Fish reproductive biology - Reflecting on five decades of fundamental and translational research

Understanding the links between micro/nanoplastics-induced gut microbes dysbiosis and potential diseases in fish: A review

At present, the quantity of micro/nano plastics in the environment is steadily rising, and their pollution has emerged as a global environmental issue. The tendency of their bioaccumulation in aquatic organisms (especially fish) has intensified people's attention to their persistent ecotoxicology. This review critically studies the accumulation of fish in the intestines of fish through active or passive intake of micro/nano plastics, resulting in their accumulation in intestinal organs and subsequent disturbance of intestinal microflora. The key lies in the complex toxic effect on the host after the disturbance of fish intestinal microflora. In addition, this review pointed out the characteristics of micro/nano plastics and the effects of their combined toxicity with adsorbed pollutants on fish intestinal microorganisms, in order to fully understand the characteristics of micro/nano plastics and emphasize the complex interaction between MNPs and other pollutants. We have an in-depth understanding of MNPs-induced intestinal flora disorders and intestinal dysfunction, affecting the host's systemic system, including immune system, nervous system, and reproductive system. The review also underscores the imperative for future research to investigate the toxic effects of prolonged exposure to MNPs, which are crucial for evaluating the ecological risks posed by MNPs and devising strategies to safeguard aquatic organisms.

Inhibition of the NF-κB signaling pathway affects gonadal differentiation and leads to male bias in Paramisgurnus dabryanus

In recent years, sex-controlled breeding has emerged as an effective strategy to enhance the yields of economic animals with different growth characteristics, while increasing the economic benefits of aquaculture. It is known that the NF-κB pathway participates in gonadal differentiation and reproduction. Therefore, we used the large-scale loach as a research model for the present study and selected an effective inhibitor of the NF-κB signaling pathway (QNZ). This, to investigates the impacts of the NF-κB signaling pathway on gonadal differentiation during a critical period of gonad development and after maturation. Simultaneously, the sex ratio bias and the reproductive capacities of adult fish were analyzed. Our results indicated that the inhibition of the NF-κB signaling pathway influenced the expression of genes related to gonad development, regulated the gene expression related to the brain-gonad-liver axis of juvenile loaches, and finally impacted the gonadal differentiation of the large-scale loach and promoted a male-biased sex ratio. Meanwhile, high QNZ concentrations affected the reproductive abilities of adult loaches and inhibited the growth performance of offspring. Thus, our results deepened the exploration of sex control in fish and provided a certain research basis for the sustainable development of the aquaculture industry.

The Effect of [(D-Ala6, Pro9NEt)mGnRH-a + Metoclopramide] (Ovopel) on Propagation Effectiveness of Two Breeding Lines of Common Carp (Cyprinus carpio L.) and on Luteinizing Hormone and 17α,20β-Dihydroxyprogesterone Levels in Females during Ovulation Induction

The study evaluates the impact of Ovopel on the reproductive effectiveness of carp from Polish line 6 and Lithuanian line B and the release of luteinizing hormone (LH) and 17α,20β-dihydroxyprogesterone (17α,20β-DHP) in females from these lines during ovulation induction. The levels of both hormones were determined in blood plasma samples taken just before the priming injection of Ovopel (0 h), at the time of administering the resolving dose of Ovopel (12 h), and after the next 12 h (24 h). Following Ovopel treatment, the mean egg weight obtained for line 6 was higher, but not statistically different, than that observed for line B. Egg quality, on the other hand, was significantly higher in line B. Female provenance did not significantly affect the number of eggs and living embryos after 70 h incubation. However, the total egg number for line 6 was higher. The mean number of living embryos (70 h) was similar for both lines. LH concentrations at 0, 12, and 24 h were not statistically different between the lines. A comparison of LH concentrations between ovulated and non-ovulated females at different sampling times revealed no significant differences either within or between the lines. Statistically significant differences in LH levels were found for both ovulated and non-ovulated females from a given line between the sampling times. The results for 17α,20β-DHP were similar, with only one difference: 24 h after the priming dose of Ovopel, 17α,20β-DHP levels in ovulated fish were significantly higher compared with non-ovulated females, but only in line 6.

The effectiveness of Ovaprim, Ovopel, and their combinations in artificial reproduction of common rudd Scardinius erythrophthalmus under controlled conditions

In this study, a practical protocol for artificial reproduction was developed for the rudd, Scardinius erythrophthalmus, to help to produce this fish for aquaculture industries and also for restocking programs. For this purpose, the efficiency of different hormonal agents and their combinations for spawning induction of female breeders of rudd was evaluated. Ovulations were stimulated using different treatments as: two injections of Ovaprim (Ova), two injections of Ovopel (Ovo), a priming dose of Ovopel with a resolving dose of Ovaprim (Comb1), a priming dose of Ovaprim with a resolving dose of Ovopel (Comb2), and two injections of sterile 0.9% NaCl solution as a control group. During the study, ovulation success, egg developmental competence as well as the performance of the freshly hatched larvae were recorded. There was no ovulation in females from the control group. In hormone-treated groups, 84-100% of fish ovulated, but no differences were observed in ovulation success (P > 0.05). The shortest latency period in treated fish was recorded in the Ovo group (431.6 degree-hour, P < 0.05). The best results in terms of working fecundity (number of obtained eggs per fish), relative fecundity, fertilization success, hatching rate, and embryo survival up to the eyed stage were achieved in the Ova and Comb1 groups (P < 0.05). Moreover, better survival rates up to the absorbing yolk sac stage and the lowest abnormality of larvae were observed in Ova and Comb1 groups (P < 0.05). There was no significant difference in the incubation time among different groups (P > 0.05). The obtained results indicate that two injections of Ovaprim and/or a priming dose of Ovopel with a resolving dose of Ovaprim are suitable for the artificial reproduction of rudd female breeders. Due to the proper effects and ease of use, two injections of Ovaprim could be recommended for the production of this species for restocking or aquaculture programs.

Identification of fish spermatogenic cells through high-throughput immunofluorescence against testis with an antibody set

Image-based identification and quantification of different types of spermatogenic cells is of great importance, not only for reproductive studies but also for genetic breeding. Here, we have developed antibodies against spermatogenesis-related proteins in zebrafish (Danio rerio), including Ddx4, Piwil1, Sycp3, and Pcna, and a high-throughput method for immunofluorescence analysis of zebrafish testicular sections. By immunofluorescence analysis of zebrafish testes, our results demonstrate that the expression of Ddx4 decreases progressively during spermatogenesis, Piwil1 is strongly expressed in type A spermatogonia and moderately expressed in type B spermatogonia, and Sycp3 has distinct expression patterns in different subtypes of spermatocytes. Additionally, we observed polar expression of Sycp3 and Pcna in primary spermatocytes at the leptotene stage. By a triple staining of Ddx4, Sycp3, and Pcna, different types/subtypes of spermatogenic cells were easily characterized. We further demonstrated the practicality of our antibodies in other fish species, including Chinese rare minnow (Gobiocypris rarus), common carp (Cyprinus carpio), blunt snout bream (Megalobrama amblycephala), rice field eel (Monopterus albus) and grass carp (Ctenopharyngodon idella). Finally, we proposed an integrated criterion for identifying different types/subtypes of spermatogenic cells in zebrafish and other fishes using this high-throughput immunofluorescence approach based on these antibodies. Therefore, our study provides a simple, practical, and efficient tool for the study of spermatogenesis in fish species.

Roundup in the Reproduction of Crucian Carp (Carassius carassius): An In Vitro Effect on the Pituitary Gland and Ovary

Roundup, the most popular herbicide in global agriculture, is regarded as an endocrine disruptor causing alterations of important hormones at the hypothalamic-pituitary-gonadal axis as well as impairment of gametogenesis. The whole pituitary glands of crucian carp (Carassius carassius) were incubated for 3 h in the medium containing Roundup (0-control, 1 and 10 ng/mL). The level of luteinizing hormone (LH), and mRNA transcript abundance of kisspeptin (kiss-1) and its receptor (gpr54), were determined. The isolated ovarian fragments were incubated for 24 h in the presence of Roundup and the following effects on reproductive parameters were determined: the final oocyte maturation and ovulation, structural changes in follicles, secretion of 17,20β-progesterone (17,20β-P) as well as mRNA transcript abundance of the luteinizing hormone receptor (lhr), estrogen receptors (erα, erβ1, erβ2), and zona radiata (chorion) proteins (zp2 and zp3). Roundup inhibited final oocyte maturation and decreased the percentage of ovulated eggs, and furthermore, caused structural changes in the ovarian follicular components. There were no significant changes in the measured hormone levels and analyzed genes mRNA transcript abundance. Summing up, obtained results indicate that Roundup may adversely affect oocyte maturation and the quality of eggs, suggesting that exposure to this herbicide can lead to reproductive disorders in fish.

An Overview of the Current Known and Unknown Roles of Vitamin D3 in the Female Reproductive System: Lessons from Farm Animals, Birds, and Fish

Recent studies have clearly shown that vitamin D₃ is a crucial regulator of the female reproductive process in humans and animals. Knowledge of the expression of vitamin D₃ receptors and related molecules in the female reproductive organs such as ovaries, uterus, oviduct, or placenta under physiological and pathological conditions highlights its contribution to the proper function of the reproductive system in females. Furthermore, vitamin D₃ deficiency leads to serious reproductive disturbances and pathologies including ovarian cysts. Although the influence of vitamin D₃ on the reproductive processes of humans and rodents has been extensively described, the association between vitamin D₃ and female reproductive function in farm animals, birds, and fish has rarely been summarized. In this review, we provide an overview of the role of vitamin D₃ in the reproductive system of those animals, with special attention paid to the expression of vitamin D₃ receptors and its metabolic molecules. This updated information could be essential for better understanding animal physiology and overcoming the incidence of infertility, which is crucial for optimizing reproductive outcomes in female livestock.

Reproductive roles of the vasopressin/oxytocin neuropeptide family in teleost fishes

The vertebrate nonapeptide families arginine vasopressin (AVP) and oxytocin (OXT) are considered to have evolved from a single vasopressin-like peptide present in invertebrates and termed arginine vasotocin in early vertebrate evolution. Unprecedented genome sequence availability has more recently allowed new insight into the evolution of nonapeptides and especially their receptor families in the context of whole genome duplications. In bony fish, nonapeptide homologues of AVP termed arginine vasotocin (Avp) and an OXT family peptide (Oxt) originally termed isotocin have been characterized. While reproductive roles of both nonapeptide families have historically been studied in several vertebrates, their roles in teleost reproduction remain much less understood. Taking advantage of novel genome resources and associated technological advances such as genetic modifications in fish models, we here critically review the current state of knowledge regarding the roles of nonapeptide systems in teleost reproduction. We further discuss sources of plasticity of the conserved nonapeptide systems in the context of diverse reproductive phenotypes observed in teleost fishes. Given the dual roles of preoptic area (POA) synthesized Avp and Oxt as neuromodulators and endocrine/paracrine factors, we focus on known roles of both peptides on reproductive behaviour and the regulation of the hypothalamic-pituitary-gonadal axis. Emphasis is placed on the identification of a gonadal nonapeptide system that plays critical roles in both steroidogenesis and gamete maturation. We conclude by highlighting key research gaps including a call for translational studies linking new mechanistic understanding of nonapeptide regulated physiology in the context of aquaculture, conservation biology and ecotoxicology.

A half century of fish gonadotropin-releasing hormones: Breaking paradigms

The field of fish gonadotropin-releasing hormones (GnRHs) is also celebrating its 50th anniversary this year. This review provides a chronological history of fish GnRH biology over the past five decades. It demonstrates how discoveries in fish regarding GnRH and GnRH receptor multiplicity, dynamic interactions between GnRH neurons, and additional neuroendocrine factors acting alongside GnRH, amongst others, have driven a paradigm shift in our understanding of GnRH systems and functions in vertebrates, including mammals. The role of technological innovations in enabling scientific discoveries is portrayed, as well as how fundamental research in fish GnRH led to translational outcomes in aquaculture. The interchange between fish and mammalian GnRH research is discussed, as is the value and utility of using fish models for advancing GnRH biology. Current challenges and future perspectives are presented, with the hope of expanding the dialogue and collaborations within the neuroendocrinology scientific community at large, capitalizing on diversifying model animals and the use of comparative strategies.

The Ovarian Transcriptome at the Early Stage of Testis Removal-Induced Male-To-Female Sex Change in the Protandrous Black Porgy Acanthopagrus schlegelii

Unlike gonochoristic fishes, sex is fixed after gonadal differentiation (primary sex determination), and sex can be altered in adults (secondary sex determination) of hermaphroditic fish species. The secondary sex determination of hermaphroditic fish has focused on the differences between testicular tissue and ovarian tissue during the sex change process. However, comprehensive studies analyzing ovarian tissue or testicular tissue independently have not been performed. Hermaphroditic black porgy shows a digonic gonad (ovarian tissue with testicular tissue separated by connective tissue). Protandrous black porgy has stable maleness during the first two reproductive cycles (&lt;2 years old), and approximately 50% enter femaleness (natural sex change) during the third reproductive cycle. Precocious femaleness is rarely observed in the estradiol-17β (E2)-induced female phase (oocytes maintained at the primary oocyte stage), and a reversible female-to-male sex change is found after E2 is withdrawn in &lt;2-year-old fish. However, precocious femaleness (oocytes entering the vitellogenic oocyte stage) is observed in testis-removed fish in &lt;2-year-old fish. We used this characteristic to study secondary sex determination (femaleness) in ovarian tissue via transcriptomic analysis. Cell proliferation analysis showed that BrdU (5-bromo-2′-deoxyuridine)-incorporated germline cells were significantly increased in the testis-removed fish (female) compared to the control (sham) fish (male) during the nonspawning season (2 months after surgery). qPCR analysis showed that there were no differences in pituitary-releasing hormones (lhb and gtha) in pituitary and ovarian steroidogenesis-related factors (star, cyp11a1, hsd3b1, and cyp19a1a) or female-related genes (wnt4a, bmp15, gdf9, figla, and foxl2) in ovarian tissues between intact and testis-removed fish (2 months after surgery). Low expression of pituitary fshb and ovarian cyp17a1 was found after 2 months of surgery. However, we did find small numbers of genes (289 genes) showing sexual fate dimorphic expression in both groups by transcriptomic analysis (1 month after surgery). The expression profiles of these differentially expressed genes were further examined by qPCR. Our present work identified several candidate genes in ovarian tissue that may be involved in the early period of secondary sex determination (femaleness) in black porgy. The data confirmed our previous suggestion that testicular tissue plays an important role in secondary sex determination in protandrous black porgy.

Effects of Early Thermal Environment on Growth, Age at Maturity, and Sexual Size Dimorphism in Arctic Charr

The effects of early thermal environment on growth, age at maturity, and sexual size dimorphism in Arctic charr (Salvelinus alpinus) are investigated. This study is a 654-day long rearing trial split into two sequential experimental phases termed EP1 and EP2 and lasting 315 and 339 days, respectively. EP1 started at the end of the yolk sac stage when the experimental fish were divided into three groups and reared at different target temperatures (7, 10 and 12 °C). During EP2, all groups were reared at the same temperature (7–8 °C) until harvest (~1300 g). Growth rates increased with temperature from 7 to 12 °C, and at the end of EP1 the 12C group had 49.0% and 19.2% higher mean weight than groups 7C and 10C, respectively. Elevated early rearing temperatures were, however, found to cause precocious sexual maturation and reduce the long-term growth performance. At the end of EP2, the 7C group had 3.6% and 14.1% higher mean weight than 10C and 12C, respectively. Elevated early rearing temperatures had a much stronger effect on the maturity incidence of females, and while male-biased sexual size dimorphism (SSD) was found in all groups, the magnitude of SSD was positively associated with temperature.

Antidepressants as Endocrine Disrupting Compounds in Fish

As antidepressant usage by the global population continues to increase, their persistent detection in aquatic habitats from municipal wastewater effluent release has led to concerns of possible impacts on non-target organisms, including fish. These pharmaceuticals have been marketed as mood-altering drugs, specifically targeting the monoaminergic signaling in the brain of humans. However, the monoaminergic systems are highly conserved and involved in the modulation of a multitude of endocrine functions in vertebrates. While most studies exploring possible impact of antidepressants on fish have focused on behavioural perturbations, a smaller spotlight has been placed on the endocrine functions, especially related to reproduction, growth, and the stress response. The purpose of this review is to highlight the possible role of antidepressants as endocrine disruptors in fish. While studies linking the effects of environmentally relevant levels of antidepressant on the endocrine system in fish are sparse, the emerging evidence suggests that early-life exposure to these compounds have the potential to alter the developmental programming of the endocrine system, which could persist as long-term and multigenerational effects in teleosts.

Coordinate regulation of feeding, metabolism, and growth: Perspectives from studies in fish

This paper develops a model for coordinate regulation of feeding, metabolism, and growth based on studies in fish. Many factors involved with the control of feeding [e.g., cholecystokinin (CCK) and ghrelin (GRLN)], energy metabolism [e.g., insulin (INS), glucagon (GLU), glucagon-like peptide (GLP), and somatostatins (SS), produced in the endocrine pancreas; and leptin (LEP) produced broadly], and growth [e.g., GRLN, growth hormone (GH), insulin-like growth factors (IGFs), GH receptors (GHR), IGF receptors (IGFR)] interact at various levels. Many such interactions serve to coordinate these systems to favor anabolic processes (i.e., lipid and protein synthesis, glycogenesis) and growth, including GH promotion of feeding and stimulation of INS production/secretion and the upregulation of GHR and IGFR by GRLN. As nutrient and stored energy status change, various feedbacks serve to curtail feeding and transition the animal from an anabolic/growth state to a catabolic state. Many factors, including LEP and IGF, promote satiety, whereas SS downregulates INS signaling as well as IGF production and GHR and IGFR abundance. As INS and IGF levels fall, GH becomes disconnected from growth as a result of altered linkage of GHR to cell signaling pathways. As a result, the catabolic actions of GH, GLU, GLP, LEP, and SS prevail, mobilizing stored energy reserves. Coordinate regulation involves relative abundances of blood-borne hormones as well as the ability to adjust responsiveness to hormones (via receptor and post-receptor events) in a cell-/tissue-specific manner that results from genetic and epigenetic programming and modulation by the local milieu of hormones, nutrients, and autocrine/paracrine interactions. The proposed model of coordinate regulation demonstrates how feeding, metabolism, and growth are integrated with each other and with other processes, such as reproduction, and how adaptive adjustments can be made to energy allocation during an animal's life history and/or in response to changes in environmental conditions.

Developmental aspects of the hypothalamic-pituitary network related to reproduction in teleost fish

The hypothalamic-pituitary-gonadal axis is the main system that regulates reproduction in vertebrates through a complex network that involves different neuropeptides, neurotransmitters, and pituitary hormones. Considering that this axis is established early on life, the main goal of the present work is to gather information on its development and the actions of its components during early life stages. This review focuses on fish because their neuroanatomical characteristics make them excellent models to study neuroendocrine systems. The following points are discussed: i) developmental functions of the neuroendocrine components of this network, and ii) developmental disruptions that may impact adult reproduction. The importance of the components of this network and their susceptibility to external/internal signals that can alter their specific early functions and/or even the establishment of the reproductive axis, indicate that more studies are necessary to understand this complex and dynamic network.

Igf3: a novel player in fish reproduction†

As in other vertebrates, fish reproduction is tightly controlled by gonadotropin signaling. One of the most perplexing aspects of gonadotropin action on germ cell biology is the restricted expression of gonadotropin receptors in somatic cells of the gonads. Therefore, the identification of factors conveying the action of gonadotropins on germ cells is particularly important for understanding the mechanism of reproduction. Insulin-like growth factors (Igfs) are recognized as key factors in regulating reproduction by triggering a series of physiological processes in vertebrates. Recently, a novel member of Igfs called Igf3 has been identified in teleost. Different from the conventional Igf1 and Igf2 that are ubiquitously expressed in a majority of tissues, Igf3 is solely or highly expressed in the fish gonads. The role of Igf3 in mediating the action of gonadotropin through Igf type 1 receptor on several aspects of oogenesis and spermatogenesis have been demonstrated in several fish species. In this review, we will summarize existing data on Igf3. This new information obtained from Igf3 provides insight into elucidating the molecular mechanism of fish reproduction, and also highlights the importance of Igf system in mediating the action of gonadotropin signaling on animal reproduction.

Atresia of ovarian follicles in fishes, and implications and uses in aquaculture and fisheries

Atresia of ovarian follicles, that is the degenerative process of germ cells and their associated somatic cells, is a complex process involving apoptosis, autophagy and heterophagy. Follicular atresia is a normal component of fish oogenesis and it is observed throughout the ovarian cycle, although it is more frequent in regressing ovaries during the postspawning period. An increased occurrence of follicular atresia above physiological rates reduces fish fecundity and even causes reproductive failure in both wild and captive-reared fish stocks, and hence, this phenomenon has a wide range of implications in applied sciences such as fisheries and aquaculture. The present article reviews the available literature on both basic and applied traits of oocyte loss by atresia, including its morpho-physiological aspects and factors that cause a supraphysiological increase of follicular atresia. Finally, the review presents the use of early follicular atresia identification in the selection process of induced spawning in aquaculture and the implications of follicular atresia in fisheries management.

Molecular characterization of fshb and lhb subunits and their expression profiles in captive white-edged rockfish, Sebastes taczanowskii

Fundamental knowledge on the regulation of reproduction by gonadotropins (Gths) is quite limited in viviparous fishes. In the present study, we performed molecular cloning and characterization of cDNAs encoding two Gth subunits (fshb and lhb) from the pituitaries of viviparous white-edged rockfish, Sebastes taczanowskii; expression profiles of both gene transcripts were elucidated in the pituitaries of reproductive males and females which were kept in a captive environment. The cloned fshb and lhb fragments exhibited high sequence identities with corresponding β-subunit sequences from black rockfish, S. schlegelii. Notably, the fshb of white-edged rockfish appeared to lack a putative N-glycosylation site, whereas lhb conserved it. Expression of fshb and lhb transcripts in the rockfish pituitaries largely changed in synchrony but for minor exceptions. In males, levels of both transcripts increased with progression of spermatogenesis, although the peak for fshb (October) appeared slightly earlier than that for lhb (November). In females, both gene transcripts exhibited synchronous bimodal changes. High expression of fshb and lhb transcripts in the female pituitary during the gestation period, followed by the drastic decrease at parturition, suggest their possible involvement in regulation of gestation of this species. The knowledge gained for Sebastes in this study superimposes fundamental information necessary for further physiological understanding of viviparity in teleost fish.

Neuromodulatory effects of GnRH on the caudal neurosecretory Dahlgren cells in female olive flounder

Gonadotropin-releasing hormone (GnRH) is considered a key player in reproduction. The caudal neurosecretory system (CNSS) is a unique neurosecretory structure of fish that may be involved in osmoregulation, nutrition, reproduction, and stress-related responses. However, a direct effect of GnRH on Dahlgren cells remains underexplored. Here, we examined the electrophysiological response of Dahlgren cell population of the CNSS to GnRH analog LHRH-A₂ and the transcription of related key genes of CNSS. We found that GnRH increased overall firing frequency and may be changed the firing pattern from silent to burst or phasic firing in a subpopulation of Dahlgren cells. The effect of GnRH on a subpopulation of Dahlgren cells firing activity was blocked by the GnRH receptor (GnRH-R) antagonist cetrorelix. A positive correlation was observed between the UII and GnRH-R mRNA levels in CNSS or gonadosomatic index (GSI) during the breeding season. These findings are the first demonstration of the ability of GnRH acts as a modulator within the CNSS and add to our understanding of the physiological role of the CNSS in reproduction and seasonal adaptation.

Mismatch between critical and accumulated temperature following river damming impacts fish spawning

Dam operations considerably influence water temperature regimes in rivers, which affects fish spawning activities. Previous studies have focused on the effects of critical temperature (CT) alterations during the spawning period, and largely ignored the effects of accumulated temperature (AT) alterations on gonadal development. Successful spawning relies on the simultaneous achievement of the two thermal requirements at appropriate times. River damming may cause a mismatch between the times of achieving CT and AT thresholds, and in turn influence fish reproduction. In the present study, spawning events of Coreius heterodon (C. heterodon) from 2009 to 2015 in the upper reaches of the Yangtze River, which are under the influence of cascade dams, were analysed based on the times of achievement of CT and AT thresholds. The CT and AT thresholds for C. heterodon spawning were 18.4 °C and 1324.9 °C·d, respectively. Under pre-impoundment conditions, the time of achievement of the AT threshold was 23 d on average later than that under post-impoundment conditions; however, the time of achievement of the CT threshold was similar under both conditions. The time of achievement of the AT threshold was 10 d earlier than that of achievement of the CT threshold in post-impoundment conditions. Earlier achievement of AT thresholds was followed by reduced spawning. The alteration of temperature rhythm caused by reservoir operations could be the major factor decreasing spawning abundance after river damming. The results of the present study could facilitate sustainable reservoir operations with regards to water temperature management, and thereby improve the conservation of fish resources.