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Fish is an important source of food and income for a significant portion of the Amazonian population, especially those who live along the rivers and lakes in the region. Pseudoplatystoma punctifer (Castelnau, 1855), known as surubim, is a species of Neotropical catfish widely exploited by fisheries and commercially valuable in the Guaporé River basin, Brazil. However, population dynamics are poorly known in the region. To understand the population structure and reproductive biology aspects of the surubim, monthly experimental fisheries were carried out in the São Miguel River, state of Rondônia, Brazil, between August 2020 and July 2021. The captured fish were weighed, and its gonads were removed and weighed for histological analyses (microscopic description) and classification of the maturation stages (macroscopic description). The collected gonads were fixed in 10% buffered formalin, dehydrated, cut into 4-μm-thick sections, and stained with hematoxylin and eosin. A total of 34 individuals were collected (20 females and 14 males), showing positive allometric growth and condition factor from 0.81 to 1.79 for females and males, respectively. Females were larger in size and weight than males. P. punctifer reaches its first maturation at an average length of 68.30 cm, indicating the importance of respecting the minimum capture size as an alternative to ensure the natural stocks of this fishery resource in the region. The results provide support for the establishment of public policies and actions for conservation, management, and regulation of fishing., (© 2024 Fisheries Society of the British Isles.)

Fish experiencing abnormally high or prolonged elevations in temperature can exhibit impaired reproduction, even for species adapted to warm water environments. Such high temperature inhibition of reproduction has been linked to diminished gonadal steroidogenesis, but the mechanisms whereby hypothalamic-pituitary-gonadal (HPG) axis signaling is impacted by high temperature are not fully understood. Here, we characterized differences in HPG status in adult sheepshead minnow (Cyprinodon variegatus), a eurythermal salt marsh and estuarine species of eastern North America, exposed for 14 d to temperatures of 27 °C or 37 °C. Males and females at 37 °C had lower gonadosomatic index (GSI) values compared to fish at 27 °C, and females at 37 °C had fewer spawning capable eggs and lower circulating 17β-estradiol (E 2 ). Gene transcripts encoding gonadotropin-inhibitory hormone (gnih) and gonadotropin-releasing hormone-3 (gnrh3) were higher in relative abundance in the hypothalamus of both sexes at 37 °C. While pituitary mRNAs for the β-subunits of follicle-stimulating hormone (fshβ) and luteinizing hormone (lhβ) were lowered only in males at 37 °C, Fsh and Lh receptor mRNA levels in the gonads were at lower relative levels in both the ovary and testis of fish at 37 °C. Females at 37 °C also showed reduced ovarian mRNA levels for steroid acute regulatory protein (star), P450 side-chain cleavage enzyme (cyp11a1), 3β-hydroxysteroid dehydrogenase (3βhsd), 17β-hydroxysteroid dehydrogenase (hsd17β3), and ovarian aromatase (cyp19a1a). Females at the higher 37 °C temperature also had a lower liver expression of mRNAs encoding estrogen receptor α (esr1) and several vitellogenin and choriogenin genes, but elevated mRNA levels for hepatic sex hormone-binding globulin (shbg). Our results substantiate prior findings that exposure of fish to high temperature can inhibit gonadal steroidogenesis and oogenesis, and point to declines in reproductive performance emerging from alterations at several levels of HPG axis signaling including increased hypothalamic Gnih expression, depressed gonadal steroidogenesis, and reduced egg yolk and egg envelope protein production in the liver., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Although ruffe (Gymnocephalus cernua) are widely distributed in Eurasia, in some regions (i.e., North America) ruffe are considered an invasive species. There have been no reports on artificial reproduction of this species. A study, therefore, was conducted to evaluate reproduction of ruffe with results of specimens captured from their natural habitat and cultured (F 1 generation) specimens being compared. Spawning specimens from both stocks were treated with hormonal preparations: carp pituitary homogenate (CPH), Ovopel, Ovaprim and human chorionic gonadotropin (hCG) and results were analyzed by comparing response to the specimens of control groups. Spermiation outcomes and sperm motility of the captured and cultured ruffe were similar and with all hormonal treatments, there was a slightly greater sperm motility (55.6 %-57.1 %) in comparison to specimens of control groups (46.7 %-47.1 %). For captured specimens, there was no asynchronous development of oocytes, whereas in cultured specimens 32 % of females had asynchronous development of oocytes. The ovulation rate in specimens of all treated groups was 100 %, whereas specimens in the control groups did not reproductively mature and have ovulations. The latency time from time of hormonal treatments to initiation of reproductive functions depended on the spawning agent used and oocyte maturation stage and there was the shortest latency after using CPH and the longest with hCG treatment. The embryo survival and hatching rates varied with use of different hormonal preparations to induce reproduction: greatest hatching rates with hCG treatment (86.4 %-88.9 %), followed by Ovaprim (78.2 %-80.2 %) and least hatching rate with Ovopel and CPH treatments (66.0 %-67.1 % and 64.0 %-66.0 %, respectively)., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A study was conducted to understand the potential for ibuprofen to impact the hypothalamus-pituitary-gonadal endocrine axis resulting in disruption of fish reproduction. The Good Laboratory Practice study was conducted according to the Organisation for Economic Co-operation and Development 229 Protocol, Fish Short-Term Reproduction Assay, and extended an additional 4 d to evaluate hatching success in the F1 generation. Test organisms were exposed to nominal test concentrations of 0.5, 2.4, 11.5, 55.3, and 265.4 µg ibuprofen/L and a negative control (dilution water). To strengthen the statistical power of the study, twice the number of replicates were used in the negative control versus individual treatment levels. A 21-d pre-exposure to identify groups of actively spawning fish was immediately followed by a 36-d exposure. Results for apical endpoints of survival, growth, and reproduction (fecundity and fertility), as well as the biomarker vitellogenin in the F0 generation and time to hatch and hatching success in the F1 generation are presented. Based on mean measured exposure concentrations and effects on fecundity in the F0 generation and hatching success in the F1 generation, overall no-observed-effect concentration and lowest-observed-effect concentration for the present study were 55.2 and 265.9 µg ibuprofen/L, respectively. Results from the present study indicate a lack of endocrine-mediated reproductive effects in zebrafish at environmentally relevant concentrations of ibuprofen. Environ Toxicol Chem 2020;39:1534-1545. © 2020 SETAC., (© 2020 SETAC.)

Anthropogenic emissions of carbon dioxide in the atmosphere have generated rapid variations in atmospheric composition which drives major climate changes. Climate change related effects include changes in physico-chemical proprieties of sea and freshwater, such as variations in water temperature, salinity, pH/pCO 2 and oxygen content, which can impact fish critical physiological functions including reproduction. In this context, the main aim of the present review is to discuss how climate change related effects (variation in water temperature and salinity, increases in duration and frequency of hypoxia events, water acidification) would impact reproduction by affecting the neuroendocrine axis (brain-pituitary-gonad axis). Variations in temperature and photoperiod regimes are known to strongly affect sex differentiation and the timing and phenology of spawning period in several fish species. Temperature mainly acts at the level of gonad by interfering with steroidogenesis, (notably on gonadal aromatase activity) and gametogenesis. Temperature is also directly involved in the quality of released gametes and embryos development. Changes in salinity or water acidification are especially associated with reduction of sperm quality and reproductive output. Hypoxia events are able to interact with gonad steroidogenesis by acting on the steroids precursor cholesterol availability or directly on aromatase action, with an impact on the quality of gametes and reproductive success. Climate change related effects on water parameters likely influence also the reproductive behavior of fish. Although the precise mechanisms underlying the regulation of these effects are not always understood, in this review we discuss different hypothesis and propose future research perspectives., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Understanding the fundamental reproductive biology of a species is the first step toward identifying parameters that are critical for reproduction and for the development of assisted reproductive techniques. Ejaculates were collected from aquarium (n = 24) and in situ (n = 34) sand tiger sharks Carcharias taurus. Volume, pH, osmolarity, sperm concentration, motility, status, morphology, and plasma membrane integrity were assessed for each ejaculate. Semen with the highest proportion of motile sperm was collected between April and June for both in situ and aquarium sand tiger sharks indicating a seasonal reproductive cycle. Overall, 17 of 30 semen samples collected from aquarium sharks from April through June contained motile sperm compared to 29 of 29 of in situ sharks, demonstrating semen quality differences between aquarium and in situ sharks. Sperm motility, status, morphology, and plasma membrane integrity were significantly higher (P < 0.05) for in situ compared to aquarium sand tiger sharks. Testosterone was measured by an enzyme immunoassay validated for the species. Testosterone concentration was seasonal for both aquarium and in situ sharks with highest concentrations measured in spring and lowest in summer. In situ sharks had higher (P < 0.05) testosterone concentration in spring than aquarium sharks. This study demonstrated annual reproduction with spring seasonality for male sand tiger sharks through marked seasonal differences in testosterone and semen production. Lower testosterone and poorer semen quality was observed in aquarium sharks likely contributing to the species' limited reproductive success in aquariums., (© The Author(s) 2019. Published by Oxford University Press on behalf of Society for the Study of Reproduction.)

Estrogens play fundamental roles in regulating reproductive activities and they act through estrogen receptor (ESR) in all vertebrates. Most vertebrates have two ESR subtypes (ESR1 and ESR2), whereas teleost fish have at least three (Esr1, Esr2a and Esr2b). Intricate functionalization has been suggested among the Esr subtypes, but to date, distinct roles of Esr have been characterized in only a limited number of species. Study of loss-of-function in animal models is a powerful tool for application to understanding vertebrate reproductive biology. In the current study, we established esr1 knockout (KO) medaka using a TALEN approach and examined the effects of Esr1 ablation. Unexpectedly, esr1 KO medaka did not show any significant defects in their gonadal development or in their sexual characteristics. Neither male or female esr1 KO medaka exhibited any significant changes in sexual differentiation or reproductive activity compared with wild type controls. Interestingly, however, estrogen-induced vitellogenin gene expression, an estrogen-responsive biomarker in fish, was limited in the liver of esr1 KO males. Our findings, in contrast to mammals, indicate that Esr1 is dispensable for normal development and reproduction in medaka. We thus provide an evidence for estrogen receptor functionalization between mammals and fish. Our findings will also benefit interpretation of studies into the toxicological effects of estrogenic chemicals in fish., (© 2017 Japanese Society of Developmental Biologists.)

An adequate understanding of fish behaviors and their interaction with farmspecific environments is pivotal for enhancing fish welfare in aquaculture. The fair-fish database aims to provide a consistent overview of the welfare of farmed fish. This platform consolidates ethological knowledge into profiles of farmed aquatic species. Its WelfareCheck profiles are organized around welfare indicators, with each criterion receiving classifications (no findings, unclear, low, medium, and high) regarding the likelihood and potential for individuals of a given species to experience good welfare in aquaculture systems, along with the associated certainty level. These criteria include home range, depth range, migration patterns, reproduction, aggregation patterns, aggressive behavior, substrate needs, stress responses, malformations, and slaughtering protocols. We investigated which of these 10 criteria are most relevant to the overall welfare of a species, considering the likelihood, potential, and certainty of good welfare in aquaculture. To achieve this, we reviewed and recorded the high classifications across each criterion and dimension from all published WelfareCheck profiles. To further investigate knowledge gaps across the criteria, we also recorded classifications marked as unclear and no findings. These were then compared across the criteria to assess the frequency of such classifications. While no significant differences were found between the criteria regarding the likelihood that the surveyed species meet their basic welfare needs, criteria related to reproduction, slaughter practices, and substrate needs demonstrated a high potential for better welfare outcomes. Moreover, reproduction and migration patterns exhibited high certainty in the available literature. Based on these findings, we conclude that improving the reproduction of farmed aquatic species, considering their natural needs and behavior, could be an effective and reliable approach to improving welfare. However, we also found a low certainty of information on aggression and an absence or conflicting data on home range, aggregation patterns, stress, and malformations. This highlights an urgent need for research in these areas, which are fundamental for developing more accurate assessments and recommendations for farmed aquatic species. [ABSTRACT FROM AUTHOR]

Despite significant advancements in ichthyoplankton collection and data processing, challenges persist in the taxonomic identification of these organisms, particularly their eggs. To overcome these challenges, a novel technique has been developed to facilitate the identification of live eggs collected directly in wild. This user-friendly technique includes the collection, processing of the material, and field incubation. Sampling must be conducted using a pelagic net towed at low speed, preferably during early evening. The material processing involves pre-sorting and sorting to remove eggs and larvae. The separated eggs, kept in an aerated bowl, can be identified based on their morphological and meristic characteristics. Unidentified eggs can be placed in plastic bags with oxygen and incubated directly in the aquatic environment for 48–72 h. After this incubation period, the hatched larvae at the yolk-sac or preflexion stage, are identified to the lowest possible taxonomic level. Depending on the study's purpose, hatched larvae and field-collected larvae can be transported to research centers for further development, released back into the natural environment, or fixed to complete the collection. The application of this technique supports management and monitoring programs by identifying spawning areas through egg identification, forming broodstock, and replenishing threatened species, thereby enhancing scientific collections of ichthyoplankton. Additionally, it reduces mortality in ichthyoplankton techniques, including endangered species. Therefore, we believe that this novel taxonomic technique for identifying live ichthyoplankton represents a paradigm shift in the monitoring, management, and conservation of fish, as well as in ecological stewardship and advances in this area of research. [ABSTRACT FROM AUTHOR]

The effects of feeding frequency on Hippocampus reidi broodstock were examined using oocyte fatty acid profile, reproduction, and larval resistance to starvation as evaluation criteria. Twelve breeding pairs (approx. 27 g; 18 cm per individual) were fed to satiation with defrosted enriched caridean shrimp Palaemon sp. in one (F1), two (F2), three (F3), or four (F4) meals per day. Three broodstock pairs were subjected to each feeding regime and treatments were continued for 101 days. Fish of both sexes fed once a day had lower weight gain and specific growth rates than broodstock from the other treatments (p < 0.05). Newly born larvae produced by the pairs in F3 and F4 treatments presented similar weight and length (mean 2.06 ± 0.11 mg; 7.9 ± 0.06 mm, respectively) and were larger than those produced by pairs that received one or two daily feedings (mean 1.62 ± 0.17 mg; 6.7 ± 0.05 mm) (p < 0.05). Mean number of larvae per parturition in F3 and F4 (928.5) was almost two times the mean number of larvae in F1 and F2. The total mortality of the starved larvae was observed after 72 h in the couples of treatments F1 and F2, while in treatments F3 and F4 it occurred after 96 h. The highest concentrations of polyunsaturated fatty acids, arachidonic acid (AA), and docosahexaenoic acid (DHA) were observed in the oocytes produced by fish subjected to the F4 treatment. It is recommended that when broodstock H. reidi are given defrosted enriched shrimp to apparent satiation, they should be fed three to four times per day to promote egg production and to give good quality larvae. [ABSTRACT FROM AUTHOR]

All organisms require the ability to engage in either sexual or asexual reproduction in order to ensure their own survival. In aquaculture, when one sex outgrows the other faster, farmers use hormones to stimulate growth. Furthermore, the production of fish based on sexual dimorphism is predominantly executed through the utilization of estrogens and androgens. Environmentally, these compounds may pollute the ecosystem and cause endocrine system alterations that cause harmful effects; thus, they must be handled carefully to assure environmental, biological, and food safety. Phytoestrogens as natural non-steroidal phenolic plant chemicals that resemble 17-β-estradiol, could be employed as a safe alternative source of natural estrogens. The phytoestrogens have many biological effects due to their ability to compete with estrogen receptors, but they may negatively affect fish production, reproduction, and behaviors under controlled conditions. Thus, the current literature emphasizes on the beneficial effects of phytoestrogens on aquatic animal performance, behaviors, and some reproductive features. [ABSTRACT FROM AUTHOR]

The guntea loach, Lepidocephalichthys guntea, is categorically common freshwater fish in Southeast Asia. Current study is the first elucidation on the reproductive feature of L. guntea including population structure, sex ratio (SR), size at first maturity (Lm), breeding period, and condition factor, emphasizing on the effect of environmental factors on reproduction of this fish in the Payra River (Southern Bangladesh) during July 2021 to June 2022. Using various conventional gears, 1128 individuals (534 males and 594 females) have been collected. Total length (TL), standard length (SL), and body weight (BW) of each fish were measured. Ovaries were cautiously dissected, removed, and precisely weighed. TL ranges from 4.6 to 9.7 cm (BW = 0.7–9.27 g) for male and 4.6–10.3 cm (BW = 0.8–10.75 g) for female. Both male (47.34%) and female (52.66%) populations were the leading group in 7.00–7.99 cm TL. Overall SR was not notably altered from anticipated value of 1:1 (male:female = 1:1.11). Nonetheless, monthly variations of SR specified females were considerably outnumbered males in each month excluding March–May. Lm range was 6.4–7.0 cm, so larger than Lm is recommended to exploit. Monthly changes in GSI indicated that the main spawning season was from March to June. The spawning season was substantially correlated with rainfall, nonetheless with temperature. Additionally, relative weight indicated that habitat was imbalanced with higher predators. A fishing ban is recommended during peak spawning to protect L. guntea in the Payra River and its surroundings based on current research. [ABSTRACT FROM AUTHOR]

Hilsa (Tenualosa ilisha), a highly prized edible fish, is consumed by over 250 million peopleworldwide. Estrogens are essential hormones required during reproduction and bind with estrogen receptors in target organs for biological activity. The two unique subtypes of the estrogen receptor found in fish are alpha (a) and beta (b) and exhibit distinctive roles in reproduction. The present study aimed to understand the breeding physiology of hilsa during the seasonal gonadal cycles through GSI seasonal variation, histological study, and molecular identification, characterization, and transcriptional modification of estrogen receptors in hilsa. Monthly GSI analysis from females showed that during September, the GSI value was maximum (22.01 ± 0.68), followed by the May GSI value (18.78 ± 0.97). Histological observation showed the formation of asynchronous gametes during the development of ovaries. The histological analysis revealed the formation of developing oocytes, nucleus, presence of primary oogonia, secondary oogonia, chromatin nucleolar oocytes, and early perinucleolar oocytes in the ovary (January-early July). Progressively, formations of the yolk vesicles, yolk granule stage, premature stage, and mature stage with post-ovulatory follicles were also identified. Linear observation was recorded during the monsoon season from July to November. Furthermore, partial length cDNAs for estrogen receptors were characterized, and their mRNA expression patterns demonstrate that ER-a expression significantly increased in September, followed by April and August in the ovary and liver tissue. Both the liver and ovary showed the highest mRNA expression of ER-b in September. The study revealed that ER-a expression was higher in the ovary as compared with liver tissue. Furthermore, we introduce threedimensional (3D) models depicting the hilsa estrogen receptors in complex with estradiol (E2), constructed through homology modeling. This investigation contributes valuable insights into the molecular characteristics of estrogen receptors in this teleost fish. Our present work provided preliminary evidence of estrogen receptors during reproduction in hilsa. [ABSTRACT FROM AUTHOR]

Reproduction is among the most vital biological processes in the life cycle of any organism, such as fish. The biology of Oreochromis niloticus reproduction in Lake Nasser and Lake Nubia was studied using different mesh sizes of gill nets. A total of 480 Oreochromis niloticus were caught from Lake Nasser, Egypt, and 369 from Lake Nubia, Sudan, from January through December 2021. Sex ratio size at first maturity and maturity stages of O. niloticus were examined. In Nasser's Lake, the sex ratio of male to female was 1:1.02, whereas in Lake Nubia, it was 1:0.89. The first maturity length in Lake Nasser was 27.5cm for males and 27cm for females, while in Lake Nubia, it was 32cm for males and 26cm for females. The gonado somatic index indicated that the species breeds in Lake Nasser and Nubia during summer and spring, respectively. [ABSTRACT FROM AUTHOR]

Araruama Lagoon is one of the world's largest permanent hypersaline lagoons, and knowledge about the reproduction of fish assemblages is very scarce. This study aimed to evaluate the reproductive functionality of fishes of the Araruama Lagoon in the seasons of 2011, using functional diversity metrics. We also assessed the influence of abiotic factors (salinity, temperature, dissolved oxygen, and pH) on the distribution of sexes and reproductive stages of fish assemblages. Gonads were analyzed in 709 fish across 18 species, mainly females and juveniles. In winter, when there was a lower abundance of species, the highest reproductive incidence (gonadal development/maturation) and high salinity occurred. Summer and spring corresponded with the highest percentage of juveniles. Salinity was the abiotic factor behind the structuring of the community, while the temperature set off the start of the reproductive cycle in autumn. Thus, Araruama Lagoon played a crucial role as a nursery and reproductive area for the fish assemblage. Reproduction in Araruama Lagoon (2011). The vertical arrows indicate the main abiotic variables: temperature and salinity, which structure the fish community. Colors indicate larger (darker) and smaller (lighter) numerical values. The graphs show the percentage of juveniles, males and females, in the seasons corresponding to each season: spring (green), summer (yellow), autumn (orange), and winter (gray). The number of fish next to each graph indicates fish abundance in season, and fish colors indicate diversity. [ABSTRACT FROM AUTHOR]

Alteration of water levels of the lake/reservoir due to changes in river discharges, upstream abstraction, and drawdown regulation due to hydropower generation has been reported as among the major challenges to fish physiology and ultimately reproduction. Variations in lake/reservoir water levels influence biodiversity and the abundance of lake/reservoir biota. Variations have the greatest impacts in the littoral zones hence, interfering with fish spawning, incubation, and hatching of eggs, as well as the development of larvae, postlarvae, and juveniles. This particular paper reviews the literature available on the effect of the reservoirs/lakes' water level fluctuations on fish reproduction success using the documentary view method. The literature argues that water level fluctuations have both positive and negative impacts depending on frequency, magnitude, and duration and the species exposed. Extreme fluctuations tend to bring more adverse impacts. It further indicates that extreme and untimely water level fluctuation has direct impacts on the aquatic habitats and ultimately impacts fish assemblage and their populations. Few articles indicate the range of decrease or increase of water level, duration of such events, and effects they have on reservoir/lake ecosystem functions and fish physiology. Nevertheless, quantification of moderate and extreme water level fluctuation and associated effects is lacking. Although water level fluctuation is an important environmental cue for aquatic organisms, literature shows that the reduction of extreme water level variations especially multiannual variations is vital for fish reproduction. Therefore, upstream water use and reservoir operations should take into consideration the effects of water level fluctuations on reservoir structure, biological functions, and ultimate effects on fish reproduction. [ABSTRACT FROM AUTHOR]

Understanding environmental requirements for fish reproduction in natural habitats is crucial for population conservation and restoration. However, such information is extremely scarce for the highly threatened schizothoracine fishes that cover large elevation ranges on the Tibetan Plateau. This research investigated the spawning time, output and environmental conditions of wild Schizopygopsis thermalis along an elevational gradient (i.e., from 1766 to 4372 m) in the upper Nu‐Salween River. It found that the spawning grounds of S. thermalis were mainly located at elevations between 3600 and 4372 m, and spawning habitats mostly consist of still marginal areas (still water <10 cm deep) with gravel substrates. Otolith microstructure analysis revealed, for the first time, that S. thermalis spawns in two seasons (i.e., winter: from December to next February, and spring: from April to May), with the winter spawning period generally longer than the spring spawning period. Winter spawning started earlier and ended earlier at higher elevations, while spring spawning occurred earlier at lower elevations but ended simultaneously at higher elevations. As elevation increases, reproductive output also increases, and spawning cohorts shift from winter‐dominant to spring‐dominant. Winter spawning cohorts were associated with lower water temperatures but higher discharges than the spring spawning cohort, and both cohorts showed elevation‐related environmental preferences. Our results suggest that schizothoracine fish can adapt spawning strategies to elevation‐related environmental conditions, which fill the gaps in the reproductive characteristics of schizothoracine fishes, and highlight the importance of conserving schizothoracine habitats at high elevations in the Qinghai‐Tibetan rivers. [ABSTRACT FROM AUTHOR]

Reproduction in fishes is sensitive to temperature. Elevated temperatures and anomalous 'heat waves' associated with climate change have the potential to impact fish reproductive performance and, in some cases, even induce sex reversals. Here we examine how thermal sensitivity in the hormone pathways regulating reproduction provides a framework for understanding impacts of warmer conditions on fish reproduction. Such effects will differ depending on evolved variation in temperature sensitivity of endocrine pathways regulating reproductive processes of sex determination/differentiation, gametogenesis and spawning, as well as how developmental timing of those processes varies with reproductive ecology. For fish populations unable to shift geographical range, persistence under future climates may require changes in temperature responsiveness of the hormone pathways regulating reproductive processes. How thermal sensitivity in those hormone pathways varies among populations and species, how those pathways generate temperature maxima for reproduction, and how rapidly reproductive thermal tolerances can change via adaptation or transgenerational plasticity will shape which fishes are most at risk for impaired reproduction under rising temperatures. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'. [ABSTRACT FROM AUTHOR]

The blackfin snook, Centropomus medius, is a valuable fish in American and Mexican markets, mainly from catches. Nonetheless, information and studies about the biology of this species still need to be made available; thus, its aquaculture should be developed. This study aimed to describe the seasonal changes of proximate composition during a reproductive cycle of C. medius, analyzing differences between tissues and their changes related to the reproductive process. The snook specimens were collected in Magdalena Bay, Baja California Sur, Mexico, and measured every month from September 2001 to November 2002. Liver, gonads, muscle tissue, and intraperitoneal fat (IPF) were sampled and weighed. The gonadosomatic index (GSI), hepatosomatic index (HSI), IPF ratio, and condition factor index (K) were calculated. The biochemical composition was analyzed in the gonad, liver, and muscle. The reproductive period (RP) of wild C. medius in Baja California Sur, Mexico, was from June to December. The spawning period was recorded at summer temperature (25-30°C) and photoperiod (>13 h daylight) starting in September. High GSI values (gonad development), low HSI values (lipid reserve mobilization), low IPF, and low K ratio were related to elevated temperatures. Moreover, variations were observed in protein, total lipid, triglycerides, and glycogen content in muscle, liver, and gonad according to the reproductive phase. A positive correlation was demonstrated between protein contents in muscle, gonad, and K, with lower concentrations during RP, while liver protein composition showed an opposite pattern. Lipids were mainly present in the liver, and the concentration decreased during RP while muscle increased. The results obtained in this study show differences in the proximate analyses in the liver, muscle, and gonads throughout the year concerning different phases of the reproductive cycle, indicating a great dependence of this process on the mobilization of reserves during C. medius reproduction. Therefore, understanding the feeding requirements to pursue the management of this species in captivity for aquaculture development is greatly important. [ABSTRACT FROM AUTHOR]

Objective: Fish population surveys in north‐temperate lakes are often conducted in the fall or spring when individuals are easy to capture with traditional fisheries techniques. Because some fishes are preparing to spawn or are spawning during these seasons, there is a critical need to better understand the potential influences of these surveys on decisions that are related to fish reproduction. Methods: We tested whether spring mark–recapture surveys using fyke nets followed by electrofishing affect the reproductive behaviors of male Smallmouth Bass Micropterus dolomieu in a northern Wisconsin lake. Fyke netting, electrofishing, and whole‐lake nest snorkeling surveys were conducted during 2001–2008, and Floy‐tagged males were tracked across years to test whether capture in the fyke nets only or capture in the electrofishing survey influenced interyear nest site fidelity and reproductive timing. Result: The mark–recapture surveys were conducted preceding the spawning of Smallmouth Bass, and returning males that were caught in the electrofishing survey nested ~50 m farther from their prior year's nest than both males that were captured only in fyke nets and males that were captured by neither method. Average interyear nest distances were ~200 m, and median interyear nest distances were ~90 m for males that were not captured in the electrofishing survey. Electrofishing and fyke netting did not influence the timing of reproduction. Conclusion: Spring electrofishing surveys for Smallmouth Bass have the potential to displace breeding males from preferred nesting habitats. If displacement negatively influences fitness (i.e., age‐0 survivorship to maturation), spring electrofishing surveys would not be recommended for assessing Smallmouth Bass populations. However, spring population surveys often occur soon after ice off, and surveys that are conducted at these colder temperatures are typically less stressful and less likely to result in mortality. Future research should test for fitness implications of reduced nest site fidelity following electrofishing in Smallmouth Bass while considering potential fitness trade‐offs if surveys are moved later in the year. Impact statementFish populations are often surveyed in the spring because many species move to the shoreline to spawn at this time. Being near the shoreline makes fish easier to catch, but we do not understand well how electrofishing surveys impact reproduction. This study helps address this gap to allow better management of Smallmouth Bass populations. [ABSTRACT FROM AUTHOR]

The complementary operation of hydropower and photovoltaic power, aimed at meeting real-time demand, has led to frequent adjustments in power generation, causing significant fluctuations in hydrological systems and adversely affecting fish reproduction. The traditional hydrological regime alteration assessment index is based on index of hydrologic alternation (IHA) and mostly focuses on annual and daily runoff alterations. This study proposes a new set of indicators considering the characteristics of subdaily hydrological regime alterations, including magnitude, rate of change, duration, frequency, and timing. Using the hourly outflow from Longyangxia, an analysis of indicator redundancy was conducted. The alteration of the indicators before and after hydropower and photovoltaic operation was then analyzed using the cumulative probability distribution curve. Additionally, a concentration index was introduced to analyze the variations in hydrological impacts during different months. The results show that the hydro–photovoltaic complementary operation changed the subdaily natural flow regime, significantly increasing the rate of flow increase or decrease and the duration, with most indexes increasing by more than 100% compared with the natural flow regime. Furthermore, the concentration values of the indexes for the hydro–photovoltaic complementary operation were less than 10, indicating a more significant impact on the subdaily flow regime throughout the year. This research provides crucial data for mitigating ecological impacts under multi-source complementary scheduling. [ABSTRACT FROM AUTHOR]

The age, growth, and reproduction of Schizothorax pseudaksaiensis (Herzenstein, 1889), a second-level key protected aquatic species in Xinjiang, were studied using fish ecology methods, and the biological characteristics of its population are discussed. A total of 735 specimens were collected on a seasonal basis from 2021 to 2022 using cages and nets in the Turks River. The fish length ranged from 47.30 mm to 538.60 mm, and the minimum age and maximum age were 1 years old and 23 years old, respectively. The fitting correlations revealed that S. pseudaksaiensis is a uniformly growing fish. The ages at the inflection point for S. pseudaksaiensis were 22.28 (female) and 19.55 (male). The sex ratio was 0.89 (females):1 (males), and the spawning period occurred from April to July. The absolute fecundity was 55,652.01 ± 25,468.78 eggs per individual, and the relative fecundity was 25.92 ± 10.69 eggs per gram. This study provides life history trait data for S. pseudaksaiensis and has theoretical and practical importance for maintaining population dynamics and fishery ecological balance. Additionally, a basis for the protection of fishery germplasm plateau resources is provided. [ABSTRACT FROM AUTHOR]

Simple Summary: Oxidative stress represents a significant threat to fish health, resulting in cellular damage and a host of health challenges. Astaxanthin, a powerful antioxidant, plays a pivotal role in reducing the reactivity of harmful reactive oxygen species and safeguarding crucial biomolecules within fish. Beyond its antioxidant properties, astaxanthin also regulates redox-sensitive signaling pathways, potentially enhancing fish health and well-being. Oxidative stress can impact fish reproduction, and astaxanthin supplementation has demonstrated promise in bolstering reproductive performance, encompassing improvements in egg quality and hormone levels. Furthermore, the integration of astaxanthin into aquaculture practices holds substantial potential for enhancing fish health and overall productivity, aligning with the sustainability goals of the aquaculture industry. Fish, constantly exposed to environmental stressors due to their aquatic habitat and high metabolic rates, are susceptible to oxidative stress. This review examines the interplay between oxidative stress and fish reproduction, emphasizing the potent antioxidant properties of astaxanthin. Our primary objective is to highlight astaxanthin's role in mitigating oxidative stress during critical reproductive stages, leading to improved gamete quality, ovary development, and hormone levels. We also explore its practical applications in aquaculture, including enhanced pigmentation and overall fish health. We conducted a comprehensive literature review, analyzing studies on astaxanthin's antioxidant properties and its impact on fish reproduction. Astaxanthin, a carotenoid pigment, effectively combats reactive oxygen species, inhibiting lipid peroxidation and maintaining membrane integrity. It significantly enhances reproductive success in fish and improves overall fish health in aquaculture settings. This review reveals astaxanthin's multifaceted benefits in fish health and reproduction, offering economic advantages in aquaculture. Future research should delve into species-specific responses, optimal dosages, and the long-term effects of astaxanthin supplementation to inform sustainable aquaculture strategies. [ABSTRACT FROM AUTHOR]

The biological rhythm is regulated through endogenous circadian clock and synchronizes with photoperiodic signal in an environmental light-dark cycle. The hypothalamic suprachiasmatic nucleus (SCN) containing clock genes acts as a 'time keeper' of the rhythmic functions as the environmental signal perceives through retino-hypothalamic tract and coordinates with oscillators present in almost all organs throughout the body. This coordination with external environment is governed by neuronal and hormonal cues. The pineal hormone melatonin (N-acetyl-5-methoxytryptamine) is synthesized rhythmically in all vertebrates with a peak during dark phase and nadir during light phase. It is considered as a 'hormone of darkness' involved primarily in maintaining the zeitgeber in the central and peripheral clocks. Melatonin regulates gonadal growth and maturation in fish by acting directly and/or on hypothalamo-pituitary-gonadal (HPG) axis. Exogenous administration of melatonin and/or altered photoperiods has a significant impact on the functions of gonads depending on the reproductive status of several fish species, particularly in carp. Seasonal fluctuations of ovarian melatonin concentration, high during the spawning season and a sharp decline during the post-spawning, in an annual reproductive cycle in female carp also suggested its involvement in the oocyte development. The hormone activates the structural components of maturation promoting factor (MPF), cyclin B and Cdc2, to promote germinal vesicle breakdown (GVBD). Melatonin also up-regulates several antioxidative enzymes in fish ovary and reduces oxidative stress to augment the spawning process. Thus, present review focus on the interactions of seasonal rhythmicity of melatonin secretions and gonadal functions for unravel its role in fish reproduction. [ABSTRACT FROM AUTHOR]

Ecosystem services provided by communities are related to the diversity of functional traits, and biotic functional simplification occurs when this diversity is reduced. Thus, we used the approach of functional indices, applied to the abundance of fish larvae and traits of the spawning stock, to evaluate the spatial and temporal variations in the functional diversity of the fish community of a Neotropical reservoir. The following hypotheses were tested: (i) different environmental conditions between reproductive periods lead to temporal variations in the functional diversity of the community, and (ii) the spatial heterogeneity (longitudinal and lateral) of the environmental conditions formed in the reservoir causes functional biotic simplification to occur from lotic towards lentic areas since the original community was formed by rheophilic species. Larval collections were carried out monthly, at night, between October and March, from 2009 to 2016, with plankton nets equipped with a flowmeter in nine sample areas categorised into three longitudinal zones (fluvial‐FLU, transition‐TRA and lacustrine‐LAC) and three sides (upper‐UPP, middle‐MID and lower‐LOW). Water samples were obtained to measure the temperature and turbidity. Precipitation and reservoir quotas were obtained from official agencies. After the identification of captured larvae, we determined which species were present and used the functional traits of the adults (parental stock), obtained from specialised literature, and functional richness (FRic) and its corresponding standardised effect size (SES.FRic) were computed. The spatiotemporal variations in these indices were evaluated through the two‐way block factorial MANOVA/ANOVA. Their association with environmental variables was inferred through multiple linear regression models. Altogether, 51,995 larvae were captured with the highest abundance in the period V, longitudinally in LAC and TRA and laterally in LOW. Among these, the functional indices were higher in periods IV and V. The highest values of FRic occurred longitudinally in FLU and laterally in LOW. Among the abiotic conditions, rainfall and water temperature were the most influential variables over functional indices and total larvae abundance. The results indicate that fish reproduction is linked to spatiotemporal variations in abiotic conditions confirming our first hypothesis. The second hypothesis was partially supported because functional biotic simplification was observed in the longitudinal gradient, with reductions in FRic in LAC. However, this reduction was not observed in the lateral gradient. We showed that the temporal variability of abiotic conditions is important for the high functional diversity of reservoirs. [ABSTRACT FROM AUTHOR]

Melatonin, the pineal hormone, is synthesized and secreted rhythmically in accordance with various environmental cues especially photo-thermal conditions. The reproductive physiology of seasonal breeders is synchronized with the surroundings by melatonin as a neuroendocrine mediator to acts as an important factor in fish reproduction. However, the data on the participation of melatonin in male reproduction and the putative interaction with the process of spermatogenesis in fish is scarce till date. So, major objectives of the current study are to determine for the first time, the relationship, if any, between seasonal levels of melatonin and testicular development and maturation of the germ cells, and also the involvements of specific meteorological parameters in spermatogenesis under natural photo-thermal conditions. We measured the concentration of circulatory and testicular melatonin; value of gonadosomatic index (GSI), relative percentages of different developing spermatogenic cells, area and perimeter (size and shape) of seminiferous lobules along with the level/duration of rainfall, water temperature and day length in six reproductive phases throughout an annual cycle in adult male catfish (Clarias batrachus). Intra-testicular and serum melatonin concentration showed a similar seasonal pattern with a peak during "functional maturity" phase and trough during "slow spermatogenesis" phase. Correlation as well as regression analyses also supported this positive relationship. Interestingly, intra-testicular melatonin also showed a significant positive correlation with GSI and relative percentage as well as lobular size of mature stages (spermatid and spermatozoa) of germ cells in an annual cycle. Furthermore, meteorological factors exhibited as critical cues to regulate the dynamics (in %) of spermatogenic cells and the level of testicular melatonin throughout the annual gonadal cycle. Our results corroborated by principal component (PC) analysis and showed very clearly that active "functional maturity" state is characterized by GSI, testicular melatonin, relative abundance and lobular size of mature spermatogenic stages as key internal oscillators; and studied environmental variables as the external clues for the regulation of spawning process. Collectively, the present data revealed that there is a relationship between melatonin levels and testicular growth and development of germ cells in Clarias batrachus under natural photo-thermal conditions. • Testicular melatonin exhibits seasonal variations in a gonadal cycle of Clarias batrachus. • Meteorological factors and testicular melatonin significantly correlated with the spermatogenesis. • Gonadosomatic index (GSI) and mature stages of germ cells are positively associated with testicular melatonin. [ABSTRACT FROM AUTHOR]

Aquaculture contributes significantly to the food source for human consumption. Tilapia Oreochromis niloticus is one of the main fish in aquaculture production, so its reproduction phases are vital to ensure the quality and quantity of organisms available for production systems. The reproductive parameters in fish aquaculture activities, such as fertility, fecundity, egg diameter, gonadosomatic index, survival rate in larvae and fingerlings, among others, are relevant for an economically profitable and sustainable production, and these can vary according to the diet, environmental conditions, age, genetic characteristics of the fish or the quality of the water. Therefore, this document aims to identify the reproductive parameters that influence on the production of fingerlings tilapia to present a general description in a simple way of the different reproductive parameters involved in aquaculture production activities of fingerlings tilapia. A search of the information in the last 20 years incorporated in various specialized databases was carried out. In this research, information is compiled to date on the reproductive parameters in tilapia, the results indicate that there is no more important reproductive parameter than another, since it is a cluster of factors and synergy that intervene in reproduction, hence it is necessary to establish clear management plans and research in the production systems to improve and enhance their production. Knowing the reproductive parameters of tilapia can help reduce production costs, thus it is necessary to establish clear management plans and research in production systems to improve and enhance their production. [ABSTRACT FROM AUTHOR]

Teleosts exhibit the highest reproductive diversity of all vertebrates, but this diversity has not been extensively analyzed, in part due to a lack of synthesis of life history information. The original STOREFISH (STrategies Of REproduction in FISH) database was published in 2007, and then released online in 2020 to facilitate data visualization and utilization (www.storefish.org). The original database contains information on 50 life history traits from ~1,200 references for 80 freshwater and anadromous species, mostly from Europe. Here, we describe the process and results of an international effort to update and extend the database for 14 egg and larval traits from North American freshwater and anadromous species, and then reassess previous bivariate relationships. Students in the United States and France used data from nearly 800 references to increase the STOREFISH database to 8,081 records (70% increase) for 368 species (360% increase) and 41 families (116% increase). We extracted fewer records per species than the original database because we included many species for which relatively little information was known. However, the distribution of records among trait values was similar to the original database. Updating and expanding the database improved the accuracy of the incubation time-temperature relationship below 10°C, and challenged a previous assumption regarding the larval sizeegg diameter relationship. Our expansion effort progressed smoothly and quickly via an educational model that emphasized supervised research and collaboration. We are extending this approach to include validators for data curation, and both pure and applied research that demonstrates the utility of the STOREFISH database to biodiversity research, conservation, assessment, management, and aquaculture. [ABSTRACT FROM AUTHOR]

Climate change threatens fisheries health through changing ecosystem dynamics; however, the impacts on the physiology and ecology of commercial fish populations are unclear. Here, annually deposited growth increments of female yelloweye rockfish (Sebastes ruberrimus) opercula collected in the Gulf of Alaska were used to successfully reconstruct lifetime (∼1-year resolution) steroid hormone, stable isotope, spawning, and stress data. We assessed how hormone profiles, spawning and distress frequencies related to sea surface temperature (SST), chlorophyll a concentrations as well as climate indices. Further, we assessed whether incorporating indicators of foraging depth and diet, stable isotope values (ẟ13C and ẟ15N), would improve model interpretations. Progesterone and estradiol concentrations decreased with increasing SST, suggesting that increasing SSTs may negatively impact juvenile and subadult females' reproductive development. Spawning frequency was positively linked to changes in the North Pacific Gyre Oscillation (NPGO) index, potentially timed with favorable conditions for larval survival. This was supported by juveniles having a lower probability of a distress event during positive NPGO years compared to negative NPGO years. While relationships among environmental data and yelloweye rockfish physiology were weak, this study provides insight into the environmental impacts on the lifetime reproduction and stress of a commercially important teleost species. [ABSTRACT FROM AUTHOR]

This study experimentally explored the influence of periodic consumption of polystyrene (PS) microplastic fragments on the body condition and fitness of a tropical marine fish. Adult damselfish, Acanthochromis polyacanthus , were pulse fed microplastic fragments bound with one of two different common plasticizers [di-2-ethylhexyl phthalate (DEHP), di-2-ethylhexyl terephthalate (DEHT)] together with virgin-plastic and no-plastic controls. Ingestion of plastic over a 150d period had no detectable effect on growth, indices of body condition, or gonadosomatic indices. Histology of the liver showed no detrimental effects of ingesting any of the plastic treatments on hepatocyte density or vacuolation. Plastic consumption had no effect on the number of clutches produced over the breeding period, the number of eggs, or the survival of embryos. It is believed that the relatively inert nature of PS, the low amount of plasticizers leached from the fragments and fast gut through-put times meant fish were exposed to low levels of toxic compounds. [ABSTRACT FROM AUTHOR]

Over the last 50 years, the concept of sustainable development has been introduced all across the world. It involves the transformation of all branches of the economy based on the "green economy". Fishery, which is based on the exploitation of natural resources and directly affects the ecological and food security of the country, is primarily subject to restructuring due to the need to achieve the goals of sustainable development. The latter means that the needs of the current generation must be fulfilled without creating obstacles for future generations. Accordingly, there is a problem of resource conservation in combination with the restoration of populations. Therefore, the preservation and sustainable development of humanity is possible only under the conditions of stable functioning and guaranteed reproduction of other components of the biosphere which can be considered as resources. Reproduction is one of the most important parts of fishery in general and aquaculture in particular. This is explained by the fact that the result of reproduction is the production of fish seeds. The latter can be aimed both at restoring natural populations and at the use in aquaculture farms. The actual reproduction process of aquatic organisms is carried out using different technologies. Their main difference is the degree of control over natural processes. In turn, it is largely determined by the degree of controllability of the selected methods. Thus, it can be stated that the highest level of controllability and technology of reproduction is achieved in the conditions of closed (recirculating) water supply system, while the lowest in the conditions of the arrangement of artificial spawning grounds in water bodies. Among the main technologies of fish reproduction, in addition to the two mentioned above, there are following: reproduction in cages, ponds, tanks, and combined. The last four are mainly used to work with one of the most valuable native fish species in Europe, the pikeperch (Sander lucioperca Linnaeus 1958). However, each technology includes pre-spawning work with brood fish regarding their preparation for reproduction, actual spawning campaign, and the subsequent incubation of the obtained eggs. All these links are formed on the basis of a combination of biological features of this species with existing environmental conditions as well as financial and organizational capabilities of certain farms. The main aspects of pikeperch reproduction include: the terms and conditions for reaching sexual maturity, the characteristics of the broodstock and reproduction conditions, working with brood fish, the actual selection and insemination of eggs, and the subsequent incubation of the embryos obtained in this way. The objective of this study was analytical review of the abovementioned technological processes of artificial reproduction of pikeperch based on information sources that highlight the results of scientific research. [ABSTRACT FROM AUTHOR]

Early offspring separation from mothers causes social deprivation. Mouthbrooding, when eggs and fry are incubated in the buccal cavity of the parent, is one of the reproductive strategies in fish. The mother is the incubating parent in African lake cichlids from the genus Tropheus. Many of these are produced in captivity and some producers use artificial incubators in which eggs are incubated separately from the mother. We hypothesized that this practice may dramatically modify the reproduction rate of fish individuals produced by the method of artificial incubation. The long-term experiment focused on Tropheus sp. "Caramba" had been carried out for 10 years when maternally incubated and separated individuals were compared. We found a negative effect of artificial egg and offspring incubation out of the mother's buccal cavity. The deprived females laid the same number of eggs as maternally incubated females, but most eggs were lost during the incubation. Moreover, the reproduction frequency was significantly lower in deprived females in comparison with those maternally incubated. This study should be perceived as preliminary. For this reason and with respect to welfare principles, we strongly recommend similarly designed experiments focused on other potentially sensitive fish mouthbrooders. Once the syndrome would be confirmed, we recommend avoiding artificial incubation of mouthbrooding fish in general. [ABSTRACT FROM AUTHOR]

Fish reproduction is closely related to the regulation of the brain and liver, making it essential to identify the factors that control this process. The turbot (Scophthalmus maximus) is an economically significant species that has been successfully breeding through industrial aquaculture. Investigation of factors into the involvement of gonadal development is crucial for artificial breeding. In this study, a new insulin-like growth factor 3 igf3 gene was cloned and characterized. Additionally, all three types of turbot IGFs contain a distinct IGF domain, with IGF3 and IGF2 being grouped with other teleosts, demonstrating a closely related genetic relationship. The expression analysis showed that igf3 mRNA is predominantly expressed in the gonad and brain (specifically in the pituitary and hypothalamus), suggesting its effects at multiple levels in the brain–pituitary–gonadal axis. Furthermore, the mRNA levels of igfs during gonadal development were examined. In the gonad and liver of female turbots, the expression levels of igfs mRNA significantly increased from stage II to VI during the process of oogenesis, including maturation and degeneration. In the testis and liver of male turbots, igf3 mRNA maintained high expression levels during the proliferation of spermatogonia at stages II and III. In addition, the highest levels of igf1 and igf2 were observed at the beginning of spermatogenesis and during sperm production at stages V and VI. All the results suggest that the IGFs were closely related to the gonadal development in turbot and improve a better understanding of the IGF system in the regulation of gonadal development in teleost. [ABSTRACT FROM AUTHOR]

Benzophenone-3 (BP3), an organic UV filter widely used in personal care products, is ubiquitous in aquatic environments. Previous studies have shown that BP3 can interfere with oocytes development in the ovary. The current study was conducted to evaluate the effects of embryonic BP3 exposure on reproductive outcomes in later life. Zebrafish embryos were exposed to different concentrations of BP3 (0, 1, 10, 100 μg/L) for 5 days in the developmental stage and subsequently fed for 4 months without any toxins. The body length, body weight, and ovary weight in F0 female adult zebrafish and morphology indices in F1 offspring embryos were measured. The reproductive behaviors of adult zebrafish were recorded by a digital camera. HE staining was used to estimate the development of oocytes and the proportion of different phases was calculated. qPCR was used to detect the expression levels of reproduction-related genes of the hypothalamic-pituitary-gonadal (HPG) axis. Our findings revealed that the body length and body weight were not changed with embryonic BP3 exposure, but BP3 exposure inhibited the development and maturation of ovaries in later-life female zebrafish, accompanied by an increased proportion of follicles in the primary growth and early vitellogenic stages, and a decline in the full-growth stage in ovaries. Meanwhile, reduced egg production, delayed hatching rate, altered somite count and increased mortality rate were observed at 100 μg/L in offspring embryos. Behavioral results showed that BP3 exposure reduced the frequency of chasing, touching, entering the spawning area, and the duration of fish entering the spawning area later in life, qPCR analysis showed that the expression levels of reproduction-related genes of the HPG axis were downregulated in females, following a decreasing trend in plasma E2 and 11-KT levels. These results suggested that embryonic BP3 exposure negatively affected the fertility of fish and the development of their offspring embryos, which may cause potential risks to aquatic ecosystems and human health. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Determination of sex in fish without external sexual dimorphism is important. Sex determination of the flathead grey mullet (Mugil cephalus) in the culture system and spawn‐producing and fish reproduction system is very important. Currently, there are several methods to determine the sex of fish; however, they are time‐consuming, expensive and sometimes dangerous for the fish. Objective: The purpose of this study was the sex determination of flathead grey mullet by ultrasonography as a safe and accurate method. Methods: In this regard, 30 flathead grey mullets (early in their maturation) from a farm in Gomishan‐Golestan province, Iran were examined using a portable ultrasound machine with a 6–12 MHz waterproof linear transducer. Scanning was performed on the ventral body surface in the sagittal and transverse planes, between ventral and anal fins. Results: Differences in shape, qualitative size, echogenicity and the wall layers of the ovary and testis were evaluated for sex determination. Results of ultrasonography were confirmed immediately at necropsy. Ultrasonographic accuracy for sex determination was 100%. The speed of the procedure was around 30 s per fish. Conclusions: Overall, the sex determination of flathead grey mullet by ultrasonography was high in accuracy and speed, non‐invasive and safe for fish and consumers, and may be considered a priority. Place of the organs in the M. cephalus coelomic cavity and the obtained experience showed that for rapid and easy sex identification, the best place to put the transducer is on the ventral surface of the fish in the caudal part of the coelomic cavity for taking transverse and sagittal ultrasonograms. [ABSTRACT FROM AUTHOR]

The reproductive capability of an organism is the main factor to determine the stability of the population. Till now, numerous reproductive strategies have been used, to successfully breed the fish in captivity but the desired performance is yet to be achieved. Nanotechnology has transformed the reproductive capacity of higher animals to a greater extent and has a huge potential in the aquaculture sector too. The use of nanotechnology in fish reproduction and breeding is limited to the delivery of drugs, hormones, vaccines, or genes and still, an immense scope is left in the area that needs to be explored. Here, the recent progress of nanotechnology in fish reproduction, breeding and conservation of germplasm is reviewed. Further, the key successes in the development of cryopreservation, semen imaging, sperm sorting, germplasm preservation, prototypes of smart nanobiosensors and drug delivery systems in animals including fish are highlighted. The potential future opportunities for nanotechnology to enhance reproductive output and conservative management of fish have been presented. In general, the current review summarises some of the applications of nanotechnology that are performing well in higher animals and could be a game‐changer in manipulating the reproductive potential or conserving the fish germplasm. [ABSTRACT FROM AUTHOR]

Xenoturbella is a marine invertebrate with a simple body plan, with recent phylogenomic studies suggesting that it forms the phylum Xenacoelomorpha together with the acoelomorphs. The phylogenetic position of the phylum is still under debate, whether it is an early branching bilaterian or a sister group to the Ambulacraria. Phylogenetic traits often appear during development, and larva resembling the cnidarian planula has been reported for Xenoturbella. However, subsequent developmental studies on Xenoturbella have been scarce. This is mainly due to the difficulties in collecting and keeping adult animals, resulting in the lack of data on the reproduction of the animal, such as the breeding season and the spawning pattern. Here we report on the reproduction of X. bocki and confirm that its breeding season is winter. Spawning induction resulted in gametes being released from body ruptures and not the mouth. No evidence supported the animal as a simultaneous hermaphrodite. The marine invertebrate Xenoturbella bocki breeds in the winter and the induction of spawning leads to gamete release through body ruptures, not the mouth. [ABSTRACT FROM AUTHOR]

Introduction: As in all vertebrates, reproduction in fish is regulated by gonadotrophin-releasing hormone (GnRH) control on gonadotrophic hormones (GtHs) activity. However, the neuroendocrine factors that promote GnRH and GtH activity are unknown. In Nile tilapia (Oreochromis niloticus), sexual activity and reproduction ability depend on social rank; only dominant males and females reproduce. Here, this characteristic of dominant fish allows us to compare brain and pituitary gene expression in animals that do and do not reproduce, aiming to reveal mechanisms that regulate reproduction. Methods: An extensive transcriptome analysis was performed, combining two sets of transcriptomes: a novel whole-brain and pituitary transcriptome of established dominant and subordinate males, together with a cell-specific transcriptome of luteinizing hormone (LH) and follicle-stimulating hormone cells. Pituitary incubation assay validated the direct effect of steroid application on chosen genes and GtH secretion. Results: In most dominant fish, as determined behaviorally, the gonadosomatic index was higher than in subordinate fish, and the leading upregulated pituitary genes were those coding for GtHs. In the brain, various neuropeptide genes, including isotocin, cholecystokinin, and MCH, were upregulated; these may be related to reproductive status through effects on behavior and feeding. In a STRING network analysis combining the two transcriptome sets, brain aromatase, highly expressed in LH cells, is the most central gene with the highest number of connections. In the pituitary incubation assay, testosterone and estradiol increased the secretion of LH and specific gene transcription. Conclusions: The close correlation between behavioral dominance and reproductive capacity in tilapia allows unraveling novel genes that may regulate the hypothalamic-pituitary-gonadal axis, highlighting aromatase as the main factor affecting the brain and pituitary in maintaining a sexually active organism. [ABSTRACT FROM AUTHOR]

Temperature is a preeminent factor in the regulation of fish reproduction and hinders gonadal development beyond a specific threshold. To comprehend the molecular mechanism responsible for reproductive suppression at different temperature, expression of the genes encoding kisspeptin (kiss2), gonadotropin-releasing hormone (gnrh1) and their receptors (gpr54, gnrh1r) in the brain, and the gonadotropin (GTH) subunits (fshb and lhb) in the pituitary were studied in juvenile Nile tilapia (Oreochromis niloticus) along with gonadal histology. Fish were acclimatized to three distinct temperatures, including 31 °C, 34 °C and 37 °C for 14 days. The mRNA levels of kiss2, gpr54, gnrh1, and gnrh1r were significantly decreased at 37 °C compared to 31 °C and 34 °C in the both sexes. In parallel, the expression level of fshb in the both sexes and lhb in the female were significantly lower at 37 °C in the pituitary. Histologically, the gonads of both sexes had normal growth of gametes at control temperature (31 °C), whereas the spermatogenesis and oocyte maturation were slowed down and atretic oocytes were found in the ovary at 37 °C acclimation temperature. Taken together, the results imply that elevated temperature beyond the specific threshold may have a negative impact on reproduction by suppressing the gene expressions of kisspeptin/GnRH1/GTH system and eventually restrains normal growth and maturation of gametes in the both sexes of Nile tilapia. [Display omitted] • Male and female Nile tilapia were acclimatized to three distinct temperature (31 °C, 34 °C and 37 °C). • The mRNA levels of kiss2 , gpr54 , gnrh1 and gnrh1r in the brain significantly decreased at 37 °C of both sexes. • The expression of fshb in both sexes and lhb in the female were significantly lower at 37 °C in the pituitary. • The spermatogenesis and oocyte maturation were slowed down at 37 °C. • Elevated temperature harms gonadal development by suppressing the expression of the genes for Kisspeptin/GnRH1/GTH system in Nile tilapia. [ABSTRACT FROM AUTHOR]

Microplastic (MP) contamination is a worldwide threat to aquatic organisms and human health. Aquatic environments are ideal and ultimate sinks for the MPs. They are negatively impacting the physical and physiological fitness of various fish species. Virgin MPs and nanoparticles (NPs) compromise immune, digestive, and reproductive systems, induce intestinal dysbiosis, and may have transgenerational effects. Even prolonged exposure to small ambient levels of MPs in aquatic environments has been found hazardous for fish. Moreover, plastisphere formation in aquatic habitats provides an excellent source and carrier for transporting contaminants, antimicrobial-resistant genes, and pathogens. Also,numerous studies utilize artificially produced virgin MPs and NPs containing toxic chemicals used in their manufacture. When these plastics interact with water and organisms, they may release the toxic compounds, leading to the promulgation of detrimental effects. However, in nature, MPs and NPs produced or introduced in aquatic environments appear to have varying degrees of adverse impact on aquatic organisms, due to their presence in substantial diluting environments. The work done so far suggests that evaluations of MP impact in aquatic habitats should be performed at a mass scale and in diverse fish species to get a clear picture of this hazard. This article reviews the most recent literature on the influence of virgin MPs and NPs on fish welfare, with a particular focus on their health and reproductive functions. [Display omitted] • Naturally occurring MPs and NPs are relatively low toxic for fish • Virgin MPs and NPs are more toxic for fish • Virgin MPs and NPs have an impact on fish health and reproductive potential • Intestinal dysbiosis is common after exposure to virgin MP • MPs have a role in the transfer of pathogens and antibiotic-resistant genes [ABSTRACT FROM AUTHOR]

The calanoid copepod Eurytemora pacifica is the most abundant species of zooplankton inhabiting waters in the western and southern bays of Korea during winter and spring. In this study, we sought to determine the effects of four photoperiodic regimes (0L:24D, 10L:14D, 12L:12D, 14L:10D) on the egg clutch size, hatching success, and naupliar production of E. pacifica. We found that photoperiod had a significant effect on E. pacifica clutch size, with egg production being the highest and lowest under photoperiods of 12L:12D and 14L:10D, respectively. In terms of hatching success, the highest hatch rate (73.4%) was obtained at 0L:24D, whereas eggs derived from females exposed to a 14L:10D photoperiod failed to hatch. Furthermore, naupliar production was found to be highest at 12L:12D (35.1 ± 6.5 nauplii female−1 day−1). Our findings indicate that the clutch size, hatchability, and naupliar productivity of E. pacifica can be significantly influenced by photoperiodic conditions, with a notably pronounced decline in hatching success and naupliar production occurring in response to a 14L:10D photoperiod. These observations provide valuable insights into the reproductive biology of E. pacifica over a wide photoperiodic range and can potentially contribute to the culturing of this copepod as a source of live larval feed in aquaculture hatcheries. [ABSTRACT FROM AUTHOR]

Among vertebrates, teleosts display a wide array of sex determination and differentiation mechanisms ranging from chromosomal sex determination on one end of the spectrum to environmental sex determination on the other end. However, the interplay of both these mechanisms is also not uncommon. Several gonochoristic fishes exhibit gonadal plasticity often resulting in sex reversal. The major manipulation of sex differentiation in teleost is affected by sex steroids. In this context, the increasing contamination of aquatic ecosystems by estrogen-like compounds, commonly known as xenoestrogens, is of major concern. This often leads to deleterious effects on the reproductive success of fish and thereby adversely impacts aquatic biodiversity. In the present review, we have focused on impact of xenoestrogen at different levels of the reproductive system influencing not only gonadal differentiation in teleosts but also their reproductive functions. The review would also explore the mitigation strategies and regulations in place for aquatic xenoestrogen management. [ABSTRACT FROM AUTHOR]

This study describes for the first time the reproductive biology of the coastal trevally (Carangoides coeruleopinnatus) (Ruppel, 1830) caught from Terengganu waters, Malaysia. Monthly sample collection from April 2019 to March 2020 was done at Pulau Kambing fish landing port in Terengganu, Malaysia. A total of 687 individuals comprise of 362 males (52.69%) ranged from 6.3 cm to 26.6 cm (mean ± SD: 13.2 ± 3.84 cm) and 325 females (47.31%) ranged from 9.0 cm to 26.4 cm (mean ± SD: 13.9 ± 3.34 cm) were observed. The sex ratio significantly deviated in favor of males (1: 0.90) (χ2 = 1.99). However, there are significant differences between sexes over months in June (χ2 = 10.89), July (χ2 = 11.91), August (χ2 = 6.10) and September (χ2 = 4.41). The monthly variation of the gonadosomatic index (IG) peaked between February and April for males and females, indicating its spawning period. The interpretation between condition factor (K) and hepatosomatic index (IH) showed that the energy mobilization from the body assists the gonad maturation. The batch fecundity of 42 mature females ranged from 15.7 cm to 21.4 cm, and mass was 142.6 g-333.0 g giving 20,438 to 121,829 eggs. The length at first maturity of males and females were 12.45 cm and 15.78 cm, respectively. The male reached earlier maturity than the female. This study increases the understanding of reproductive aspects of C. coeruleopinnatus for future formulation of rules and regulations for suitable fishery management in Terengganu waters. [ABSTRACT FROM AUTHOR]

Climate change is a growing threat to marine organisms and ecosystems, and it is already modifying ocean properties by, for example, increasing temperature and decreasing pH. Increasing water temperature may also lead to an impairment of primary productivity and an overall depletion of available zooplankton. Understanding how the crossover between warming and zooplankton availability impacts fish populations has paramount implications for conservation and mitigation strategies. Through a cross factorial design to test the effects of ocean temperature and food availability in a temperate marine teleost, Pomatochistus flavescens, we showed that hindered feeding impacted sheltering and avoidance behaviour. Also, low food availability impaired fish reproduction, particularly male reproduction, as the expression of cyp11b1, a gene with a pivotal role in the synthesis of the most important fish androgen, 11-ketotestosterone, was significantly reduced under a low food regime. In contrast, temperature alone did not affect reproductive success, but offspring showed increased saturated fatty acid content (embryos) and increased lipid peroxidation (larvae). Altogether, food availability had a stronger effect on fitness, showing that coping with elevated temperatures, an ability that may be expected in shallow-water fish, can be indirectly impacted, or even overwhelmed, by the effects of ocean warming on primary productivity and downstream ecological processes. [ABSTRACT FROM AUTHOR]