Seasonal Dynamics and Host Factors Influencing Eustrongylides spp. Infestation in Spotted Snakeheads, Channa punctata in Mymensingh, Bangladesh

Seasonal Dynamics and Host Factors Influencing Eustrongylides spp. Infestation in Spotted Snakeheads, Channa punctata in Mymensingh, Bangladesh | 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 Short Report Seasonal Dynamics and Host Factors Influencing Eustrongylides spp. Infestation in Spotted Snakeheads, Channa punctata in Mymensingh, Bangladesh Jarin Tasnim Tanwi, Anita Rani Dey, Johir Raihan, A.G.M.Sofi Uddin Mahamud, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5891800/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 Eustrongylides nematodes represent an emerging zoonotic threat, especially with the increasing global consumption of raw or undercooked fish. The present study aimed to investigate the seasonal variation of Eustrongylides spp. infestation in spotted snakehead, Channa punctata , from August 2020 to July 2021 and to assess the influence of the host. A total of 414 experimental C. punctata , captured from the ditches and beels connected with the Brahmaputra river, were collected for 12 months from three adjacent fish markets under Mymensingh Sadar sub-district, Mymensingh, Bangladesh. Stage four larval (L 4 ) Eustrongylides spp. were isolated from the abdominal cavity, musculature, and ovaries of 133 sampled fish, washed with 0.85% sterile physiological saline and examined under light microscope using lactophenol. Prevalence was recorded as 32.12%, with a notable mean intensity of 1.53 and an abundance of 0.49. The highest prevalence was found in autumn (45.83%). Larger fish (>18 cm) exhibited a higher prevalence (62.1%) compared to the smaller (<13 cm) (26.5%). Interestingly, females had a higher prevalence and mean intensity of infestation (35.7%, 1.69±0.10) compared to males (27.2%, 1.24±0.06). Results indicated that female and higher-weighted fish exhibit higher parasitic prevalence in C. punctata , likely due to biological and environmental factors and the immunity level of the host. Eustrongylides spp C. punctata Infestation Seasonal dynamics Host factors Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Spotted snakehead Channa punctata (Bloch, 1793), is one of the nutritionally enriched and delicious small indigenous species (SIS) from the snakehead group, which usually reaches a length up to 25 cm (9 inches). This species is prevalent across various Southeast Asian countries, including Bangladesh, and is commonly encountered in diverse freshwater habitats. Their resilience and robust adaptability are crucial for thriving in challenging aquatic environments, making them excellent candidates for commercial aquaculture (Datta et al. 2013 ; Hossain et al. 2020 ; Raihan et al. 2020 ). Notably, snakeheads exhibit an exceptional air-breathing ability, allowing them to survive out of water for extended periods. This unique trait of C. punctata ensures their viability in market conditions for long durations (Shafi and Quddus 1982 ; Raihan et al. 2020 ). The commercial value of C. punctata is underscored by its significant contribution to the fisheries sector in Bangladesh. The annual yield of snakeheads reached 2,631 metric tons in ponds, 229 metric tons in seasonal waterbodies, and 39.26 metric tons in Kaptai Lake during the 2018-19 fiscal year (DoF 2019 ). Channa punctata is well known for its taste, high nutritive value and medicinal qualities (Haniffa et al. 2004 ). Despite their economic importance, C. punctata may act as an intermediate host for many helminth parasites (Chandra et al. 1997 ) due to their food habit and mud-loving nature, which pose substantial threats to fish health and productivity (Das et al. 2018 ; Kumar et al. 2024 ). Among the helminth parasites, a concerning one is Eustrongylides spp., which belongs to the super-family Dioctophymatoidea, family Dioctophymatidae Railliet, 1915, and the sub-family Eustrongylinae Chitwood and Chitwood, 1937 (Anderson et al. 2009 ). These parasites are particularly important due to their complex life cycles involving multiple hosts, including fish-eating birds and oligochaetes (Coyner et al. 2003 ). They can cause severe inflammatory responses and significant tissue damage in their hosts, leading to reduced growth, high mortality rates, and considerable economic losses in the fisheries sector (Caudill et al. 2014 ; Dezfuli et al. 2015 ). Eustrongylides spp. are known for their wide geographic distribution and pathogenicity across various fish species, making them a notable threat to aquaculture and public health due to the risk of zoonotic transmission through the consumption of raw or undercooked fish (Goncharov et al. 2018 ). Several factors, including host size, age, diet, and environmental conditions such as water temperature and quality, influence the fish infestation by Eustrongylides spp. Generally, fourth-stage larvae (L 4 ) of this parasite are found in predatory fish viz , C. punctata (Honcharov et al. 2022 ). Seasonal variations, in particular, play a critical role in the prevalence and intensity of parasitic infections, with different seasons affecting the rates of infestation differently due to changes in water temperature, pH, and dissolved oxygen levels (Buchmann and Lindenstrøm, 2002 ; Gautam et al. 2018 ). Previous studies have documented that the highest rates of Eustrongylides spp. infestations often occur during the monsoon months, highlighting the significance of climatic factors in the epidemiology of parasitic diseases in fish (Kaur et al. 2013 ). Previously, C. punctata of the Mymensingh region were investigated and found to be infected with nematode parasites Porrocaecum sp, Ascaridia sp. and Contracaecum sp (Farzana et al. 2019 ). Despite the importance of Eustrongylides spp. in fish health, minimal research has been conducted on the seasonal dynamics of these parasites in C. punctata within Bangladesh. Understanding the life cycle, host interactions, and seasonal variations of this parasite is essential for effective management and control strategies to mitigate their impact on fish populations and aquaculture. Therefore, this study aims to investigate the seasonal variation in Eustrongylides spp. infestation in C. punctata and assess how host factors such as sex and size influence the prevalence and intensity of infestation. The findings of this research will provide fundamental information regarding parasitic prevalence, abundance and intensity that may reveal valuable insights into the life cycle of Eustrongylides spp., contributing to the development of effective strategies for preventing and managing parasitic infections in fish, thereby supporting the sustainability of the snakehead fisheries in Bangladesh. 2. Materials and Methods 2.1 Sampling Sites Three regional daily fish markets, located at Mymensingh Sadar (sub-district) (24°45′N 90°25′E) under Mymensingh district, Bangladesh viz, Seshmor market (24°43'03.9"N, 90°26'39.0"E), Kewatkhali bazar (24°44'18.5"N, 90°25'30.9"E) and Pouro supermarket (24°45'43.6"N, 90°24'30.2"E) (Fig. 1A-B) were selected for collecting experimental fish . Habitually, C. punctata is found in ditches, beels (Rahman, 1989), and stagnant waters in muddy streams (Talwar and Jhingran, 1991). Selected fish markets are located adjacent to the river Brahmaputra (Fig. 1B). The local fishermen mainly capture different fish, including C. punctata , from the local ditch, beel or stagnant water of the streams created naturally from the above-mentioned river and regularly brought to sell at the above-mentioned markets. 2.2 Sample Collection and Pre-experimental Preparation Live C. punctata were collected fortnightly for 12 months from August 2020 to July 2021, encompassing four distinct seasons: winter (November-January), summer (February-April), rainy (May-July), and autumn (August-October). A total of 414 fish were collected and transported in live condition to the Fish Disease Laboratory, Department of Aquaculture at Bangladesh Agricultural University (BAU), using oxygenated polythene bags placed in large rectangular Styrofoam boxes for subsequent analysis. Data regarding the size, weight, and infestation sites were recorded and documented for further investigation. The fish were categorized by length into small (18 cm) groups, and by weight into three categories: 10-35 g, 36-60 g, and >60 g. Microscopic examination and data analysis of the collected parasites were conducted in the Diagnostic Laboratory, Department of Parasitology at BAU. 2.3 Isolation of Nematodes Nematodes were collected from experimental fish by dissecting along the mid-ventral line using surgical scissors and isolating them from targeted organs such as the surface of visceral organs, mesenteries, and body cavities using forceps. Nematodes, if found, were isolated carefully and placed in sterile petri dishes filled with 0.85% physiological saline using forceps, excysted with a fine needle and washed three times using 0.85% physiological saline. After washing, the parasites were preserved in glycerin alcohol. Temporary slides were prepared using lactophenol, and coverslips were used to cover the parasites. Microscopic examination was done within 24 hours of parasite collection. Slides were examined under a microscope (ZEISS Primo Star, Germany) at 10× or 40× magnification for morphological identification (Fig. 2). 2.4 Infestation Studies The identification of the collected parasites was performed using the keys and descriptions provided by Yamaguti (1962), Abe (2011), and Gupta (2019). Infestations were observed following Margolis et al. (1982) by using the following formula (a-c); a) Prevalence (%) = (Total number of hosts infected/ Total number of hosts examined) × 100 b) Mean intensity = Total number of parasites collected/ Total number of infected hosts c) Abundance = Total number of parasites collected/ Total number of hosts examined. 2.5 Statistical Analysis Data analysis was conducted using the Statistical Package for Social Science (SPSS) software (Version 26.0, IBM Corp Armonk, NY) to assess associations between predictor variables by univariate analysis. The mean parasitic load was compared using the Kruskal-Wallis test. The level of significance was considered as P<0.05. Graphs were prepared using GraphPad Prism version 9.5.1.733 (GraphPad Software, Boston, MA, USA). 3. Results 3.1 Gross Identification of Nematodes No external signs of infection were observed in C. punctata . However, upon autopsy, highly coiled nematode parasites were found in the abdominal cavity, musculature, ovaries, and stomach lumen, with some encapsulated within the stomach wall. Some larvae of Eustrongylides spp. were predominantly found encysted in the body cavity and musculature (Fig. 2 A-B). The characteristics, considered for the identification were: reddish coloration, cephalic extremity, a small oral cavity surrounded by 12 cephalic papillae of similar size arranged in two concentric rings, and well-differentiated genital primordia that allowed to recognize of L 4 larvae as male and female. Eustrongylides spp. exhibited tapering ends with dense transverse striations, featuring a pink anterior end and a progressively deeper red color toward the mid-anterior section. Anterior part showing tapering end with inner labial papilla (spine-like apex), outer labial papilla (nipple-like apex), oesophagus lumen, posterior blunt end of female; caudal extremity of female larvae presenting vulva and oesophageal-intestinal junction (Fig. 3 ). The posterior end culminating in a terminal anal aperture. The number of nematodes per fish ranged from 1 to 8. 3.2 Infestation of Eustrongylides spp. in C. punctata Among the examined fish samples, 133 were found to be infected with a total of 204 Eustrongylides spp. (Fig. 4 A). The overall prevalence was 32.12%, the mean intensity of infection was 1.53, and the abundance was 0.49. Month-wise data was illustrated in Fig. 4 B. 3.3 Epidemiological Factors of Eustrongylides spp. 3.3.1 Seasonal distribution of Eustrongylides spp. in C. punctata Throughout the year, the prevalence ranged from 0–65%, with notable peaks observed in September (65%) and the lowest were recorded both in May and June (0%). Autumn season exhibited the highest average prevalence (45.83%), average mean intensity (1.74), and average abundance (0.75), while the rainy season recorded the lowest values, which were 8.97%, 0.17, and 0.62, respectively (Fig. 5 A-C and Supplementary Table 1). 3.3.2 Host factors associated with Eustrongylides spp. infestation During the experiment, larger fish (> 18 cm) exhibited the highest average prevalence (62.1%), particularly among those weighing over 60 g (52.9%). The body cavity showed the highest larval distribution (34.3%), and the remaining (18.2%) Eustrongylides spp. were isolated from the muscle. Females were more susceptible, with a prevalence of 35.7%, compared to males, who possessed a prevalence of 27.2% (Table 1 ). Table 1 Host factors associated with Eustrongylides spp. in C. punctata . Variables - Infected (n) Negative (n) Prevalence (%) 95% CI OR 95% Parasitic Load (Mean ± SE) Length (cm) 18 (n = 29) 18 11 62.1 c 44.4–79.7 4.52 (1.91–10.68) 1.66 a ± 0.21 Weight (gm) 10–35 (n = 253) 65 188 25.7 a 20.3–31.1 1 1.43 a ± 0.08 36–60 (n = 127) 50 77 39.4 b 30.9–47.9 1.87 (1.19–2.95) 1.64 a ± 0.15 > 60 (n = 34) 18 16 52.9 c 36.2–69.7 3.25 (1.56–6.75) 1.57 a ± 0.17 Site of infection Body Cavity (n = 359) 123 236 34.3 a 29.4–39.2 2.34 (1.14–4.81) 1.56 a ± 0.08 Muscle (n = 55) 10 45 18.2 b 8-28.4 1 1.09 a ± 0.09 Sex Female (n = 241) 86 155 35.7 a 29.6–41.7 1.48 (0.97–2.27) 1.69 a ± 0.10 Male (n = 173) 47 126 27.2 a 20.5–33.8 1 1.24 b ± 0.06 Note: Values with different letters (a,b,c) within a column in each variable differ significantly (p < 0.05); SE, Standard Error. 4. Discussion Eustrongylides spp. commonly known as big red worm, follows an indirect life cycle involving multiple hosts where piscivorous birds act as definitive hosts, oligochaetes (a class within Annelida) as the initial intermediate hosts and benthic fish function as secondary intermediate hosts (Coyner et al. 2003 ). C. punctata is thought to act like a paratenic host. Humans can sometimes become accidental hosts by consuming raw or undercooked freshwater fish (Menconi et al. 2020 ; Di Maggio et al. 2024 ). These parasites can cause severe inflammation and mortality in their hosts (Dezfuli et al. 2015 ; Menconi et al. 2020 ), making them a notable concern due to their potential for transmission and pathogenicity. Despite their extensive geographic distribution and broad host range, information regarding species identification, host specificity, and seasonal variation remains scarce. Numerous studies have investigated the distribution of Eustrongylides spp. in different regions, focusing on their host range and the pathology they induce (Measures, 1988 ; Junker et al. 2006 ). In Bangladesh, a case of Eustrongylides infestation was reported first in 2020 in C. punctata (Raihan et al. 2020 ) with their morphological and molecular identification but studies regarding seasonal variations and host factors influencing Eustrongylides spp. infestation were not conducted. The current research is the first to report on these issues. Parasites, collected from the various body parts of C. punctate in this study, exhibiting typical morphological characteristics viz , a large, twisted cylindrical body with subtle transverse striations on the surface. They displayed a pinkish to deep red coloration, with the cephalic extremity showing 12 labial papillae organized into inner and outer circles, which are similar to morphological characteristics observed in the previous study of Raihan et al. ( 2020 ). According to Anderson ( 2000 ), these features are crucial for characterizing the genus Eustrongylides . Large pointed apices characterized the inner circle cephalic papillae, while the outer circle papillae had nipple-like apices and wider bases, consistent with previous findings by Gupta ( 2019 ). Our study examined C. punctata and identified fourth-stage larvae (L 4 ) of Eustrongylides spp., via microscopic examination. Of these, 613 nematodes were collected, with 133 fish found to be infested with Eustrongylides spp., resulting in an overall prevalence of 32.12%. The mean intensity of infection was 1.53, and the abundance was 0.49. This is in line with findings from Kundu et al. (2015), who reported a similar prevalence rate of 44.28% for Eustrongylides spp. in C. punctata . Eustrongylides spp. have also been isolated from other fish species, such as perch ( Perca flavescens ), largemouth bass ( Micropterus salmoides ), and sand smelt ( Atherina presbyter ), with varying prevalence rates (Soylu, 2013 ; Branciari et al. 2016 ). The variation in infestation rates may be influenced by several factors, including the host’s feeding habits, geographical locations of water bodies, and the presence of intermediate hosts viz , oligochaetes, snails, and fish-eating birds. Increased parasitic infestation often correlates with elevated water temperatures and organic enrichment of water bodies due to pollution, agricultural runoff, and the indiscriminate use of antibiotics, leading to higher densities of intermediate hosts. Abiotic factors such as water temperature, along with host-related factors including sex, age, resistance, and mortality, might also be critical determinants influencing the seasonal prevalence and mean intensity of parasites (Bakke et al. 2002 ; Ozer et al. 2004 ). Throughout the study period, fish were categorized into different length and weight groups. Higher prevalence rates were observed among fish longer than 18 cm, with a prevalence of 62.1%, and in the heavier weight group (> 60 g), where prevalence reached 52.9%. The mean intensity was also higher (1.66 ± 0.21) in fish from larger length groups. This finding might be similar to the statistical analysis of Datta et al. ( 2015 ), which showed that growth was negatively allometric, i.e , length increases more rapidly than weight as C. punctata grows. Moreover, the result of this study also aligns with Upadhyay et al. ( 2012 ), who reported a significant positive correlation between fish size and parasitization, with fish above 15 cm showing a parasitic infestation rate of 64.7%, while smaller fish were nearly parasite-free. Kaur et al. ( 2012 ) demonstrated that an increase in the size of host fish is accompanied by increased parasitic infection. This pattern is likely due to larger fish consuming more food, including intermediate hosts with earlier stages of the parasite, which increases the likelihood of infestation (Das 2003 ; Ahmad et al. 2018 ). In our study, larvae of Eustrongylides spp. were most frequently found in the body cavity rather than muscles, aligning with the findings of Kaur et al. ( 2013 ) and Gupta ( 2019 ), where the body cavity and ovaries were the most common sites of infection. Environmental conditions and diet could influence this distribution pattern, as Measures ( 1988 ) suggested. Palm et al. ( 1998 ) noted that parasites like Contracaecum exhibit tissue or organ tropism essential for their development and transmission. For instance, Contracaecum radiatum generally infects the gastric wall of the host. Similarly, Eustrongylides spp. often prefer specific organs and may migrate among them based on population density or developmental needs (Balbuena et al. 2000 ; Larsen et al. 2002 ). In the present study, female C. punctata were significantly (p < 0.05) more parasitized than males, which is consistent with the findings of Vasquez and Rogers ( 1992 ) and Martins et al. ( 2009 ) in other fish species. Ibiwoye et al. ( 2004 ) also noted higher infection densities in female fish compared to males in Clarias from the Bida floodplain, supporting our findings. According to Ahmad et al. ( 2018 ), the sex of the host does not show any notable difference in helminth parasitic infection; however, this negligible increase in infection in females can be attributed to their reproductive functions because the breeding period of fish is physically demanding and stressful (Kortet et al. 2003 ) which may lead to continued chronic stress that can weaken the immune system. Thus, the preference of Eustrongylides spp. in female C. punctata may be attributed to physiological factors, as suggested by Kennedy and Lie ( 1976 ). Additionally, the actively swimming behaviour of female fish in search of spawning and feeding opportunities could potentially lead to their increased exposure to parasites (Karvonen and Lindström ( 2018 ), which interestingly contradicts the general trend of males being more susceptible to parasitic infections because of sex hormones that can suppress immune function as stated by Klein ( 2004 ). The present investigation revealed that the highest prevalence, abundance and mean intensity of Eustrongylides spp. in C. punctata occurred in the Autumn season, followed by winter, which aligns with the findings of Gautam et al. ( 2018 ), where helminth infestation was picked in Autumn in C. punctata and C. striata. Vincent and Font ( 2003 ) had slightly different findings where prevalence, mean abundance and mean intensity of nematodes were higher in summer than in winter. Bhuiyan et al. ( 2007 ) found that reduced water volume during dry seasons can lead to imbalanced nutritional conditions, making fish more susceptible to infestation. This statement corporates our study as we found the lowest parasitic infestation in the rainy season. Decreased water temperature could weaken fish immune systems and increase susceptibility to infestations. Besides, the spawning season of C. punctata ranges from April to September (Mahmud et al. 2023 ). The parasitic infestation was found to be higher during the pre-spawning (March) and post-spawning periods (October and November) in C. punctata in this study, which aligns with the findings reported by Kaur et al. ( 2013 ). The relationship between reproduction and an increase in parasite infestation is attributed to the physiological stress experienced by the host during the breeding period, which might have made the infestations more likely (Tort 2011 ). Higher reproductive investment can reduce energy allocated to the immune system, thereby facilitating parasitic infestation (White et al. 1996 ; Lizama et al. 2006 ). The seasonal dynamics and host factors of the Eustrongylides demonstrated in this research mark the first report on Eustrongylides spp. found in C. punctata under Mymensingh, Bangladesh. The findings highlight the need for further detailed epidemiological and genetic studies to confirm species identification, understand their distribution factors, and investigate transmission dynamics. 5. Conclusion The present study highlights the seasonal dynamics of Eustrongylides spp. infestations in C. punctata , focusing on their identification, distribution, and associated epidemiological factors. The findings emphasize the widespread season-wise prevalence of parasites. The morphological traits observed confirm the presence of fourth-stage larvae, contributing to the knowledge base regarding their lifecycle and host interactions. Seasonal patterns in infestation suggest significant ecological influences, with certain periods aligning with increased susceptibility in fish. The study underscores the critical role of abiotic factors, such as water, temperature and pollution, in influencing parasite prevalence and intensity. Additionally, host-specific factors like size, sex, and physiological conditions were found to markedly affect infestation rates. This research provides valuable insights into the seasonal variation and epidemiology of Eustrongylides spp. infestation in C. punctata , setting a foundation for future studies aimed at understanding their ecological impact and devising effective management strategies to mitigate the effects of these parasites on fish health and aquatic ecosystems. Declarations Author Contributions J.T.T. : Implementation of the study, investigation, data collection and processing, interpretation, and initial manuscript drafting; A.R.D. : Conceptualization, resource management, experimental designing, validation, manuscript review and editing; J.R. : Literature review, methodology, infestation studies, data processing and analysis; A.U.M. : Data curation, validation, visualization, manuscript drafting, review, and editing; S.H. : Implementation of the study, literature review, methodology, infestation studies, data processing and analysis; J.T.S. : Investigation, molecular analysis, data processing, interpretation, and initial manuscript drafting; S.S.N. : Data recording, data curation, formal analysis and organizing the manuscript; T.K. : Data curation, validation, manuscript review and editing; J.P.J. : Investigation, data collection and recording, manuscript editing; S.S.B. : Literature review, methodology and initial manuscript drafting; S.P. : Methodology, investigation and data recording; K.T.K. : Methodology, investigation and data recording; M.A.R.F. : Editing and critically revising the manuscript; T.R. : Conceptualization, experimental designing, supervision, funding acquisition, project administration, resource management, manuscript review and editing. Declaration of Interest Statement The authors declare that there is no conflict of interest. Data Availability Statement The datasets generated and/or analyzed during this study are available from the corresponding author upon reasonable request. Ethical approval This study followed the Ethical Standard of the Research Committee of Bangladesh Agricultural Research System (BAURES), Bangladesh Agricultural University, Mymensingh-2202, Bangladesh. Acknowledgement and Declaration of funding The authors are grateful to Bangladesh Agricultural University Research System (BAURES) for the financial assistance to carry out a part of this research work under the project “Towards understanding nematode infestations in the spotted snakehead, Channa punctata : Morphological and molecular approaches to determine the causal agents”; grant number: 2021/113/BAU. 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Helminthologia 59:127-142. https://doi.org/10.2478/helm-2022-0013 Hossain MN, Banu MR, Islam MR, Haque F, Hossain MA (2020) Spotted snakehead, Channa punctata (Bloch, 1793), stocking density effects on water quality, live food, and growth performances in Indian major carp polyculture system. International Journal of Fisheries and Aquatic Studies 8:116-122. Ibiwoye TII, Balogun AM, Ogunsusi RA, Agbontale JJ (2004) Determination of the infection densities of mudfish Eustrongylides in Clarias gariepinus and C. anguillaris from Bida floodplain of Nigeria. Journal of Applied Sciences and Environmental Management 8:39-44. Junker K, Bain O, Boomker J (2006) Eustrongylides sp (Nematoda: Dioctophymatoidea) from the stomach of a Nile crocodile, Crocodylus niloticus Laurenti, 1768, in Botswana. Onderstepoort Journal of Veterinary Research 73:315-317. Karvonen A, Lindström K (2018) Spatiotemporal and gender-specific parasitism in two species of gobiid fish. Ecology and Evolution 8:6114-6123. https://doi.org/10.1002/ece3.4151 Kaur P, Qureshi T, Shrivastav R, Manohar S, Bilal A (2012) Histopathological and haematological investigations on Nandus nandus (Ham.) parasitized by metacercariae of Clinostomum complanatum . International Journal of Environmental Science and Technology 2: 1324-1330. https://doi.org/10.6088/ijes.00202030019 Kaur, P, Shrivastav, R, Qureshi, TA (2013) Pathological effects of Eustrongylides sp. larvae (Dioctophymatidae) infection in freshwater fish, Glossogobius giuris (Ham.) with special reference to ovaries. Journal of Parasitic Diseases 37: 245-250. https://doi.org/10.1007/s12639-012-0173-5 Kennedy CR, Lie SF (1976) The distribution and pathogenicity of larvae of Eustrongylides (Nematoda) in brown trout Salmo trutta L. in Fernworthy Researvior, Devon. Journal of Fish Biology 8:289-302. https://doi.org/10.1111/j.1095-8649.1976.tb03952.x Klein SL (2004) Hormonal and immunological mechanisms mediating sex differences in parasite infection. Parasite Immunology 26:247-264. https://doi.org/10.1111/j.0141-9838.2004.00710.x Kortet R, Taskinen J, Sinisalo T, Jokinen I (2003) Breeding-related seasonal changes in immunocompetence, health state and condition of the cyprinid fish, Rutilus rutilus , L. Biological Journal of the Linnean Society 78:117-127. https://doi.org/10.1046/j.1095-8312.2003.00136.x Kumar V, Roy S, Parida SN, Bisai K, Dhar S, Jana AK, Das BK (2024) Deciphering the impact of endoparasitic infection on immune response and gut microbial composition of Channa punctata . Frontiers in Cellular and Infection Microbiology 14:1296769. https://doi.org/10.3389/fcimb.2024.1296769 Kundu I, Bandyopadhyay PK, Mandal DR, Gurelli G (2016) Study of pathophysiological effects of the nematode parasite Eustrongylides sp. on freshwater fish Channa punctatus by hematology, serum biochemical and histological studies. Turkish Journal of Parasitology 40:42. https://doi.org/10.5152/tpd.2016.4551 Larsen AH, Bresciani J, Buchmann K (2002) Interactions between Ecto-and Endoparasites in Trout Salmo trutta . Veterinary Parasitology 103:167-173. https://doi.org/10.1016/s0304-4017(01)00577-5 Lizama MAP, Takemoto RM, Pavanelli GC (2006) Influence of the seasonal and environmental patterns and host reproduction on the metazoan parasites of Prochilodus lineatus. Brazilian Archives of Biology and Technology 49:611-622. https://doi.org/10.1590/S1516-89132006000500011 Mahmud Y, Bhadra A, Khanom M, Awal MR, Rahman M (2023) Assessment of sexual maturity and spawning biology of Channa punctata (Bloch, 1793): conservation and reproduction. Asian Journal of Fisheries and Aquatic Research 25:95-104. https://doi.org/10.9734/ajfar/2023/v25i5703 Margolis L, Esch GW, Holmes JC, Kuris AM, Schad GA (1982) The use of ecological terms in parasitology. Journal of Parasitology 68:131-133. https://doi.org/10.2307/3281335 Martins ML, Santos R, Marengoni NG, Takahashi HK, Onaka EM (2009) Seasonality of Eustrongylides sp (Nematoda: Dioctophymatoidea) larvae in fishes from Parana river, South-Western Brazil. Veterinary Parasitology 35:29-37. Measures LN (1988) The development and pathogenesis of Eustrongylides tubifex (Nematoda: Dioctophymatoidea) in piscivorous birds. Canadian Journal of Zoology 66:2223-2232. https://doi.org/10.1139/z88-330 Menconi V, Riina, MV, Pastorino P, Mugetti D, Canola S, Pizzul E, Prearo M (2020) First occurrence of Eustrongylides spp (Nematoda: Dioctophymatidae) in a Subalpine Lake in Northwest Italy: New data on distribution and host range. International Journal of Environmental Research and Public Health 17:4171. https://doi.org/10.3390/ijerph17114171 Ozer A, Oztruk T, Oztruk MO (2004) Prevalence and intensity of Gyrodactylus arcuatus Bychowsky, 1933 (Monogenea) infestations on the three-spined stickleback, Gasterosteus aculeatus L, 1758. Turkish Journal of Veterinary and Animal Sciences 28:807-812. Palm HW, Reimann N, Spindler M, Plotz J (1998) The role of the rock cod Notothenia coriiceps Richardson, 1844 in the life-cycle of Antarctic parasites. Polar Biology 19:399-406. https://doi.org/10.1007/s003000050265 Rahman AKA (1989) Freshwater fishes of Bangladesh. Zoological Society of Bangladesh. Department of Zoology, University of Dhaka, Dhaka, p 364. Raihan J, Dey AR, Rahman T, Chandra KJ (2020) Morphological and molecular identification of nematode parasite Eustrongylides sp. isolated from Channa punctatus : A preliminary study. Journal of Bangladesh Agricultural University 18:760-767. https://doi.org/10.5455/JBAU.113219 Shafi M, Quddus AMM (1982) Bangladesh Matsha Shampad (in Bangla), Bangla Academy, Dhaka, pp 198-200. Soylu E (2013) Metazoan parasites of perch, Perca fluviatilis L. from Lake Sigirci, Ipsala, Turkey. Pakistan Journal of Zoology 45:47-52. Talwar PK, Jhingran AG (1991) Inland fishes of India and adjacent countries. Reviews in Fish Biology and Fisheries 4:135-136. https://doi.org/10.1007/BF00043269 Tort L (2011) Stress and immune modulation in fish. Developmental & Comparative Immunology 35:1366-1375. https://doi.org/10.1016/j.dci.2011.07.002 Upadhyay J, Jauhari RK, Pemola DN (2012) Parasitic incidence in a cyprinid fish Labeo rohita (Ham.) at river Song in Doon valley (Uttarakhand). Journal of Parasitic Diseases36:56-60. https://doi.org/10.1007/s12639-011-0065-0 Vasquez OE, Rogers WA (1992) First Report of Larval Eustrongylides ignotus (Nematoda: Dioctophymatidae) in Peacock Bass in Gatun Lake, Republic of Panama. Journal of Aquatic Animal Health 4:152. https://doi.org/10.1577/1548-8667(1992)0042.3.CO;2 Vincent AG, Font WF (2003) Seasonal and yearly population dynamics of two exotic helminths, Camallanus cotti (Nematoda) and Bothriocephalus acheilognathi (Cestoda: parasitizing exotic fishes in Waianu stream, O’Ahu, Hawaii. Journal of Parasitology 89:756-760. https://doi.org/10.1645/ge-90r White KAJ, Grenfel BT, Hendry RJ, Lejeune O, Murray JD (1996) Effect of seasonal host reproduction on host-macroparasite dynamics. Mathematical Biosciences 137:79-99. https://doi.org/10.1016/S0025-5564(96)00061-2 Yamaguti S (1962) Systemahelminthum. The nematodes of vertebrates; Interscience Publishers, New York and London, pp 1261. Additional Declarations No competing interests reported. Supplementary Files Suppl.docx 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5891800","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":408466630,"identity":"4bb0ad43-9150-4ee4-b428-041786d925f3","order_by":0,"name":"Jarin Tasnim Tanwi","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Jarin","middleName":"Tasnim","lastName":"Tanwi","suffix":""},{"id":408466633,"identity":"9d4e50e1-3f79-4076-9d4e-17080fafe5b1","order_by":1,"name":"Anita Rani Dey","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Anita","middleName":"Rani","lastName":"Dey","suffix":""},{"id":408466639,"identity":"18d6f7e4-ad85-4c67-8bec-c1ea767812f4","order_by":2,"name":"Johir Raihan","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Johir","middleName":"","lastName":"Raihan","suffix":""},{"id":408466648,"identity":"f3ad8130-9377-4c3a-9237-aae8d160ab08","order_by":3,"name":"A.G.M.Sofi Uddin Mahamud","email":"","orcid":"","institution":"University of Georgia","correspondingAuthor":false,"prefix":"","firstName":"A.G.M.Sofi","middleName":"Uddin","lastName":"Mahamud","suffix":""},{"id":408466649,"identity":"7f67302f-d777-4f29-b25f-2629bde2488c","order_by":4,"name":"Siyam Hossain","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Siyam","middleName":"","lastName":"Hossain","suffix":""},{"id":408466654,"identity":"e00d20d9-0c91-45e0-b9b0-e4cceda7ce5a","order_by":5,"name":"Julfat Tasnim Suchona","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Julfat","middleName":"Tasnim","lastName":"Suchona","suffix":""},{"id":408466655,"identity":"69c92935-91f0-4151-b611-55469e0741c6","order_by":6,"name":"Salman Shahriar Nibir","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Salman","middleName":"Shahriar","lastName":"Nibir","suffix":""},{"id":408466657,"identity":"a91f5bfa-b385-4428-ae0a-1f2285bc0db6","order_by":7,"name":"Tabassum Keya","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Tabassum","middleName":"","lastName":"Keya","suffix":""},{"id":408466659,"identity":"e39e0b30-68bc-4ed8-b0be-4890ca4de74f","order_by":8,"name":"Jubaida Parveen Juthy","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Jubaida","middleName":"Parveen","lastName":"Juthy","suffix":""},{"id":408466661,"identity":"946f3ba5-9656-4715-8d3d-83d586b8ec3f","order_by":9,"name":"Savayan Sadad Bushra","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Savayan","middleName":"Sadad","lastName":"Bushra","suffix":""},{"id":408466664,"identity":"c72f1f90-a7f9-4a09-9283-d2bff3eef913","order_by":10,"name":"Sandhya Paul","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Sandhya","middleName":"","lastName":"Paul","suffix":""},{"id":408466665,"identity":"a42537c5-e379-4ec3-83e2-c8df2d4b9dd4","order_by":11,"name":"Khadiza Tul Kubra","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Khadiza","middleName":"Tul","lastName":"Kubra","suffix":""},{"id":408466666,"identity":"4ffce41d-f0fa-4ebc-a1bc-e21ae9374a1d","order_by":12,"name":"Md. Ali Reza Faruk","email":"","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Md.","middleName":"Ali Reza","lastName":"Faruk","suffix":""},{"id":408466667,"identity":"37c6b42c-81b6-4231-9311-d6fbf1388695","order_by":13,"name":"Tanvir Rahman","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYLCCBBDB3gNmMzYw8DBI4FPNA9fCc4YULWAgkUOkFnv2s8ckHu5hkOe7+fbgZx4GG9kNB3gP3sBrC09emkTCMwbDmbfzkqV5GNKMNxzgS7bA77AcY4OEAwyMG27nGAC1HE7ccIDHDL9f+N+AtdhvuHnG+DcPw38itEjkGD4AaknccIPHDGjLASK03HgD0iKRPPNMXprlHINk45mHCfiFvT/H4OCPAza2fcfPHr7xpsJOtu94L/4QgwKgSw6AaAMgZiZCPQQcIFrlKBgFo2AUjDQAAFaqSPOGbeoBAAAAAElFTkSuQmCC","orcid":"","institution":"Bangladesh Agricultural University","correspondingAuthor":true,"prefix":"","firstName":"Tanvir","middleName":"","lastName":"Rahman","suffix":""}],"badges":[],"createdAt":"2025-01-24 02:38:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5891800/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5891800/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":75078112,"identity":"cfc612fb-a7f9-46e3-8b53-7f3ef4f7c7e2","added_by":"auto","created_at":"2025-01-30 08:15:18","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":31604463,"visible":true,"origin":"","legend":"\u003cp\u003eMap of the study area from where the experimental fish were collected. Note: A. Map of Bangladesh and Mymensingh sadar, Mymensingh; B. Location of the river, Brahmaputra and adjacent fish markets.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5891800/v1/4abf96bbb7f24b9ac6c9ad4f.png"},{"id":75078436,"identity":"ce776a63-4125-428c-b43c-eed8abca31d3","added_by":"auto","created_at":"2025-01-30 08:23:18","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":89480646,"visible":true,"origin":"","legend":"\u003cp\u003eObservation of\u003cstrong\u003e \u003c/strong\u003e\u003cem\u003eC. punctata \u003c/em\u003eorgans to collect and identify morphologically the \u003cem\u003eEustrongylides\u003c/em\u003e sp. Note: A. Dissection of fish to observe parasites inside the fish body; B. Collection of nematodes from fish organs; C. Collected fish parasitic nematodes; D. Observation of collected parasites under a microscope; and E. Temporary preservation of morphologically identified \u003cem\u003eEustrongylides\u003c/em\u003e sp.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-5891800/v1/92b540c307112ed84d3f7d31.png"},{"id":75078127,"identity":"f3f6afa3-c2b9-4b67-8c10-65ad0a51f0c9","added_by":"auto","created_at":"2025-01-30 08:15:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":88615187,"visible":true,"origin":"","legend":"\u003cp\u003eA. Anterior part showing tapering end: a. Inner labial papilla (spine-like apex); b. Outer labial papilla (nipple-like apex); c. Oesophagus lumen; B. Posterior blunt end of female; d. Caudal extremity of female larvae presenting vulva; C. Oesophageo-intestinal junction (arrow).\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-5891800/v1/7561b76c6fec0908d08d3340.png"},{"id":75078121,"identity":"de5c587d-6caf-46d6-ba90-54026b977177","added_by":"auto","created_at":"2025-01-30 08:15:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":6887953,"visible":true,"origin":"","legend":"\u003cp\u003eInfestation rate of \u003cem\u003eEustrongylides\u003c/em\u003e sp. in the experimental\u003cstrong\u003e \u003c/strong\u003e\u003cem\u003eC. punctata.\u003c/em\u003eA. Percentages of infested and non-infested fishes; B. Infestation over sampling period (Aug 2020-July 2021).\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-5891800/v1/82b61f8bbd7fdbf176d7c126.png"},{"id":75078128,"identity":"d7732654-831a-4365-b1da-c996fa6a946b","added_by":"auto","created_at":"2025-01-30 08:15:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":8286824,"visible":true,"origin":"","legend":"\u003cp\u003eSeasonal changes in infestation of \u003cem\u003eEustrongylides\u003c/em\u003e sp. in \u003cem\u003eC. punctata\u003c/em\u003e at Mymensingh Sadar, Mymensingh, Bangladesh. A. Seasonal changes in the prevalence of infestation; B. Seasonal changes in mean intensity of infestation; C. Seasonal changes in abundance of infestation.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-5891800/v1/14c8d1aa4ff8de2692c21e66.png"},{"id":75078115,"identity":"77ecffaa-60e8-49c0-bcaf-8a57d1ee147e","added_by":"auto","created_at":"2025-01-30 08:15:18","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":16576,"visible":true,"origin":"","legend":"","description":"","filename":"Suppl.docx","url":"https://assets-eu.researchsquare.com/files/rs-5891800/v1/989c8d3d36331c649de87ab1.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Seasonal Dynamics and Host Factors Influencing Eustrongylides spp. Infestation in Spotted Snakeheads, Channa punctata in Mymensingh, Bangladesh","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSpotted snakehead \u003cem\u003eChanna punctata\u003c/em\u003e (Bloch, 1793), is one of the nutritionally enriched and delicious small indigenous species (SIS) from the snakehead group, which usually reaches a length up to 25 cm (9 inches). This species is prevalent across various Southeast Asian countries, including Bangladesh, and is commonly encountered in diverse freshwater habitats. Their resilience and robust adaptability are crucial for thriving in challenging aquatic environments, making them excellent candidates for commercial aquaculture (Datta et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Hossain et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Raihan et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Notably, snakeheads exhibit an exceptional air-breathing ability, allowing them to survive out of water for extended periods. This unique trait of \u003cem\u003eC. punctata\u003c/em\u003e ensures their viability in market conditions for long durations (Shafi and Quddus \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Raihan et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The commercial value of \u003cem\u003eC. punctata\u003c/em\u003e is underscored by its significant contribution to the fisheries sector in Bangladesh. The annual yield of snakeheads reached 2,631 metric tons in ponds, 229 metric tons in seasonal waterbodies, and 39.26 metric tons in Kaptai Lake during the 2018-19 fiscal year (DoF \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). \u003cem\u003eChanna punctata\u003c/em\u003e is well known for its taste, high nutritive value and medicinal qualities (Haniffa et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Despite their economic importance, \u003cem\u003eC. punctata\u003c/em\u003e may act as an intermediate host for many helminth parasites (Chandra et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) due to their food habit and mud-loving nature, which pose substantial threats to fish health and productivity (Das et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kumar et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAmong the helminth parasites, a concerning one is \u003cem\u003eEustrongylides\u003c/em\u003e spp., which belongs to the super-family Dioctophymatoidea, family Dioctophymatidae Railliet, 1915, and the sub-family Eustrongylinae Chitwood and Chitwood, 1937 (Anderson et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These parasites are particularly important due to their complex life cycles involving multiple hosts, including fish-eating birds and oligochaetes (Coyner et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). They can cause severe inflammatory responses and significant tissue damage in their hosts, leading to reduced growth, high mortality rates, and considerable economic losses in the fisheries sector (Caudill et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Dezfuli et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). \u003cem\u003eEustrongylides\u003c/em\u003e spp. are known for their wide geographic distribution and pathogenicity across various fish species, making them a notable threat to aquaculture and public health due to the risk of zoonotic transmission through the consumption of raw or undercooked fish (Goncharov et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Several factors, including host size, age, diet, and environmental conditions such as water temperature and quality, influence the fish infestation by \u003cem\u003eEustrongylides\u003c/em\u003e spp. Generally, fourth-stage larvae (L\u003csub\u003e4\u003c/sub\u003e) of this parasite are found in predatory fish \u003cem\u003eviz\u003c/em\u003e, \u003cem\u003eC. punctata\u003c/em\u003e (Honcharov et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Seasonal variations, in particular, play a critical role in the prevalence and intensity of parasitic infections, with different seasons affecting the rates of infestation differently due to changes in water temperature, pH, and dissolved oxygen levels (Buchmann and Lindenstr\u0026oslash;m, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Gautam et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Previous studies have documented that the highest rates of \u003cem\u003eEustrongylides\u003c/em\u003e spp. infestations often occur during the monsoon months, highlighting the significance of climatic factors in the epidemiology of parasitic diseases in fish (Kaur et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePreviously, \u003cem\u003eC. punctata\u003c/em\u003e of the Mymensingh region were investigated and found to be infected with nematode parasites \u003cem\u003ePorrocaecum\u003c/em\u003e sp, \u003cem\u003eAscaridia\u003c/em\u003e sp. and \u003cem\u003eContracaecum\u003c/em\u003e sp (Farzana et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Despite the importance of \u003cem\u003eEustrongylides\u003c/em\u003e spp. in fish health, minimal research has been conducted on the seasonal dynamics of these parasites in \u003cem\u003eC. punctata\u003c/em\u003e within Bangladesh. Understanding the life cycle, host interactions, and seasonal variations of this parasite is essential for effective management and control strategies to mitigate their impact on fish populations and aquaculture. Therefore, this study aims to investigate the seasonal variation in \u003cem\u003eEustrongylides\u003c/em\u003e spp. infestation in \u003cem\u003eC. punctata\u003c/em\u003e and assess how host factors such as sex and size influence the prevalence and intensity of infestation. The findings of this research will provide fundamental information regarding parasitic prevalence, abundance and intensity that may reveal valuable insights into the life cycle of \u003cem\u003eEustrongylides\u003c/em\u003e spp., contributing to the development of effective strategies for preventing and managing parasitic infections in fish, thereby supporting the sustainability of the snakehead fisheries in Bangladesh.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cp\u003e\u003cstrong\u003e2.1 Sampling Sites\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThree regional daily fish markets, located at Mymensingh Sadar (sub-district) (24°45′N 90°25′E) under Mymensingh district, Bangladesh \u003cem\u003eviz,\u0026nbsp;\u003c/em\u003eSeshmor market (24°43'03.9\"N, \u0026nbsp; \u0026nbsp; 90°26'39.0\"E), Kewatkhali bazar (24°44'18.5\"N, 90°25'30.9\"E) and Pouro supermarket (24°45'43.6\"N, 90°24'30.2\"E)\u0026nbsp;(Fig. 1A-B)\u0026nbsp;were selected for\u0026nbsp;collecting experimental fish\u003cem\u003e.\u0026nbsp;\u003c/em\u003eHabitually, \u003cem\u003eC. punctata\u003c/em\u003e is found in ditches, beels (Rahman, 1989), and stagnant waters in muddy streams (Talwar and Jhingran, 1991). Selected fish markets are located adjacent to the river Brahmaputra (Fig. 1B). The local fishermen mainly capture different fish, including \u003cem\u003eC. punctata\u003c/em\u003e, from the local ditch, beel or stagnant water of the streams created naturally from the above-mentioned river and regularly brought\u0026nbsp;to sell at the above-mentioned markets.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Sample Collection and Pre-experimental Preparation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Live \u003cem\u003eC. punctata\u003c/em\u003e were collected fortnightly for 12 months from August 2020 to July 2021, encompassing four distinct seasons: winter (November-January), summer (February-April), rainy (May-July), and autumn (August-October). A total of 414 fish were collected and transported in live condition to the Fish Disease Laboratory, Department of Aquaculture at Bangladesh Agricultural University (BAU),\u0026nbsp;using oxygenated polythene bags placed in large rectangular Styrofoam boxes for subsequent analysis. Data regarding the size, weight, and infestation sites were recorded and documented for further investigation. The fish were categorized by length into small (\u0026lt;13 cm), medium (13-18 cm), and large (\u0026gt;18 cm) groups, and by weight into three categories: 10-35 g, 36-60 g, and \u0026gt;60 g. Microscopic examination and data analysis of the collected parasites were conducted in the Diagnostic Laboratory, Department of Parasitology at BAU.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Isolation of Nematodes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNematodes were collected from experimental fish by dissecting along the mid-ventral line using surgical scissors and isolating them from targeted organs such as the surface of visceral organs, mesenteries, and body cavities using forceps. Nematodes, if found, were isolated carefully and placed in sterile petri dishes filled with 0.85% physiological saline using forceps, excysted with a fine needle and washed three times using 0.85% physiological saline. After washing, the parasites were preserved in glycerin\u0026nbsp;alcohol. Temporary slides were prepared using lactophenol, and coverslips were used to cover the parasites. Microscopic examination was done within 24 hours of parasite collection.\u0026nbsp;Slides were examined under a microscope (ZEISS Primo Star, Germany) at 10× or 40× magnification for morphological identification (Fig. 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4 Infestation Studies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe identification of the collected parasites was performed using the keys and descriptions provided by Yamaguti (1962), Abe (2011), and Gupta (2019). Infestations were observed following Margolis et al. (1982) by using the following formula (a-c);\u003c/p\u003e\n\u003cp\u003ea)\u0026nbsp; \u0026nbsp;Prevalence (%) = (Total number of hosts infected/ Total number of hosts examined) × 100\u003c/p\u003e\n\u003cp\u003eb)\u0026nbsp; \u0026nbsp;Mean intensity = Total number of parasites collected/ Total number of infected hosts\u003c/p\u003e\n\u003cp\u003ec)\u0026nbsp; \u0026nbsp;Abundance = Total number of parasites collected/ Total number of hosts examined.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5 Statistical Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData analysis was conducted using the Statistical Package for Social Science (SPSS) software (Version 26.0, IBM Corp Armonk, NY) to assess associations between predictor variables by univariate analysis. The mean parasitic load was compared using the Kruskal-Wallis test. The level of significance was considered as P\u0026lt;0.05. Graphs were prepared using GraphPad Prism version 9.5.1.733 (GraphPad Software, Boston, MA, USA).\u003c/p\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Gross Identification of Nematodes\u003c/h2\u003e \u003cp\u003eNo external signs of infection were observed in \u003cem\u003eC. punctata\u003c/em\u003e. However, upon autopsy, highly coiled nematode parasites were found in the abdominal cavity, musculature, ovaries, and stomach lumen, with some encapsulated within the stomach wall. Some larvae of \u003cem\u003eEustrongylides\u003c/em\u003e spp. were predominantly found encysted in the body cavity and musculature (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA-B). The characteristics, considered for the identification were: reddish coloration, cephalic extremity, a small oral cavity surrounded by 12 cephalic papillae of similar size arranged in two concentric rings, and well-differentiated genital primordia that allowed to recognize of L\u003csub\u003e4\u003c/sub\u003e larvae as male and female.\u003c/p\u003e \u003cp\u003e \u003cem\u003eEustrongylides\u003c/em\u003e spp. exhibited tapering ends with dense transverse striations, featuring a pink anterior end and a progressively deeper red color toward the mid-anterior section. Anterior part showing tapering end with inner labial papilla (spine-like apex), outer labial papilla (nipple-like apex), oesophagus lumen, posterior blunt end of female; caudal extremity of female larvae presenting vulva and oesophageal-intestinal junction (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The posterior end culminating in a terminal anal aperture. The number of nematodes per fish ranged from 1 to 8.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Infestation of \u003cem\u003eEustrongylides\u003c/em\u003e spp. in \u003cem\u003eC. punctata\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eAmong the examined fish samples, 133 were found to be infected with a total of 204 \u003cem\u003eEustrongylides\u003c/em\u003e spp. (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). The overall prevalence was 32.12%, the mean intensity of infection was 1.53, and the abundance was 0.49. Month-wise data was illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Epidemiological Factors of \u003cem\u003eEustrongylides\u003c/em\u003e spp.\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Seasonal distribution of \u003cem\u003eEustrongylides\u003c/em\u003e spp. in \u003cem\u003eC. punctata\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eThroughout the year, the prevalence ranged from 0\u0026ndash;65%, with notable peaks observed in September (65%) and the lowest were recorded both in May and June (0%). Autumn season exhibited the highest average prevalence (45.83%), average mean intensity (1.74), and average abundance (0.75), while the rainy season recorded the lowest values, which were 8.97%, 0.17, and 0.62, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA-C and Supplementary Table\u0026nbsp;1).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 Host factors associated with \u003cem\u003eEustrongylides\u003c/em\u003e spp. infestation\u003c/h2\u003e \u003cp\u003eDuring the experiment, larger fish (\u0026gt;\u0026thinsp;18 cm) exhibited the highest average prevalence (62.1%), particularly among those weighing over 60 g (52.9%). The body cavity showed the highest larval distribution (34.3%), and the remaining (18.2%) \u003cem\u003eEustrongylides\u003c/em\u003e spp. were isolated from the muscle. Females were more susceptible, with a prevalence of 35.7%, compared to males, who possessed a prevalence of 27.2% (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eHost factors associated with \u003cem\u003eEustrongylides\u003c/em\u003e spp. in \u003cem\u003eC. punctata\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariables\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInfected\u003c/p\u003e \u003cp\u003e(n)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNegative\u003c/p\u003e \u003cp\u003e(n)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePrevalence\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eOR 95%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eParasitic Load\u003c/p\u003e \u003cp\u003e(Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SE)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eLength (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;13 (n\u0026thinsp;=\u0026thinsp;113)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e26.5\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e18.4\u0026ndash;34.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.34\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13 to 18 (n\u0026thinsp;=\u0026thinsp;272)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e187\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.3\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e25.7\u0026ndash;36.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.25 (0.77\u0026ndash;2.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.57\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;18 (n\u0026thinsp;=\u0026thinsp;29)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e62.1\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e44.4\u0026ndash;79.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.52 (1.91\u0026ndash;10.68)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.66\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eWeight (gm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u0026ndash;35 (n\u0026thinsp;=\u0026thinsp;253)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e188\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.7\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20.3\u0026ndash;31.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.43\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026ndash;60 (n\u0026thinsp;=\u0026thinsp;127)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e39.4\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e30.9\u0026ndash;47.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.87 (1.19\u0026ndash;2.95)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.64\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;60 (n\u0026thinsp;=\u0026thinsp;34)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e52.9\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e36.2\u0026ndash;69.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.25 (1.56\u0026ndash;6.75)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.57\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSite of infection\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBody Cavity (n\u0026thinsp;=\u0026thinsp;359)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e123\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e236\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34.3\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.4\u0026ndash;39.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.34 (1.14\u0026ndash;4.81)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.56\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMuscle (n\u0026thinsp;=\u0026thinsp;55)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18.2\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e8-28.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.09\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFemale (n\u0026thinsp;=\u0026thinsp;241)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e155\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e35.7\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.6\u0026ndash;41.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.48 (0.97\u0026ndash;2.27)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.69\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMale (n\u0026thinsp;=\u0026thinsp;173)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e126\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20.5\u0026ndash;33.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.24\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003eNote: Values with different letters (a,b,c) within a column in each variable differ significantly (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05); SE, Standard Error.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003e \u003cem\u003eEustrongylides\u003c/em\u003e spp. commonly known as big red worm, follows an indirect life cycle involving multiple hosts where piscivorous birds act as definitive hosts, oligochaetes (a class within Annelida) as the initial intermediate hosts and benthic fish function as secondary intermediate hosts (Coyner et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). \u003cem\u003eC. punctata\u003c/em\u003e is thought to act like a paratenic host. Humans can sometimes become accidental hosts by consuming raw or undercooked freshwater fish (Menconi et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Di Maggio et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). These parasites can cause severe inflammation and mortality in their hosts (Dezfuli et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Menconi et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), making them a notable concern due to their potential for transmission and pathogenicity. Despite their extensive geographic distribution and broad host range, information regarding species identification, host specificity, and seasonal variation remains scarce. Numerous studies have investigated the distribution of \u003cem\u003eEustrongylides\u003c/em\u003e spp. in different regions, focusing on their host range and the pathology they induce (Measures, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Junker et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). In Bangladesh, a case of \u003cem\u003eEustrongylides\u003c/em\u003e infestation was reported first in 2020 in \u003cem\u003eC. punctata\u003c/em\u003e (Raihan et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) with their morphological and molecular identification but studies regarding seasonal variations and host factors influencing \u003cem\u003eEustrongylides\u003c/em\u003e spp. infestation were not conducted. The current research is the first to report on these issues.\u003c/p\u003e \u003cp\u003eParasites, collected from the various body parts of \u003cem\u003eC. punctate\u003c/em\u003e in this study, exhibiting typical morphological characteristics \u003cem\u003eviz\u003c/em\u003e, a large, twisted cylindrical body with subtle transverse striations on the surface. They displayed a pinkish to deep red coloration, with the cephalic extremity showing 12 labial papillae organized into inner and outer circles, which are similar to morphological characteristics observed in the previous study of Raihan et al. (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). According to Anderson (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), these features are crucial for characterizing the genus \u003cem\u003eEustrongylides\u003c/em\u003e. Large pointed apices characterized the inner circle cephalic papillae, while the outer circle papillae had nipple-like apices and wider bases, consistent with previous findings by Gupta (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOur study examined \u003cem\u003eC. punctata\u003c/em\u003e and identified fourth-stage larvae (L\u003csub\u003e4\u003c/sub\u003e) of \u003cem\u003eEustrongylides\u003c/em\u003e spp., via microscopic examination. Of these, 613 nematodes were collected, with 133 fish found to be infested with \u003cem\u003eEustrongylides\u003c/em\u003e spp., resulting in an overall prevalence of 32.12%. The mean intensity of infection was 1.53, and the abundance was 0.49. This is in line with findings from Kundu et al. (2015), who reported a similar prevalence rate of 44.28% for \u003cem\u003eEustrongylides\u003c/em\u003e spp. in \u003cem\u003eC. punctata\u003c/em\u003e. \u003cem\u003eEustrongylides\u003c/em\u003e spp. have also been isolated from other fish species, such as perch (\u003cem\u003ePerca flavescens\u003c/em\u003e), largemouth bass (\u003cem\u003eMicropterus salmoides\u003c/em\u003e), and sand smelt (\u003cem\u003eAtherina presbyter\u003c/em\u003e), with varying prevalence rates (Soylu, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Branciari et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The variation in infestation rates may be influenced by several factors, including the host\u0026rsquo;s feeding habits, geographical locations of water bodies, and the presence of intermediate hosts \u003cem\u003eviz\u003c/em\u003e, oligochaetes, snails, and fish-eating birds. Increased parasitic infestation often correlates with elevated water temperatures and organic enrichment of water bodies due to pollution, agricultural runoff, and the indiscriminate use of antibiotics, leading to higher densities of intermediate hosts. Abiotic factors such as water temperature, along with host-related factors including sex, age, resistance, and mortality, might also be critical determinants influencing the seasonal prevalence and mean intensity of parasites (Bakke et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Ozer et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThroughout the study period, fish were categorized into different length and weight groups. Higher prevalence rates were observed among fish longer than 18 cm, with a prevalence of 62.1%, and in the heavier weight group (\u0026gt;\u0026thinsp;60 g), where prevalence reached 52.9%. The mean intensity was also higher (1.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21) in fish from larger length groups. This finding might be similar to the statistical analysis of Datta et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), which showed that growth was negatively allometric, \u003cem\u003ei.e\u003c/em\u003e, length increases more rapidly than weight as \u003cem\u003eC. punctata\u003c/em\u003e grows. Moreover, the result of this study also aligns with Upadhyay et al. (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), who reported a significant positive correlation between fish size and parasitization, with fish above 15 cm showing a parasitic infestation rate of 64.7%, while smaller fish were nearly parasite-free. Kaur et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) demonstrated that an increase in the size of host fish is accompanied by increased parasitic infection. This pattern is likely due to larger fish consuming more food, including intermediate hosts with earlier stages of the parasite, which increases the likelihood of infestation (Das \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Ahmad et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn our study, larvae of \u003cem\u003eEustrongylides\u003c/em\u003e spp. were most frequently found in the body cavity rather than muscles, aligning with the findings of Kaur et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and Gupta (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), where the body cavity and ovaries were the most common sites of infection. Environmental conditions and diet could influence this distribution pattern, as Measures (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1988\u003c/span\u003e) suggested. Palm et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1998\u003c/span\u003e) noted that parasites like \u003cem\u003eContracaecum\u003c/em\u003e exhibit tissue or organ tropism essential for their development and transmission. For instance, \u003cem\u003eContracaecum radiatum\u003c/em\u003e generally infects the gastric wall of the host. Similarly, \u003cem\u003eEustrongylides\u003c/em\u003e spp. often prefer specific organs and may migrate among them based on population density or developmental needs (Balbuena et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Larsen et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the present study, female \u003cem\u003eC. punctata\u003c/em\u003e were significantly (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) more parasitized than males, which is consistent with the findings of Vasquez and Rogers (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1992\u003c/span\u003e) and Martins et al. (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) in other fish species. Ibiwoye et al. (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) also noted higher infection densities in female fish compared to males in \u003cem\u003eClarias\u003c/em\u003e from the Bida floodplain, supporting our findings. According to Ahmad et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), the sex of the host does not show any notable difference in helminth parasitic infection; however, this negligible increase in infection in females can be attributed to their reproductive functions because the breeding period of fish is physically demanding and stressful (Kortet et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) which may lead to continued chronic stress that can weaken the immune system. Thus, the preference of \u003cem\u003eEustrongylides\u003c/em\u003e spp. in female \u003cem\u003eC. punctata\u003c/em\u003e may be attributed to physiological factors, as suggested by Kennedy and Lie (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1976\u003c/span\u003e). Additionally, the actively swimming behaviour of female fish in search of spawning and feeding opportunities could potentially lead to their increased exposure to parasites (Karvonen and Lindstr\u0026ouml;m (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), which interestingly contradicts the general trend of males being more susceptible to parasitic infections because of sex hormones that can suppress immune function as stated by Klein (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe present investigation revealed that the highest prevalence, abundance and mean intensity of Eustrongylides spp. in \u003cem\u003eC. punctata\u003c/em\u003e occurred in the Autumn season, followed by winter, which aligns with the findings of Gautam et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), where helminth infestation was picked in Autumn in \u003cem\u003eC. punctata\u003c/em\u003e and \u003cem\u003eC. striata.\u003c/em\u003e Vincent and Font (\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) had slightly different findings where prevalence, mean abundance and mean intensity of nematodes were higher in summer than in winter. Bhuiyan et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) found that reduced water volume during dry seasons can lead to imbalanced nutritional conditions, making fish more susceptible to infestation. This statement corporates our study as we found the lowest parasitic infestation in the rainy season. Decreased water temperature could weaken fish immune systems and increase susceptibility to infestations. Besides, the spawning season of \u003cem\u003eC. punctata\u003c/em\u003e ranges from April to September (Mahmud et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The parasitic infestation was found to be higher during the pre-spawning (March) and post-spawning periods (October and November) in \u003cem\u003eC. punctata\u003c/em\u003e in this study, which aligns with the findings reported by Kaur et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The relationship between reproduction and an increase in parasite infestation is attributed to the physiological stress experienced by the host during the breeding period, which might have made the infestations more likely (Tort \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Higher reproductive investment can reduce energy allocated to the immune system, thereby facilitating parasitic infestation (White et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Lizama et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe seasonal dynamics and host factors of \u003cem\u003ethe Eustrongylides\u003c/em\u003e demonstrated in this research mark the first report on \u003cem\u003eEustrongylides\u003c/em\u003e spp. found in \u003cem\u003eC. punctata\u003c/em\u003e under Mymensingh, Bangladesh. The findings highlight the need for further detailed epidemiological and genetic studies to confirm species identification, understand their distribution factors, and investigate transmission dynamics.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThe present study highlights the seasonal dynamics of \u003cem\u003eEustrongylides\u003c/em\u003e spp. infestations in \u003cem\u003eC. punctata\u003c/em\u003e, focusing on their identification, distribution, and associated epidemiological factors. The findings emphasize the widespread season-wise prevalence of parasites. The morphological traits observed confirm the presence of fourth-stage larvae, contributing to the knowledge base regarding their lifecycle and host interactions. Seasonal patterns in infestation suggest significant ecological influences, with certain periods aligning with increased susceptibility in fish. The study underscores the critical role of abiotic factors, such as water, temperature and pollution, in influencing parasite prevalence and intensity. Additionally, host-specific factors like size, sex, and physiological conditions were found to markedly affect infestation rates. This research provides valuable insights into the seasonal variation and epidemiology of \u003cem\u003eEustrongylides\u003c/em\u003e spp. infestation in \u003cem\u003eC. punctata\u003c/em\u003e, setting a foundation for future studies aimed at understanding their ecological impact and devising effective management strategies to mitigate the effects of these parasites on fish health and aquatic ecosystems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eJ.T.T.\u003c/strong\u003e: Implementation of the study, investigation, data collection and processing, interpretation, and initial manuscript drafting; \u003cstrong\u003eA.R.D.\u003c/strong\u003e: Conceptualization, resource management, experimental designing, validation, manuscript review and editing; \u003cstrong\u003eJ.R.\u003c/strong\u003e: Literature review, methodology, infestation studies, data processing and analysis; \u003cstrong\u003eA.U.M.\u003c/strong\u003e: Data curation, validation, visualization, manuscript drafting, review, and editing; \u003cstrong\u003eS.H.\u003c/strong\u003e: Implementation of the study, literature review, methodology, infestation studies, data processing and analysis; \u003cstrong\u003eJ.T.S.\u003c/strong\u003e: Investigation, molecular analysis, data processing, interpretation, and initial manuscript drafting; \u003cstrong\u003eS.S.N.\u003c/strong\u003e: Data recording, data curation, formal analysis and organizing the manuscript; \u003cstrong\u003eT.K.\u003c/strong\u003e: Data curation, validation, manuscript review and editing; \u003cstrong\u003eJ.P.J.\u003c/strong\u003e: Investigation, data collection and recording, manuscript editing; \u003cstrong\u003eS.S.B.\u003c/strong\u003e: Literature review, methodology and initial manuscript drafting; \u003cstrong\u003eS.P.\u003c/strong\u003e: Methodology, investigation and data recording; \u003cstrong\u003eK.T.K.\u003c/strong\u003e: Methodology, investigation and data recording; \u0026nbsp;\u003cstrong\u003eM.A.R.F.\u003c/strong\u003e: Editing and critically revising the manuscript; \u003cstrong\u003eT.R.\u003c/strong\u003e: Conceptualization, experimental designing, supervision, funding acquisition, project administration, resource management, manuscript review and editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Interest Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that there is no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study followed the Ethical Standard of the Research Committee of Bangladesh Agricultural Research System (BAURES), Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement and Declaration of funding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors are grateful to Bangladesh Agricultural University Research System (BAURES) for the financial assistance to carry out a part of this research work under the project “Towards understanding nematode infestations in the spotted snakehead, \u003cem\u003eChanna punctata\u003c/em\u003e: Morphological and molecular approaches to determine the causal agents”; grant number: 2021/113/BAU.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAbe N (2011) Molecular and morphological identification of helminthes found in Japanese smelt, \u003cem\u003eHypomesus transpacificus nipponensis\u003c/em\u003e, with notes on new host records of \u003cem\u003eEustrongylides ignotus\u003c/em\u003e and \u003cem\u003eRaphidascaris gigi\u003c/em\u003e. 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The nematodes of vertebrates; Interscience Publishers, New York and London, pp 1261.\u003c/li\u003e\n\u003c/ol\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":false,"isPdf":false,"isPdfUpToDate":false,"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":"Eustrongylides spp, C. punctata, Infestation, Seasonal dynamics, Host factors","lastPublishedDoi":"10.21203/rs.3.rs-5891800/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5891800/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cem\u003eEustrongylides\u003c/em\u003e\u0026nbsp;nematodes represent an emerging zoonotic threat, especially with the increasing global consumption of raw or undercooked fish. The present study aimed to investigate the seasonal variation of \u003cem\u003eEustrongylides\u003c/em\u003e\u0026nbsp;spp. infestation in\u0026nbsp;spotted snakehead,\u0026nbsp;\u003cem\u003eChanna punctata\u003c/em\u003e, from August 2020 to July 2021 and to assess the influence of the host. A total of\u0026nbsp;414 experimental\u0026nbsp;\u003cem\u003eC. punctata\u003c/em\u003e,\u0026nbsp;captured from the ditches and beels connected with the Brahmaputra river, were collected for 12 months from three adjacent fish markets under Mymensingh Sadar sub-district, Mymensingh, Bangladesh.\u0026nbsp; Stage four larval (L\u003csub\u003e4\u003c/sub\u003e) \u003cem\u003eEustrongylides\u003c/em\u003e\u0026nbsp;spp. were isolated from the abdominal cavity, musculature, and ovaries of 133 sampled fish,\u0026nbsp;washed with 0.85% sterile physiological saline and examined under light microscope using lactophenol.\u0026nbsp;\u0026nbsp;Prevalence was recorded as 32.12%, with a notable mean intensity of 1.53 and an abundance of 0.49. The highest prevalence was found in autumn (45.83%). \u0026nbsp;Larger fish (\u0026gt;18 cm) exhibited a higher prevalence (62.1%) compared to the smaller (\u0026lt;13 cm) (26.5%). Interestingly, females had a higher prevalence and mean intensity of infestation (35.7%, 1.69±0.10) compared to males (27.2%, 1.24±0.06). Results indicated that female and higher-weighted fish exhibit higher parasitic prevalence in \u003cem\u003eC. punctata\u003c/em\u003e, likely due to biological and environmental factors and the immunity level of the host.\u003cstrong\u003e \u003c/strong\u003e\u0026nbsp;\u003c/p\u003e","manuscriptTitle":"Seasonal Dynamics and Host Factors Influencing Eustrongylides spp. Infestation in Spotted Snakeheads, Channa punctata in Mymensingh, Bangladesh","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-30 08:15:12","doi":"10.21203/rs.3.rs-5891800/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":"0887b51b-8ea8-4a77-afdd-407c49e63b7b","owner":[],"postedDate":"January 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-02-18T23:08:26+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-30 08:15:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5891800","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5891800","identity":"rs-5891800","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}