Fishways play a critical role in restoring river connectivity and conserving fishery resources, yet their efficiency is often limited by mismatches between hydraulic conditions and species-specific behavioral traits. To quantify the upstream migration behavior of fish under the combined influence of flow heterogeneity and schooling effects, this study examined the endangered species L. elongata in the Yangtze River Basin. Volitional swimming behavior was tested in an open-channel flume under three spatially heterogeneous flow regimes (I: Low-Moderate-High; II: High-Moderate-Low; III: Moderate-High-Low). A video monitoring system recorded the upstream movement of solitary fish and three-individual schools. Swimming trajectories, upstream migration time, preferred flow velocities, and schooling metrics-including nearest neighbor distance (NND) and mean pairwise distance (MPD)-were analyzed. Linear mixed-effects models were employed to account for repeated measures and individual variability. Results showed that schooling behavior significantly enhanced upstream migration efficiency: schooling fish arrived at the target area on average 8.93 s earlier than solitary individuals (p < 0.01), while flow condition alone had no detectable effect on arrival time. L. elongata consistently preferred low-velocity zones (0.20-0.50 m/s) and avoided high-velocity regions (0.75-1.25 m/s), with meandering upstream trajectories predominating. NND showed no significant differences across flow conditions (p > 0.05), indicating stable schooling cohesion. However, MPD increased significantly under Flow III compared to Flows I and II (p < 0.01), suggesting that higher flow heterogeneity leads to more dispersed group spacing while overall cohesion is maintained. Distinct movement strategies were observed: solitary fish predominantly utilized boundary regions as hydraulic refuges (wall-following: 63.8-80.5%), whereas schools exhibited greater spatial exploration and reduced wall-following. These findings demonstrate that schooling enhances migration efficiency while preserving a cohesive group structure and that flow heterogeneity influences within-group spatial organization. To optimize fishway performance for L. elongata, we recommend maintaining flow velocities within 0.20-0.50 m/s. This study provides scientific guidance for hydraulic regulation in fishway design and habitat restoration, emphasizing the combined effects of flow heterogeneity and schooling behavior on migration performance.

In recent years, heavy metal emissions in Lhasa have been increasing, which has an impact on the local water environment. The negative effects of copper (Cu2+) on aquatic ecosystems have attracted much attention, as even low concentrations of Cu2+ can exert toxic effects on aquatic organisms. However, the impact of Cu2+ on native fish species from the Lhasa River remains poorly understood. In this study, Schizopygopsis younghusbandi (S. younghusbandi) larvae were exposed to Cu2+ at concentrations of 0. 5, 5, 50, and 500 μg/L for 7 or 14 days to evaluate its toxic effects on thyroid function and the antioxidant system. The results indicate that whole-body total thyroxine (T4) and triiodothyronine (T3) levels were significantly decreased following Cu2+ exposure. This decrease was accompanied by a marked increase in dio1 and dio2 gene expression and decreased expression of thyroid hormone synthesis genes (nis, tg, ttf1 and pax8) after exposure to Cu2+. Furthermore, the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) and the content of lipid peroxidation were increased, while the content of glutathione (GSH) was decreased. In addition, the survival rates and body lengths of S. younghusbandi larvae were significantly reduced following 7- and 14-day Cu2+ exposure. The Integrated Assessment of Biomarker Response (IBR) analysis further revealed dose- and time-dependent effects of Cu2+ on the larvae. In conclusion, the findings demonstrate that Cu2+ exposure induced disruption of thyroid endocrine and antioxidant systems and caused developmental toxicity in S. younghusbandi larvae.

The ecologically and economically vital Hypophthalmichthys nobilis has been bred in National Fish Stock Farm (NFSF) in China since the 1960s to conserve genetics and combat overfishing. This long-term domestication has likely caused selection-driven genomic changes. To investigate this genetic diversity and selection pressure, a whole-genome resequencing was conducted on 341 NFSF H. nobilis from 13 populations and 21 wild counterparts from 3 populations (WP). Population genomics delineated eight genetically distinct populations (AN1-AN8), with six endemics to five NFSF populations and two (AN5, AN8) widespread in both NFSF and WP populations. Low inter-population FST versus high inter-strain FST implies NFSF's key role in preserving H. nobilis genetic diversity, particularly evident in higher within-NFSF diversity levels compared to natural populations. The divergence in these genetic populations predated the structured breeding and domestication efforts that began during the Tang Dynasty, indicating natural lineage divergence in H. nobilis. Genomic scans detected hundreds to thousands of selective sweeps per strain versus WP, including 30 divergent genes associated with environmental stress adaptation and immune defense. Furthermore, 75 genes linked to growth, development, and immunity-notably mTOR, eif4g, kdm4a, atp9b, fgf12, and interleukin receptors (il21r, il4r)-showed selection signals in domestication and improvement. Population genomics reveals NFSF-sustained adaptive divergence in H. nobilis driven by environmental stressors and immune adaptation, with candidate genes enabling genetic improvement of key traits (growth, disease resistance, and production). These findings establish a conservation genetic paradigm: NFSF populations sustain adaptive diversity in ex situ-managed H. nobilis, guiding vital fish germplasm stewardship.

The Ten-Year Fishing Ban in the Yangtze River provides an unprecedented opportunity to evaluate the long-term effectiveness of stock enhancement. This study focused on silver carp (Hypophthalmichthys molitrix) broodstock enhancement in the Jianli section of the middle Yangtze River from 2015 to 2017. Using microsatellite parentage assignment, we analyzed samples collected during the fishing ban period (2023–2024) to trace the offspring of the released broodstock. By comparing the genetic diversity and growth performance between hatchery-origin offspring, comprising offspring with both parents from released broodstock (R group) and offspring with only one parent from released broodstock (H group), and wild individuals (W group), we assessed whether the offspring can survive to sexual maturity and contribute to the recruitment population under natural conditions. A total of 6 R-group and 19H-group individuals were identified. The body length and weight of all hatchery-origin offspring ranged from 500 to 780 mm and from 2200 to 8837 g, respectively. Based on published studies on the sexual maturity of silver carp in the middle Yangtze River, it can be inferred that these individuals have reached sexual maturity and entered the recruitment population. Genetic diversity analysis revealed that the hatchery-origin offspring were comparable to the W group across all measured genetic parameters, and principal coordinate analysis (PCoA) showed that all individuals were intermingled in genetic space without clear clustering. Growth analysis indicated isometric growth for hatchery-origin offspring, with condition factor distributions highly overlapping with those of the W group. Combined with our previous larval study conducted in the same river section in 2019, this study provides the first complete line of evidence—from successful reproduction to recruitment—for silver carp broodstock enhancement in the middle Yangtze River, confirming the biological feasibility of broodstock enhancement for supplementing wild breeding populations. These findings provide scientific support for optimizing stock enhancement strategies under the Ten-Year Fishing Ban in the Yangtze River and offer a methodological example for assessing the long-term effectiveness of aquatic species restoration initiatives in large rivers.

Cascade hydropower development in the upper Yangtze River has substantially altered riverine habitat conditions. However, quantitative information on fish substrate preferences remains limited. Based on field surveys, six representative substrate types were identified in the Yibin and Jiangjin reaches, and substrate selection patterns of Leptobotia elongata were quantified under controlled flume conditions. This study examined sex-specific and population-level differences in substrate preference. A total of 50 samples were analyzed using one-way ANOVA and the Kolmogorov–Smirnov test. The results are summarized as follows: (1) Substrates of 40–20 mm: Individual female L. elongata exhibited the longest residence time on the 40 mm substrate (1640 s), while individual males also spent the longest time on the 40 mm substrate (1549 s). Within this substrate range, males showed a preference only for the 40 mm substrate (PR = 739), whereas females preferred three substrate types, with the strongest preference for the 40 mm substrate (PR = 7543). (2) Substrates of 10–2.5 mm: Female individuals spent the longest time on the 10 mm substrate (1468 s), and male individuals likewise showed the longest residence time on the 10 mm substrate (1568 s). In this range, males did not show a significant preference for any substrate (PR = −907), whereas females preferred three substrate types, with the 2.5 mm substrate exhibiting the highest preference intensity (PR = 2059). (3) Population-level patterns for 40–20 mm substrates: The population spent the longest time on the 40 mm substrate (1799 s) and preferred three substrate types, among which the 20 mm substrate had the highest preference ratio relative to the other preferred substrates (PR = 4750). (4) Population-level patterns for 10–2.5 mm substrates: The longest residence time was observed on the 10 mm substrate (1762 s). The population preferred three substrate types, with the 10 mm substrate showing the highest preference ratio (PR = 5709). Overall, L. elongata showed a general tendency to prefer larger-sized substrates. This preference is likely associated with enhanced habitat complexity, improved foraging opportunities, and the formation of low-velocity refuges. Our results suggest that maintaining or restoring coarse substrate patches in regulated reaches may improve habitat suitability for L. elongata and potentially benefit other benthic fishes with similar ecological requirements.

This study evaluated the relative size selectivity of four trammel nets for black bream (Megalobrama skolkovii) using the Share Each LEngth's Catch Total (SELECT) method and a generalized additive model (GAM) framework. The mesh sizes (knot-to-knot, mean ± SE) of the inner layers were 2.85 ± 0.002, 6.27 ± 0.008, 9.79 ± 0.018, and 14.06 ± 0.034 cm, corresponding to hanging ratios of 0.49, 0.33, 0.23 and 0.22, respectively. Initial SELECT analysis identified the bilognormal model as the best relative fit among candidates but showed lack of fit and overdispersion. Consequently, GAM models were adopted as the primary analysis tool. Maximum retention occurred at a length-to-mesh ratio (l/m) of ∼ 3.5. The curve similarity of GAM models before and after inclusion of zero-catch length classes suggested that the estimated selectivity pattern was stable. The relative fishing power had little effect on the overall shape of the selectivity curve. Because mesh size and hanging ratio were perfectly confounded in this study, the estimated selectivity curves represented specific gear configurations (fixed mesh-size/hanging-ratio packages) rather than mesh size alone. The population distribution demonstrated consistent bimodal structure (modes at ∼20 cm and ∼48 cm) under different fishing power assumptions. The encountered length structure should be interpreted as a combined outcome of gear selectivity and fishing power, and these factors should be disentangled to avoid systematic bias when doing population assessments.

Human activities are causing a severe decline in fish species diversity globally. Although biodiversity is inherently multidimensional, most previous studies have concentrated on taxonomic changes, neglecting functional and phylogenetic dimensions, therefore limiting our understanding of biodiversity changes. The Yangtze River, an ecologically and economically critical system, supports high fish biodiversity and important fisheries. Yet, the spatio temporal patterns and anthropogenic drivers of biodiversity changes over the past decades remain unclear. We compiled a comprehensive fish occurrence dataset covering 56 geographic units across the Yangtze River Basin for historical (1976–2010) and current (2011–2020) periods. We assessed taxonomic, functional, and phylogenetic richness and dissimilarity, and quantified overall changes using the Cumulative Change in Biodiversity Facets (CCBF) index. Over 80

River intakes are critical to national water supply networks and water resource utilization, but intake operations in river channels can cause entrainment effects that lead to the loss of early fish resources and disrupt functional ecological connectivity between key habitats. This study investigated the Jingangtuo intake on the Yangtze River using 28 larval flow events recorded between 2021 and 2022. Each event lasted about 4 d on average and showed a strong positive correlation with flood duration. Based on these observations, a larval drift model was developed by coupling an Eulerian concentration diffusion method with a Lagrangian particle-tracking approach. The model simulated larval passage time and behavior near the intake during different events. Results indicated that at river discharges of 5,700 to 13,100 m3/s, larval passage time ranged from 3.8 to 5.0 h, with a 1,000 m3/s increase reducing passage time by 0.16 h. Nonuniform upstream larval distribution—shaped by flow field heterogeneity—markedly affected downstream movement. Higher larval densities in the main channel led to a 0.5-h reduction in passage time. To reduce entrainment risk, a tiered ecological scheduling strategy was proposed, integrating real-time larval flow monitoring with dynamic response timing, shutdown durations, and optimized monitoring layouts. This approach ensures sufficient early warning and operational flexibility. The study provides a theoretical and practical basis for ecological intake operation and protection of early-stage fish.

China’s Yangtze ten-year fishing ban (YTFB) is a long-term, basin-scale ecological conservation policy, which provides an important case for understanding the large-scale ecosystem restoration of a mega-river basin. By integrating aquatic biodiversity monitoring, longitudinal surveys of former fishers, industrial statistics, and enforcement records, we developed a comprehensive assessment framework to evaluate the outcomes and underlying mechanisms of YTFB after its mid-term implementation. The results show that ecological recovery signals have emerged across the Yangtze River basin following the ban, as indicated by increases in fish biomass, higher native fish species richness, trophic restructuring, and improvements in the Index of Biotic Integrity. Ecological responses were spatially and temporally heterogeneous, potentially reflecting differences in hydrological regimes, river–lake connectivity, historical resource conditions, habitat status, and regional enforcement intensity. Targeted policies such as large-scale exit of fishers, employment transition, pension insurance and social assistance have mitigated the livelihood impacts of the fishing ban on former fishers. Multi-agency enforcement, digital surveillance, and grid-based patrols strengthened the policy implementation capacity. Additionally, fisheries-related industries have undergone a structural transformation, shifting from natural capture fisheries toward aquaculture, recreational fisheries, and potential aquatic ecological product values realization. The outcomes of the YTFB do not represent a single ecological intervention but rather reflect the combined effects of ecological pressure reduction, governance scale matching, livelihood transition of former fishers, and alternative economic pathways. Yet long-term recovery remains constrained by habitat fragmentation, hydrological alteration, climate variability, enforcement costs, and other persistent pressures. The next five years should prioritize integrated aquatic ecosystem restoration and habitat protection, the ultimate objective of the YTFB, through spatially differentiated adaptive management. This case provides a socio-ecological perspective on how large-scale conservation interventions can be designed and sustained in highly modified mega-river systems.

Environmental DNA (eDNA) metabarcoding has emerged as a powerful tool for biodiversity monitoring, yet its accuracy is fundamentally constrained by the completeness and taxonomic reliability of reference sequence databases. For the Three Gorges Reservoir (TGR), no integrated multi-marker eDNA reference library exists, hampering standardized fish conservation monitoring under the Yangtze River Ten-Year Fishing Ban. Here, we constructed a comprehensive, multi-marker eDNA reference database for the fish fauna of the TGR, encompassing mitochondrial 12S rRNA, 16S rRNA, and cytochrome c oxidase subunit I (COI) gene sequences from 173 specimens (120 species) collected between 2021 and 2024. After integrating publicly available sequences, the final database comprised 161 species. Then, we quantitatively compared species annotation performance between this local database and public repositories. Results showed that while public databases achieved higher nominal species coverage (94.67%), they exhibited critical deficiencies in annotation accuracy, correctly annotating only 77.97% (12S rRNA), 75.00% (16S rRNA), and 38.14% (COI) of sequences from shared species under controlled conditions. In contrast, the local database exhibited 92.37%, 93.10% and 100% annotation accuracy for the respective markers. Optimal interspecific Kimura 2-parameter (K2P) thresholds for species delimitation were 0.00448 (12S rRNA), 0.00531 (16S rRNA), and 0.00734 (COI). In addition, 15, 0, and 4 species pairs exhibited zero interspecific distance for 12S rRNA, 16S rRNA, and COI, respectively. These limitations reinforce the need for cautious interpretation of eDNA metabarcoding results and the integration of multiple markers or complementary nuclear loci. This study provides preliminary evidence that regionally curated, multi-marker reference libraries could improve taxonomic assignment reliability in eDNA metabarcoding compared to uncurated public repositories, providing a foundational resource for biodiversity conservation.

Coptodon zillii and Oreochromis niloticus are dominant invasive fish species that have successfully established and coexisted in the Jinghong Reservoir of the lower Lancang River, Southwest China. To explore the mechanisms underlying their invasion and coexistence from the perspective of reproductive traits, we conducted monthly sampling from January to December 2025 to compare key reproductive parameters, including size at first sexual maturity, sex ratio, breeding season, spawning pattern and fecundity. The results showed that the predicted sizes at first sexual maturity for females and males of C. zillii (83.4 mm and 81.7 mm, respectively) were significantly smaller than those of O. niloticus (127.7 mm and 125.8 mm, respectively). Both species exhibited early sexual maturation. The sex ratio of C. zillii was approximately 1:1, whereas that of O. niloticus was significantly female-biased. The breeding season of C. zillii lasted from April to September, peaking in May and June, while O. niloticus spawned from May to November, with a peak in August, showing a staggered temporal distribution. Both species were batch spawners; however, O. niloticus had significantly larger egg diameters than C. zillii. Absolute fecundity, length-relative fecundity and weight-relative fecundity were significantly higher in C. zillii than in O. niloticus. Moreover, the absolute fecundity of C. zillii showed stronger correlations with body length, body weight, net weight and gonadal weight. C. zillii adopted a more r-selected strategy, while O. niloticus exhibited a more K-selected strategy. The two species displayed clear divergence in their reproductive strategies, including size at maturity, breeding season, egg diameter and fecundity, which reduced interspecific competition and promoted niche separation and coexistence in the Jinghong Reservoir.

In recent years, large areas of reeds were abandoned for harvesting in Lake Dongting, adding unique hydrological conditions, which may alter the biogeochemical cycle of nitrogen (N) and phosphorus (P). To identify the influence of unharvested reeds on N and P cycles in Lake Dongting, areas near the reeds and central area of East Lake Dongting in August 2024 were investigated. Total and labile organic matter, P fractionation and sorption behaviors, extracellular enzymatic activities, dehydrogenase activity, and iron in sediment, different forms of N and P in surface and interstitial water as well as chlorophyll a (Chl a) were analyzed. In areas near the reeds, organic matter decomposition caused by reeds decay led to a higher anaerobic degree, yet the release of iron bound P from the sediment was relatively low due to the extremely low content. Chl a of the two areas was similar, but P required for algae in areas near the reeds mainly came from the hydrolysis of organic P in terms of higher organic P content and alkaline phosphatase activity, while in central area mainly from nutrients deposited and high P release potential in terms of high equilibrium phosphorus concentration. Although high ammonium in interstitial water caused by decomposition of protein, low dissolved inorganic N existed in the surface water of the areas near the reeds due to few N migration from interstitial water caused by short-term flooding and the absorption of N by reed leaves. The decline of unharvested reeds would not result in eutrophication and algae blooms due to unique hydrological conditions, and both hydrology and vegetation cause differences in the migration and transformation of sediments nutrients in Lake Dongting.

Silver carp (Hypophthalmichthys molitrix) has been identified as one of the four famous Chinese carps. The Yangtze River is the main home to silver carp. However, during the “ten-year fishing ban”, illegal fishing frequently occurred, law enforcement agencies failing to discriminate between farmed and wild fish from the Yangtze River. Therefore, there is a strong need to develop a simple and effective method to discriminate between farmed and wild silver carp from the Yangtze River. In this study, 76 fatty acids were analyzed in 266 silver carp samples. The top 8 fatty acids that exhibited the best performance were identified as candidate biomarkers. The different origins of wild silver carp were also identified. Based on receiver operating characteristic (ROC) curve analysis, myristic acid proportion of total fatty acids was considered as a biomarker which has high sensitivity and specificity in discrimination of farmed and wild silver carp.

This study aimed to determine the practical efficacy of passive eDNA samplers (PEDS) for monitoring fish diversity in riverine ecosystems. It investigated the utility of environmental DNA (eDNA) in accurately depicting fish composition and diversity within the Lancang River. Environmental DNA technology, particularly PEDS, may be used as a substitute for traditional water filtration techniques. However, its effectiveness in natural water ecosystems remains to be proven. The filter materials included mixed cellulose acetate and nitrate (MCE), nylon (NL), glass fiber (GF), and polyvinyl chloride filter membrane (PVC). This study used four different types of filters, each with identical pore sizes and dimensions but constructed from various materials, to assess eDNA capture under laboratory and field conditions in the water samples. The filter materials included mixed cellulose acetate and nitrate (MCE), nylon (NL), glass fiber (GF), and polyvinyl chloride filter membrane (PVC). Environmental DNA macrobarcoding was used to analyze fish biodiversity and to understand the environmental effects on species distribution. Our study identified 50 fish species inhabiting the Lancang River, with equal representation of exotic and native species. A comparative analysis of four filter-based environmental DNA samplers and traditional environmental DNA sampling methods demonstrated comparable species richness. Redundancy analysis indicated that environmental variables, elevation, electrical conductivity, salinity, and chlorophyll-a significantly influenced the distribution patterns of both non-native and native fish species in the river. This study highlights the significance of eDNA technology in evaluating fish diversity across diverse habitats, thereby establishing a theoretical framework for the sustained monitoring and management of fish biodiversity in protected areas.

The Yangtze River has experienced severe ecological degradation due to intensive human activities, including dam construction, land reclamation, and overfishing. These disturbances have disrupted the natural habitats of the Yangtze River, leading to a sharp decline in fish biodiversity and fishery resources. To address this ecological crisis, the Chinese government implemented a 10-year fishing ban in January 2021 to mitigate pressures on fish populations, restore aquatic habitats, and promote biodiversity recovery. The middle reaches of the Yangtze River are characterized by diverse fish species and a critical habitat for aquatic life, this study seeks to assess the effects of the fishing ban on fish diversity, body structure, population and community dynamics in this region. Fish monitoring data collected from 2017–2019 (pre-ban) and 2021–2023 (post-ban) were analyzed to evaluate changes in fish body size, species diversity, and community structure. The analysis results using the PSD method indicate that fish body size has increased following the fishing ban, suggesting the improvement of population structures, and a change in the complexity of food web structure. Species diversity indices showed partial recovery, but the recovery was uneven across different sampling sites. While fish populations showed signs of improvement, particularly in terms of body size and community stability, species diversity remained at relatively low levels in some areas, indicating that full recovery in biodiversity and resource levels may require extended conservation efforts. These findings suggest that while the fishing ban has had a positive initial impact on fish populations and ecological conditions, continued and long-term conservation measures are essential for fully recovering the river’s biodiversity and restoring its fishery resources. The study also highlights the importance of monitoring fish species diversity, body structure, and community dynamics as part of ongoing efforts to evaluate the effectiveness of the fishing ban and refine resource management strategies for the middle reaches of the Yangtze River.

Determining redox state threshold for nitrous oxide (N2O) emissions and revealing the indirect regulatory impact of organic carbon on N2O production rates helps to further clarify the biogeochemical mechanism of sediment N2O emissions in shallow lakes. Different forms of nitrogen (N) and phosphorus (P) in surface and interstitial water, carbon (C), P and iron (Fe) compounds, N2O production rate, oxidation-reduction potential (ORPsed), as well as functional genes (nirS, nirK, and nosZ genes) in sediments were analyzed. Sediment N2O production rates changed non-monotonically with the changing of redox state (ORPsed and ratio of ferrous ion (Fe(Ⅱ)) and total iron (TFe) (Fe(Ⅱ)/TFe)), forming an inverted V-shaped curve, and with the highest N2O production rate at an intermediate ORPsed (around 126.5 mV) and Fe(Ⅱ)/TFe (around 0.72) in some light and middle eutrophic lakes. Hypereutrophic lakes showed lower sediment redox states, thus had lower N2O production rates, which was attributed to the shift from incomplete to complete denitrification. Sediment redox state was regulated by organic carbon directly or indirectly through the coupling of C, N, P, oxygen (O) and Fe cycling processes. The community structure and function of nitrite-reducing bacteria (i.e. nirS and nirK) and N2O-reducing bacteria (i.e. nosZ) were mainly shaped by C, N, P, O, and Fe in sediment, which were all controlled by organic carbon. Organic carbon shaped sediment redox state and microbial community structure of N2O-producers and N2O-reducers directly and indirectly by altering N, P, O and Fe cycles in sediment, and further regulated N2O emissions.

Animal behavior diversity is a key element of biodiversity, and the establishment of an ethogram provides a crucial framework for exploring the relationship between behavioral patterns and environmental factors. However, the development of ethograms and the quantitative analysis of behavioral diversity in fish remain underexplored. In this study, focal animal sampling and instantaneous scan sampling methods, paired with the PAE (Posture-Act-Environment) coding system, were employed to investigate the ethogram and reproductive behavior diversity of silver carp. The findings revealed 12 postures, 20 actions, and 34 behaviors documented during the breeding period of silver carp. Analysis of reproductive behavior diversity revealed that the absolute behavioral diversity index (H), relative behavioral diversity index (r), and regulated diversity index (r-variable) all peaked during the 10-15 h interval following induced spawning. Notably, significant differences (p < 0.001) were observed in these indices across different post-induction time intervals and between sexes. Throughout the breeding cycle, females demonstrated lower diversity and intensity in reproductive behaviors compared to males, suggesting distinct reproductive strategies between the sexes. The reproductive behavior of silver carp exhibited distinct chronobiological disorganization patterns. This study provides a scientific basis for future research on the behavioral ecology of silver carp and the conservation of their wild populations.

The status of the fishery resources in Poyang Lake, China, during periods of abnormal drought was examined using a comparative analysis of data from four fishery resource surveys performed during 2022 and 2023, in the first half (April–June) and the second half (September–November) of each year. A total of 91 fish species (11 orders, 17 families, 54 genera) were collected, with Cyprinidae accounting for 54.95% of the total species and Megalobrama skolkovii, Aristichthys nobilis, and Hypophthalmichthys molitrix as the dominant species. The Shannon-Weiner diversity, Pielou evenness, Simpson diversity, and Margalef richness indices were 3.30, 0.73, 0.95, and 6.93, respectively. The corresponding catch per unit effort (CPUE) values of the fish were 5.49 kg·(1000 m2·h)−1, 4.45 kg·(1000 m2·h)−1, 3.03 kg·(1000 m2·h)−1, and 2.75 kg·(1000 m2·h)−1, showing a clear decreasing trend across the successive sampling periods. The abnormal drought did not cause significant differences in the number of fish species and diversity indices (p > 0.05), but altered the fish community structure, characterized by reduced dominance of small, sedentary, and herbivorous fish, and led to a significant decline in CPUE (p < 0.05). This demonstrates that abnormal hydrological regimes can undermine the effectiveness of the 10-year fishing ban and threaten the recovery of fishery resources in river-connected lakes.

Human activities have altered rivers worldwide, but how their combined effects shape fish assemblages remains unclear. We therefore surveyed fish and habitats seasonally along the middle and lower reaches of the Han River, China, during 2022, specifically in June–August (wet season) and October–November (dry season). This study analyzed the spatial distribution pattern of fish diversity, explored the effects of natural factors (e.g., hydrology, water quality) and human stressors (e.g., dam, land use) on the spatial pattern of fish diversity, and identified the key driving factors. Cluster analysis and Non-metric Multidimensional Scaling (NMDS) showed that the fish communities could be divided into three groups: the Danjiangkou reservoir area (DRA), the middle reaches (MR), and the lower reaches (LR). For α-diversity, the LR had the highest value, followed by the DRA, with the MR being the lowest. For β-diversity, the MR had the highest value, followed by the LR, with the DRA being the lowest. Random Forest model showed that fish diversity was mainly affected by natural factors; among these factors, the key drivers of α-diversity were hydrological factors such as the water level (3.56–5.97%) and river width (4.53–4.69%), while for β-diversity, the key drivers were water quality factors, including the dissolved oxygen (10.08–12.36%), total nitrogen (6.49–9.31%), and chlorophyll a (8.26–8.40%). Structural Equation Modeling further revealed that natural factors affected β-diversity mainly through direct pathways, while human stressors affected β-diversity mainly through indirect pathways. The results revealed the differential roles of natural factors and human stressors in driving the patterns of fish α-diversity and β-diversity in human-disturbed rivers, which will provide a scientific basis for the conservation of fish diversity in the Han River.

In the context of the ten-year fishing ban on the Yangtze River, illegal poaching for profit persists. To support the enforcement of this ban and protect the river's ecosystem, an efficient and precise method for distinguishing between wild and farmed common carp is essential. This study utilized ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) combined with metabolomics technology to analyze and compare the metabolic differences between wild and farmed common carp. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) revealed a clear separation between the two groups, which was further verified by metabolic fingerprint profiles. Moreover, 16 metabolites with high discriminatory potential were identified from 491 differentially metabolites, such as phytosphingosine, succinic acid and threonine. In addition, a cluster analysis of the differential metabolites classified them into four classes: peptides, fatty acyls, steroids and steroid derivatives, and glycerophospholipids. Furthermore, candidate biomarkers, including 3-hydroxybutyrylcarnitine, 3-hydroxyhexanoylcarnitine and jasminoside were identified to potential distinguish wild populations. To our knowledge, this is the first study to apply metabolomics technology to differentiate wild from farmed common carp, providing a new theoretical basis for ecological restoration efforts in the context of the Yangtze River fishing ban.