Effects of Different Strategies of Low Temperature on Egg Hatching of Dactylogyrus Vastator (Monogenea: Dactylogyridae)

Effects of Different Strategies of Low Temperature on Egg Hatching of Dactylogyrus Vastator (Monogenea: Dactylogyridae) | 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 Effects of Different Strategies of Low Temperature on Egg Hatching of Dactylogyrus Vastator (Monogenea: Dactylogyridae) Xiaoping Zhang, Baodi Shang, Yingyin Cheng, Guitang Wang, Wenxiang Li This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-560786/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 Background: The development of dactylogyrids is water temperature dependent, and their eggs fail to hatch below 5°C. The dactylogyrids are supposed to overwinter with adults on hosts or eggs in the water. In the field investigation, however, mean abundance of some Dactylogyrus species increases and reaches to a high level in winter, which suggests that the eggs may hatch into infective oncomiracidia in winter. Therefore, effects of low water temperature on egg hatching of D. vastator were determined on gills of goldfish ( Carassius auratus ) in laboratory. Results: The eggs of D. vastator hatched and the hatching success was 65.3%, 62.7%, 42.6% and 22.3% when eggs were firstly incubated for 0, 7, 14 and 21 days at 5 °C and then maintained for 15 days at 20 °C. Hatching success in 14 and 21-day group was significantly lower than in 0 and 7-day group. When eggs were directly incubated at 5 °C, eggs failed to hatch within one month. However, the hatching success was 69.8% and 66.7%, respectively, when maintained at 5 °C after12 and 24 h incubation at 20 °C. Conclusions: Egg incubation for more than two weeks at low temperature had significant impacts on hatching success of D. vastator at room temperature. But low temperature had little effects on hatching success when eggs are firstly exposed to suitable temperature range for a short time. Once the embryonic development of eggs is activated, egg hatching will continue regardless of the low temperature. D. vastator eggs laid in late autumn are able to hatch in winter. Parasitology Monogenea Dactylogyrus vastator low water temperature egg hatching Background Monogeneans, belonging to the parasitic Platyhelminth, are usually found on gills, fins and scales of fish, and transmit rapidly because of the direct life cycle and short-generation time [ 1 ]. Hooks and hamuli of the opisthaptor penetrate deep into the gill lamellae and produce erosion and inflammation of the epithelium of the primary and secondary lamellae [ 2 ]. Some blood-feeding monogeneans on gills of fish cause the anemia [ 3 ]. Infection of the ectoparasites often cause great losses of farming fish [ 4 , 5 ] and wild fish [ 6 ]. In the field investigation, different monogeneans species display different patterns of seasonal occurrence [ 7 ]. Mean abundance of Pseudodactylogyrus anguillae in eel Anguilla anguilla [ 8 ] and Dactylogyrus ctenopharyngodonis on grass carp ( Ctenopharyngodon idellus ) [ 9 ] is high in summer and autumn, which are warmth-loving species [ 7 ]. Whereas, the number of D. lamellatus peaks in late winter and spring [ 9 ], which is cold-loving type. Under laboratory condition, development of monogeneans is water temperature dependent [ 10 , 11 , 12 ]. The monogenean Dactylogyrus vastator Nybelin, 1924 (Dactylogyridae) is common on gills of common carp ( Cyprinus carpio ) and goldfish ( Carassius auratus ) [ 13 , 14 , 15 ]. Heavy infection with D. vastator results in host death[ 16 , 17 ]. The egg hatching and the development of D. vastator are also shown to be temperature-dependent [ 1 , 18 ]. Bychowsky (1957) supposes that the adult individuals survive the winter on host and no egg laying and hatching occurs in winter [ 1 ]. Actually, mean abundance of D. lamellatus on grass carp [ 9 ] and D. vastator on goldfish (unpublished data) increases and reaches to a high level in winter. This phenomenon suggests that egg hatching maybe occur in winter. Although many researches focus on effects of temperature on development of monogeneans [ 10 , 11 , 12 , 18 , 19 , 20 , 21 , 22 ], few involve the effect of temperature change on development of monogeneans to simulate the scenario of seasonal variation. Therefore, effects of different strategies of low water temperature on egg hatching of D. vastator were investigated on gills of goldfish in laboratory. Methods Collection of Dactylogyrus vastator Goldfish infected with Dactylogyrus vastator were obtained from our lab [23] and reared in a 40 L glass tank indoor. The water temperature was maintained at around 20 °C and the goldfish were fed daily on commercial pellet feed. Subsequently, the gills of the goldfish were removed and examined for D. vastator under a stereomicroscope. D. vastator was collected from the gills using fine needles. Based on body size and color, the matured individuals were selected and placed in 24-well culture plates for egg hatching experiments. The effect of low water temperature on egg hatching Eggs laid in the 24-well plate were collected immediately and randomly distributed to 7 groups with 3 replicates per group. At least 60 eggs were included in each group. To determine whether the duration of egg hatching at low temperature affected hatching success, eggs were incubated for 0 (control), 7, 14 and 21 days at 5 °C, and then transferred to maintain for 15 days at 20 °C. To determine whether the eggs deposited in late autumn can hatch during winter, eggs were exposed to 20 °C for 0 (control), 12 and 24 h, and then maintained for one month at 5 °C. Eggs were observed under an inverted microscope every 12 h. The empty eggs with open opercula were recorded as the number of hatching success. Hatching success was expressed as the proportion of the number of empty eggs out of the total number of eggs incubated. Statistical analysis A Chi-square test was used to evaluate whether there were significant differences in egg hatching success among the different temperature groups. Analyses were performed using the program SPSS 13.0. Results The eggs hatched when eggs initially incubated for 0, 7, 14 and 21 days at 5 °C and then maintained for 15 days at 20 °C. The hatching success of eggs declined with the increasing days at 5 °C (Table 1). Hatching success in the groups of 14 and 21 days (42.6% and 22.3%) was significantly lower than the groups of 0 and 7 days (65.3% and 62.7%) ( P < 0.05). The hatching success incubated for 21 days was significantly lower than that of incubation of 14 days ( P < 0.05). No egg hatched after one month of incubation at 5 °C. However, the hatching success of eggs was 69.8% and 66.7%, respectively when eggs were firstly incubated for 12 and 24 h at 20 °C and then maintained for one month at 5 °C (Table 1). The hatching success show no significant differences with tthat of direct incubation at 20 °C (65.3%) ( P < 0.05). Discussion Development of monogeneans is usually water temperature dependent [1, 12, 19]. Hatching times are inversely related to water temperature [10, 21]. Hatching success increases with the rise of water temperature [18, 24]. Eggs fail to hatch at extremely low water temperature [10, 24]. In the present study, eggs of D. vastator also failed to hatch when directly incubated at the water temperature of 5 °C. However, the eggs exposed to low temperature hatched when subsequently maintained at 20 °C, and the hatching success decreased with the duration of cold exposure (7-21 days at 5 °C). These results suggested that a short period of cold shock (within one week) had limited impact on egg viability, whereas long-term exposure to low temperature had serious impacts on embryonic development. Eggs may be arrested at low temperature but retained high viability; their development resumed and hatching occurred after the period normally required at this higher temperature [25]. Eggs of Pseudodactylogyrus bini did not hatched when incubated for 10 days at 5 °C, but hatched with 75.5% hatching success after being transferred to room temperature [26]. The eggs of Heterobothrium okamotoi did not hatch after 23 days of incubation at 10 °C, but high hatching rates were detected when transferred to 15 °C [22]. The eggs of Protopolystoma orientalis and P. xenopodis apparently retained a relatively high viability when exposed to 5 °C for a short period (18 h) and then incubated at 25 °C [24]. But all eggs of P. xenopodis were found to have died after incubation for 3 months at 10 and 12 °C [27]. More than three weeks of incubation at 5 °C had significant impacts on hatching success of Diplectanum aequans eggs before incubation at room temperature [19]. Our results revealed that 2 weeks of exposure to 5 °C appeared to have significant impacts on the hatching success of. D. vastator , and the effects of low temperature on egg viability were dependent on exposure time. Although viability of eggs of D. vastator was related to exposure time to low temperature, hatching success was hardly affected at low temperature after short-term incubation at room temperature. This result suggested that eggs of D. vastator laid in late autumn could hatch in winter. Generally, monogeneans survived winter mainly as adults on host or eggs in the water (Bychowsky 1957). As a rule, reproduction does not take place during winter for freshwater monogeneans [1]. When directly incubated at low temperature, eggs did not hatch for Diplectanum aequans [10], Pseudodactylogyrus bini [26], Heterobothrium okamoto [22], Protopolystoma orientalis and P. xenopodis [24, 27]. In the present study, however, a high hatching success was detected when eggs incubated at 5 °C after 12-24 h incubation at 20 °C. This result indicated that short exposure to moderate temperatures activated embryonic development of the eggs of D. vastator , and the developing eggs eliminated the effects of low temperature and continued hatching. The eggs of Entobdellu soleue are originally colourless inside the reproductive adults, but become darker in the uterus or after laying [28]. The change in colour of the E. soleue eggs corresponds with the hardening of the egg shell [29]. Hatching success was significantly higher at day 35 than at day 6 when treated with freshwater and formalin since the harder egg shell was less flexible and more impermeable [30]. Therefore, the eggshell of monogeneans had the capability to protect the developing embryo and unhatched larva from detrimental osmotic effects [31]. Based on this result, some eggs of D. vastator laid in late autumn were supposed to hatch during winter. Seasonal occurrence of D. vastator also provided some evidences for eggs hatching in winter. In the field investigation, mean abundance of D. vastator in C. auratus increased in winter and reached a high level in early spring (unpublished data). In addition, the host goldfish tends to shoal at the bottom of water bodies, where the water temperature is higher than 5 °C. So it is possible that the hatched oncomiracidia have the infective ability to find hosts and locomote to the gills of goldfish in winter. Conclusions Long-term egg incubation (more than two weeks) at low temperature had negative impacts on hatching success of D. vastator at room temperature. But low temperature had little effects on hatching success when eggs are firstly exposed to suitable temperature range for a short time. Since the eggshell of D. vastator had the capability to protect the developing embryo and unhatched larva from detrimental osmotic effects, once the embryonic development of eggs is activated, the developing eggs of D. vastator can eliminate the effects of low temperature and continue hatching. That is why some eggs laid in late autumn can hatch in winter. Besides the adults on hosts or eggs in the water, hatched oncomiracidia is also a potential pathway to overwinter. Declarations Ethics approval and consent to participate All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. Consent for publication Not applicable Competing interests The authors declare that they have no competing interests. Funding This work was funded by the National Key Research and Development Program of China (Grant No. 2019YFD0900703), the National Natural Science Foundation of China (31872604) and the China Agriculture Research System of MOF and MARA. Authors' contributions XPZ performed the laboratory work, performed the analysis and wrote the manuscript. WXL designed the experiment and analysed the data. All authors contributed to the interpretation of the findings and approved the final manuscript. References Bychowsky BE. Monogenetic trematodes, their classification and phylogeny. Moscow: Leningrad: Academy of science. USSR; 1957. Dezfuli BS, Giari L, Simoni E, Menegatti R, Shinn AP, Manera M. Gill histopathology of cultured European sea bass, Dicentrarchus labrax (L.), infected with Diplectanum aequans (Wagener 1857) Diesing 1958 (Diplectanidae : Monogenea). Parasitol Res. 2007;100 4:707-13. Yoshinaga T, Kamaishi T, Segawa I, Yamano K, Ikeda H, Sorimachi M. Anemia caused by challenges with the monogenean Neoheterobothrium hirame in the Japanese flounder. Fish Pathol. 2001;36 1:13-20. Bondad-Reantaso MG, Subasinghe RP, Arthur JR, Ogawa K, Chinabut S, Adlard R, et al. Disease and health management in Asian aquaculture. Vet Parasitol. 2005;132 3-4:249-72. Thoney DA, Hargis WJ, Jr. Monogenea (platyhelminthes) as hazards for fish in confinement. Annual Reviews of Fish Diseases. 1991;1:133-53. Shirakashi S, Yamada T, Yamada T, Ogawa K. Infection dynamics of Neoheterobothrium hirame (Monogenea) on juvenile olive flounder, Paralichthys olivaceus (Temminck & Schlegel), in coastal waters of Japan. J Fish Dis. 2006;29 6:319-29. Chubb JC. Seasonal occurrence of helminths in freshwater fishes Part I. Monogenea. Advances in Parasitology Volume 15; 1977. p. 133-99. Nie P, Kennedy CR. Occurrence and seasonal dynamics of Pseudodactylogyrus anguillae (Yin & Sproston) (Monogenea) in eel, Anguilla anguilla (L), in England. J Fish Biol. 1991;39 6:897-900. Yang BJ, Zou H, Zhou S, Wu SG, Wang GT, Li WX. Seasonal dynamics and spatial distribution of the Dactylogyrus species on the gills of grass carp ( Ctenopharyngodon idellus ) from a fish pond in Wuhan, China. Journal of Parasitology. 2016;102 5:507-13. Cecchini S, Saroglia M, Berni P, Cognetti-Varriale AM. Influence of temperature on the life cycle of Diplectanum aequans (Monogenea, Diplectanidae), parasitic on sea bass, Dicentrarchus labrax (L.). J Fish Dis. 1998;21 1:73-5. Jackson JA, Tinsley RC. Effects of temperature on oviposition rate in Protopolystoma xenopodis (Monogenea: Polystomatidae). Int J Parasitol. 1998;28 2:309-15. Lackenby JA, Chambers CB, Ernst I, Whittington ID. Effect of water temperature on reproductive development of Benedenia seriolae (Monogenea: Capsalidae) from Seriola lalandi in Australia. Dis Aquat Organ. 2007;74 3:235-42. Li WX, Zou H, Wu SG, Xiong F, Li M, Ma XR, et al. Composition and diversity of communities of Dactylogyrus spp. in wild and farmed goldfish Carassius auratus . Journal of Parasitology. 2018;104 4:353-8. Ling F, Tu X, Huang A, Wang G. Morphometric and molecular characterization of Dactylogyrus vastator and D. intermedius in goldfish ( Carassius auratus ). Parasitol Res. 2016;115 5:1755-65. Ogawa K, Egusa S. Six species of Dactylogyrus (Monogenea : Dactylogyridae) collected from goldfish and carp cultured in Japan. Fish Pathol. 1979;14:21-31. Paperna I. Dynamics of Dactylogyrus vastator Nybelin (Monogenea) populations on the gills of carp fry in fish ponds. Bamidgeh. 1963;5:31-50. Molnar K. Effect of decreased water oxygen content on common carp fry with Dactylogyrus vastator (Monogenea) infection of varying severity. Dis Aquat Organ. 1994;20 2:153-7. Zhang XP, Shang BD, Wang GT, Li WX, Yang X, Li ZY. The effects of temperature on egg laying, egg hatching and larval development of Dactylogyrus vastator . Acta Hydrobiologica Sinica. 2011;39:1191-7. Cecchini S, Saroglia M, Cognetti-Varriale AM, Terova G, Sabino G. Effect of low environmental temperature on embryonic development and egg hatching of Diplectanum aequans (Monogenea, Diplectanidae) infecting European sea bass, Dicentrarchus labrax . Fish Pathol. 2001;36 1:33-4. Hirazawa N, Takano R, Hagiwara H, Noguchi M, Narita M. The influence of different water temperatures on Neobenedenia girellae (Monogenea) infection, parasite growth, egg production and emerging second generation on amberjack Seriola dumerili (Carangidae) and the histopathological effect of this parasite on fish skin. Aquaculture. 2010;299 1-4:2-7. Tubbs LA, Poortenaar CW, Sewell MA, Diggles BK. Effects of temperature on fecundity in vitro, egg hatching and reproductive development of Benedenia seriolae and Zeuxapta seriolae (Monogenea) parasitic on yellowtail kingfish Seriola lalandi . Int J Parasitol. 2005;35 3:315-27. Yamabata N, Yoshinaga T, Ogawa K. Effect of water temperature on the egg production and egg viability of the monogenean Heterobothrium okamotoi infecting tiger puffer Takifugu rubripes . Fish Pathol. 2004;39 4:215-7. Zhang XP, Li WX, Ai TS, Zou H, Wu SG, Wang GT. The efficacy of four common anthelmintic drugs and traditional Chinese medicinal plant extracts to control Dactylogyrus vastator (Monogenea). Aquaculture. 2014;420-421:302-7. Jackson JA, Tinsley RC, Du Preez LH. Differentiation of two locally sympatric Protopolystoma (Monogenea: Polystomatidae) species by temperature-dependent larval development and survival. Int J Parasitol. 2001;31 8:815-21. Jackson JA: Systematic and ecological studies on the helminth parasites of Xenopus species. University of London, London, UK.; 1993. Chan BZ, Wu BW. Studies on the pathogenicity, biology and treatment of Pseudodactylogyrus for the eels in fish farms. Acta Zool Sinica. 1984;30 2:173-80. Tinsley RC, York JE, Stott LC, Everard ALE, Chapple SJ, Tinsley MC. Environmental constraints influencing survival of an African parasite in a north temperate habitat: effects of temperature on development within the host. Parasitology. 2011;138 8:1039-52. Kearn GC. Observations on egg production in the monogenean Entobdella soleae . Int J Parasitol. 1985;15 2:187-94. Llewellyn J. The evolution of parasitic platyhelminths. In: Taylor A, editor. Third Symposium of the British Society for Parasitology. Blackwell: Oxford; 1965. p. 47-78. Svendsen YS, Haug T. Effectiveness of formalin, benzocaine, and hyposaline and hypersaline exposures against adults and eggs of Entobdella hippoglossi (Muller), an ectoparasite on Atlantic halibut ( Hippoglossus hippoglossus L.). Laboratory studies. Aquaculture. 1991;94 4:279-89. Kearn GC. The eggs of monogeneans. Adv Parasit. 1986;25:175-273. Tables Table 1. Effect of low water temperature on the hatching success of Dactylogyrus vastator . Treatment 1, the eggs were incubated at 5 °C for different days and then maintained for 15 days at 20 °C; Control 1, the eggs were maintained at 20 °C; Treatment 2, the eggs were incubated at 20 °C for 12 and 24 h and then transferred to maintain for 30 days at 5 °C; Control 2, the eggs were maintained at 5 °C. Groups Incubation time No. of eggs Hatching success (%) 20 °C 5 °C 20 °C Control 1 0 0 15 d 72 65.3 Treatment 1 0 7 d 15 d 61 62.7 0 14 d 15 d 115 42.6 0 21 d 15 d 112 22.3 Control 2 0 h 30 d 0 72 0 Treatment 2 12 h 30 d 0 86 69.8 24 h 30 d 0 93 66.7 Supplementary Files egghatching.png Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-560786","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research","associatedPublications":[],"authors":[{"id":30009914,"identity":"bbbdf363-2e0f-4a6c-ad15-1ed216b9b791","order_by":0,"name":"Xiaoping Zhang","email":"","orcid":"","institution":"Institute of Hydrobiology Chinese Academy of Sciences","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xiaoping","middleName":"","lastName":"Zhang","suffix":""},{"id":30009915,"identity":"5a7ff756-6669-4894-824b-e947c80a13c0","order_by":1,"name":"Baodi Shang","email":"","orcid":"","institution":"Guizhou Fisheries Research Institute","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Baodi","middleName":"","lastName":"Shang","suffix":""},{"id":30009916,"identity":"9b244648-3a91-4923-9500-d4140b8cb152","order_by":2,"name":"Yingyin Cheng","email":"","orcid":"","institution":"Institute of Hydrobiology Chinese Academy of Sciences","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yingyin","middleName":"","lastName":"Cheng","suffix":""},{"id":30009917,"identity":"735f68ca-57df-4aa5-a02f-e37899d37566","order_by":3,"name":"Guitang Wang","email":"","orcid":"","institution":"Institute of Hydrobiology Chinese Academy of Sciences","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Guitang","middleName":"","lastName":"Wang","suffix":""},{"id":30009918,"identity":"eb767282-f987-458d-8de2-fb2601b66934","order_by":4,"name":"Wenxiang Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAoUlEQVRIiWNgGAWjYBACPmYg8cHgQALxWtiAWhhnkKYFiJl5GEjSws5jJm1TcCePgf3wA4afO4hyGI+xcY7Bs2IGnjQDxt4zRGnh3fg4x+BwYgNDDgMzYxtxWjYctgBp4X9DvJaNjxlAWiSIt4X/s2GPweFiNolnBgd7idHCz38sTeLHn8N5/PzJDx/8JEYLwjogPkCKhlEwCkbBKBgFeAAAmGstau/nJEMAAAAASUVORK5CYII=","orcid":"","institution":"Institute of Hydrobiology Chinese Academy of Sciences","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Wenxiang","middleName":"","lastName":"Li","suffix":""}],"badges":[],"createdAt":"2021-05-26 04:54:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-560786/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-560786/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":15673493,"identity":"9543e032-ae62-40a4-8e5d-11bf3cd3fadb","added_by":"auto","created_at":"2021-11-18 14:18:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":240568,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-560786/v1/87c50041-0cc7-49c6-a159-a9100bdd14e2.pdf"},{"id":9905518,"identity":"8264433f-2d03-44c6-8e4a-6ef32350e699","added_by":"auto","created_at":"2021-06-02 19:41:20","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":87505,"visible":true,"origin":"","legend":"","description":"","filename":"egghatching.png","url":"https://assets-eu.researchsquare.com/files/rs-560786/v1/a439298689ec79f2c560d5c9.png"}],"financialInterests":"","formattedTitle":"\u003cp\u003eEffects of Different Strategies of Low Temperature on Egg Hatching of \u003cem\u003eDactylogyrus Vastator\u003c/em\u003e (Monogenea: Dactylogyridae)\u003c/p\u003e","fulltext":[{"header":"Background","content":" \u003cp\u003eMonogeneans, belonging to the parasitic Platyhelminth, are usually found on gills, fins and scales of fish, and transmit rapidly because of the direct life cycle and short-generation time [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Hooks and hamuli of the opisthaptor penetrate deep into the gill lamellae and produce erosion and inflammation of the epithelium of the primary and secondary lamellae [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Some blood-feeding monogeneans on gills of fish cause the anemia [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Infection of the ectoparasites often cause great losses of farming fish [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] and wild fish [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the field investigation, different monogeneans species display different patterns of seasonal occurrence [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Mean abundance of \u003cem\u003ePseudodactylogyrus anguillae\u003c/em\u003e in eel \u003cem\u003eAnguilla anguilla\u003c/em\u003e [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and \u003cem\u003eDactylogyrus ctenopharyngodonis\u003c/em\u003e on grass carp (\u003cem\u003eCtenopharyngodon idellus\u003c/em\u003e) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] is high in summer and autumn, which are warmth-loving species [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Whereas, the number of \u003cem\u003eD. lamellatus\u003c/em\u003e peaks in late winter and spring [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], which is cold-loving type. Under laboratory condition, development of monogeneans is water temperature dependent [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe monogenean \u003cem\u003eDactylogyrus vastator\u003c/em\u003e Nybelin, 1924 (Dactylogyridae) is common on gills of common carp (\u003cem\u003eCyprinus carpio\u003c/em\u003e) and goldfish (\u003cem\u003eCarassius auratus\u003c/em\u003e) [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Heavy infection with \u003cem\u003eD. vastator\u003c/em\u003e results in host death[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The egg hatching and the development of \u003cem\u003eD. vastator\u003c/em\u003e are also shown to be temperature-dependent [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Bychowsky (1957) supposes that the adult individuals survive the winter on host and no egg laying and hatching occurs in winter [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Actually, mean abundance of \u003cem\u003eD. lamellatus\u003c/em\u003e on grass carp [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] and \u003cem\u003eD. vastator\u003c/em\u003e on goldfish (unpublished data) increases and reaches to a high level in winter. This phenomenon suggests that egg hatching maybe occur in winter. Although many researches focus on effects of temperature on development of monogeneans [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], few involve the effect of temperature change on development of monogeneans to simulate the scenario of seasonal variation. Therefore, effects of different strategies of low water temperature on egg hatching of \u003cem\u003eD. vastator\u003c/em\u003e were investigated on gills of goldfish in laboratory.\u003c/p\u003e "},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eCollection of \u003cem\u003eDactylogyrus vastator\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGoldfish infected with \u003cem\u003eDactylogyrus\u003c/em\u003e \u003cem\u003evastator\u003c/em\u003e were obtained from our lab [23] and reared in a 40 L glass tank indoor. The water temperature was maintained at around 20 \u0026deg;C and the goldfish were fed daily on commercial pellet feed.\u003c/p\u003e\n\u003cp\u003eSubsequently, the gills of the goldfish were removed and examined for \u003cem\u003eD. vastator\u003c/em\u003e under a stereomicroscope.\u003cem\u003e D. vastator\u003c/em\u003e was collected from the gills using fine needles. Based on body size and color, the matured individuals were selected and placed in 24-well culture plates for egg hatching experiments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe effect of low water temperature on egg hatching\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEggs laid in the 24-well plate were collected immediately and randomly distributed to 7 groups with 3 replicates per group. At least 60 eggs were included in each group.\u003c/p\u003e\n\u003cp\u003eTo determine whether the duration of egg hatching at low temperature affected hatching success, eggs were incubated for 0 (control), 7, 14 and 21 days at 5 \u0026deg;C, and then transferred to maintain for 15 days at 20 \u0026deg;C. To determine whether the eggs deposited in late autumn can hatch during winter, eggs were exposed to 20 \u0026deg;C for 0 (control), 12 and 24 h, and then maintained for one month at 5 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003eEggs were observed under an inverted microscope every 12 h. The empty eggs with open opercula were recorded as the number of hatching success. Hatching success was expressed as the proportion of the number of empty eggs out of the total number of eggs incubated.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA Chi-square test was used to evaluate whether there were significant differences in egg hatching success among the different temperature groups. Analyses were performed using the program SPSS 13.0.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe eggs hatched when eggs initially incubated for 0, 7, 14 and 21 days at 5 \u0026deg;C and then maintained for 15 days at 20 \u0026deg;C. The hatching success of eggs declined with the increasing days at 5 \u0026deg;C (Table 1). Hatching success in the groups of 14 and 21 days (42.6% and 22.3%) was significantly lower than the groups of 0 and 7 days (65.3% and 62.7%) (\u003cem\u003eP \u003c/em\u003e\u0026lt; 0.05). The hatching success incubated for 21 days was significantly lower than that of incubation of 14 days (\u003cem\u003eP \u003c/em\u003e\u0026lt; 0.05).\u003c/p\u003e\n\u003cp\u003eNo egg hatched after one month of incubation at 5 \u0026deg;C. However, the hatching success of eggs was 69.8% and 66.7%, respectively when eggs were firstly incubated for 12 and 24 h at 20 \u0026deg;C and then maintained for one month at 5 \u0026deg;C (Table 1). The hatching success show no significant differences with tthat of direct incubation at 20 \u0026deg;C (65.3%) (\u003cem\u003eP \u003c/em\u003e\u0026lt; 0.05).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eDevelopment of monogeneans is usually water temperature dependent [1, 12, 19]. Hatching times are inversely related to water temperature [10, 21]. Hatching success increases with the rise of water temperature [18, 24]. Eggs fail to hatch at extremely low water temperature [10, 24]. In the present study, eggs of\u003cem\u003e D. vastator\u003c/em\u003e also failed to hatch when directly incubated at the water temperature of 5 \u0026deg;C. However, the eggs exposed to low temperature hatched when subsequently maintained at 20 \u0026deg;C, and the hatching success decreased with the duration of cold exposure (7-21 days at 5 \u0026deg;C).\u003c/p\u003e\n\u003cp\u003eThese results suggested that a short period of cold shock (within one week) had limited impact on egg viability, whereas long-term exposure to low temperature had serious impacts on embryonic development. Eggs may be arrested at low temperature but retained high viability; their development resumed and hatching occurred after the period normally required at this higher temperature [25]. Eggs of\u003cem\u003e Pseudodactylogyrus bini\u003c/em\u003e did not hatched when incubated for 10 days at 5 \u0026deg;C, but hatched with 75.5% hatching success after being transferred to room temperature [26]. The eggs of \u003cem\u003eHeterobothrium okamotoi\u003c/em\u003e did not hatch after 23 days of incubation at 10 \u0026deg;C, but high hatching rates were detected when transferred to 15 \u0026deg;C [22]. The eggs of\u003cem\u003e Protopolystoma orientalis\u003c/em\u003e and \u003cem\u003eP. xenopodis\u003c/em\u003e apparently retained a relatively high viability when exposed to 5 \u0026deg;C for a short period (18 h) and then incubated at 25 \u0026deg;C [24]. But all eggs of\u003cem\u003e P. xenopodis\u003c/em\u003e were found to have died after incubation for 3 months at 10 and 12 \u0026deg;C [27]. More than three weeks of incubation at 5 \u0026deg;C had significant impacts on hatching success of \u003cem\u003eDiplectanum aequans\u003c/em\u003e eggs before incubation at room temperature [19]. Our results revealed that 2 weeks of exposure to 5 \u0026deg;C appeared to have significant impacts on the hatching success of.\u003cem\u003e D. vastator\u003c/em\u003e, and the effects of low temperature on egg viability were dependent on exposure time.\u003c/p\u003e\n\u003cp\u003eAlthough viability of eggs of\u003cem\u003e D. vastator\u003c/em\u003e was related to exposure time to low temperature, hatching success was hardly affected at low temperature after short-term incubation at room temperature. This result suggested that eggs of\u003cem\u003e D. vastator\u003c/em\u003e laid in late autumn could hatch in winter. Generally, monogeneans survived winter mainly as adults on host or eggs in the water (Bychowsky 1957). As a rule, reproduction does not take place during winter for freshwater monogeneans [1]. When directly incubated at low temperature, eggs did not hatch for \u003cem\u003eDiplectanum aequans\u003c/em\u003e [10], \u003cem\u003ePseudodactylogyrus bini\u003c/em\u003e [26], \u003cem\u003eHeterobothrium okamoto\u003c/em\u003e [22],\u003cem\u003e Protopolystoma orientalis\u003c/em\u003e and \u003cem\u003eP. xenopodis\u003c/em\u003e [24, 27].\u003c/p\u003e\n\u003cp\u003eIn the present study, however, a high hatching success was detected when eggs incubated at 5 \u0026deg;C after 12-24 h incubation at 20 \u0026deg;C. This result indicated that short exposure to moderate temperatures activated embryonic development of the eggs of \u003cem\u003eD. vastator\u003c/em\u003e, and the developing eggs eliminated the effects of low temperature and continued hatching. The eggs of \u003cem\u003eEntobdellu soleue\u003c/em\u003e are originally colourless inside the reproductive adults, but become darker in the uterus or after laying [28]. The change in colour of the \u003cem\u003eE. soleue\u003c/em\u003e eggs corresponds with the hardening of the egg shell [29]. Hatching success was significantly higher at day 35 than at day 6 when treated with freshwater and formalin since the harder egg shell was less flexible and more impermeable [30]. Therefore, the eggshell of monogeneans had the capability to protect the developing embryo and unhatched larva from detrimental osmotic effects [31]. Based on this result, some eggs of \u003cem\u003eD. vastator\u003c/em\u003e laid in late autumn were supposed to hatch during winter.\u003c/p\u003e\n\u003cp\u003eSeasonal occurrence of \u003cem\u003eD. vastator\u003c/em\u003e also provided some evidences for eggs hatching in winter. In the field investigation, mean abundance of \u003cem\u003eD. vastator\u003c/em\u003e in \u003cem\u003eC. auratus\u003c/em\u003e increased in winter and reached a high level in early spring (unpublished data). In addition, the host goldfish tends to shoal at the bottom of water bodies, where the water temperature is higher than 5 \u0026deg;C. So it is possible that the hatched oncomiracidia have the infective ability to find hosts and locomote to the gills of goldfish in winter.\u003c/p\u003e"},{"header":"Conclusions","content":" \u003cp\u003eLong-term egg incubation (more than two weeks) at low temperature had negative impacts on hatching success of \u003cem\u003eD. vastator\u003c/em\u003e at room temperature. But low temperature had little effects on hatching success when eggs are firstly exposed to suitable temperature range for a short time. Since the eggshell of \u003cem\u003eD. vastator\u003c/em\u003e had the capability to protect the developing embryo and unhatched larva from detrimental osmotic effects, once the embryonic development of eggs is activated, the developing eggs of \u003cem\u003eD. vastator\u003c/em\u003e can eliminate the effects of low temperature and continue hatching. That is why some eggs laid in late autumn can hatch in winter. Besides the adults on hosts or eggs in the water, hatched oncomiracidia is also a potential pathway to overwinter.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll applicable international, national, and/or institutional guidelines for the care and use of animals were followed.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was funded by the National Key Research and Development Program of China (Grant No. 2019YFD0900703), the National Natural Science Foundation of China (31872604) and the China\u0026nbsp;Agriculture\u0026nbsp;Research\u0026nbsp;System\u0026nbsp;of\u0026nbsp;MOF\u0026nbsp;and\u0026nbsp;MARA.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors' contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eXPZ performed the laboratory work, performed the analysis and wrote the manuscript. WXL designed the experiment and analysed the data. All authors contributed to the interpretation of the findings and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBychowsky BE. Monogenetic trematodes, their classification and phylogeny. Moscow: Leningrad: Academy of science. USSR; 1957.\u003c/li\u003e\n\u003cli\u003eDezfuli BS, Giari L, Simoni E, Menegatti R, Shinn AP, Manera M. Gill histopathology of cultured European sea bass,\u003cem\u003e Dicentrarchus labrax\u003c/em\u003e (L.), infected with \u003cem\u003eDiplectanum aequans\u003c/em\u003e (Wagener 1857) Diesing 1958 (Diplectanidae : Monogenea). Parasitol Res. 2007;100 4:707-13.\u003c/li\u003e\n\u003cli\u003eYoshinaga T, Kamaishi T, Segawa I, Yamano K, Ikeda H, Sorimachi M. Anemia caused by challenges with the monogenean\u003cem\u003e Neoheterobothrium hirame\u003c/em\u003e in the Japanese flounder. 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Occurrence and seasonal dynamics of \u003cem\u003ePseudodactylogyrus anguillae\u003c/em\u003e (Yin \u0026amp; Sproston) (Monogenea) in eel, \u003cem\u003eAnguilla anguilla\u003c/em\u003e (L), in England. J Fish Biol. 1991;39 6:897-900.\u003c/li\u003e\n\u003cli\u003eYang BJ, Zou H, Zhou S, Wu SG, Wang GT, Li WX. Seasonal dynamics and spatial distribution of the \u003cem\u003eDactylogyrus\u003c/em\u003e species on the gills of grass carp (\u003cem\u003eCtenopharyngodon idellus\u003c/em\u003e) from a fish pond in Wuhan, China. Journal of Parasitology. 2016;102 5:507-13.\u003c/li\u003e\n\u003cli\u003eCecchini S, Saroglia M, Berni P, Cognetti-Varriale AM. Influence of temperature on the life cycle of \u003cem\u003eDiplectanum aequans\u003c/em\u003e (Monogenea, Diplectanidae), parasitic on sea bass, \u003cem\u003eDicentrarchus labrax\u003c/em\u003e (L.). J Fish Dis. 1998;21 1:73-5.\u003c/li\u003e\n\u003cli\u003eJackson JA, Tinsley RC. Effects of temperature on oviposition rate in \u003cem\u003eProtopolystoma xenopodis\u003c/em\u003e (Monogenea: Polystomatidae). Int J Parasitol. 1998;28 2:309-15.\u003c/li\u003e\n\u003cli\u003eLackenby JA, Chambers CB, Ernst I, Whittington ID. Effect of water temperature on reproductive development of \u003cem\u003eBenedenia seriolae\u003c/em\u003e (Monogenea: Capsalidae) from\u003cem\u003e Seriola lalandi\u003c/em\u003e in Australia. Dis Aquat Organ. 2007;74 3:235-42.\u003c/li\u003e\n\u003cli\u003eLi WX, Zou H, Wu SG, Xiong F, Li M, Ma XR, et al. Composition and diversity of communities of\u003cem\u003e Dactylogyrus \u003c/em\u003espp. in wild and farmed goldfish\u003cem\u003e Carassius auratus\u003c/em\u003e. Journal of Parasitology. 2018;104 4:353-8.\u003c/li\u003e\n\u003cli\u003eLing F, Tu X, Huang A, Wang G. 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Aquaculture. 2014;420-421:302-7.\u003c/li\u003e\n\u003cli\u003eJackson JA, Tinsley RC, Du Preez LH. Differentiation of two locally sympatric \u003cem\u003eProtopolystoma\u003c/em\u003e (Monogenea: Polystomatidae) species by temperature-dependent larval development and survival. Int J Parasitol. 2001;31 8:815-21.\u003c/li\u003e\n\u003cli\u003eJackson JA: Systematic and ecological studies on the helminth parasites of\u003cem\u003e Xenopus\u003c/em\u003e species. University of London, London, UK.; 1993.\u003c/li\u003e\n\u003cli\u003eChan BZ, Wu BW. Studies on the pathogenicity, biology and treatment of \u003cem\u003ePseudodactylogyrus\u003c/em\u003e for the eels in fish farms. Acta Zool Sinica. 1984;30 2:173-80.\u003c/li\u003e\n\u003cli\u003eTinsley RC, York JE, Stott LC, Everard ALE, Chapple SJ, Tinsley MC. Environmental constraints influencing survival of an African parasite in a north temperate habitat: effects of temperature on development within the host. Parasitology. 2011;138 8:1039-52.\u003c/li\u003e\n\u003cli\u003eKearn GC. Observations on egg production in the monogenean \u003cem\u003eEntobdella soleae\u003c/em\u003e. Int J Parasitol. 1985;15 2:187-94.\u003c/li\u003e\n\u003cli\u003eLlewellyn J. The evolution of parasitic platyhelminths. In: Taylor A, editor. Third Symposium of the British Society for Parasitology. Blackwell: Oxford; 1965. p. 47-78.\u003c/li\u003e\n\u003cli\u003eSvendsen YS, Haug T. Effectiveness of formalin, benzocaine, and hyposaline and hypersaline exposures against adults and eggs of\u003cem\u003e Entobdella hippoglossi\u003c/em\u003e (Muller), an ectoparasite on Atlantic halibut (\u003cem\u003eHippoglossus hippoglossus\u003c/em\u003e L.). Laboratory studies. Aquaculture. 1991;94 4:279-89.\u003c/li\u003e\n\u003cli\u003eKearn GC. The eggs of monogeneans. Adv Parasit. 1986;25:175-273.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1. Effect of low water temperature on the hatching success of \u003cem\u003eDactylogyrus vastator\u003c/em\u003e. Treatment 1, the eggs were incubated at 5 \u0026deg;C for different days and then maintained for 15 days at 20 \u0026deg;C; Control 1, the eggs were maintained at 20 \u0026deg;C; Treatment 2, the eggs were incubated at 20 \u0026deg;C for 12 and 24 h and then transferred to maintain for 30 days at 5 \u0026deg;C; Control 2, the eggs were maintained at 5 \u0026deg;C.\u003c/p\u003e\n\u003ctable border=\"1\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"2\" width=\"104\"\u003e\n\u003cp\u003eGroups\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"3\" width=\"246\"\u003e\n\u003cp\u003eIncubation time\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" width=\"79\"\u003e\n\u003cp\u003eNo. of eggs\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" width=\"93\"\u003e\n\u003cp\u003eHatching success (%)\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e20 \u0026deg;C\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e5 \u0026deg;C\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e20 \u0026deg;C\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd width=\"104\"\u003e\n\u003cp\u003eControl 1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e15 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"79\"\u003e\n\u003cp\u003e72\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"93\"\u003e\n\u003cp\u003e65.3\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"3\" width=\"104\"\u003e\n\u003cp\u003eTreatment 1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e7 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e15 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"79\"\u003e\n\u003cp\u003e61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"93\"\u003e\n\u003cp\u003e62.7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e14 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e15 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"79\"\u003e\n\u003cp\u003e115\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"93\"\u003e\n\u003cp\u003e42.6\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e21 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e15 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"79\"\u003e\n\u003cp\u003e112\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"93\"\u003e\n\u003cp\u003e22.3\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd width=\"104\"\u003e\n\u003cp\u003eControl 2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e0 h\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e30 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"79\"\u003e\n\u003cp\u003e72\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"93\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"2\" width=\"104\"\u003e\n\u003cp\u003eTreatment 2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e12 h\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e30 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"79\"\u003e\n\u003cp\u003e86\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"93\"\u003e\n\u003cp\u003e69.8\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd width=\"88\"\u003e\n\u003cp\u003e24 h\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"76\"\u003e\n\u003cp\u003e30 d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"83\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"79\"\u003e\n\u003cp\u003e93\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd width=\"93\"\u003e\n\u003cp\u003e66.7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"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":"Monogenea, Dactylogyrus vastator, low water temperature, egg hatching","lastPublishedDoi":"10.21203/rs.3.rs-560786/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-560786/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003eThe development of dactylogyrids is water temperature dependent, and their eggs fail to hatch below 5°C. The dactylogyrids are supposed to overwinter with adults on hosts or eggs in the water. In the field investigation, however, mean abundance of some \u003cem\u003eDactylogyrus\u003c/em\u003e species increases and reaches to a high level in winter, which suggests that the eggs may hatch into infective oncomiracidia in winter. Therefore, effects of low water temperature on egg hatching of \u003cem\u003eD. vastator\u003c/em\u003e were determined on gills of goldfish (\u003cem\u003eCarassius auratus\u003c/em\u003e) in laboratory.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e The eggs of\u003cem\u003e D. vastator\u003c/em\u003e hatched and the hatching success was 65.3%, 62.7%, 42.6% and 22.3% when eggs were firstly incubated for 0, 7, 14 and 21 days at 5 °C and then maintained for 15 days at 20 °C. Hatching success in 14 and 21-day group was significantly lower than in 0 and 7-day group. When eggs were directly incubated at 5 °C, eggs failed to hatch within one month. However, the hatching success was 69.8% and 66.7%, respectively, when maintained at 5 °C after12 and 24 h incubation at 20 °C. \u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConclusions: \u003c/strong\u003eEgg incubation for more than two weeks at low temperature had significant impacts on hatching success of \u003cem\u003eD. vastator\u003c/em\u003e at room temperature. But low temperature had little effects on hatching success when eggs are firstly exposed to suitable temperature range for a short time. Once the embryonic development of eggs is activated, egg hatching will continue regardless of the low temperature. \u003cem\u003eD. vastator\u003c/em\u003e eggs laid in late autumn are able to hatch in winter.\u003c/p\u003e","manuscriptTitle":"Effects of Different Strategies of Low Temperature on Egg Hatching of Dactylogyrus Vastator (Monogenea: Dactylogyridae)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-06-02 19:41:18","doi":"10.21203/rs.3.rs-560786/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":"95c7b6cd-bceb-4195-894e-7e6c65cb7080","owner":[],"postedDate":"June 2nd, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":4714773,"name":"Parasitology"}],"tags":[],"updatedAt":"2021-06-23T15:10:49+00:00","versionOfRecord":[],"versionCreatedAt":"2021-06-02 19:41:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-560786","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-560786","identity":"rs-560786","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}