Seasonal dynamics of plasma estradiol 17β level, gonadosomatic index, and ovarian development in female golden trevally (Gnathanodon speciosus)

Seasonal dynamics of plasma estradiol 17β level, gonadosomatic index, and ovarian development in female golden trevally (Gnathanodon speciosus) | 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 Article Seasonal dynamics of plasma estradiol 17β level, gonadosomatic index, and ovarian development in female golden trevally (Gnathanodon speciosus) Hung Quoc Pham, Hoang Minh Le, Ut Van Phan, Minh Van Nguyen, Khuong V. Dinh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7193848/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 03 Dec, 2025 Read the published version in Scientific Reports → Version 1 posted 14 You are reading this latest preprint version Abstract Plasma estradiol 17β (E 2 ) and gonadosomatic index (GSI) are reliable biomarkers for assessing gonadal maturity in fish. This study investigated seasonal variations in GSI and plasma E 2 concentrations and their correlation with ovarian development stages in female golden trevally ( Gnathanodon speciosus ) over an annual reproductive cycle. From November to February, plasma E 2 levels and GSI remained low, followed by a significant increase from March to October, with E 2 peaking during vitellogenesis. Ovarian histology revealed asynchronous oocyte development from March to October, with multiple oocyte stages coexisting, confirming G. speciosus as a multiple-spawning species with a breeding season spanning March to October. Elevated plasma E 2 levels during oocyte growth underscore its pivotal role in driving vitellogenesis. These findings enhance understanding of G. speciosus reproductive physiology, providing valuable insights for optimizing broodstock management, conditioning protocols, and strategic planning for artificial reproduction and seed production for marine aquaculture. Biological sciences/Developmental biology Biological sciences/Ecology Earth and environmental sciences/Ecology Biological sciences/Physiology Biological sciences/Zoology Estradiol 17β ovarian development gonadosomatic index golden trevally broodstock aquaculture Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Effective broodstock management is essential for successful artificial reproduction in aquaculture, as it promotes gonadal maturity and gamete quality 1 , 2 . Both intrinsic and extrinsic factors, including water quality (e.g., temperature, salinity, dissolved oxygen), nutrition, and sex steroid hormones, significantly influence broodstock maturation, reproduction, and health 3 , 4 . Understanding the reproductive physiology, gonadal development stages and associated biomarkers is critical for developing optimized rearing strategies, such as tailored feeding regimes, and environmental adjustments of temperature, salinity or dissolved oxygen to support broodfish conditioning in captivity. Key indicators of gonadal maturity in teleost fish include the gonadosomatic index (GSI), oocyte development, and plasma sex steroid hormone levels, particularly estradiol 17β (E 2 ) 5 , 6 . An increase in GSI typically reflects gonadal development, while elevated plasma E 2 levels signal the onset of sexual maturity, particularly during vitellogenesis 7 – 9 . These biomarkers enable aquaculturists to assess reproductive status, predict breeding seasons, and thereby design strategic plans for artificial reproduction and seed production. Reproductive hormones, notably gonadotropins (follicle-stimulating hormone, FSH; and luteinizing hormone, LH) play a crucial role in regulating gonadal development in fish 10 , 11 . FSH and LH stimulate the gonads to synthesize and secrete sex steroids, which, in turn, act on hepatic and gonadal cells to promote oocyte growth and maturation 12 , 13 . In female fish, plasma E 2 is a key regulator of vitellogenesis, inducing hepatic synthesis of vitellogenin (Vtg), a critical yolk precursor 14 , 15 . During gametogenesis, surges in plasma FSH correspond closely with elevated E 2 and Vtg levels, driving oocyte development, particularly during vitellogenesis 16 – 18 . The positive correlation between plasma E 2 and vitellogenesis underscores its central role in reproductive physiology 19 , 20 , but this relationship has not been investigated in golden trevally. Golden trevally ( Gnathanodon speciosus ) is a marine finfish species of high economic value and holds potential for commercial aquaculture in Southeast Asia. However, seed production remains limited, with many hatcheries relying on wild-caught fry due to challenges in artificial breeding 21 – 23 . In countries like Vietnam, G. speciosus is a priority species for marine aquaculture development, necessitating scalable seed production to reduce dependence on natural stocks. Comprehensive knowledge of its reproductive physiology, endocrinology, ovarian development, and breeding season is critical for achieving consistent, commercial-scale artificial reproduction. However, such knowledge remains a major gap in seed production of G. speciosus . This study investigated seasonal changes in GSI, ovarian development, and plasma E 2 levels across one annual cycle of female G. speciosus , elucidating the relationship among these parameters. The findings provide robust data on reproductive physiology, breeding seasonality, and the annual reproductive pattern of golden trevally. These findings contribute to improving broodstock management and enable hatchery operators to develop effective strategies for artificial reproduction and seed production. Results Seasonal changes in gonadosomatic index and ovarian development From January to February, the GSI in female golden trevally was low and ranged from 0.76–0.85% with no statistically significant difference between months ( P > 0.05). In March, GSI increased significantly to 2.66% ( P 0.05). GSI values ​​decreased sharply to 1.12 in November and further to 0.77% in December ( P < 0.05, Fig. 1 ). These data indicate that the reproductive season of female golden trevally in captivity extends from March to October. GSI varied significantly across ovarian developmental stage (Fig. 2 ). Stage II ovaries exhibited the lowest GSI (0.86%), while stage III ovaries showed a marked increase to 2.88% ( P 0.05). Histological analysis revealed distinct seasonal patterns in ovarian development. From November to December, ovaries were in the degenerative or resting phase, characterizing by previtellogenic oocytes, degenerative oocytes, residual vitellogenic oocytes and postovulatory follicle (Fig. 3 A). From January to February, ovaries contained primarily previtellogenic oocytes, including primary and secondary oocytes (Fig. 3 B). From March to October, ovaries exhibited asynchronous development, with oocytes at multiple stages (previtellogenic, vitellogenic and mature), coexisting, indicating a prolonged breeding season with multiple spawning events (Fig. 3 C-F). These findings confirm that G. speciosus is an asynchronous, multiple-spawning species. Seasonal changes in plasma estradiol 17β Plasma E 2 levels were low from January to February, ranging from 156 to 210 pg/mL. From March, E 2 levels increased rapidly to 460 pg/mL and remained elevated through October, peaking at 712 pg/mL in June. No statistically significant differences in plasma E 2 levels were found between April to September ( P > 0.05). E 2 levels tended to decline in November to 320 pg/mL and further to 160 pg/mL in December (Fig. 4 ). Analysis of E 2 levels by ovarian development stage revealed a peak of 720 pg/mL during stage III (vitellogenesis, Fig. 5 ). E 2 levels were lower in stages IV (670 pg/mL) and V (450 pg/mL), with no statistically significant differences among stages III, IV and V ( P > 0.05). The lowest E 2 level (360 pg/ml) was observed in stage II ( P > 0.05). These patterns highlight the critical role of E2 in driving vitellogenesis during the reproductive season. Discussion Ovarian development and gonadosomatic index The gonadosomatic index (GSI) and ovarian developmental stages are critical indicators of reproductive maturity in teleost fish 5 , 24 . In female golden trevally, GSI increased significantly from March to October (2.46–3.05%), coinciding with the breeding season, and remained low (0.76–0.85%) from November to February during the post-spawning or resting phase. This seasonal pattern reflects active vitellogenesis during the breeding season, where oocyte growth increases ovarian mass, leading to elevated GSI 25 , 26 . The highest GSI values (2.95–3.08%) were observed in ovarian stages IV and V, consistent with peak gonadal development prior to spawning, while the lowest GSI (0.86%) occurred in stage II, indicating minimal gonadal activity. The asynchronous ovarian development observed histologically, with coexisting previtellogenic, vitellogenic, and mature oocytes from March to October, confirms G. speciosus as a multiple-spawning species with a prolonged reproductive season. This asynchrony explains the sustained high GSI during the breeding season, as continuous vitellogenesis supports multiple spawning events 27 . The absence of stage I (juvenile) and stage II (immediate post-spawning) ovaries in this study aligns with sampling mature adults and the transient nature of stage IV, characterized by postovulatory follicles and residual mature oocytes 25 – 27 . Compared to other tropical marine fish species in the same region, such as rabbitfish ( Siganus gusttatus ), waigieu seaperch ( Psammoperca waigiensis ), the GSI value of the golden trevally was lower (maximum 3%), although their mature body size was much bigger than these fish. Waigieu seaperch has the average mature size between 200–300 g/fish, the highest GSI value was around 8% 6 , and absolute fecundity was between 100,000–120,000 eggs/female 28 . In rabbitfish, the average mature size was between 500–550 g/fish, the highest GSI value was around 5.8% 29 , and absolute fecundity was between 570,000–625,000 eggs/female 30 . In golden trevally, the average mature size was between 800–1000 g/fish, and the absolute fecundity was around 121,000 eggs/female 31 . This suggests species-specific differences in reproductive investment, potentially influenced by egg size or spawning frequency. Generally, when the GSI is low, the ovary size is small, which can lead to lower fecundity. However, the fecundity could be affected by the size of the egg. From available GSI values, fecundity could be estimated, which can help determine the number of eggs in female fish in each spawn, thereby building appropriate seed production plans. The histological presence of degenerative oocytes and postovulatory follicles from November to December suggests follicular atresia and resorption of unspawned oocytes. For hatchery management, temporarily reducing feeding post-spawning could facilitate reorption of residual oocytes, promoting new oocyte development and reducing feed costs. Additionally tailored nutritional regimes targeting vitellogenesis (stages III – IV) could enhance oocyte quality, fertilization rate, and larval viability. Environmental factors, particularly water temperature, significantly influence reproductive physiology. In Southeast Asian countries like Vietnam, higher temperatures (26–30°C) from March to October likely accelerated metabolism and vitellogenesis, promoting gonadal maturation. In contrast, lower temperatures (20–25°C) from November to February corresponded with reproductive quiescence 32 . Similar temperature-driven reproductive patterns are reported in other tropical fish species, including rabbitfish 29 , waigieu seaperch 6 , and longfin batfish Platax teira 33 . These findings underscore the importance of aligning broodstock management with seasonal environmental cues to optimize spawning outcomes. Fisheries management could also leverage this knowledge to enforce seasonal fishing restrictions, protecting G. speciosus during its breeding season to support sustainable populations. Relationship between plasma E 2 and ovarian development Plasma E 2 is a key regulator of vitellogenesis in teleosts, stimulating hepatic vitellogenin synthesis and oocyte growth 34 , 35 . In G. speciosus plasma E 2 levels remained high, and peaked at 712 pg/ml during the breeding season from March to October, particularly in ovarian stage III. This sustained high E2 reflects continuous vitellogenesis in a multi-spawning fish, where oocytes at various developmental stages coexist 12 . In contrast, E2 levels dropped to 156–310 pg/mL during the post-spawning season from November to February, consistent with reduced gonadal activity. Compared to regional species like rabbitfish (E2 ~ 1446 pg/mL 29 ) and waigieu seaperch (E2 ~ 900 pg/mL 6 ), G. speciosus exhibits lower peak E2 levels, potentially reflecting differences in reproductive strategies or hormonal regulation. Unlike single-spawning species, where E2 typically declines post-ovulation 36 , the sustained E2 in G. speciosus during IV – V suggests ongoing vitellogenesis to support multiple-spawning events 37 . This is consistent with observations in other multiple-spawning species, where E2 remains elevated to maintain oocyte development across spawning cycles 12 . The complexity of steroid hormone dynamics in multiple-spawning species, as seen in G. speciosus , highlights the challenge of detecting peak E2 levels due to their transient nature 6 . In some species, androgens like testosterone may dominate during certain reproductive phases, complicating endocrine profiles 38 . Monitoring E2 and other steroid hormones provides a valuable tool for assessing physiological status of fish, thereby reproductive status and optimizing broodstock conditioning in aquaculture. Conclusion This study reveals that the golden trevally is a multiple-spawning fish species with a prolonged reproductive season from March to October, characterized by asynchronous ovarian development and sustained high GSI (2.46–3.05%) and plasma E 2 levels (460–712 pg/mL). The peak E 2 during vitellogenesis (stage III) underscores its critical role in oocyte development. These findings enhance understanding of G. speciosus reproductive physiology and endocrinology, providing actionable insights for aquaculture. Broodstock managers can optimize feeding and environmental regimes to align with seasonal reproductive cycles, improving gamete quality and seed production efficiently. Additionally, these data support sustainable fisheries management by informing seasonal protections for wild populations, contributing to the development of commercial aquaculture in Southeast Asia. Materials and methods Broodstock rearing and sampling Farmed female golden trevally ( Gnathanodon speciosus ) were reared in floating sea cages in the south-central coastal waters of Vietnam (12.2099° N, 109.0929° E). Those females originated from the local hatcheries and have been reared in the aquaculture facilities of Nha Trang University for over six years. The stocking density was maintained at 3 kg/m 3 with a 1:1 male-to-female ratio. Fish were held under ambient environmental conditions, with salinity ranging from 30–34‰, water temperature from 22–30°C, pH from 7.8–8.6 and dissolved oxygen from 4.5–6.5 mg/L. Broodstock were fed daily with raw trash fish at 2–3% of body weight. Monthly, 10 female fish (mean body weight: 900 ± 200 g and mean total length of 40 ± 5 cm) were randomly sampled for ovarian tissues and blood collection. Blood was collected from the caudal vein using syringes, transferred into heparinized tubes, and stored in -80°C until analysis. The gonadosomatic index (GSI) was calculated as the percentage of gonadal weight to total body weight. Gonadal development was classified into six stages based on the most advanced gamete stage, following established criteria 25 , 26 . Ethics declarations All procedures involving live animals complied with the Vietnam Veterinary Law 2015 and Government Decree 90/2017. We confirm compliance with the ARRIVE guidelines for animal research. The research and experimental protocols were approved by Nha Trang University and the National Foundation of Science and Technology Development of Vietnam (NAFOSTED). Histological analysis The ovarian samples were removed from the fixative solution, washed, and dehydrated by soaking in absolute ethanol for 4–8 h, then cleared in methyl salicylate for 12–24 h. Thereafter, samples were infiltrated with molten paraffin at 65°C for a minimum of 6 h, embedded in paraffin molds, and cooled for 30 minutes to solidify. Paraffin blocks containing the sample were trimmed into trapezoidal or rectangular shapes, mounted on wooden bases, and labeled. Sections were sliced at 5–7 µm thickness using a microtome, floated in warm water (40–45°C) for 1–2 minutes to expand, and then dried at 45–60°C for 1–4 h. After drying, the sample was deparaffinized by immersion in xylene solutions and then immersion in ethanol solution at different concentrations for 2–3 minutes. Finally, the sample was stained in Hematoxylin-Mayer solution (4–6 minutes) and Eosin (2 minutes), then dried, covered with adhesive, and labeled. Gonadal histological sections were examined using an Olympus microscope (Japan), at 10× and 40× magnification to assess oocyte development stages. Plasma estradiol 17β assay We conducted the plasma estradiol 17β assay following the methodology described in our previous study 39 . Briefly, the plasma E 2 levels were analyzed using enzyme-linked immunosorbent assay (ELISA) with Steroid hormone enzyme immunoassay (EIA) Kits (Cayman Chemical Company, Ann Arbor, MI, USA). Blood samples were centrifuged at 10,000× g for 10 minutes at 4°C to isolate plasma. Plasma was purified through organic solvent extraction to eliminate interference. Specifically, we used a vortex mixer to mix plasma with 5 mL of diethyl ether. Following phase separation, the aqueous layer was frozen in an ethanol/dry ice bath, the lipophilic phase was transferred into a clean tube, and the ether phase was removed via vacuum centrifugation. The resulting dry extract was resuspended in 300 µl EIA buffer by vortexing. Enzyme immunoassays were performed per the manufacturer’s protocol with a 75-minute development time. Absorbance was measured at 405 nm using a Thermo Multiskan EX 96-well spectrophotometer (Netherlands). E2 concentrations were calculated using a standard curve linearized through a logit transformation of bound sample/maximum bound (B/B 0 ). The intra- and inter-assay coefficients of variation for all EIAs were approximately 10% and 8%, respectively. Cross-reactivity for E 2 EIAs was 2.2% with 100% specificity for their respective steroid. On average, both intra- and inter-assay variations for steroid analyses remained below 5%. Statistical analysis Data were analyzed using SPSS statistical software (version, IBM Corp., Armonk, NY, USA). Monthly variations in GIS, plasma E2 concentrations, and ovarian development stages were compared using one-way analysis of variance (ANOVA). Post hoc comparisons were conducted using Duncan's multiple range test at a 95% confidence level (α = 0.05). All data were tested for normality and homogeneity of variance prior to analysis, with transformation applied as needed to meet ANOVA assumptions. Declarations Conflict of interest statement The authors declare no competing financial interests. Funding statement This research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 106.05-2021.09. Authors are very grateful for the support and funding from the NAFOSTED of Vietnam. Author Contribution Conceptualization and funding acquisition: Hung Quoc Pham; Methodology: Hung Quoc Pham (equal), Hoang Minh Le (equal), Khuong V. Dinh (equal); Experiment and sampling: Minh Van Nguyen (equal), Ut Van Phan (equal); Samples and data analysis: Hoang Minh Le (equal), Minh Van Nguyen (equal), Ut Van Phan (equal); Writing - original draft: Hung Quoc Pham; Writing - review & editing: Hung Quoc Pham (lead), Hoang Minh Le (equal), Minh Van Nguyen (equal), Ut Van Phan (equal), Khuong V. 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Cite Share Download PDF Status: Published Journal Publication published 03 Dec, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 13 Oct, 2025 Reviews received at journal 09 Oct, 2025 Reviews received at journal 08 Oct, 2025 Reviewers agreed at journal 29 Sep, 2025 Reviewers agreed at journal 29 Sep, 2025 Reviews received at journal 28 Sep, 2025 Reviewers agreed at journal 17 Sep, 2025 Reviews received at journal 09 Sep, 2025 Reviewers agreed at journal 20 Aug, 2025 Reviewers invited by journal 17 Aug, 2025 Editor assigned by journal 12 Aug, 2025 Editor invited by journal 12 Aug, 2025 Submission checks completed at journal 01 Aug, 2025 First submitted to journal 01 Aug, 2025 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7193848","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":503153206,"identity":"300bc79e-57fc-46bc-986b-d6235841e6ac","order_by":0,"name":"Hung Quoc Pham","email":"","orcid":"","institution":"Nha Trang University","correspondingAuthor":false,"prefix":"","firstName":"Hung","middleName":"Quoc","lastName":"Pham","suffix":""},{"id":503153207,"identity":"f5cce979-0208-479f-8f3d-8fa4eaa4b95d","order_by":1,"name":"Hoang Minh Le","email":"","orcid":"","institution":"Nha Trang University","correspondingAuthor":false,"prefix":"","firstName":"Hoang","middleName":"Minh","lastName":"Le","suffix":""},{"id":503153208,"identity":"4c8d3049-2bb6-4095-9011-94be861398cc","order_by":2,"name":"Ut Van Phan","email":"","orcid":"","institution":"Nha Trang University","correspondingAuthor":false,"prefix":"","firstName":"Ut","middleName":"Van","lastName":"Phan","suffix":""},{"id":503153209,"identity":"378ae989-f70b-4774-9e83-4512431ba92e","order_by":3,"name":"Minh Van Nguyen","email":"","orcid":"","institution":"Nha Trang University","correspondingAuthor":false,"prefix":"","firstName":"Minh","middleName":"Van","lastName":"Nguyen","suffix":""},{"id":503153210,"identity":"b0cde8ea-902c-42dc-8ab8-376174b4777c","order_by":4,"name":"Khuong V. Dinh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYJACxgYGZh4GCeYDh0E8NhK0sCWQpoWBQYLHgJkoRxkcP3uAcQaDtYy5dM/Hw4VtDIl97A1sDz7g03ImL4FxA0M6j+WcsxsOzwRqaeM5wG44A48WyYYcA8YHDId5DG7kbjjMcwaoRSKBTZoHn5b+NzAtOQ+I08IvAbRlA0QLkKwgSssbg4MzDNKBWtIMDs+okDBu4znYJonPL2z8OYYPeyqs7Q1uJD/+XGBgIzu/vfmYBL4QA4EDDAZwtgQDOJ5GwSgYBaNgFFAGAK+NRk/FoZ1lAAAAAElFTkSuQmCC","orcid":"","institution":"University of Oslo","correspondingAuthor":true,"prefix":"","firstName":"Khuong","middleName":"V.","lastName":"Dinh","suffix":""}],"badges":[],"createdAt":"2025-07-23 08:23:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7193848/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7193848/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-30370-1","type":"published","date":"2025-12-03T15:58:15+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":89867618,"identity":"1ffb2c7b-7970-45e9-bd54-d3e44f4a42a2","added_by":"auto","created_at":"2025-08-26 01:23:16","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":59866,"visible":true,"origin":"","legend":"\u003cp\u003eMonthly changes in gonadosomatic index (%) in female golden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e) during an annual reproductive season. Different letters indicate significant difference (\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05), analyzed using one-way ANOVA, followed by Duncan tests.\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7193848/v1/5e205fc9b9e732369f304a6f.jpeg"},{"id":89867596,"identity":"b2788bea-b96a-4aab-8066-4bded8e4d0a1","added_by":"auto","created_at":"2025-08-26 01:23:15","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":48790,"visible":true,"origin":"","legend":"\u003cp\u003eRelationships between stages of ovarian development and gonadosomatic index (%) in female golden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e). Different letters indicate significant differences (\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05), analyzed using one‐way ANOVA, followed by Duncan tests.\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7193848/v1/bb186d7841daf46d77f84f53.jpeg"},{"id":89867623,"identity":"8b9359a2-fb80-46e8-9091-fd5398e01af6","added_by":"auto","created_at":"2025-08-26 01:23:17","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":645508,"visible":true,"origin":"","legend":"\u003cp\u003eHistological sections of golden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e) ovaries in the annual reproductive cycle showing\u003cstrong\u003e \u003c/strong\u003ethe presence of oocytes in different developmental stages. Lu, ovarian lumen; po, primary oocytes; so, secondary oocytes; vo, vitellogenic oocytes; of, ovulated follicle; do, degenerative oocytes; yv, yolk vacuoles; gv, germinal vesicle; St II, St III, St IV, St V and St II represent ovarian developmental stages II, III, IV and V, respectively. A, B, C, D, E, F are representative sections of ovaries collected in Nov-Dec, Jan-Feb, Mar-Apr, May-Jun, July-Aug, Sep-Oct, respectively. Scale bars: 100 µm.\u003c/p\u003e","description":"","filename":"image3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7193848/v1/f259b277a5f3e0c417cb3447.jpeg"},{"id":89867624,"identity":"928b0dc4-1c46-4ce1-9ddf-6b62aed8eb21","added_by":"auto","created_at":"2025-08-26 01:23:17","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":65007,"visible":true,"origin":"","legend":"\u003cp\u003eMonthly changes in plasma estradiol levels (pg/ml) in female golden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e) during an annual reproductive season. Different letters indicate significant difference (\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05), analyzed using one-way ANOVA, followed by Duncan tests.\u003c/p\u003e","description":"","filename":"image4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7193848/v1/487971164560ef594f366720.jpeg"},{"id":89867631,"identity":"761ca7af-65d2-4435-bcab-0a1b5b8b865c","added_by":"auto","created_at":"2025-08-26 01:23:17","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":52412,"visible":true,"origin":"","legend":"\u003cp\u003eRelationships between stages of ovarian development and estradiol level (pg/ml) in female golden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e). Different letters indicate significant differences (\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05), analyzed using one‐way ANOVA, followed by Duncan tests.\u003c/p\u003e","description":"","filename":"image5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7193848/v1/c79fd989fd933e42eef60239.jpeg"},{"id":97724096,"identity":"791dc698-bc44-4038-867f-73136e3a835f","added_by":"auto","created_at":"2025-12-08 16:11:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1427391,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7193848/v1/9ea3a247-b962-479c-b3cd-de9f7de71cd0.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Seasonal dynamics of plasma estradiol 17β level, gonadosomatic index, and ovarian development in female golden trevally (Gnathanodon speciosus)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eEffective broodstock management is essential for successful artificial reproduction in aquaculture, as it promotes gonadal maturity and gamete quality\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Both intrinsic and extrinsic factors, including water quality (e.g., temperature, salinity, dissolved oxygen), nutrition, and sex steroid hormones, significantly influence broodstock maturation, reproduction, and health\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Understanding the reproductive physiology, gonadal development stages and associated biomarkers is critical for developing optimized rearing strategies, such as tailored feeding regimes, and environmental adjustments of temperature, salinity or dissolved oxygen to support broodfish conditioning in captivity.\u003c/p\u003e\u003cp\u003eKey indicators of gonadal maturity in teleost fish include the gonadosomatic index (GSI), oocyte development, and plasma sex steroid hormone levels, particularly estradiol 17β (E\u003csub\u003e2\u003c/sub\u003e)\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. An increase in GSI typically reflects gonadal development, while elevated plasma E\u003csub\u003e2\u003c/sub\u003e levels signal the onset of sexual maturity, particularly during vitellogenesis\u003csup\u003e\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. These biomarkers enable aquaculturists to assess reproductive status, predict breeding seasons, and thereby design strategic plans for artificial reproduction and seed production.\u003c/p\u003e\u003cp\u003eReproductive hormones, notably gonadotropins (follicle-stimulating hormone, FSH; and luteinizing hormone, LH) play a crucial role in regulating gonadal development in fish\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. FSH and LH stimulate the gonads to synthesize and secrete sex steroids, which, in turn, act on hepatic and gonadal cells to promote oocyte growth and maturation\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. In female fish, plasma E\u003csub\u003e2\u003c/sub\u003e is a key regulator of vitellogenesis, inducing hepatic synthesis of vitellogenin (Vtg), a critical yolk precursor\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. During gametogenesis, surges in plasma FSH correspond closely with elevated E\u003csub\u003e2\u003c/sub\u003e and Vtg levels, driving oocyte development, particularly during vitellogenesis\u003csup\u003e\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. The positive correlation between plasma E\u003csub\u003e2\u003c/sub\u003e and vitellogenesis underscores its central role in reproductive physiology\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, but this relationship has not been investigated in golden trevally.\u003c/p\u003e\u003cp\u003eGolden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e) is a marine finfish species of high economic value and holds potential for commercial aquaculture in Southeast Asia. However, seed production remains limited, with many hatcheries relying on wild-caught fry due to challenges in artificial breeding\u003csup\u003e\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. In countries like Vietnam, \u003cem\u003eG. speciosus\u003c/em\u003e is a priority species for marine aquaculture development, necessitating scalable seed production to reduce dependence on natural stocks. Comprehensive knowledge of its reproductive physiology, endocrinology, ovarian development, and breeding season is critical for achieving consistent, commercial-scale artificial reproduction. However, such knowledge remains a major gap in seed production of \u003cem\u003eG. speciosus\u003c/em\u003e.\u003c/p\u003e\u003cp\u003eThis study investigated seasonal changes in GSI, ovarian development, and plasma E\u003csub\u003e2\u003c/sub\u003e levels across one annual cycle of female \u003cem\u003eG. speciosus\u003c/em\u003e, elucidating the relationship among these parameters. The findings provide robust data on reproductive physiology, breeding seasonality, and the annual reproductive pattern of golden trevally. These findings contribute to improving broodstock management and enable hatchery operators to develop effective strategies for artificial reproduction and seed production.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003e\u003cem\u003eSeasonal changes in gonadosomatic index and ovarian development\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFrom January to February, the GSI in female golden trevally was low and ranged from 0.76\u0026ndash;0.85% with no statistically significant difference between months (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). In March, GSI increased significantly to 2.66% (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and remained elevated, fluctuating between 2.46\u0026ndash;3.05% from April to October, with no significant differences among these months (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). GSI values ​​decreased sharply to 1.12 in November and further to 0.77% in December (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These data indicate that the reproductive season of female golden trevally in captivity extends from March to October.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eGSI varied significantly across ovarian developmental stage (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Stage II ovaries exhibited the lowest GSI (0.86%), while stage III ovaries showed a marked increase to 2.88% (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). GSI continued to rise gradually in stages IV and V, reaching 2.95 and 3.08%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), with no statistically significant differences among the ovary stages III, IV and V (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eHistological analysis revealed distinct seasonal patterns in ovarian development. From November to December, ovaries were in the degenerative or resting phase, characterizing by previtellogenic oocytes, degenerative oocytes, residual vitellogenic oocytes and postovulatory follicle (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). From January to February, ovaries contained primarily previtellogenic oocytes, including primary and secondary oocytes (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). From March to October, ovaries exhibited asynchronous development, with oocytes at multiple stages (previtellogenic, vitellogenic and mature), coexisting, indicating a prolonged breeding season with multiple spawning events (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC-F). These findings confirm that \u003cem\u003eG. speciosus\u003c/em\u003e is an asynchronous, multiple-spawning species.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003e\u003cem\u003eSeasonal changes in plasma estradiol 17β\u003c/em\u003e\u003c/p\u003e\u003cp\u003ePlasma E\u003csub\u003e2\u003c/sub\u003e levels were low from January to February, ranging from 156 to 210 pg/mL. From March, E\u003csub\u003e2\u003c/sub\u003e levels increased rapidly to 460 pg/mL and remained elevated through October, peaking at 712 pg/mL in June. No statistically significant differences in plasma E\u003csub\u003e2\u003c/sub\u003e levels were found between April to September (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). E\u003csub\u003e2\u003c/sub\u003e levels tended to decline in November to 320 pg/mL and further to 160 pg/mL in December (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAnalysis of E\u003csub\u003e2\u003c/sub\u003e levels by ovarian development stage revealed a peak of 720 pg/mL during stage III (vitellogenesis, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). E\u003csub\u003e2\u003c/sub\u003e levels were lower in stages IV (670 pg/mL) and V (450 pg/mL), with no statistically significant differences among stages III, IV and V (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The lowest E\u003csub\u003e2\u003c/sub\u003e level (360 pg/ml) was observed in stage II (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). These patterns highlight the critical role of E2 in driving vitellogenesis during the reproductive season.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003e\u003cem\u003eOvarian development and gonadosomatic index\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe gonadosomatic index (GSI) and ovarian developmental stages are critical indicators of reproductive maturity in teleost fish\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. In female golden trevally, GSI increased significantly from March to October (2.46\u0026ndash;3.05%), coinciding with the breeding season, and remained low (0.76\u0026ndash;0.85%) from November to February during the post-spawning or resting phase. This seasonal pattern reflects active vitellogenesis during the breeding season, where oocyte growth increases ovarian mass, leading to elevated GSI\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. The highest GSI values (2.95\u0026ndash;3.08%) were observed in ovarian stages IV and V, consistent with peak gonadal development prior to spawning, while the lowest GSI (0.86%) occurred in stage II, indicating minimal gonadal activity.\u003c/p\u003e\u003cp\u003eThe asynchronous ovarian development observed histologically, with coexisting previtellogenic, vitellogenic, and mature oocytes from March to October, confirms \u003cem\u003eG. speciosus\u003c/em\u003e as a multiple-spawning species with a prolonged reproductive season. This asynchrony explains the sustained high GSI during the breeding season, as continuous vitellogenesis supports multiple spawning events\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The absence of stage I (juvenile) and stage II (immediate post-spawning) ovaries in this study aligns with sampling mature adults and the transient nature of stage IV, characterized by postovulatory follicles and residual mature oocytes\u003csup\u003e\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eCompared to other tropical marine fish species in the same region, such as rabbitfish (\u003cem\u003eSiganus gusttatus\u003c/em\u003e), waigieu seaperch (\u003cem\u003ePsammoperca waigiensis\u003c/em\u003e), the GSI value of the golden trevally was lower (maximum 3%), although their mature body size was much bigger than these fish. Waigieu seaperch has the average mature size between 200\u0026ndash;300 g/fish, the highest GSI value was around 8%\u003csup\u003e6\u003c/sup\u003e, and absolute fecundity was between 100,000\u0026ndash;120,000 eggs/female\u003csup\u003e28\u003c/sup\u003e. In rabbitfish, the average mature size was between 500\u0026ndash;550 g/fish, the highest GSI value was around 5.8%\u003csup\u003e29\u003c/sup\u003e, and absolute fecundity was between 570,000\u0026ndash;625,000 eggs/female\u003csup\u003e30\u003c/sup\u003e. In golden trevally, the average mature size was between 800\u0026ndash;1000 g/fish, and the absolute fecundity was around 121,000 eggs/female\u003csup\u003e31\u003c/sup\u003e. This suggests species-specific differences in reproductive investment, potentially influenced by egg size or spawning frequency. Generally, when the GSI is low, the ovary size is small, which can lead to lower fecundity. However, the fecundity could be affected by the size of the egg. From available GSI values, fecundity could be estimated, which can help determine the number of eggs in female fish in each spawn, thereby building appropriate seed production plans.\u003c/p\u003e\u003cp\u003eThe histological presence of degenerative oocytes and postovulatory follicles from November to December suggests follicular atresia and resorption of unspawned oocytes. For hatchery management, temporarily reducing feeding post-spawning could facilitate reorption of residual oocytes, promoting new oocyte development and reducing feed costs. Additionally tailored nutritional regimes targeting vitellogenesis (stages III \u0026ndash; IV) could enhance oocyte quality, fertilization rate, and larval viability.\u003c/p\u003e\u003cp\u003eEnvironmental factors, particularly water temperature, significantly influence reproductive physiology. In Southeast Asian countries like Vietnam, higher temperatures (26\u0026ndash;30\u0026deg;C) from March to October likely accelerated metabolism and vitellogenesis, promoting gonadal maturation. In contrast, lower temperatures (20\u0026ndash;25\u0026deg;C) from November to February corresponded with reproductive quiescence\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. Similar temperature-driven reproductive patterns are reported in other tropical fish species, including rabbitfish\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, waigieu seaperch\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, and longfin batfish \u003cem\u003ePlatax teira\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. These findings underscore the importance of aligning broodstock management with seasonal environmental cues to optimize spawning outcomes. Fisheries management could also leverage this knowledge to enforce seasonal fishing restrictions, protecting \u003cem\u003eG. speciosus\u003c/em\u003e during its breeding season to support sustainable populations.\u003c/p\u003e\u003cp\u003e\u003cem\u003eRelationship between plasma E\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e \u003cem\u003eand ovarian development\u003c/em\u003e\u003c/p\u003e\u003cp\u003ePlasma E\u003csub\u003e2\u003c/sub\u003e is a key regulator of vitellogenesis in teleosts, stimulating hepatic vitellogenin synthesis and oocyte growth\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. In \u003cem\u003eG. speciosus\u003c/em\u003e plasma E\u003csub\u003e2\u003c/sub\u003e levels remained high, and peaked at 712 pg/ml during the breeding season from March to October, particularly in ovarian stage III. This sustained high E2 reflects continuous vitellogenesis in a multi-spawning fish, where oocytes at various developmental stages coexist\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. In contrast, E2 levels dropped to 156\u0026ndash;310 pg/mL during the post-spawning season from November to February, consistent with reduced gonadal activity.\u003c/p\u003e\u003cp\u003eCompared to regional species like rabbitfish (E2\u0026thinsp;~\u0026thinsp;1446 pg/mL\u003csup\u003e29\u003c/sup\u003e) and waigieu seaperch (E2\u0026thinsp;~\u0026thinsp;900 pg/mL\u003csup\u003e6\u003c/sup\u003e), \u003cem\u003eG. speciosus\u003c/em\u003e exhibits lower peak E2 levels, potentially reflecting differences in reproductive strategies or hormonal regulation. Unlike single-spawning species, where E2 typically declines post-ovulation\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, the sustained E2 in \u003cem\u003eG. speciosus\u003c/em\u003e during IV \u0026ndash; V suggests ongoing vitellogenesis to support multiple-spawning events\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. This is consistent with observations in other multiple-spawning species, where E2 remains elevated to maintain oocyte development across spawning cycles\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe complexity of steroid hormone dynamics in multiple-spawning species, as seen in \u003cem\u003eG. speciosus\u003c/em\u003e, highlights the challenge of detecting peak E2 levels due to their transient nature\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. In some species, androgens like testosterone may dominate during certain reproductive phases, complicating endocrine profiles\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. Monitoring E2 and other steroid hormones provides a valuable tool for assessing physiological status of fish, thereby reproductive status and optimizing broodstock conditioning in aquaculture.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThis study reveals that the golden trevally is a multiple-spawning fish species with a prolonged reproductive season from March to October, characterized by asynchronous ovarian development and sustained high GSI (2.46\u0026ndash;3.05%) and plasma E\u003csub\u003e2\u003c/sub\u003e levels (460\u0026ndash;712 pg/mL). The peak E\u003csub\u003e2\u003c/sub\u003e during vitellogenesis (stage III) underscores its critical role in oocyte development. These findings enhance understanding of \u003cem\u003eG. speciosus\u003c/em\u003e reproductive physiology and endocrinology, providing actionable insights for aquaculture. Broodstock managers can optimize feeding and environmental regimes to align with seasonal reproductive cycles, improving gamete quality and seed production efficiently. Additionally, these data support sustainable fisheries management by informing seasonal protections for wild populations, contributing to the development of commercial aquaculture in Southeast Asia.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003e\u003cem\u003eBroodstock rearing and sampling\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFarmed female golden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e) were reared in floating sea cages in the south-central coastal waters of Vietnam (12.2099\u0026deg; N, 109.0929\u0026deg; E). Those females originated from the local hatcheries and have been reared in the aquaculture facilities of Nha Trang University for over six years. The stocking density was maintained at 3 kg/m\u003csup\u003e3\u003c/sup\u003e with a 1:1 male-to-female ratio. Fish were held under ambient environmental conditions, with salinity ranging from 30\u0026ndash;34\u0026permil;, water temperature from 22\u0026ndash;30\u0026deg;C, pH from 7.8\u0026ndash;8.6 and dissolved oxygen from 4.5\u0026ndash;6.5 mg/L. Broodstock were fed daily with raw trash fish at 2\u0026ndash;3% of body weight. Monthly, 10 female fish (mean body weight: 900\u0026thinsp;\u0026plusmn;\u0026thinsp;200 g and mean total length of 40\u0026thinsp;\u0026plusmn;\u0026thinsp;5 cm) were randomly sampled for ovarian tissues and blood collection. Blood was collected from the caudal vein using syringes, transferred into heparinized tubes, and stored in -80\u0026deg;C until analysis. The gonadosomatic index (GSI) was calculated as the percentage of gonadal weight to total body weight. Gonadal development was classified into six stages based on the most advanced gamete stage, following established criteria\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003cem\u003eEthics declarations\u003c/em\u003e\u003c/p\u003e\u003cp\u003e All procedures involving live animals complied with the Vietnam Veterinary Law 2015 and Government Decree 90/2017. We confirm compliance with the ARRIVE guidelines for animal research. The research and experimental protocols were approved by Nha Trang University and the National Foundation of Science and Technology Development of Vietnam (NAFOSTED).\u003c/p\u003e\u003cp\u003e\u003cem\u003eHistological analysis\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe ovarian samples were removed from the fixative solution, washed, and dehydrated by soaking in absolute ethanol for 4\u0026ndash;8 h, then cleared in methyl salicylate for 12\u0026ndash;24 h. Thereafter, samples were infiltrated with molten paraffin at 65\u0026deg;C for a minimum of 6 h, embedded in paraffin molds, and cooled for 30 minutes to solidify. Paraffin blocks containing the sample were trimmed into trapezoidal or rectangular shapes, mounted on wooden bases, and labeled. Sections were sliced at 5\u0026ndash;7 \u0026micro;m thickness using a microtome, floated in warm water (40\u0026ndash;45\u0026deg;C) for 1\u0026ndash;2 minutes to expand, and then dried at 45\u0026ndash;60\u0026deg;C for 1\u0026ndash;4 h. After drying, the sample was deparaffinized by immersion in xylene solutions and then immersion in ethanol solution at different concentrations for 2\u0026ndash;3 minutes. Finally, the sample was stained in Hematoxylin-Mayer solution (4\u0026ndash;6 minutes) and Eosin (2 minutes), then dried, covered with adhesive, and labeled. Gonadal histological sections were examined using an Olympus microscope (Japan), at 10\u0026times; and 40\u0026times; magnification to assess oocyte development stages.\u003c/p\u003e\u003cp\u003e\u003cem\u003ePlasma estradiol 17β assay\u003c/em\u003e\u003c/p\u003e\u003cp\u003eWe conducted the plasma estradiol 17β assay following the methodology described in our previous study\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. Briefly, the plasma E\u003csub\u003e2\u003c/sub\u003e levels were analyzed using enzyme-linked immunosorbent assay (ELISA) with Steroid hormone enzyme immunoassay (EIA) Kits (Cayman Chemical Company, Ann Arbor, MI, USA). Blood samples were centrifuged at 10,000\u0026times; g for 10 minutes at 4\u0026deg;C to isolate plasma. Plasma was purified through organic solvent extraction to eliminate interference. Specifically, we used a vortex mixer to mix plasma with 5 mL of diethyl ether. Following phase separation, the aqueous layer was frozen in an ethanol/dry ice bath, the lipophilic phase was transferred into a clean tube, and the ether phase was removed via vacuum centrifugation. The resulting dry extract was resuspended in 300 \u0026micro;l EIA buffer by vortexing. Enzyme immunoassays were performed per the manufacturer\u0026rsquo;s protocol with a 75-minute development time. Absorbance was measured at 405 nm using a Thermo Multiskan EX 96-well spectrophotometer (Netherlands). E2 concentrations were calculated using a standard curve linearized through a logit transformation of bound sample/maximum bound (B/B\u003csub\u003e0\u003c/sub\u003e). The intra- and inter-assay coefficients of variation for all EIAs were approximately 10% and 8%, respectively. Cross-reactivity for E\u003csub\u003e2\u003c/sub\u003e EIAs was 2.2% with 100% specificity for their respective steroid. On average, both intra- and inter-assay variations for steroid analyses remained below 5%.\u003c/p\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eData were analyzed using SPSS statistical software (version, IBM Corp., Armonk, NY, USA). Monthly variations in GIS, plasma E2 concentrations, and ovarian development stages were compared using one-way analysis of variance (ANOVA). Post hoc comparisons were conducted using Duncan's multiple range test at a 95% confidence level (α\u0026thinsp;=\u0026thinsp;0.05). All data were tested for normality and homogeneity of variance prior to analysis, with transformation applied as needed to meet ANOVA assumptions.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eConflict of interest statement\u003c/h2\u003e\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e\u003ch2\u003eFunding statement\u003c/h2\u003e\u003cp\u003eThis research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 106.05-2021.09. Authors are very grateful for the support and funding from the NAFOSTED of Vietnam.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization and funding acquisition: Hung Quoc Pham; Methodology: Hung Quoc Pham (equal), Hoang Minh Le (equal), Khuong V. Dinh (equal); Experiment and sampling: Minh Van Nguyen (equal), Ut Van Phan (equal); Samples and data analysis: Hoang Minh Le (equal), Minh Van Nguyen (equal), Ut Van Phan (equal); Writing - original draft: Hung Quoc Pham; Writing - review \u0026amp; editing: Hung Quoc Pham (lead), Hoang Minh Le (equal), Minh Van Nguyen (equal), Ut Van Phan (equal), Khuong V. Dinh (equal).\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 106.05-2021.09. Authors are very grateful for the support and funding from the NAFOSTED of Vietnam.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and/or analysed during the current study are not publicly available due to intellectual property rights relating to the study species, but are available from the first author (Hung Quoc Pham, email: [email protected]) on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMigaud, H. et al. Gamete quality and broodstock management in temperate fish. \u003cem\u003eReviews Aquaculture\u003c/em\u003e. \u003cb\u003e5\u003c/b\u003e, S194\u0026ndash;S223. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/raq.12025\u003c/span\u003e\u003cspan address=\"10.1111/raq.12025\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNgo, M. 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Biochem.\u003c/em\u003e \u003cb\u003e46\u003c/b\u003e, 1111\u0026ndash;1120. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10695-020-00776-x\u003c/span\u003e\u003cspan address=\"10.1007/s10695-020-00776-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2020).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Estradiol 17β, ovarian development, gonadosomatic index, golden trevally, broodstock, aquaculture","lastPublishedDoi":"10.21203/rs.3.rs-7193848/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7193848/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePlasma estradiol 17β (E\u003csub\u003e2\u003c/sub\u003e) and gonadosomatic index (GSI) are reliable biomarkers for assessing gonadal maturity in fish. This study investigated seasonal variations in GSI and plasma E\u003csub\u003e2\u003c/sub\u003e concentrations and their correlation with ovarian development stages in female golden trevally (\u003cem\u003eGnathanodon speciosus\u003c/em\u003e) over an annual reproductive cycle. From November to February, plasma E\u003csub\u003e2\u003c/sub\u003e levels and GSI remained low, followed by a significant increase from March to October, with E\u003csub\u003e2\u003c/sub\u003e peaking during vitellogenesis. Ovarian histology revealed asynchronous oocyte development from March to October, with multiple oocyte stages coexisting, confirming \u003cem\u003eG. speciosus\u003c/em\u003e as a multiple-spawning species with a breeding season spanning March to October. Elevated plasma E\u003csub\u003e2\u003c/sub\u003e levels during oocyte growth underscore its pivotal role in driving vitellogenesis. These findings enhance understanding of \u003cem\u003eG. speciosus\u003c/em\u003e reproductive physiology, providing valuable insights for optimizing broodstock management, conditioning protocols, and strategic planning for artificial reproduction and seed production for marine aquaculture.\u003c/p\u003e","manuscriptTitle":"Seasonal dynamics of plasma estradiol 17β level, gonadosomatic index, and ovarian development in female golden trevally (Gnathanodon speciosus)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-26 01:23:08","doi":"10.21203/rs.3.rs-7193848/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-13T09:08:37+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-09T19:20:03+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-08T06:29:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"40559692020247040643230054177364266696","date":"2025-09-30T01:11:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"46512595785043051678891846583632844534","date":"2025-09-29T23:51:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-28T15:04:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"116822415464124918481449450172914865774","date":"2025-09-17T09:08:53+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-09T12:52:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"283681046318332718504733155664030700388","date":"2025-08-20T13:23:44+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-17T15:57:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-12T13:44:23+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-08-12T12:42:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-01T08:49:31+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-08-01T08:46:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7fcfaadc-b9fe-495a-97b6-ce63c327cf05","owner":[],"postedDate":"August 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":53452552,"name":"Biological sciences/Developmental biology"},{"id":53452553,"name":"Biological sciences/Ecology"},{"id":53452554,"name":"Earth and environmental sciences/Ecology"},{"id":53452555,"name":"Biological sciences/Physiology"},{"id":53452556,"name":"Biological sciences/Zoology"}],"tags":[],"updatedAt":"2025-12-08T16:07:29+00:00","versionOfRecord":{"articleIdentity":"rs-7193848","link":"https://doi.org/10.1038/s41598-025-30370-1","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-12-03 15:58:15","publishedOnDateReadable":"December 3rd, 2025"},"versionCreatedAt":"2025-08-26 01:23:08","video":"","vorDoi":"10.1038/s41598-025-30370-1","vorDoiUrl":"https://doi.org/10.1038/s41598-025-30370-1","workflowStages":[]},"version":"v1","identity":"rs-7193848","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7193848","identity":"rs-7193848","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}