualization. Sergey Sokolov: writing – review and editing. Lubov Mugue: molecular analysis, writing – review and editing. Nikolai Mugue: methodology, writing – review and editing. Funding The research was supported by the Russian Science Foundation (project No. 23-24-10073) and Venture Capital Fund of the Republic of Karelia (No. 18-P23). Data availability All data used in this study are included within this paper and they can be available upon request. Ethical approval The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional guides on the collecting, care, and dissection of animals. Clinical trial number: not applicable. Consent to participate and consent to publish All authors read and approved the final manuscript. The authors have accepted responsibility for the entire content of this manuscript and approved its submission. Competing interests The authors declare no competing interests. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5433938","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":377720363,"identity":"9fdef672-eb64-4fb2-ac2c-ced9818c55c4","order_by":0,"name":"Aleksey Parshukov","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0001-9917-186X","institution":"Karelian Research Centre Russian Academy of Sciences: FGBUN Federal'nyj issledovatel'skij centr Karel'skij naucnyj centr Rossijskoj akademii nauk","correspondingAuthor":true,"prefix":"","firstName":"Aleksey","middleName":"","lastName":"Parshukov","suffix":""},{"id":377720364,"identity":"853a4581-0f7b-4ce5-8247-105688dcb244","order_by":1,"name":"Evgeny Ieshko","email":"","orcid":"","institution":"Karelian Research Centre Russian Academy of Sciences: FGBUN Federal'nyj issledovatel'skij centr Karel'skij naucnyj centr Rossijskoj akademii nauk","correspondingAuthor":false,"prefix":"","firstName":"Evgeny","middleName":"","lastName":"Ieshko","suffix":""},{"id":377720365,"identity":"67a8aad9-66a2-4c16-bb8c-d72ad802e7ed","order_by":2,"name":"Sergey Sokolov","email":"","orcid":"","institution":"FGBUN Institut problem ekologii i evolucii imeni A N Severcova Rossijskoj akademii nauk","correspondingAuthor":false,"prefix":"","firstName":"Sergey","middleName":"","lastName":"Sokolov","suffix":""},{"id":377720366,"identity":"77628cfb-8ad1-47fc-8a57-f87f98a04432","order_by":3,"name":"Lubov Mugue","email":"","orcid":"","institution":"VNIRO: FGBNU Vserossijskij naucno-issledovatel'skij institut rybnogo hozajstva i okeanografii","correspondingAuthor":false,"prefix":"","firstName":"Lubov","middleName":"","lastName":"Mugue","suffix":""},{"id":377720367,"identity":"a2bc1ea3-11d6-4171-af30-2f792c40b434","order_by":4,"name":"Nikolai Mugue","email":"","orcid":"","institution":"VNIRO: FGBNU Vserossijskij naucno-issledovatel'skij institut rybnogo hozajstva i okeanografii","correspondingAuthor":false,"prefix":"","firstName":"Nikolai","middleName":"","lastName":"Mugue","suffix":""}],"badges":[],"createdAt":"2024-11-11 17:52:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5433938/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5433938/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71266160,"identity":"5c73cad2-b117-4fc4-b8e4-a15bfb2ed352","added_by":"auto","created_at":"2024-12-12 17:46:49","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":278929,"visible":true,"origin":"","legend":"\u003cp\u003eHaptoral hard parts of \u003cem\u003eGyrodactylus teuchis\u003c/em\u003e from caged rainbow trout (White Sea drainage system, Russian Karelia). A. Marginal hook B. Hamulus and ventral bar. Scale bar = 10 μm\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5433938/v1/44f886a70a055eac8c8b38e8.png"},{"id":91963337,"identity":"69e6bf27-e222-4427-80e6-5044335f6abe","added_by":"auto","created_at":"2025-09-23 08:03:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":740781,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5433938/v1/bd3291a3-f0c9-4dbe-a16c-9dacb31f72a9.pdf"}],"financialInterests":"\u003cp\u003eAll experimental procedures with fish were reviewed and approved by the Ethics Committee of the Use of Animals in Research of the Institute of Biology, Karelian Research Centre of Russian Academy of Sciences, Russian Federation.\u003c/p\u003e","formattedTitle":"\u003cp\u003eFirst report of \u003cem\u003eGyrodactylus teuchis\u003c/em\u003e (Monopisthocotyla: Gyrodactylidae) in farmed rainbow trout \u003cem\u003eOncorhynchus mykiss\u003c/em\u003e from Eastern Europe\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe development of the freshwater aquaculture of the rainbow trout, \u003cem\u003eOncorhynchus mykiss\u003c/em\u003e (Walbaum, 1792), brings about risks of alien parasite introductions and transfer from farmed fish to native salmonid species. A pressing parasitological problem of trout farming in the north of European Russia is the infection of farmed fish with \u003cem\u003eGyrodactylus\u003c/em\u003e spp. (Ziętara et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Kuusela et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Evseeva et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Ieshko et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Hansen et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cem\u003eGyrodactylus teuchis\u003c/em\u003e Lautraite, Blanc, Thiery, Daniel \u0026amp; Vigneulle, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1999\u003c/span\u003e is a widespread in Central and Western Europe parasite of wild and farmed salmonid fishes, namely \u003cem\u003eO. mykiss, Salmo trutta\u003c/em\u003e Linnaeus, 1758, and \u003cem\u003eSalmo salar\u003c/em\u003e Linnaeus, 1758 (Johnston et al. 1996; Lautraite et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Cunningham et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Harris et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Rokicka et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Paladini et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Hahn et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Thus far, \u003cem\u003eG. teuchis\u003c/em\u003e was encountered in European Russia only once, in June 2013, on cage-reared brown trout (\u003cem\u003eSalmo trutta lacustris\u003c/em\u003e Linnaeus, 1758) from a farm in Lake J\u0026auml;nisj\u0026auml;rvi (Lake Ladoga catchment, Baltic Sea drainage system) (Ieshko et al. 2015). Originally, these worms were identified based on the sequence of mitochondrial and nuclear DNA fragments as \u003cem\u003eGyrodactylus\u003c/em\u003e cf. \u003cem\u003eteuchis\u003c/em\u003e (a hybrid between \u003cem\u003eG. teuchis\u003c/em\u003e and \u003cem\u003eGyrodactylus\u003c/em\u003e sp. maternally and paternally, respectively) (Ieshko et al. 2015). The ideas about the hybrid status of \u003cem\u003eGyrodactylus\u003c/em\u003e cf. \u003cem\u003eteuchis\u003c/em\u003e found in fish from Lake J\u0026auml;nisj\u0026auml;rvi were based on the limited data on ITS region polymorphism available to the authors. Simultaneously, Hahn et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) published new data on the ITS-marker haplotypic diversity in \u003cem\u003eG. teuchis\u003c/em\u003e. Relying on these data, Leis et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) later identified worms from Lake J\u0026auml;nisj\u0026auml;rvi as true \u003cem\u003eG. teuchis.\u003c/em\u003e\u003c/p\u003e \u003cp\u003eDuring parasitological studies of farmed rainbow trout from Lake Kalmozero (White Sea drainage system) in Russian Karelia, we discovered \u003cem\u003eG. teuchis\u003c/em\u003e. Our data represent the first record of this parasite species in the White Sea drainage system supported by molecular and morphological evidence.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eCage-reared trout were sampled in one of the farms situated within Lake Kalmozero (catchment of the Kemʹ River, draining to the White Sea), Russian Karelia. In total, 18 one-year-old (age 1) rainbow trout individuals were sampled in May 2023 and 12 yearlings (1+) were collected in October 2023. The fish were immobilized, measured, fixed in 96\u0026deg; ethanol, and transported to the laboratory. In the laboratory, all fins of the fixed fish were cut off and were examined under LOMO MSP\u0026ndash;2 stereomicroscope with magnification ranging from \u0026times;7 to \u0026times;45. \u003cem\u003eGyrodactylus\u003c/em\u003e specimens were transferred for storage to 5 ml Eppendorf tubes with 96\u0026deg; ethanol. The infection rates were quantified by standard metrics: prevalence (%) and mean abundance (ind.) (Bush et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe parasite specimens were identified based on morphological and molecular characteristics. The morphological study of \u003cem\u003eG. teuchis\u003c/em\u003e mainly focused on marginal hooks as the most significant structures in the traditional taxonomy of \u003cem\u003eGyrodactylus\u003c/em\u003e spp. (e.g., Ergens \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Shinn et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2001\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). The haptoral disc of the worms picked out of 96\u0026deg; ethanol was cut off by a micro-scalpel and transferred with a mounting needle to micro-volume vessels with fresh water for 1\u0026ndash;2 minutes, from where it was moved into a droplet of Proteinase K (60 \u0026micro;g/ml) on a glass slide for several minutes to digest the soft tissues (Ziętara et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). After that, the region of the glass slide containing the separated hard parts of the disc was rinsed with fresh water, a single drop of liquefied glycerol gelatin was added, and a coverslip was placed over it. The slides were then observed through a light microscope Olympus BX-53 (Nagano, Japan) equipped with the differential interference contrast at the Core Facility of the Karelian Research Centre of the Russian Academy of Sciences, Petrozavodsk, Russia. The morphometric parameters of the haptoral hard parts were measured as suggested by Shinn et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDNA was extracted separately from body parts (anterior body remaining after haptoral disc severance) of three \u003cem\u003eG. teuchis\u003c/em\u003e specimens according to the methods described elsewhere (Ziętara et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2000\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). The \u003cem\u003eG. teuchis\u003c/em\u003e body parts were transferred from tubes with 96% ethanol into individual 0.2 ml tubes containing 10 \u0026micro;l of lysis buffer. The buffer consisted of 2.5x PCR buffer, 0.5% Tween 20, 0.5% Igepal, and 60 \u0026micro;g/ml Proteinase K. The tubes were incubated for 25 min at 65\u0026deg;C and denatured for 10 min at 94\u0026deg;C. The process was stopped at 4\u0026ndash;6\u0026deg;C. Aliquots of 2 \u0026micro;l of this lysate were used as templates for PCR amplification.\u003c/p\u003e \u003cp\u003eTo amplify a 413-bp region of the mitochondrial DNA gene belonging to subunit I of cytochrome c oxidase (cox1), we designed and used primers based on sequences available in GenBank (G_teu_COIF (5ʹ-AGTAG GTGTA TGAGC CGGGT-3ʹ) and G_teu_COIR (5ʹ-GGATG CCCRA AGAAC CAGAA-3ʹ)). These primers were also used for sequencing. The amplification reaction contained 8 \u0026micro;l 2.5˟PCR Buffer (DIALAT Ltd., Russia), 0.6 mM dNTPs (Evrogen, Russia), 1 \u0026micro;M of each primer, 1 U of HF-fuzz DNA polymerase (DIALAT Ltd., Russia), 2 \u0026micro;l of template and nuclease-free water, making the final volume of 20 \u0026micro;l. The cox1 gene was amplified as in Ziętara et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). PCR products were electrophoresed on 2% agarose gels containing 0.5 \u0026micro;g ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e ethidium bromide and visualized under UV light.\u003c/p\u003e \u003cp\u003eSequencing was performed on an ABI 3500 sequencer with BigDye v3.1 kit, followed by analysis and alignment of the obtained sequences using the LaserGene 17.2.1 bioinformatics software package.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cem\u003eGyrodactylus teuchis\u003c/em\u003e (Fig. 1) was recorded when studying two cage-reared rainbow trout samples from May (n=18; mean weight 21.1\u0026plusmn;1.3 g) and October (n=12; mean weight 240.4\u0026plusmn;57.1 g) 2023. The prevalence of the parasite in the spring (May 2023) sample of the host was somewhat higher than in the fall (October 2023) \u0026ndash; 100% \u003cem\u003evs\u003c/em\u003e 75%. Also, mean abundance was higher in May compared to October (20.8\u003cem\u003e\u0026nbsp;vs\u0026nbsp;\u003c/em\u003e18.1). The infection intensity (min\u0026ndash;max) varied from 1 to 126 ind. in May 2023 and from 2 to 86 ind. in October 2023. All host individuals appeared healthy, without any visible clinical signs of disease.\u003c/p\u003e\n\u003cp\u003eThe morphometric characteristics (min-max (mean\u0026plusmn;SD), \u0026mu;m) of marginal hooks in the studied \u003cem\u003eG. teuchis\u0026nbsp;\u003c/em\u003especimens (n=20) were the following: marginal hook sickle length (MHSL) 7.3\u0026ndash;8.2 (7.7\u0026plusmn;0.3), marginal hook sickle proximal width (MHSPW) 4.7\u0026ndash;5.5 (5.1\u0026plusmn;0.2), marginal hook toe length (MHSTL) 1.5\u0026ndash;2.3 (2.0\u0026plusmn;0.2), marginal hook sickle distal width (MHSDW) 6.6\u0026ndash;7.9 (7.3\u0026plusmn;0.3), marginal hook aperture (MHAD) 6.1\u0026ndash;6.9 (6.5\u0026plusmn;0.2), marginal hook total length (MHTL) 33.7\u0026ndash;37.6 (35.2\u0026plusmn;1.1), and marginal hook shaft length (MHSHL) 26.6\u0026ndash;30.2 (28.0\u0026plusmn;1.0). Pressing down of the coverslip into a strictly lateral position often deformed the hamuli and the ventral bar. As a result, their dimensions could be measured only in a few individuals (\u0026mu;m): hamulus total length (HTL) \u0026ndash; 60.2, hamulus aperture distance (HAD) \u0026ndash; 25.0, hamulus point length (HPL) \u0026ndash; 37.7, ventral bar total width (VBTW) \u0026ndash; 30.0, ventral bar total length (VBTL) \u0026ndash; 27.8, ventral bar membrane length (VBMBL) \u0026ndash; 14.7.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe obtained partial sequences of the cox1 gene (373bp) for three specimens of \u003cem\u003eG. teuchis\u003c/em\u003e collected in May 2023 on farmed rainbow trout from Lake Kalmozero. These sequences were identical both among themselves and with those obtained for \u003cem\u003eG. teuchis\u003c/em\u003e specimens from aquacultured brook trout from River Bistrica, Slovenia (GenBank accession number KJ748454) and Lake J\u0026auml;nisj\u0026auml;rvi, Karelia, Russia (GenBank accession number KR080723).\u003c/p\u003e\n\u003cp\u003eThis is the first report on \u003cem\u003eG. teuchis\u003c/em\u003e finding in the White Sea drainage basin as well as in cage-reared rainbow trout in Russia. Data on the rates of infection of farmed rainbow trout by this parasite in different European localities are scarcely intercomparable because the literature provides no data on \u003cem\u003eG. teuchis\u0026nbsp;\u003c/em\u003eabundance (Lautraite et al. 1999). Such data are available only for cage-reared and wild brown trout sampled in the same cold (for northern latitudes) seasons. Compared to our results, \u003cem\u003eG. teuchis\u003c/em\u003e in brown trout exhibited similar prevalence but lower mean abundance: prevalence 75%, mean intensity 5.9 ind. (Ieshko et al. 2015); prevalence 100%, mean intensity 14.0 ind. (Hahn et al. 2011).\u003c/p\u003e\n\u003cp\u003eThe morphometric features of haptoral hard parts in\u0026nbsp;\u003cem\u003eG. teuchis\u0026nbsp;\u003c/em\u003especimens collected\u003cem\u003e\u0026nbsp;\u003c/em\u003efrom\u0026nbsp;farmed rainbow trout in\u0026nbsp;Lake Kalmozero are the most similar to those of conspecific individuals on the same host from France (Cunningham et al. 2001).\u003c/p\u003e\n\u003cp\u003eThis finding adds to the list of \u003cem\u003eGyrodactylus\u003c/em\u003e species recorded on cage-reared rainbow trout in Northwestern Russia. To date, the total list of identified helminths includes \u003cem\u003eGyrodactylus salaris\u003c/em\u003e RBT and the Ossetian strain of \u003cem\u003eG. salaris\u003c/em\u003e, \u003cem\u003eGyrodactylus lavareti\u0026nbsp;\u003c/em\u003eMalmberg, 1957\u003cem\u003e,\u003c/em\u003e as well as one interspecific hybrid \u003cem\u003eGyrodactylus pomeraniae\u0026nbsp;\u003c/em\u003e\u0026acute;\u003cem\u003e\u0026nbsp;Gyrodactylus lavareti\u003c/em\u003e (e. g., Karasev et al. 1997; Evseeva et al. 2009; Ieshko et al. 2016). Meanwhile, \u003cem\u003eG. lavareti\u003c/em\u003e and \u003cem\u003eG. pomeraniae\u0026nbsp;\u003c/em\u003ex\u003cem\u003e\u0026nbsp;G. lavareti\u003c/em\u003e has only been found once in Northwestern Russia (Karasev et al. 1997; Ieshko et al. 2016).\u003c/p\u003e\n\u003cp\u003eIt is difficult to say, for now, whether \u003cem\u003eG. teuchis\u0026nbsp;\u003c/em\u003eis a native species in the White Sea drainage basin or, otherwise, it is an alien species introduced together with its farmed trout host.\u0026nbsp;To further our understanding of\u0026nbsp;\u003cem\u003eG. teuchis\u003c/em\u003e range and distributions more research is needed. The new data consistently demonstrate the importance of monitoring fish health in order to prevent the transfer of parasites between water bodies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e The authors thank Olga Kislova for language editing.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003eAleksey Parshukov: writing\u003cem\u003e\u0026ndash;\u003c/em\u003eoriginal draft preparation, conceptualization, collecting samples, methodology, morphological analysis, funding acquisition, resources, supervision. Evgeny Ieshko: writing\u003cem\u003e\u0026ndash;\u003c/em\u003ereview and editing, collecting samples, conceptualization. Sergey Sokolov: writing\u003cem\u003e\u0026ndash;\u003c/em\u003ereview and editing. Lubov Mugue: molecular analysis, writing\u003cem\u003e\u0026ndash;\u003c/em\u003ereview and editing. Nikolai Mugue: methodology, writing\u003cem\u003e\u0026ndash;\u003c/em\u003ereview and editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e The research was supported by the Russian Science Foundation (project No. 23-24-10073) and Venture Capital Fund of the Republic of Karelia (No. 18-P23).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003eAll data used in this study are included within this paper and they can be available upon request.\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional guides on the collecting, care, and dissection of animals.\u0026nbsp;Clinical trial number: not applicable.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate and consent to publish\u003c/strong\u003e All authors read and approved the final manuscript. The authors have accepted responsibility for the entire content of this manuscript and approved its submission.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003cp\u003eBush AO, Lafferty KD, Lotz JM, Shostak AW (1997) Parasitology meets ecology on its own terms: Margolis et al. revisited. J Parasitol 83:575\u0026ndash;583. \u003ca href=\"https://doi.org/10.2307/3284227\"\u003ehttps://doi.org/10.2307/3284227\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eEvseeva N, Barskaya J, Lebedeva D (2009) The first case of\u0026nbsp;gyrodactylosis of the rainbow trout in aquaculture of Karelia.\u0026nbsp;In: Strelkov Yu, Kuznetsova E, Chernysheva N (eds)\u0026nbsp;Proceedings of GosNIORH.\u0026nbsp;St. Petersburg,\u0026nbsp;pp\u0026nbsp;71\u0026ndash;76 (In Russian)\u003c/p\u003e\n\u003cp\u003eErgens R (1985) Order Gyrodactylidea Bychowsky, 1937.\u0026nbsp;In: Bauer O.N. (Ed.) [Key to the parasites of freshwater fish of the fauna of the USSR. 2. Parasitic metazoans. Part 1.] Leningrad: Izdatel\u0026apos;tsvo \u0026ldquo;Nauka\u0026rdquo;, pp 269\u0026ndash;347 (In Russian)\u003c/p\u003e\n\u003cp\u003eCunningham C, Mo T, Collins C, Buchmann K, Thiery R, Blanc G, Lautraite A (2001) Redescription of \u003cem\u003eGyrodactylus teuchis\u003c/em\u003e Lautraite, Blanc, Thiery, Daniel \u0026amp; Vigneulle, 1999 (Monogenea: Gyrodactylidae); a species identified by ribosomal RNA sequence. Syst Parasitol 48:141\u0026ndash;150. \u003ca href=\"https://doi.org/10.1023/A:1006407428666\"\u003ehttps://doi.org/10.1023/A:1006407428666\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eIeshko E, Barskaya Y, Parshukov A, Lumme J, Khlunov O (2016)\u0026nbsp;Occurrence and morphogenetic characteristics of Gyrodactylus\u0026nbsp;(Monogenea: Gyrodactylidae) from a rainbow trout farm (Lake\u0026nbsp;Ladoga, Russia). Acta Parasitol 61:151\u0026ndash;157.\u0026nbsp;\u003ca href=\"https://doi.org/10.1515/ap-2016-0020\"\u003ehttps://doi.org/10.1515/ap-2016-0020\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eIeshko E, Lebedeva D, Lumme J (2014) A new Gyrodactylus strain on brown trout (\u003cem\u003eSalmo trutta\u003c/em\u003e) in J\u0026auml;nisj\u0026auml;rvi, Russian Karelia, and a literature revision of salmonid parasites of the genus Gyrodactylus in North-Western Russia and adjacent areas.\u0026nbsp;Acta Parasitol 60(1):75\u0026ndash;84. \u003ca href=\"https://doi.org/10.1515/ap-2015-0010\"\u003ehttps://doi.org/10.1515/ap-2015-0010\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eJohnston By, MacKenzie K, Cunningham C, Eiras J, Bruno D (1996) Occurrence of \u003cem\u003eGyrodactylus salaris\u003c/em\u003e Malmberg, 1957, in Portugal. Bull Eur Ass Fish Pathol 16(3):89\u0026ndash;91.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHahn C, Bakke T, Bachmann L, Weiss S, Harris P (2011) Morphometric and molecular characterization of \u003cem\u003eGyrodactylus teuchis\u003c/em\u003e Lautraite, Blanc, Thiery, Daniel \u0026amp; Vigneulle, 1999 (Monogenea: Gyrodactylidae) from an Austrian brown trout population. Parasitol Int 60(4):480\u0026ndash;7. \u003ca href=\"https://doi.org/10.1016/j.parint.2011.08.016\"\u003ehttps://doi.org/10.1016/j.parint.2011.08.016\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eHahn C, Weiss S, Stojanovski S, Bachmann L (2015) Co-speciation of the ectoparasite \u003cem\u003eGyrodactylus teuchis\u003c/em\u003e (Monogenea, Platyhelminthes) and its salmonid hosts. PLoS One 10(6):e0127340. \u003ca href=\"https://doi.org/10.1371/journal.pone.0127340\"\u003ehttps://doi.org/10.1371/journal.pone.0127340\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eHansen H, Ieshko E, Rusch JC,\u0026nbsp;Samokhvalov I, Melnik V, Mugue N,\u0026nbsp;Sokolov S, Parshukov A (2022)\u0026nbsp;\u003cem\u003eGyrodactylus salaris\u003c/em\u003e Malmberg, 1957\u0026nbsp;(Monogenea, Gyrodactylidae) spreads\u0026nbsp;further \u0026ndash; a consequence of rainbow trout\u0026nbsp;farming in Northern Russia.\u0026nbsp;Aquatic\u0026nbsp;Invasions\u0026nbsp;17(2):224\u0026ndash;237.\u0026nbsp;\u003ca href=\"https://doi.org/10.3391/ai.2022.17.2.06\"\u003ehttps://doi.org/10.3391/ai.2022.17.2.06\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eHarris P, Shinn A, Cable J, Bakke T (2004) Nominal species of the genus Gyrodactylus von Nordmann 1832 (Monogenea: Gyrodactylidae), with a list of principal host species. Syst Parasitol 59: 1\u0026ndash;27. \u003ca href=\"https://doi.org/10.1023/B:SYPA.0000038447.52015.e4\"\u003ehttps://doi.org/10.1023/B:SYPA.0000038447.52015.e4\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eKarasev A, Mitenev V, Kalinina N (1997) Parasite fauna of cage-reared rainbow trout \u003cem\u003eOncorhynchus mykiss\u003c/em\u003e (Walbaum). Research in freshwater farms (Kola Peninsula, Russia). Bull Eur Ass Fish Pathol 17(5):177\u0026ndash;179.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eKuusela J, Ziętara MS, Lumme J (2008) Description of three new European cryptic species of Gyrodactylus Nordmann, 1832 supported by nuclear and mitochondrial phylogenetic characterization. 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Hereditas 143:84\u0026ndash;90. \u003ca href=\"https://doi.org/10.1111/j.2006.0018-0661.01956.x\"\u003ehttps://doi.org/10.1111/j.2006.0018-0661.01956.x\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003eZiętara M, Rokicka M, Stojanovski S, Lumme J (2010) Introgression of distant mitochondria into the genome of \u003cem\u003eGyrodactylus salaris\u003c/em\u003e: Nuclear and mitochondrial markers are necessary to identify parasite strains. Acta Parasitol 55:20\u0026ndash;28. \u003ca href=\"https://doi.org/10.2478/s11686-010-0016-4\"\u003ehttps://doi.org/10.2478/s11686-010-0016-4\u003c/a\u003e\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"aquaculture, salmonids, Russia, White Sea, cox1 gene","lastPublishedDoi":"10.21203/rs.3.rs-5433938/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5433938/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e \u003cem\u003eGyrodactylus teuchis\u003c/em\u003e is a widespread in Western and Central Europe parasite of wild and farmed salmonid fishes. We recorded this parasite species on one-year-old caged rainbow trout \u003cem\u003eOncorhynchus mykiss\u003c/em\u003e from Lake Kalmozero (White Sea drainage system, Republic of Karelia, Russia) in May and October 2023. The infection prevalence was 100% and 75%, and the mean abundance was 20.8 and 18.1 ind., respectively. Morphological identification of these specimens was confirmed by molecular data on the mitochondrial cox1 gene. This is the first report on \u003cem\u003eG. teuchis\u003c/em\u003e finding in the White Sea drainage basin as well as in cage-reared rainbow trout in Russia.\u003c/p\u003e","manuscriptTitle":"First report of Gyrodactylus teuchis (Monopisthocotyla: Gyrodactylidae) in farmed rainbow trout Oncorhynchus mykiss from Eastern Europe","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-12 17:38:34","doi":"10.21203/rs.3.rs-5433938/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"025be67a-4978-4936-ba30-2cc86b586384","owner":[],"postedDate":"December 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-23T07:55:07+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-12 17:38:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5433938","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5433938","identity":"rs-5433938","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}