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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]

The vasa gene, encoding an ATP-dependent RNA helicase, and the nanos-2 gene, an RNA-binding protein, are essential for germ cell origination, migration, maintenance, and development in vertebrates and invertebrates. The expression levels of the vasa and nanos-2 genes have not yet been investigated or reported in crappie species. These two genes were partially sequenced and characterized, and their expression patterns were analyzed using reverse-transcription quantitative polymerase chain reaction (RT-qPCR) according to age and sex. The vasa sequences of white crappie (WC) females and males showed significant similarity with the vasa homologs of largemouth bass (Micropterus salmoides; 93.1–93.98%) and smallmouth bass (M. dolomieu; 91.95–92.77%), indicating its conserved nature within the Family Centrarchidae. The vasa sequence of black crappie (BC) females showed significant similarity with the vasa homologs of white crappie (91.67%), largemouth bass (96.10%), smallmouth bass (96.10%), spotted scat (Scatophagus argus; 97.37%), mandarin fish (Siniperca chutasi; 96.15%), Japanese sea bass (Lateolabrax japonicus; 94.87%), lumpfish (Cyclopterus lumpus; 91.95%), southern bluefin tuna (Thunnus maccoyii; 94.74%), large yellow croaker (Larimichthys crocea; 92.21%), and Nile tilapia (Oreochromis niloticus; 92.21%). The nanos-2 sequences of WC females, WC males, and BC females showed significant similarity with the nanos-2 of largemouth bass (92.92–96.36%), smallmouth bass (92.92–96.36%), and mandarin fish (92.66–94.34%). The expression of vasa in BC females was significantly higher at age-2 than at age-1, while WC males and females presented no significant age-related differences. Neither species had a significant difference in nanos-2 gene expression with age. The expression levels of vasa and nanos-2 were significantly higher in WC males than females. [ABSTRACT FROM AUTHOR]

Fish spawning phenology is a major concern for conservation and fisheries management. New intensive data sources, such as GPS-based tracking data and high-resolution catch declaration data, are becoming increasingly available in the field of marine ecology. These data benefit from high spatiotemporal resolution and open new research avenues for investigating the interannual variability in fish phenology. In this paper, we demonstrate how an integrated species distribution model informed by commercial catch data combined with spatiotemporal dimension reduction methods known as empirical orthogonal functions (EOFs) can be used to synthesize spatiotemporal signals in fish reproduction phenology. Specifically, we address the following questions: (1) Can we identify seasonal spatial patterns that can be interpreted in terms of reproductive phenology and essential habitats? (2) Can we identify changes in reproductive phenology over time? (3) Are these changes related to environmental drivers? The analysis illustrates the reproductive phenology of three key commercial species in the Bay of Biscay (sole, hake, and sea bass). The EOF analysis emphasized strong seasonal spatiotemporal patterns that correspond to reproduction patterns and feeding patterns. Based on this methodology, we identified seasonal variations in the timing of reproduction, and we related these variations to sea surface temperature, a key driver of fish reproduction. [ABSTRACT FROM AUTHOR]

Batch spawner fishes develop successive clutches of oocytes which allows them to participate in many reproductive cycles during their adult life (iteroparous) and spawn in multiple events within each breeding cycle. Here, ovarian follicular development was morpho‐functionally analyzed in females of the iteroparous batch spawner fish Gymnocorymbus ternetzi. To obtain better insights into the reproductive morpho‐physiology in batch spawners, the objective of this research was to analyze the dynamics of the follicular development, with its hormonal regulation between two active reproduction events. We found that over 16 days, follicles progressed asynchronously to chromatin nucleolus, Primary and Secondary growth stages of oogenesis with progressive secretion of 17β‐estradiol (E2). During the end of secondary growth, the increase in 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐p) was measured relative to the maturation process of the ovarian follicles (e.g., nuclear migration and its rupture during the resumption of meiosis). Interestingly, an additional increase in E2 was observed after fish reproduction, probably related to the recruitment of new batch follicles for secondary growth. We also measured the high values of multiple condition factor post‐reproduction measurements, reflecting more energy invested during the pre‐reproductive process. We also quantified high concentrations of 17,20β‐p, probably related to the recruitment of a new batch of oogonia to meiosis, presumably secreted by post‐ovulatory follicles, after fish reproduction. We finally found that fish without exposure to reproductive stimulus developed a regression phase at day 24, characterized by massive follicle atresia, that allow them to recycle energy and constitutive materials of the follicles invested during oogenesis for another reproductive cycle. [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]

For the first time, ecological evolution of salmonid fishes is analyzed using the method of historical biogeography, considering formation of ecology and reproductive biology for these species under planetary climatic and geological changes. Climate cooling in the Cenozoic and associated reconstruction of the food base for salmonids had a major impact on evolution of their ecology. This process began at the Asian coast of the North Pacific much earlier than at the American coast and was much more intense there. The salmonids developed marine and oceanic feeding that led to their stocks increasing and a subsequent imbalance with freshwater prey. Adapting to this imbalance, the species of gen. Oncorhynchus came to irreversible reduction of organs and functions in the fresh water and absolute mortality of producers. Egg development lengthened in cold environments, and anadromous and semi-anadromous salmonid species were forced to spawn earlier, so that the larvae would hatch during the spring bloom of their prey. Gradually, the timing of their spawning shifted from early spring to winter and then to fall; accordingly, the spawning run to the rivers began earlier, in particular in the northern areas. The spawning season of atlantic salmon Salmo salar and brown trout Salmo trutta shifted to a fall and spring-summer spawning run in the north of their range and to a winter-spring and fall spawning run in the south of their range, but there is currently no reason to consider these runs as seasonal races, given that both cases evolved from a single run in the process of evolutionary changes when the spawning season was interrupted by either winter cooling or summer warming in the lower river reaches and at the coast. The northern and southern populations of salmonid fishes in the Pacific separated, too, because of these ecological changes in the late Pliocene, in conditions of cold climate. Being in isolation, they diverged enough to be considered as separate taxa rather than seasonal races.

Broodstock nutrition is the most essential constituent of sustainable aquaculture production. Its impact on the reproductive performance and profitability of commercial aquaculture has been the subject of considerable research. The present paper reviews the literature available on the subject, examining the implication of Nile tilapia broodstock nutrition on parameters including maturation, fecundity, fertilization, embryo development, larval quality, and survival rate. The provision of a nutritive diet composed of essential macroand micronutrients including proteins, lipids, carbohydrates, vitamins, minerals, and functional additives, such as prebiotics, enzymes, hormones, and probiotics, in different proportions is discussed. Special emphasis is given to literature dealing with the effects of dietary protein and lipid on vitellogenesis and ovarian maturation, fecundity, egg hatching rate, larval quality, and fry survival number. The impact of the feeding regime on reproductive performance is described. [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]

The development of hydroelectric projects has adversely affected the reproductive activities of downstream fish species. To facilitate the natural reproduction of fish and restore spawning grounds post‐dam construction, it is imperative to explore the ecological factors crucial for their reproduction. Currently, various research methods with different advantages and limitations are employed for this purpose. Using identified spawning locations and periods as clues, we quantitatively investigate the flow velocity, water depth, water temperature, and riverbed substrate required for spawning. The results are validated using habitat simulation methods, aiming to establish a more scientific approach to explore ecological factors affecting fish reproduction. This study provides a more scientific, systematic, and detailed report on the ecological factors required for the spawning of Gymnocypris eckloni: flow velocity ranging from 0.19 to 0.97 m/s, water depth from 0.28 to 1.12 m, water temperature between 11.4 and 15.2°C, and predominantly gravel substrate. The reliability of the results was verified in another spawning ground, with good verification results. This research provides crucial data for the bio‐mimetic reproductive technology of Gymnocypris eckloni and the restoration of spawning grounds for natural fish reproduction post‐dam construction. It addresses the lack of suitable ecological factor data for protective fish species in the upper reaches of the Yellow River. The method exhibits strong scientific, accurate, and implementable characteristics. [ABSTRACT FROM AUTHOR]

Simple Summary: The present study investigates the reproductive and immune defense systems in the gonads of black scorpionfish (Scorpaena porcus, Linnaeus 1758). This study concentrates on the initial phases of reproduction in both male and female fish and investigates the presence and function of an antimicrobial peptide, Piscidin-1. Histological analyses demonstrate morphological changes from the immature to developing stages in gonads. Immunohistochemical methods demonstrate strong reactivity to Piscidin-1 in germinal and somatic cells during early ontogeny, suggesting its crucial role in local defense mechanisms. This research contributes to the understanding of the interaction between reproductive biology and immune defense in S. porcus, offering insights that could benefit species conservation and management efforts. One of the most crucial biological indicators in tracking long-term variations in the reproductive cycle is sexual development. Scorpaena porcus (Linnaeus, 1758), commonly known as the black scorpionfish, is a small teleost from the family Scorpaenidae. Much is known about its ecology, but data on its reproductive and defense systems are still lacking. Antimicrobial peptides (AMPs), such as piscidins, are integral components of the innate immune system in fish. These peptides exhibit a wide range of activity against bacteria, fungi, viruses, and protozoa and act as the first line of host defense. This study aims to investigate the primary sexual development stages in male and female gonads of black scorpionfish, providing additional knowledge on the reproductive biology of this teleost while evaluating concomitant changes in the expression of a Piscidin-1 antimicrobial peptide. The results show a histological, morpho-structural change from the immature stage to the developing virgin stage. Immunohistochemical analyses show that germinal and somatic cells are strongly reactive to Piscidin-1 in both gonads at an early ontogeny stage. These data suggest that Piscidin-1 may play a key role in the local defense system of scorpionfish gonads at this delicate stage, which is critical for the continuation and maintenance of the species. The present findings are potentially useful for a better understanding of the reproductive cycle of this fish, improving our knowledge of the interaction between the immune system and reproduction. [ABSTRACT FROM AUTHOR]

The reproductive diversity of extant cartilaginous fishes (class Chondrichthyes) is extraordinarily broad, reflecting more than 400 million years of evolutionary history. Among their many notable reproductive specialisations are viviparity (live‐bearing reproduction) and matrotrophy (maternal provision of nutrients during gestation). However, attempts to understand the evolution of these traits have yielded highly discrepant conclusions. Here, we compile and analyse the current knowledge on the evolution of reproductive diversity in Chondrichthyes with particular foci on the frequency, phylogenetic distribution, and directionality of evolutionary changes in their modes of reproduction. To characterise the evolutionary transformations, we amassed the largest empirical data set of reproductive parameters to date covering nearly 800 extant species and analysed it via a comprehensive molecular‐based phylogeny. Our phylogenetic reconstructions indicated that the ancestral pattern for Chondrichthyes is 'short single oviparity' (as found in extant holocephalans) in which females lay successive clutches (broods) of one or two eggs. Viviparity has originated at least 12 times, with 10 origins among sharks, one in batoids, and (based on published evidence) another potential origin in a fossil holocephalan. Substantial matrotrophy has evolved at least six times, including one origin of placentotrophy, three separate origins of oophagy (egg ingestion), and two origins of histotrophy (uptake of uterine secretions). In two clades, placentation was replaced by histotrophy. Unlike past reconstructions, our analysis reveals no evidence that viviparity has ever reverted to oviparity in this group. Both viviparity and matrotrophy have arisen by a variety of evolutionary sequences. In addition, the ancestral pattern of oviparity has given rise to three distinct egg‐laying patterns that increased clutch (brood) size and/or involved deposition of eggs at advanced stages of development. Geologically, the ancestral oviparous pattern arose in the Paleozoic. Most origins of viviparity and matrotrophy date to the Mesozoic, while a few that are represented at low taxonomic levels are of Cenozoic origin. Coupled with other recent work, this review points the way towards an emerging consensus on reproductive evolution in chondrichthyans while offering a basis for future functional and evolutionary analyses. This review also contributes to conservation efforts by highlighting taxa whose reproductive specialisations reflect distinctive evolutionary trajectories and that deserve special protection and further investigation. [ABSTRACT FROM AUTHOR]

The construction and operation of large‐scale reservoirs alter the natural river flow regimes and destroy the original suitable reproduction and living conditions of aquatic organisms. Especially during the spawning season, the fluctuating water flow process is particularly important for fish reproduction. A bi‐objective optimization model considering both the environmental flow demand for fish spawning and the stability of hydropower output is established in this study and solved by one of the most widely used algorithms for multi‐objective problems, the Non‐Dominated Sorted Genetic Algorithm‐II. The derived Pareto Front can be used to guide reservoir operation during fish spawning seasons. The model proposed in this paper is applied to the Yangqu Reservoir, currently under construction on the upper Yellow River in China. The results show that the stability of hydropower output can still be improved by 4.80% to 10.56%, even if the environmental flow demand is taken into account. Even for the scheme preferring ecological recovery, the stability of hydropower output can be increased by more than 0.85%. Highlights: Fish spawning demand and hydropower stability are considered simultaneously.Derived Pareto Front can be used for reservoir operation in fish spawning seasons.Room still exists for improving hydropower stability meeting ecological demands. [ABSTRACT FROM AUTHOR]

Kisspeptin (Kiss) and kisspeptin receptor (Kissr) system is a key regulator of GnRH expression in several vertebrates. The Indian catfish, Clarias magur, is popular in the Indian sub-continent, and a neo-type of the Asian catfish, C. batrachus. Catfish breeding is constrained as males do not release milt captivity with/without stimulation. Magur Kiss/Kissr system comprising of kiss1, kiss2, kissr1, and kissr2 genes was characterized for the first time. Full-length mRNA was sequenced using RACE PCR. Neighbor-joining tree of predicted proteins shows one clade of teleost orthologs. Magur whole genome (NCBI GenBank) has single copies of each gene, though yet unannotated/misannotated. Anomalies in the nomenclature of earlier sequences in GenBank were noted. Relative gene expression was profiled during various ontogenic stages, in six tissues including brain and gonads at maturity, and also in brains and gonads of premature and spent fish. Expression of gnrh1, gnrhr1, and gnrhr2 was estimated concomitantly. The kiss1 was the first to be twofold upregulated (P < 0.05) at 12 h post fertilization. Kiss/Kissr genes expressed primarily in the brain, ovary, and testis. Though kiss2 was 10 times higher than kiss1, only kiss1 showed significant modulation across stages and appears to be the active isotype that regulates GnRH in magur. [ABSTRACT FROM AUTHOR]

AbstractReproduction is a fundamental biological process for producing offspring and ensuring the continuation of the species. With nearly 35,000 fish species worldwide exhibiting a very diverse range of reproductive systems and strategies, the study of fish reproduction is a significant challenge. Research into various fish reproductive models is driven by their use in human biomedical applications, improving the diversification and sustainability of aquaculture species, and developing strategies for biodiversity conservation. These models must be approached from an animal ethics perspective, considering the welfare of the species under study and applying the 3Rs principle (Replacement, Reduction and Refinement). This principle focusses on replacing animals with alternative methods wherever possible, reducing the number of animals used and refining procedures to minimize suffering. While destructive sampling of wild aquatic species should be minimized, the need remains to provide information on reproduction as an important parameter for delineating management and conservation programs. One of the practices that helps reduce and replace the use of animal testing is the scientific study of individuals obtained through bycatch. This is the case for some chondrichthyans, and endangered fish species included in conservation programs. Regarding fish species that are kept under human care (commonly called captivity), studies on reproduction are essential to improve well-being and increase production of farmed species. Research on fish reproduction requires expanding basic knowledge of broodstock management tools, such as gamete quality assessment, reproductive behavior studies, the use of hormone therapies to stimulate reproduction, and the development of non-lethal or less invasive methods using body fluids (e.g., mucus, seminal plasma, blood plasma, or urine) to study reproductive status, as well as novel markers from state-of-the-art omics research. This review describes a multidisciplinary approach that includes the aforementioned reproductive management tools, indicators of welfare, and next-generation sequencing techniques using samples collected by minimally invasive methods. [ABSTRACT FROM AUTHOR]

Introduction: Hypoxia is a recurring problem in the fish farming industry. Currently, it is known that the exposure of fish and fry to a hypoxic environment induces important changes in their metabolism, compromising not only their development but also their reproduction and mortality rates. Our hypothesis is that hypoxia constitutes one of the etiological factors causing deformation of the body and caudal fin in this species, as well as affecting its growth. Methods: We analyzed two hundred forty Salmo salar salmon fry, differentially cultured at 100% saturation (normoxia condition) and 60% (hypoxia condition) for 2, 4, 6, and 8 days, including a group under continuous hypoxia. We performed diaphanization and Alcian blue staining, along with standard histological techniques. The polyclonal anti-HIF-1a antibody was used as a marker of hypoxia in Salmo salar, and hypoxia in these fish was associated with the immunopositivity of this antibody. Results and discussion: The results indicate that there is an association between exposure to hypoxia and the deformation of the body and fin, as well as an agreement between hypoxia and the total length of the fry and fin. Several months after the event occurred, we were able to find and describe angiogenesis, blood vessel disorganization, and vasodilation histologically. Finally, hypoxic cells in the fry (HIF-1a) could be recognized and confirmed as hypoxia sensors. All of this indicates that hypoxia not only affects the fry during the development phase of the event, but that its results can be evident much later and affect the fry throughout their entire ontogeny. [ABSTRACT FROM AUTHOR]

Somatostatin (SST) plays diverse physiological roles in vertebrates, particularly in regulating growth hormone secretion from the pituitary. While the function of SST as a neuromodulator has been studied extensively, its role in fish and mammalian reproduction remains poorly understood. To address this gap, we investigated the involvement of the somatostatin system in the regulation of growth and reproductive hormones in tilapia. RNA sequencing of mature tilapia brain tissue revealed the presence of three SST peptides: SST6, SST3, and low levels of SST1. Four different isoforms of the somatostatin receptor (SSTR) subfamily were also identified in the tilapia genome. Phylogenetic and synteny analysis identified tiSSTR2-like as the root of the tree, forming two mega clades, with SSTR1 and SSTR4 in one and SSTR2a, SSTR3a, and SSTR5b in the other. Interestingly, the tiSSTR-5 isoforms 5x1, 5x2, and 5x3 were encoded in the sstr3b gene and were an artifact of misperception in the nomenclature in the database. RNA-seq of separated pituitary cell populations showed that SSTRs were expressed in gonadotrophs, with sstr3a enriched in luteinizing hormone (LH) cells and sstr3b significantly enriched in follicle-stimulating hormone (FSH) cells. Notably, cyclosomatostatin, an SSTR antagonist, induced cAMP activity in all SSTRs, with SSTR3a displaying the highest response, whereas octreotide, an SSTR agonist, showed a binding profile like that observed in human receptors. Binding site analysis of tiSSTRs from tilapia pituitary cells revealed the presence of canonical binding sites characteristic of peptide-binding class A G-protein-coupled receptors. Based on these findings, we explored the effect of somatostatin on gonadotropin release from the pituitary in vivo. Whereas cyclosomatostatin increased LH and FSH plasma levels at 2 h post-injection, octreotide decreased FSH levels after 2 h, but the LH levels remained unaffected. Overall, our findings provide important insights into the somatostatin system and its mechanisms of action, indicating a potential role in regulating growth and reproductive hormones. Further studies of the complex interplay between SST, its receptors, and reproductive hormones may advance reproductive control and management in cultured populations. [ABSTRACT FROM AUTHOR]

This study compiled and remodelled length selectivity studies carried out on fish caught with gill nets and trammel nets in the inland fishery in Türkiye and evaluated them based on both the initial reproduction length and minimum landing size of species. The required data for the study were obtained through a literature review. 34 selectivity studies in total were identified, and 26 (76.5%) of them were carried out with gill net while the remaining 8 (23.5%) were conducted with trammel net. 24 of the studies were carried out according to SELECT (Share Each Length-class's Catch Total) and 10 of them according to Holt (1963). In conclusion, it was found that minimum conservation reference size (MCRS) values determined by the Ministry in the inland fishery in Türkiye were substantially greater than lengths at first maturity (LFMs) of species and that fishing gears used for fishing typically tended to fish mature individuals above MCRS. The major problem in terms of management is that different ideal mesh sizes are applied to different fish species that are in the same fishing place. Set nets with an ideal-mesh size for a species has a potential of catching individuals below LFM of other species in the same fishing grounds. It is thought that this problem can only be resolved with the Ecosystem Approach to Fisheries Management (EAFm). [ABSTRACT FROM AUTHOR]

The study of reproductive biology is extremely crucial in fishery. Pachypterus atherinoides (Bloch, 1794) is a good food as well as an ornamental catfish in the World. The present study aims to examine the seasonal reproductive behavior of P. atherinoides regarding both its lentic and lotic ecosystems. The study was conducted over two years in selected lentic and lotic aquatic ecosystems of the Jhargram and Paschim Medinipur districts of West Bengal, India using the seasonally observed gonadosomatic index (GSI), fecundity, and gonad maturation stages for both habitats in the study area. The study reveals P. atherinoides to show single annual spawning between June-September. No significant difference was found regarding breeding period in terms of lentic and lotic aquatic ecosystems. This study can help aquaculturists regarding the culture, captive breeding, and conservation of P. atherinoides, as well as researchers regarding the biometric study of another fish. [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]

Background: Fish reproduction, development and growth are directly affected by temperature, investigating the regulatory mechanisms behind high temperature stress is helpful to construct a finer molecular network. In this study, we systematically analyzed the transcriptome and miRNA information of American shad (Alosa sapidissima) liver tissues at different cultivation temperatures of 24 ℃ (Low), 27 ℃ (Mid) and 30 ℃ (High) based on a high-throughput sequencing platform. Results: The results showed that there were 1594 differentially expressed genes (DEGs) and 660 differentially expressed miRNAs (DEMs) in the LowLi vs. MidLi comparison group, 473 DEGs and 84 DEMs in the MidLi vs. HighLi group, 914 DEGs and 442 DEMs in the LowLi vs. HighLi group. These included some important genes and miRNAs such as calr, hsp90b1, hsp70, ssa-miR-125a-3p, ssa-miR-92b-5p, dre-miR-15a-3p and novel-m1018-5p. The DEGs were mainly enriched in the protein folding, processing and export pathways of the endoplasmic reticulum; the target genes of the DEMs were mainly enriched in the focal adhesion pathway. Furthermore, the association analysis revealed that the key genes were mainly enriched in the metabolic pathway. Interestingly, we found a significant increase in the number of genes and miRNAs involved in the regulation of heat stress during the temperature change from 24 °C to 27 °C. In addition, we examined the tissue expression characteristics of some key genes and miRNAs by qPCR, and found that calr, hsp90b1 and dre-miR-125b-2-3p were significantly highly expressed in the liver at 27 ℃, while novel-m0481-5p, ssa-miR-125a-3p, ssa-miR-92b-5p, dre-miR-15a-3p and novel-m1018-5p had the highest expression in the heart at 30℃. Finally, the quantitative expression trends of 10 randomly selected DEGs and 10 DEMs were consistent with the sequencing data, indicating the reliability of the results. Conclusions: In summary, this study provides some fundamental data for subsequent in-depth research into the molecular regulatory mechanisms of A. sapidissima response to heat stress, and for the selective breeding of high temperature tolerant varieties. [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]

Sexual development and reproduction are largely linked to epigenetic changes in many fish species. However, understanding of epigenetic regulation in scombrid species, such as tunas and mackerels, is limited. This study investigates DNA methylation’s impact on cyp19a expression, crucial for estrogen synthesis, focusing on chub mackerel. Given the commercial significance of scombrids and susceptibility of marine fish to environmental changes, elucidating epigenetic mechanisms, particularly in the context of global warming, becomes imperative. We aimed to generalize observations from chub mackerel to other scombrids. Additionally, we studied DNA methylation patterns across fish with different sexual systems to understand aromatase regulation’s phenotypic plasticity. Our in silico analysis revealed highly conserved promoter sequences within scombrids, sharing TFBS like Foxl2, FOS::JUN, ESRR, and Sox3, while CpG content varies. This indicates a conserved regulatory network controlling gene expression. We found sexual dimorphism in DNA methylation, with males hypermethylated and aromatase expression downregulated. Despite similar dnmt1 expression, tet1, tet2, and tet3 were higher expressed in females, suggesting that the observed DNA methylation patterns are maintained through active demethylation rather than differential methylation. Gonochoristic Japanese anchovy and protogynous bamboo leaf wrasse displayed similar trends, but species-specific methylation patterns highlight DNA methylation’s complex role in gonadal changes. In vitro assays confirmed methylation’s regulatory role and identified an SF-1 binding site relevant for promoter activation in chub mackerel. Another studied SF-1 site, present in both chub mackerel and bamboo leaf wrasse, showed regulatory effects, indicating potential similar regulatory mechanisms for cyp19a expression. Overall, our findings suggest that while global methylation affects cyp19a transcription, the variation in CpG density and location could be introducing nuances in its epigenetic regulation. This study contributes to our understanding of the cyp19a regulation in fish gonad maturation. [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]

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. [ABSTRACT FROM AUTHOR]

Present study aimed to explore the adverse effects of lead (Pb) induced reactive oxygen species (ROS) generation on hypothalamo–pituitary–ovarian axis. Adult female Mystus vittatus (n = 48) were exposed to lead nitrate at 0.0 mg/L (control) and 6.02 mg/L (safe dose; 1/10th of LC50 dose) for 60 days. Fish were sacrificed at 15 days interval to collect brain, ovary and serum. Lead concentration in fish tissues increased significantly (p < 0.05) with exposure duration. ROS generation in brain and ovary increased significantly (p < 0.05) in Pb-induced group compared to control. Increased level of lipid peroxidation due to lead induced oxidative stress was marked by significant increase (p < 0.05) in malondialdehyde level in fish brain and ovary compared to control. Significant increase (p < 0.05) were found in reduced glutathione, super oxide dismutase, catalase, glutathione s-transferase, glutathione reductase level in fish brain and ovary in Pb-induced group with exposure duration. Glutathione peroxidase level decreased significantly (p < 0.05) after 30 days of exposure. Brain gonadotropin-releasing hormone and kisspeptin level decreased significantly (p < 0.05) and gonadotropin-inhibitory hormone level increased significantly (p < 0.05) in lead exposed fish. Serum follicle stimulating hormone, luteinizing hormone and ovarian vitellogenin, estradiol, maturation inducing hormone level decreased significantly (p < 0.05) with metal exposure. An increased metallothionein level was found in both brain and ovary of metal exposed fish. Current study illuminated the effect of Pb-induced oxidative stress and its consequences on the reproductive endocrine pathway in female M. vittatus. [ABSTRACT FROM AUTHOR]

A local commodity, Yellow rasbora Rasbora lateristriata (Bleeker, 1854), can potentially be used as food by the Kulon Progo community. Added to that, aquaculture is known to optimize this potential and will also prevent illegal fishing where yellow rasbora are listed as a vulnerable species in the IUCN Red list. This study induced male yellow rasbora using the hormone OODEV® injection, which comprises Pregnant Mare Serum Gonadotropin (PMSG) and anti-dopamine. Yellow rasbora was nurtured to the age of six months and treated with four different treatments (dose) for a month, namely 0 mL/Kg, 0.25 mL/Kg, 0.5 mL/Kg, and 0.75 mL/Kg. Observed parameters included motility (movement and duration) as well as sperm count, sperm viability, sperm morphology, sperm morphometry, gonad somatic index (GSI), and survival rate (SR). Data obtained were analyzed using SPSS with the One-way ANOVA test and continued with Duncan's test if the results were significant. The obtained results had no significant effect on the IGS value. In addition, administration of OODEV® also improved sperm quality with the best results at 0.75 mL/Kg in terms of motility with the highest progressive movement compared to other doses but not significant compared to the control and significantly longer movement duration compared to other doses. In terms of morphometry and tail width, it was not significant compared to other doses, longest tail length but not significant with other doses except with 0.25 mL/Kg, and significantly had the longest sperm total length. Every dose showed a 100% percentage of survival rate. [ABSTRACT FROM AUTHOR]

Reproduction is a fundamental biological process that is essential for the continuous survival of fish species. Understanding their early life history and reproductive biology can explain how the population behave over time. A total of 1,238 fish samples were examined to determine the reproductive patterns and period of fringescale sardinella (Sardinella fimbriata) from Malampaya Sound, Palawan, Philippines. Monthly sampling from April 2023 to March 2024 revealed a 1:1 sex ratio. Gonadal examination of the fish revealed the presence of spawning individuals throughout the study period. The minimum size of matured fish observed was 11.0 cm and 11.1 cm for male and female S. fimbriata, respectively. The peak of spawning was April as indicated by the highest calculated GSI of 7.62% and fecundity of 18,465. A smaller peak was again observed in the month of September. The length at maturity was estimated to be 11.4 and 8.8 cm for males and females, respectively. Fecundity ranged between 2,700 to 36,067 eggs per spawn for size class between 11.1-14.8 cm and weight 13.07-31.93 g. Regression analysis between fecundity and morphometric characteristics such as body length, weight, eviscerated weight, and gonad weight revealed a positive correlation. Very low coefficients of determination were computed, ranging between 0.0028-0.1233. A significant association between fecundity and the morphometric variable gonadal weight was observed, as shown by the p-value of 0.0000. These outcomes are valuable data in the formulation of conservation and management strategies for the area. Implementation of appropriate conservation measures, monitoring of environmental parameters, strict enforcement of fishery regulation, coupled with increased environmental awareness and community participation will guarantee the long-term sustainability of the fringescale sardinella population and the preservation and sustainable use of marine biodiversity in Malampaya Sound.

Abstract Cooling milt conserves viable spermatozoa to extend the period available for artificial fertilization and avoids the robust protocols and high costs associated with cryopreservation. Yet, the sperm quality curves of fresh and refrigerated milt have not yet been compared for pacu (Piaractus mesopotamicus), which is often used as a biological model. This study aimed to analyze the milt quality of male P. mesopotamicus across 24 h of refrigeration. Six adult males were induced with carp pituitary extract. Sperm movement, membrane integrity, and morphology was compared between extruded milt samples stored for 24 h under either ambient temperature or under refrigeration at 12.63 °C. Sperm motility differed significantly over time. After 24 h of storage, motility values were higher in refrigerated spermatozoa than in those kept at ambient temperature. Sperm cell survival rates did not differ 4–8 h post collection. After 16 h, refrigerated cells showed superior membrane integrity (82.05 ± 4.23%) compared to those stored at ambient temperature (66.98 ± 6.45%), maintaining this pattern up to 24 h. In terms of sperm morphology rate, milt from both treatment groups was still viable for use 8 h after collection. However, after 16 h of storage, both groups exhibited a large reduction in normality rates, and at 24 h, all milt were unfeasible. In conclusion, P. mesopotamicus milt can be stored up to 8 h after collection when refrigerated at 12.63 °C, without the use of extenders and/or cryoprotectants, maintaining enough quality for egg fertilization.

Dependence of the mature pink salmon returns to the mainland coast of Japan Sea (within Primorye Region) on their parents abundance and meteorological factors at the spawning grounds is analyzed. Variations of the progeny number were almost completely determined by factors acted in the freshwater period of their life, mainly by the number of spawners and total precipitation in the first winter after the spawning.

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]

Gonadal soma-derived factor (Gsdf) is a member of the transforming growth factor beta (TGF-ß) superfamily and a teleost-specific gene. Early studies suggested that Gsdf promotes spermatogonial proliferation; however recent reports have shed light on its role in sex differentiation based on expression profiles and gain- and loss-offunction studies. This paper discusses the involvement of Gsdf in gonadal sex differentiation and sex changes in teleosts. [ABSTRACT FROM AUTHOR]

This review highlights the recent developments regarding neuroendocrine mechanisms controlling teleost reproduction. In teleosts, the pituitary gland receives major neuronal innervations from Gnrh neurons as well as minor innervations from small population of neurons that will secrete neurotransmitters and/or neuropeptides. The diversity of Kiss/Kissr system in various teleost species and their actions in the context of HPG axis and reproduction has been extensively covered. In teleost model systems, zebrafish and medaka, mutant lines for key components of the HPG axis have been generated through targeted mutagenesis but surprisingly most of the mutants developed normally without major defects in reproduction; these mutant phenotypes are described. In the last decade, complex role of diverse neuropeptides in teleost reproduction is being revealed. A brief overview about the reproductive functions of neuropeptides is presented. Finally, the effects of environmental factors namely photoperiodism and temperature on the functions of HPG axis is summarised. [ABSTRACT FROM AUTHOR]

Reproduction is one of the most crucial physiological processes for the continuation of the generation of any species. Teleost are one of the most divergent aquatic species. The reproductive neuro-endocrine regulatory studies are limited to only few species. Neuroendocrine regulation is a finely tuned complex mechanistic pathways, involving mainly hypothalamic-pituitary-gonad (HPG) axis. Within the HPG axis, gonadotropin-releasing hormone (GnRH) modulates the synthesis and release of pituitary gonadotropins, which act on the gonads to stimulate steroidogenesis and gametogenesis. Very recently, several novel neuropeptides, associated with reproductive regulation, have been identified. Spexin (SPX), a novel neuropeptide coevolved with the galanin/kisspeptin family, has been identified as a regulator of the species-specific reproductive processes in teleost. Pituitary adenylate cyclase-activating polypeptide (PACAP) is another novel member of the secretin-glucagon peptide family that functions as a hypophysiotropic factor involved in regulating pituitary hormone secretion in fish. These two emerging neuropeptides have pleiotropic functions, but information regarding their exact roles in fish reproduction is very limited. An updated overview of the mechanistic reproductive functions of these two new neuropeptides are highlighted in this review. [ABSTRACT FROM AUTHOR]

Given the vital role of thyroid hormones (THs) in vertebrate development, it is essential to identify chemicals that interfere with the TH system. Whereas, among nonmammalian laboratory animals, fish are the most frequently utilized test species in endocrine disruptor research, for example, in guidelines for the detection of effects on the sex hormone system, there is no test guideline (TG) using fish as models for thyroid‐related effects; rather, amphibians are used. Therefore, the objective of the present project was to integrate thyroid‐related endpoints for fish into a test protocol combining OECD TGs 229 (Fish Short‐Term Reproduction Assay) and 234 (Fish Sexual Development Test). The resulting integrated Fish Endocrine Disruption Test (iFEDT) was designed as a comprehensive approach to covering sexual differentiation, early development, and reproduction and to identifying disruption not only of the sexual and/or reproductive system but also the TH system. Two 85‐day exposure tests were performed using different well‐studied endocrine disruptors: 6‐propyl‐2‐thiouracil (PTU) and 17α‐ethinylestradiol (EE2). Whereas the companion Part A of this study presents the findings on effects by PTU and EE2 on endpoints established in existing TGs, the present Part B discusses effects on novel thyroid‐related endpoints such as TH levels, thyroid follicle histopathology, and eye development. 6‐Propyl‐2‐thiouracil induced a massive proliferation of thyroid follicles in any life stage, and histopathological changes in the eyes proved to be highly sensitive for TH system disruption especially in younger life stages. For measurement of THs, further methodological development is required. 17‐α‐Ethinylestradiol demonstrated not only the well‐known disruption of the hypothalamic–pituitary–gonadal axis, but also induced effects on thyroid follicles in adult zebrafish (Danio rerio) exposed to higher EE2 concentrations, suggesting crosstalk between endocrine axes. The novel iFEDT has thus proven capable of simultaneously capturing endocrine disruption of both the steroid and thyroid endocrine systems. Integr Environ Assess Manag 2024;20:830–845. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points: Zebrafish were exposed to 6‐propyl‐2‐thiouracil (PTU) or 17α‐ethinylestradiol (EE2) in an experiment that merged OECD test guidelines (TGs) 229 and 234, the integrated fish endocrine disruptor test (iFEDT).PTU and EE2 had strong effects on established endocrine‐related endpoints in zebrafish adults and their offspring, but also on thyroid‐related endpoints.PTU induced a massive proliferation of thyroid follicles in any life stage, and histopathological changes in the eyes, whereas EE2 caused only slight histopathological changes in thyroid follicles.Merging of TGs 229 and 234 proved feasible, and the iFEDT provides a promising tool for assessment of thyroid hormone system disruption in zebrafish. [ABSTRACT FROM AUTHOR]

There has been increasing interest in endocrine‐disrupting chemicals (EDCs) among scientists and public authorities over the last 30 years, notably because of their wide use and the increasing evidence of detrimental effects on humans and the environment. However, test systems for the detection of potential EDCs as well as testing strategies still require optimization. Thus, the aim of the present project was the development of an integrated test protocol that merges the existing OECD test guidelines (TGs) 229 (fish short‐term reproduction assay) and 234 (fish sexual development test) and implements thyroid‐related endpoints for fish. The integrated fish endocrine disruptor test (iFEDT) represents a comprehensive approach for fish testing, which covers reproduction, early development, and sexual differentiation, and will thus allow the identification of multiple endocrine‐disruptive effects in fish. Using zebrafish (Danio rerio) as a model organism, two exposure tests were performed with well‐studied EDCs: 6‐propyl‐2‐thiouracil (PTU), an inhibitor of thyroid hormone synthesis, and 17α‐ethinylestradiol (EE2), an estrogen receptor agonist. In part A of this article, the effects of PTU and EE2 on established endpoints of the two existing TGs are reported, whereas part B focuses on the novel thyroid‐related endpoints. Results of part A document that, as expected, both PTU and EE2 had strong effects on various endocrine‐related endpoints in zebrafish and their offspring. Merging of TGs 229 and 234 proved feasible, and all established biomarkers and endpoints were responsive as expected, including reproductive and morphometric changes (PTU and EE2), vitellogenin levels, sex ratio, gonad maturation, and histopathology (only for EE2) of different life stages. A validation of the iFEDT with other well‐known EDCs will allow verification of the sensitivity and usability and confirm its capacity to improve the existing testing strategy for EDCs in fish. Integr Environ Assess Manag 2024;20:817–829. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points: Zebrafish were exposed to 6‐propyl‐2‐thiouracil (PTU) or 17α‐ethinylestradiol (EE2) in an experiment that merged OECD test guidelines 229 and 234, the integrated fish endocrine disruptor test (iFEDT).PTU and EE2 had strong effects on various endocrine‐related endpoints in zebrafish adults and their offspring.All established biomarkers and endpoints were responsive as expected, including reproductive and morphometric changes (PTU and EE2), vitellogenin levels, sex ratio, gonad maturation, and histopathology (only for EE2) of different life stages.Merging of test guidelines 229 and 234 proved feasible, and the iFEDT provides a promising tool for assessment of endocrine disruption in zebrafish. [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]

Fish bioacoustics, or the study of fish hearing, sound production, and acoustic communication, was discussed as early as Aristotle. However, questions about how fishes hear were not really addressed until the early 20th century. Work on fish bioacoustics grew after World War II and considerably in the 21st century since investigators, regulators, and others realized that anthropogenic (human-generated sounds), which had primarily been of interest to workers on marine mammals, was likely to have a major impact on fishes (as well as on aquatic invertebrates). Moreover, passive acoustic monitoring of fishes, recording fish sounds in the field, has blossomed as a noninvasive technique for sampling abundance, distribution, and reproduction of various sonic fishes. The field is vital since fishes and aquatic invertebrates make up a major portion of the protein eaten by a signification portion of humans. To help better understand fish bioacoustics and engage it with issues of anthropogenic sound, this special issue of The Journal of the Acoustical Society of America (JASA) brings together papers that explore the breadth of the topic, from a historical perspective to the latest findings on the impact of anthropogenic sounds on fishes. [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]

This study advances the understanding of climate projection uncertainties in the Nemunas River, Curonian Lagoon, and southeastern Baltic Sea continuum by analyzing a subset of climate models, focusing on a coupled ocean and drainage basin model. Four downscaled and bias-corrected high-resolution regional atmospheric climate models were used to set up the hydrological (SWAT) and hydrodynamic (SHYFEM) modeling system. This study investigates the variability and trends in environmental parameters such as water fluxes, timing, nutrient load, water temperature, ice cover, and saltwater intrusions under Representative Concentration Pathway 4.5 and 8.5 scenarios. The analysis highlights the variability among model results underscoring the inherent uncertainties in forecasting climatic impacts, hence highlighting the necessity of using multi-model ensembles to improve the accuracy of climate change impact assessments. Additionally, modeling results were used to evaluate the possible environmental impact due to climate change through the analysis of the cold water fish species reproduction season. We analyze the duration of cold periods (<1.5 °C) as a thermal window for burbot spawning, calculated assuming different climate forcing scenarios and models. The analysis indicated coherent shrinking of the cold period and presence of the changepoints during historical and different periods in the future, however, not all trends reach statistical significance, and due to high variability within the projections, they are less reliable. This means there is a considerable amount of uncertainty in these projections, highlighting the difficulty in making reliable climate change impact assessments. [ABSTRACT FROM AUTHOR]

Barred loach Nemacheilus fasciatus are unable to reproduce naturally in captivity due to the lack of environmental cues and gonadal maturation occurs slower than in the wild. To optimize breeding procedures for this fish species, we determined whether hormone application via the gills was an effective process and assessed hormone dosage treatments. Oodev™ was used to induce gonadal maturation and Ovaprim™ was used to induce spawning via a topical gill approach. Multiple maturation parameters such as gonadal-somatic index (GSI) and hepatosomatic index (HSI), fecundity, and egg diameter; and spawning parameters such as latency period, egg produce, fertilization rate (FR), hatching rate (HR), survival rate (SR) were recorded and compared between the hormone dosage treatments and control treatment. Both the Oodev™ gonadal maturation induction and Ovaprim™ spawning induction were effectively applied to barred loach via topical gill application. Gonadal maturation parameters were positively correlated with dosage and all were significantly different. Fry survival rate was not different between doses. The optimal dose of Oodev™ (0.75 µL/g fish) resulted in male GSI of 5.334 ± 0.320%, female GSI of 15.501 ± 0.675%, male HSI of 0.416 ± 0.023%, female HSI of 1.670 ± 0.104%, egg fecundity 4584.20 ± 493.216 eggs, egg diameter 0.964 ± 0.0151 mm. Ovaprim™ optimal dosage (3.00 µL/g female and 1.50 µL/g male) was resulted latency period 11.05 ± 0.52 hours, egg produced 3504.83 ± 358.57, FR 96.77 ± 0.88%, HR 83.62 ± 3.78%, and SR 91.44 ± 2.53%. [ABSTRACT FROM AUTHOR]

The phenomenon of sexual dimorphism in climbing perch, which shows that female fish grow faster than males, underlies the development of mono-sex culture. Female mono-sex culture is more applicable for farmers by crossing neo-male fish with normal females. The timing of sexual differentiation in climbing perch is still unknown. It is very useful in sex reversal procedures to produce neo-male climbing perch. This study revealed the time and status of climbing perch sexual differentiation. Ten samples of climbing perch from the spawning of five pairs of parents were taken from the nursery pond at 10–29 days post-hatching (dph). Samples were prepared through a histology preparation procedure. Observations of the structure and characteristics of the gonads were carried out using a light microscope and analyzed histologically. The results indicated that gonad samples aged 10, 11, 12, 13, 15, and 16 dph showed primordial germ cells surrounded by somatic tissue forming genital ridges and mitotic division. Meanwhile, the gonads begin to differentiate as ovaries found at 18 dph with the presence of oogonia and ovarian cavities. Gonads aged 20–21 dph increasingly showed single oogonia cells (size 20–37.5 µm), germ cell cysts, genital ridges, oocytes undergoing the vitellogenesis process, perinucleolar oocytes, and the formation of the ovarian cavity. Sex differentiation of climbing perch was predicted from 18–21 dph. This conclusion underlies that the sex reversal procedure in climbing perch must be carried out before 18 dph. [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]

Coastal lagoons are environmentally and naturally dynamic areas crucial for fish reproduction and nursery. Thus, this research aims to evaluate the importance of the species performing their biological processes and development in this ecosystem. For this purpose, a subtropical coastal lagoon in the Gulf of California was taken as a case study, where four sampling seasonal campaigns were performed within the lagoon (internal zones) and the marine environment (external) nearby zones from 2016 to 2017. Diversity, evenness, and dominance indices were determined, and the number of individuals, size, length at first maturity, and reproductive period of each species were analyzed to obtain fish use of the lagoon. This coastal lagoon shows a high abundance of juvenile organisms in the cold season, whereas mature adults were mostly present during the warm season. Environmental variables influencing fish species development and distribution, such as sea surface temperature, salinity, and chlorophyll-a, were detected. To conclude, the subtropical coastal lagoon in the Gulf of California is an important nursery area where reproduction occurs mostly near adjacent areas. [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]

Insulin-like growth factors (IGFs) are hormones that primarily stimulate and regulate animal physiological processes. In this study, we cloned and identified the open reading frame (ORF) cDNA sequences of IGF family genes: the insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), and insulin-like growth factor 3 (IGF3). We found that IGF1, IGF2, and IGF3 have a total length of 558, 648, and 585 base pairs (bp), which encoded a predicted protein with 185, 215, and 194 amino acids (aa), respectively. Multiple sequences and phylogenetic tree analysis showed that the mature golden pompano IGFs had been conserved and showed high similarities with other teleosts. The tissue distribution experiment showed that IGF1 and IGF2 mRNA levels were highly expressed in the liver of female and male fish. In contrast, IGF3 was highly expressed in the gonads and livers of male and female fish, suggesting a high influence on fish reproduction. The effect of fasting showed that IGF1 and mRNA expression had no significant difference in the liver but significantly decreased after long-term (7 days) fasting in the muscles and started to recover after refeeding. IGF2 mRNA expression showed no significant difference in the liver but had a significant difference in muscles for short-term (2 days) and long-term fasting, which started to recover after refeeding, suggesting muscles are more susceptible to both short-term and long-term fasting. In vitro incubation of 17β-estradiol (E2) was observed to decrease the IGF1 and IGF3 mRNA expression level in a dose- (0.1, 1, and 10 μM) and time- (3, 6, and 12 h) dependent manner. In addition, E2 had no effect on IGF2 mRNA expression levels in a time- and dose-dependent manner. The effect of 17α-methyltestosterone (MT) in vitro incubation was observed to significantly increase the IGF3 mRNA expression level in a time- and dose-dependent manner. MT had no effect on IGF2 mRNA but was observed to decrease the IGF1 mRNA expression in the liver. Taken together, these data indicate that E2 and MT may either increase or decrease IGF expression in fish; this study provides basic knowledge and understanding of the expression and regulation of IGF family genes in relation to the nutritional status, somatic growth, and reproductive endocrinology of golden pompano for aquaculture development. [ABSTRACT FROM AUTHOR]

Objective: We investigated if large Paddlefish Polyodon spathula invest in testis weight disproportionately more than smaller males, as expressed by the gonadosomatic index (GSI). The approach was to assess the relation between testis weight F (i.e., the combined weight of both testes) and fish weight W in the expression F = aWb. The hypothesis was that sperm competition in Paddlefish would be expected (with b > 1) based on observations of several male fish attending a female spawner in a past study in the Osage River, Missouri. Methods: We used a large, three‐state data set from three fisheries (Montana, North Dakota, and Oklahoma) to evaluate isometry and allometry in the power function relationship between fish weight and testis weight. Result: All three data sets showed hyperallometric increases in testis weight with fish weight (i.e., b > 1). For Montana males, hyperallometry was greatest (b = 1.56; n = 8798), followed by North Dakota (b = 1.36; n = 8209) and Oklahoma (b = 1.22; n = 9571). Paddlefish from Montana and North Dakota had much lower testis weights through age 18 and much lower fish weights through age 25 than Oklahoma Paddlefish. By ages 17–25, mean male GSI in Oklahoma declined, whereas it remained level at about 1.5 for combined Montana and North Dakota Paddlefish. Throughout their lives, at each age, Montana and North Dakota Paddlefish allocated a higher percentage of their total weight to testis weight and reached a higher asymptotic GSI (GSI∞) than did Oklahoma Paddlefish; GSI∞ was 1.50 for Montana fish, 1.44 for North Dakota fish, and 1.26 for Oklahoma fish. Conclusion: Results provide evidence supporting the occurrence sperm competition (i.e., b > 1), as would occur when two or more males compete to fertilize the eggs of a female spawning Paddlefish. Comparisons among species and stocks are made but were limited by an acute shortage of data on male testis weights and other testis characteristics (e.g., sperm size, energy content), and reproductive investment in Paddlefish and most other fishes in other localities. Impact statementThis is the first published account of the relation between fish weight and testis weight in Paddlefish. Results are useful in assessing the role of sperm competition in the species and the importance of maintaining larger, older individuals in harvested populations. [ABSTRACT FROM AUTHOR]

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Abstract Sperm quality is a fundamental parameter for the effective reproduction of fish in captivity and the development of reproductive techniques, such as semen cryopreservation. This study aimed to determine the composition of the seminal plasma of Pseudoplatystoma reticulatum and analyze the relationships between plasma components and sperm characteristics. Nine males were induced to spermiation with carp pituitary extract in the reproductive period of the species (November and December/2019). Semen characteristics were evaluated: subjective sperm motility, motility, duration, released sperm volume, sperm concentration, pH, osmolality, and seminal plasma composition, including levels of calcium, chloride, sodium, magnesium, potassium, glucose, fructosamine, triglycerides, and total protein. To determine the relationship between seminal plasma components and sperm motility parameters, a principal component analysis (PCA) was performed. The seminal plasma of P. reticulatum is composed mainly of the Na+ ion and organic components such as protein and glucose. Through PCA, it was observed that sperm motility had a strong positive correlation with motility time, sperm concentration, and total protein and a negative correlation with osmolality and fructosamine.

Study region: The Yangtze River Basin Study focus: To accurately quantify the impact of climate change and human activities on the hydrological regime, the Long Short-Term Memory (LSTM) models for meteorology-runoff simulation are constructed for the multi-year average monthly flow process. The Indicators of Hydrologic Alteration (IHA) method is used to quantitatively evaluate the hydrological processes in the watershed. Additionally, the grey relational analysis method is employed to explore key indicators affecting the ecological effects of fish. New hydrological insights for the region: The streamflow of the Yangtze River mainstem and its seven tributaries increases as the distance from the river mouth decreases. The degree of hydrological changes in various basins is moderate (33–66%). Except for the Jialing River, Wu River, and Poyang Lake, the streamflow changes in other basins are mainly influenced by human activities. Among them, Yichang is most affected by human activities (75.43%), while Wu River is most affected by climate change (67.05%). The rate of land use development has reached 116.9% over the past 20 years, and vegetation coverage has been increasing at a linear rate of 0.003 per year, Summer rainfall is significantly positively correlated with flow, while temperature is significantly negatively correlated. The Three Gorges Dam has reduced the spawning scale of fish and identified ''October runoff'' as the key indicator. These findings contribute to a deeper understanding of the response of watershed water resources and ecological effects.