Search Results (334)

Environmental DNA (eDNA) is a highly sensitive tool widely used in biodiversity studies and for detecting organisms of biosecurity or conservation importance. However, the persistence of eDNA, even after the removal of an organism, can complicate interpretation and lead to false indications of ongoing presence. In contrast, environmental RNA (eRNA) is short-lived and may offer improved spatiotemporal precision for detecting living organisms. In this study, we evaluated the viability of environmental messenger RNA (emRNA) for targeted detection of aquatic weeds, using Amazon frogbit (Hydrocharis laevigata) as a model species. A highly sensitive qPCR assay, targeting the chloroplast rpoB transcript, was used alongside positive and negative controls to ensure workflow reliability. Our results showed that emRNA was undetectable at low density (0.56 plants per litre) and was consistently detectable at very high abundance (over eight plants per litre), although copy numbers were very low. These findings suggest that the effective detection threshold for emRNA may exceed densities typically encountered during early invasion. Consequently, the qPCR-based emRNA approaches evaluated in this study showed limited applicability for biosecurity surveillance, where reliable detection at low abundance is essential. Future research should focus on improving detection sensitivity, including eRNA enrichment. Full article

Continuous, non-invasive fish monitoring supports aquatic animal management, biodiversity assessment, and sustainable aquaculture, but embedded deployment requires a careful balance among accuracy, speed, memory, and computation under visually degraded underwater conditions. We developed ULFD-YOLO, an ultra-lightweight detector derived from YOLOv11n through coordinated redesign of the backbone, neck, and detection head. The model combines a custom convolutional MobileNetV4-tiny backbone, a hypergraph-based multi-scale fusion neck, and a lightweight MBConv head with channel attention. Experiments were conducted on Fish-BJ, an in-house dataset of 3402 images covering 21 species-informed aquarium-fish detection categories, and on a deliberately difficult 1180-image WildFish subset after dataset-specific training. On Fish-BJ, ULFD-YOLO achieved 0.960 mAP@0.5 and 0.732 mAP@0.5:0.95 with 1.3 M parameters, 2.6 GFLOPs, and a 3.0 MB model file, reducing parameters and computation by 50.0% and 58.7% relative to YOLOv11n. Bootstrap resampling yielded 95% confidence intervals of 0.946–0.973 and 0.638–0.821 for the two metrics, respectively. The model achieved 0.803 mAP@0.5 on WildFish and 19–24 FPS at 448 × 640 on a Jetson Orin Nano under its 15 W nvpmodel power mode. These results establish a practical accuracy–efficiency trade-off for embedded fish monitoring rather than peak localization accuracy. Full article

Rice paddies function as temporary wetlands that provide important habitats for diverse aquatic macroinvertebrates. However, the relative roles of regional climatic conditions and invasive species in shaping macroinvertebrate communities remain insufficiently understood. This study investigated the effects of regional temperature variation and the invasive apple snail Pomacea canaliculata on aquatic macroinvertebrate communities in rice paddies across South Korea. Aquatic macroinvertebrates were surveyed annually from 2021 to 2024 in five regions distributed along a latitudinal gradient, and additional local-scale comparisons were conducted between rice paddies with and without P. canaliculata. A total of 42 species comprising 24,524 individuals were recorded. Community composition differed significantly among regions and variation partitioning indicated that regional temperature explained 17.5% of the community variation in paddies containing P. canaliculata, whereas the snail explained 2.3%. Several dominant aquatic insect species exhibited distinct temperature-associated distribution patterns, with Rhantus suturalis and Hydrochara affinis showing negative relationships with temperature and Sternolophus rufipes showing a positive relationship. In contrast, P. canaliculata had little influence on aquatic insects but reduced overall macroinvertebrate diversity through its negative effects on native gastropod assemblages. These findings demonstrate that regional temperature and P. canaliculata influence rice-paddy macroinvertebrate communities through different ecological pathways. Regional temperature primarily affects the distribution of several dominant aquatic insect species, whereas P. canaliculata alters community diversity by reducing native gastropod populations. This study provides ecological evidence for predicting the combined impacts of climate warming and biological invasion on rice-paddy ecosystems. Full article

Alternanthera philoxeroides (A. philoxeroides) is one of the worst invasive alien species in the world and poses serious threats to both ecological security and agricultural production in China. However, the effects of environmental factors on its growth across different habitat types remain insufficiently understood. To reveal the determining natural factors influencing the growth of A. philoxeroides, fieldwork, including 50 sample quadrats in six field sites, was conducted in the Yangtze River Basin of Hubei Province. In every quadrat, soil properties, soil moisture, pH, soil temperature, soil nutrients (N, P, and K), light intensity, plant cover, and aboveground plant fresh biomass were measured. Cluster analysis showed that A. philoxeroides habitats can be divided into five cluster groups: wetland, grassland, forest understory, farmland and aquatic communities. The results showed that both total community biomass and A. philoxeroides biomass were positively correlated with water content, whereas no significant relationships were found between biomass and soil nutrients, including N, P, and K. The biomass of A. philoxeroides was significantly higher in aquatic habitats, while no significant differences were observed among the other four terrestrial habitats. These findings suggest that hydrological management, together with early control in aquatic habitats, may be an effective strategy to limit the spread of A. philoxeroides. Full article

eDNA metabarcoding provides distinct benefits—including non-invasiveness, cost-effectiveness, and high detection sensitivity—that make it particularly appropriate for aquatic ecosystem conservation and fisheries management. An environmental DNA (eDNA) metabarcoding survey was performed in the Cuijiang River to assess the feasibility of this technique for fish diversity monitoring. Fish diversity was evaluated through water collection, eDNA extraction and purification, and subsequent bioinformatics analysis. Our results revealed that the surveyed river section harbours at least 36 fish species, belonging to 30 genera, 13 families, and 6 orders. The fish community was numerically dominated by Cypriniformes. Notably, invasive alien species represented a relatively high proportion (24.72%) of the total operational taxonomic units (OTUs). Alpha diversity indices showed spatial heterogeneity among the monitoring sites, which is likely influenced by anthropogenic activities, land-use patterns, and hydrological connectivity in the sampling areas. Overall, eDNA metabarcoding proves to be an effective approach for fish diversity assessment and can serve as a valuable supplementary tool to conventional methods, with particular utility for the early detection of elusive and invasive species. We therefore recommend its incorporation into ongoing and future aquatic monitoring and conservation frameworks to strengthen early detection, habitat management, and biodiversity protection, thereby offering essential baseline data for future conservation and management of local fish diversity. Full article

The Chinese giant salamander (CGS, Andrias davidianus) is an endangered aquatic amphibian in China. Using environmental DNA (eDNA), this study aimed to monitor the spatial distribution of this species in Zhejiang Province, providing a scientific basis for species assessment, evaluation of reintroduction effectiveness, and non-invasive monitoring. Based on historical records of species presence, 18 representative water localities were selected for sampling. Among these localities, eDNA signals of the CGS were detected at nine. After excluding sampling sites affected by historical CGS releases and surrounding breeding farms, Jinzi Peak and Huyuan were inferred as candidate potentially natural stream habitats within the province. Additionally, eDNA monitoring was conducted at two release sites, Gutian Mountain and Banshanyuan, for two consecutive years. Results revealed lower detection rates in both areas in the second year of monitoring, potentially attributed to low survival rates, dispersal and disappearance, or sampling variability. A principal component analysis (PCA) of water quality factors (including parameters such as NH₃-N, TN, TP, COD) revealed distinct geographic clustering of CGS-positive and CGS-negative sampling sites that corresponded to their separation in topographic space, suggesting that the measured physicochemical conditions may be associated with the CGS eDNA detection probability. This study demonstrates that eDNA is a feasible and efficient method for surveying CGS in Zhejiang Province. Further, it provides an efficient non-invasive monitoring approach for endangered amphibians, with broad application prospects. Full article

Water hyacinth (Eichhornia crassipes, WH) is a highly invasive aquatic plant. Although its surplus biomass has been proposed as an agricultural amendment, uncertainty remains regarding its safe use. Based on this knowledge gap, two working hypotheses were addressed: (i) WH application would enhance soil physicochemical and enzymatic attributes, particularly under water stress, and (ii) WH application would stimulate plant growth through nutrient release. To verify this, two WH amendment rates (2.5% and 5% w/w) were evaluated under normal (45%) and severe (22.5%) WHC using tomato (Solanum lycopersicum L.) as a bioindicator. WH incorporation significantly altered soil conditions, inducing progressive acidification and increasing electrical conductivity (EC), particularly at the 5% rate under well-watered conditions, where EC values reached approximately 3000 µS/cm. Although WH amendments increased soil relative humidity owing to the hydrophilic nature of the biomass, these moisture-driven benefits were transient. Acid phosphatase activity increased markedly by day 60 in WH-amended soils, especially at 45% WHC, indicating enhanced microbial activity and phosphorus mineralization associated with organic matter decomposition. Plant responses were strongly driven by water availability, with severe water restrictions consistently limiting germination and growth and potentiating osmoprotectant retention. From day 60 onward, germination and biomass declined markedly in the 5% WH treatment, likely due to the accumulation of salt and osmotic stress arising from the decomposition of biomass. Surviving seedlings in WH-amended soils exhibited increased shoot biomass relative to their roots, suggesting stress-related biomass reallocation. Overall, the results indicate that the direct application of untreated WH biomass at moderate to high rates may generate short-term benefits but may impair long-term plant establishment. Lower application rates (≤2.5% w/w) may offer limited early stage benefits, whereas higher rates pose risks under prolonged exposure, highlighting the importance of dose, water regime, and amendment processing when considering WH valorization for agricultural use. This valorization approach may contribute to incentivizing control of this invasive species while promoting plant waste valorization within circular economy goals. Full article

Water pollution and its ecological consequences have become central concerns in watershed governance and aquatic ecosystem conservation. Conventional ecotoxicological research on water pollution has long relied on physicochemical monitoring, laboratory-based single-species exposure tests, and morphology-based biological surveys. Although these approaches have provided essential support for pollutant identification, toxicity characterization, and environmental standard setting, they remain insufficient for resolving community-level responses, food-web perturbations, and ecosystem degradation under multiple-stressor conditions. Environmental DNA (eDNA) has emerged as a promising molecular tool because it is non-invasive, highly sensitive, high-throughput, and capable of detecting multiple taxa simultaneously. In aquatic systems, eDNA applications have expanded from biodiversity detection to pollution diagnosis, ecological health assessment, restoration monitoring, and early warning of ecological risk, while increasingly being integrated with eRNA, multi-omics approaches, machine learning, hydrological modeling, and ecological network analysis. However, several challenges still constrain its broader application, including incomplete methodological standardization, false-positive and false-negative detections, insufficient reference databases, limited quantitative capacity, scale mismatches caused by transport and mixing, and difficulties in causal attribution. This review synthesizes recent progress in the use of eDNA for water-pollution research, with emphasis on its technical workflow, major application domains, integrative analytical frameworks, and methodological boundaries. More specifically, three main points are highlighted: (1) eDNA is shifting water-pollution research from single-species toxicity characterization toward community- and ecosystem-level ecological interpretation; (2) its greatest value lies in its integrative role at the interface of biodiversity monitoring, ecological risk assessment, and management-oriented decision support; and (3) future progress will depend on improvements in standardization, quantitative inference, regional reference databases, and multi-source data integration. Overall, this review clarifies how eDNA can contribute to more robust, ecologically meaningful, and management-relevant assessment of water pollution. Full article

Freshwater biodiversity is increasingly threatened by biological invasions, yet the ecological processes governing invasion establishment and subsequent dominance remain poorly understood. We investigated environmental, community, and functional determinants of invasion success for three invasive aquatic macrophytes (Cabomba caroliniana, Elodea canadensis, and Paspalum distichum) across 102 freshwater sites in Serbia. The three invaders occupied distinct environmental niches, with C. caroliniana confined to canals, E. canadensis occurring mainly in reservoirs, and P. distichum associated primarily with rivers. The two submerged species occupied highly distinctive positions within regional functional trait space, whereas the emergent amphibious P. distichum was considerably less functionally distinctive. Invaded communities exhibited significantly higher functional dispersion, while invasion dominance declined with increasing resident Shannon diversity, which explained 67.5% of the variation in invasive abundance. Together, these findings support a multi-stage framework in which environmental filtering determines invader identity, resident community functional structure influences invasion occurrence, and resident taxonomic diversity constrains invasion dominance. Distinguishing invasion occurrence from invasion dominance provides a more informative basis for freshwater biodiversity monitoring and invasive species management. Full article

Introduction: Biological invasions constitute one of the main threats to freshwater ecosystems, causing significant ecological changes through the introduction of exotic species that compete with or prey upon native species. In Portugal, the introduction and spread of exotic species in lotic and lentic ecosystems, such as pike (Esox lucius), European catfish (Silurus glanis), and largemouth bass (Micropterus salmoides), all top predators, may have a big impact on autochthonous species. In contrast, bleak (Alburnus alburnus), European perch (Perca fluviatilis), and common carp (Cyprinus carpio) compete aggressively for food resources. In the Sousa River basin, gudgeon (Gobio lozanoi) is considered an exotic species with potential ecological impact, with the minnow (Phoxinus phoxinus) stand having been recently identified in Portugal and, so far, recorded only in this river basin, and not yet being classified as an invasive species in Portugal. Public knowledge regarding invasive aquatic biodiversity remains a significant bottleneck for conservation. Because recreational angling is a prominent dispersal vector, initiatives that directly target this community are relevant. Objective: The aim is to carry out a bibliographic review on the exotic ichthyofauna species present in the Sousa River, with special focus on the invasion potential of the minnow (P. phoxinus). Methodology: The literature review was conducted based on the ScienceDirect, Springer Nature Link, and Fauna Norvegica databases, selecting publications between 2006 and 2025 concerning relevant studies on the potentially invasive characteristics of the minnow (P. phoxinus). The methodology is based on the analysis of studies regarding the impacts caused on riparian ecosystems. Results: The species P. phoxinus presents a generalist diet and high adaptive capacity, allowing it to colonise new habitats and compete aggressively with native species for trophic resources. Its presence is associated with negative impacts on brown trout populations (Salmo trutta), reducing growth and productivity, especially in mountain ecosystems. Increased species density also causes a significant decrease in benthic macroinvertebrate biodiversity. Studies conducted in the Douro basin indicate that the arrival of minnow in Portugal resulted from human action, probably associated with its use as live bait in recreational fishing. Conservation programmes use diverse tactics to bridge the awareness gap. Recent initiatives feature electrofishing demonstrations to visually differentiate species, theatrical performances, and even culinary show-cooking events using invasive predators like the European catfish to promote harvesting. Conclusions: The potential transition of P. phoxinus into an exotic and invasive species may be associated with the ecological pressure exerted on native communities, particularly through competition for trophic resources, highlighting the need to assess its dispersion in the Sousa basin and its impacts on fish fauna and benthic macroinvertebrates. It is important to do more sampling to understand its real distribution in the Sousa Basin. Additionally is important to explain to recreational anglers and the general population the impacts of fish transfer and the adverse effects of invasive species on freshwater Portuguese ecosystems. Full article

The subtropical and tropical islands of East Asia host a unique and highly endemic aquatic insect fauna threatened by a variety of anthropogenic stressors (e.g., invasive species, habitat fragmentation, pollution, and climate change). This review synthesizes the impacts of these stressors on aquatic insect diversity across this region based on 206 articles published over the past 40 years (1985–2025) to evaluate the impacts of these stressors on insular aquatic insect diversity. The islands of East Asia include all or parts of China, Japan, Taiwan, and South Korea. The annual number of publications demonstrates a steady upward trend over time and has been accelerating in the last decade. Our systematic analysis reveals a large geographic disparity. Research is heavily concentrated on major islands, with Honshu Island (42%) and Taiwan Island (24%) accounting for two-thirds of the total literature, while small islands (<10,000 km²) comprise only 20%. Furthermore, current research tends to focus on independent impacts of single stressors, largely overlooking the complex additive, synergistic, or antagonistic interactions that characterize stressors on these fragile ecosystems. These research gaps, compounded by a lack of long-term monitoring data (i.e., only ~22% of the studies span more than 3 years), hinder efforts to distinguish natural inter-annual variability from anthropogenic shifts. The extinction of cryptic or endemic species may occur before these species are identified and described. In addition, the disentanglement of these interactive impacts on aquatic insect communities in East Asian islands is critical for predicting ecosystem responses to further local and global changes. Identification of non-linear ecological tipping points through these long-term monitoring networks, coupled with proactive, science-guided habitat restoration, is essential to mitigate imminent extinctions and to rebuild the functional integrity of these imperiled freshwater ecosystems. Full article

Mediterranean rivers experience various pressures that cause native fish populations to decline. This is the case of Achondrostoma asturicense, a threatened endemic species recently classified as "endangered" (EN) by the Portuguese Red Book. In northeastern Portugal, the main populations occur in the Carvalhais (Tua basin), Maçãs, and Angueira (Sabor basin) rivers. This study aimed to evaluate the effect of small weirs on the distribution, abundance, and habitat use of A. asturicense populations along the longitudinal gradient of River Angueira. Three river zones (Z1 to Z3) affected by small weirs were selected along the watercourse. In each zone, four sampling sites were distributed relative to the weir, as follows: A1—200 m downstream; A2—immediately downstream; A3—under the influence of the reservoir; and A4—200 m upstream (reference). Sampling was carried out in three seasons: winter, spring, and summer 2025. Physical–chemical (water), hydromorphological (habitats), and biological (fish) elements were assessed in accordance with the protocols of the Water Framework Directive. The results revealed the worst water quality in the summer season due to flow reduction, dissolved oxygen depletion, elevated conductivity, and high nutrient (N, P) concentrations, leading to eutrophication phenomena. The distribution and abundance of A. asturicense were negatively influenced by the presence of small weirs, which were dominated by the non-native species Lepomis gibbosus. PERMANOVA analysis (two-way, p < 0.05) identified significant differences (Pseudo-F = 28.349, p < 0.05) between sampling sites and river zones, and paired similarity analysis tests (ANOSIM; one-way, p < 0.05) confirmed that these differences occur only between the weir reservoir (A3) and the remaining sampling sites. A. asturicense showed a maximum length (Lmax) of 135 mm, isometric growth only in the upstream zone (Z1), and significant differences in body condition (0.75 < K < 0.84). This species showed a preference for rheophilic habitats, with coarse substrate and diversity of currents and distinct cover mainly guaranteed by submerged aquatic macrophytes. A. asturicense populations are severely affected in the River Angueira by habitat fragmentation, riparian degradation, pollution, invasive alien species (e.g., L. gibbosus, P. clarkii, N. vison), and climate change, justifying the development of mitigation and restoration measures for the conservation of natural habitats and native threatened species. Full article

The Iberian Peninsula hosts one of the world’s most endemic fish faunas. Its extensive evolutionary, palaeogeographic, and geological history has produced a distinctive freshwater fish fauna. Many of these species have very limited distributions, making them especially vulnerable to habitat disturbance. Past monitoring of this biodiversity has revealed alarming results, indicating that most native Spanish species are at risk. The causes of this serious situation are varied and reflect the ongoing deterioration of freshwater ecosystems. The main pressures faced by populations include pollution, loss of river connectivity caused by hydraulic infrastructure, regulation of watercourses, water extraction, fishing, and the presence of invasive species. Additionally, the effects of climate change worsen the risk of extinction for these populations, particularly through the increased frequency and intensity of droughts and heatwaves. It is evident that current planning models and investments are inadequate to conserve freshwater fish. To prevent the extinction of many populations in Spain, especially Iberian endemics, it is crucial to change the management of aquatic ecosystems and adopt integrated solutions that halt population declines and promote the sustainable use of aquatic resources. The IUCN Red Lists of Threatened Species are vital indicators of biodiversity health and are widely used to guide and structure conservation efforts. These lists, published in the Red Books, result from a thorough evaluation process that employs specific categories and criteria to assess the extinction risk of species, both globally and regionally. This report presents preliminary findings from a monitoring study on the current state of freshwater fish in Spain. The monitoring results reveal that, based on IUCN assessment criteria, two species are classified as extinct (EX), four as critically endangered (CR), eighteen as endangered (EN), and twenty-one as vulnerable (VU). Of fifty-seven species documented, 79% are considered threatened. The project’s final outcome is the development of the Atlas and Red Book of Freshwater Fish of Spain. This resource includes the main native and invasive freshwater and diadromous fish species, offers detailed information on their biological and ecological traits, and provides an up-to-date inventory of records along with an assessment of their conservation status. Full article

LIFE REVIVE aims to restore ecological status and ecosystem services in the Lima and Vouga river basins (NW Iberian Peninsula), where hydromorphological alteration and hydropower-driven flow regulation are major causes of water bodies failing to reach Good Ecological Status under the EU WFD. The project targets key pressures such as longitudinal fragmentation by weirs and dams, artificial flow regimes, degradation of spawning substrates, and the spread of invasive aquatic plants, which strongly affect fish communities, including sea lamprey, salmonids, and other diadromous species. Technically, the project combines barrier removal or eco-adaptation, nature-like fish passes, and spawning-habitat renaturalisation with optimized environmental flow regimes (EFR) downstream of important hydropower systems, explicitly accounting for present and future hydroclimatic scenarios. Multi-scale ecohydrological modelling (species distribution models, habitat suitability models, GLM/GAM approaches) will quantify fish–flow–habitat relationships and support the definition of operational EFR guidelines that balance ecological requirements with hydropower and agricultural constraints through joint work with the main Portuguese hydropower operator, EDP. Impact evaluation is structured around a rigorous BACI monitoring design in intervention and control tributaries, using standard WFD biological indices for fish and aquatic/riparian vegetation, hydromorphological indices (HQA, HMS, RHS), and project-specific Key Performance Indicators for water quality, biodiversity, and habitat. Expected outcomes include the restoration of at least 51 km of rivers towards free-flowing conditions, reduced hydromorphological pressure in more than 20 km of heavily modified river stretches, and measurable increases in the distribution and abundance of fish species and native vegetation. A strong communication and capacity-building programme underpins public engagement, while a decision matrix for barrier prioritization, technical workshops, and pilot replications in additional basins (e.g., Alva, Mouro, Deva, and Tea in Galicia) are designed to maximize transferability, policy uptake, and long-term sustainability of the solutions beyond the project lifetime. Full article

Introduction: The European catfish (Silurus glanis) has expanded rapidly across Europe, significantly impacting native freshwater biodiversity. Despite its well-documented ecological and economic effects as a top predator, reproductive biology data from non-native populations remain scarce, limiting the development of effective management strategies. Objective: This study examines key reproductive traits, sex ratio, size at first maturity, spawning period, fecundity, and oocyte diameter, of an invasive European catfish population in the Lower Tagus River (LTR), Portugal, approximately 15 years after its establishment. Methodology: A total of 674 individuals were collected monthly from January 2022 to November 2023 using electrofishing, gill nets, baited hook-lines, and catches from professional fishermen. Sex and reproductive stage were assessed via gonadal analysis. Size at first maturity was estimated using logistic regression. Fecundity was determined by the gravimetric method, and oocyte stage and diameter were assessed histologically. The gonadosomatic index (GSI) was used to characterise the reproductive cycle. Results: The sex ratio was significantly female-biased (1.4:1). Size at first maturity (TL₅₀) was 72.9 cm TL for females and 68.8 cm TL for males. The spawning season extended from February to June, coinciding with water temperatures of 11–23 °C, with the highest GSI values reported to date for this species (GSI max = 22.5%). Histological analysis confirmed asynchronous oocyte development. Absolute fecundity ranged from 8364 to 319,000 oocytes per female and was positively correlated with total length and body weight. Mean mature oocyte diameter ranged from 1.50 to 3.21 mm. Conclusions: The European catfish in the LTR exhibits high reproductive plasticity, early maturity, a prolonged spawning season, and elevated fecundity, likely facilitated by warm water temperatures and abundant prey resources. Crucially, these parameters reveal earlier maturation and greater reproductive investment relative to native populations, demonstrating an extreme phenotypic plasticity characteristic of successful invasions in southern European aquatic ecosystems. These findings provide essential biological parameters for targeted management, including selective removal of large females, intensified fishing effort during the spawning season, and population monitoring to prevent compensatory reproductive responses. Full article