Search Results (119)

Reintroduction programmes are increasingly used to restore threatened freshwater fishes, yet evaluating their success remains challenging during the early stages of population establishment. Genetic monitoring is commonly used to assess diversity but rarely provides direct evidence of natural reproduction. Here, we investigated natural reproduction following reintroduction in the endangered Zingel asper, a benthic fish endemic to the Rhône River basin. Between 2006 and 2015, more than 25,000 captive-bred individuals from two source populations were released into the Drôme River (France). Using 54 microsatellite loci, we assessed genetic diversity, effective population size, relatedness and inbreeding, reconstructed parentage relationships, and evaluated admixture among source lineages through hybrid assignment analyses. Wild source populations differed markedly in genetic diversity and effective population size, whereas captive propagation reduced genetic diversity and increased relatedness and inbreeding. Despite these effects, the reintroduced population exhibited higher allelic richness than any captive cohort. Parentage analyses provided direct genetic evidence of natural reproduction by identifying individuals whose genetic origin could not be explained by the captive breeding pedigree. Hybrid assignment analyses independently confirmed admixture between source lineages. These results show how complementary genetic approaches can provide early evidence of reintroduction success and support adaptive management of threatened fish populations. Full article

To understand the adaptive evolution of endangered plateau freshwater fishes to environmental stress and to better explore the underlying mechanisms in Aspiorhynchus laticeps—a critically endangered fish endemic to the Tarim Basin, Xinjiang, China—a combination of ecological experiments and transcriptome sequencing (RNA-seq) technology was used to study the differences in gene expression patterns among individuals under different salinities and flow conditions. This experiment included four treatment groups (CON, H-SA-S, L-SA, L-SA-S). A. laticeps specimens with an average weight of 2.92 ± 0.62 g and a body length of 58.22 ± 5.10 mm were selected, with three biological replicates for a 96 h combined stress treatment. Moreover, the relationships between these differences and the aquatic environment were analyzed. A total of 1847 differentially expressed genes (DEGs), including 935 upregulated genes and 912 downregulated genes, were identified under different aquatic environment stress modes. GO and KEGG enrichment analyses revealed that TNF signal transduction, the NF-κB pathway, and metabolic regulation were significantly enriched among the DEGs (p < 0.05). High salinity–alkali stress significantly activates the TNF/NF-κB pathway, regulates MST1, LOC107702867, LOC113110979 and other genes to enhance the body’s resistance; water flow changes mainly regulate energy metabolism through genes such as NEHOM01_1600 and gptl. These findings provide an important scientific basis for the ecological adaptability, protection, and proliferation of endemic and endangered fish in China, as well as for germplasm innovation to address ecological deterioration in plateau fishes in alpine and arid areas. This study provides a molecular-level theoretical foundation for artificial habitat regulation and the conservation of endangered Aspiorhynchus laticeps populations in the Tarim River. Full article

Leptobotia elongata, an endangered freshwater fish endemic to the upper Yangtze River, increasingly depends on artificial reproduction for conservation. However, a captive juvenile population fed a conventional diet commonly exhibits ovarian development arrested at stages I–II, representing a critical bottleneck for captive reproduction. To address this, juvenile L. elongata were reared for 6 months on either a basal diet (control group, CG) or a lipid-enriched diet in which soybean oil was replaced by fish oil and soybean lecithin, with vitamin E added (treatment group, TG). Histological examination revealed that TG ovaries advanced from stage I–II to stage III, with markedly larger oocytes and centralized nucleoli. LC-MS/MS-based untargeted metabolomics profiling identified 1773 metabolites, of which 566 differed significantly between groups (374 up- and 192 down-regulated in TG). KEGG enrichment revealed 15 significantly perturbed pathways, with nucleotide metabolism showing the highest enrichment (Rich factor = 0.22), accompanied by changes in fatty acid biosynthesis, biosynthesis of unsaturated fatty acids, glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, pantothenate and CoA biosynthesis, and TCA-related modules. Coordinated up-regulation of long-chain polyunsaturated fatty acids (DHA, EPA, ARA, α-linolenic acid), DHA-phosphatidylethanolamine, phosphatidylcholine and CDP-choline, together with depletion of their precursors (sn-glycerol-3-phosphate, LPI(20:4), pyrophosphate), was consistent with enhanced phospholipid remodeling and Lands-cycle activity. A multi-tier regulatory network was constructed, anchored on three pathway hubs (nucleotide metabolism, pyrimidine metabolism and fatty acid elongation) and five functional modules. This network indicated that dietary lipid supplementation was associated with coordinated changes across four interconnected metabolic axes: lipid supply and membrane remodeling, nucleotide synthesis and turnover, amino acid–protein translation, and energy–coenzyme metabolism. Collectively, these findings propose a metabolic framework and identify candidate biomarkers (e.g., DHA-PE, PC) for optimizing feed formulations of L. elongata. Full article

Cryopreservation of semen is an important interdisciplinary field at the intersection of reproductive biotechnology and cryobiology, and holds significant value for the genetic rescue of endangered species, long-term preservation of germplasm resources, and management of reproduction in livestock and aquaculture. Although this technology is relatively well established in fish and terrestrial mammals, it still faces numerous challenges in marine mammals, particularly cetaceans. The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), a rare and endemic freshwater porpoise of China, remains at an early stage of research regarding semen cryopreservation, and there is an urgent need to develop a technical system tailored to its unique physiological characteristics. Literature was searched in PubMed, Web of Science, and CNKI from database inception to May 2025. This structured narrative review was based on 77 core publications, including eight original studies on cetacean semen cryopreservation. This structured narrative review synthesizes evidence from cetacean semen cryopreservation research, with particular emphasis on technical insights from the bottlenose dolphin (Tursiops truncatus), Pacific white-sided dolphin (Lagenorhynchus obliquidens), killer whale (Orcinus orca), and beluga (Delphinapterus leucas). Additionally, it incorporates advances in extender formulations and cryoprotectants from studies on other species to summarize key technical parameters suitable for the cryopreservation of Yangtze finless porpoise semen, aiming to provide a theoretical basis and practical framework for establishing an efficient and safe cryopreservation system for this species. Full article

With over 140 species of primary freshwater fish, including 73 that are endemic, Greece is recognized as a biodiversity hotspot in Europe. However, like freshwater systems worldwide, these ecosystems face serious threats, particularly from the introduction of non-native species. This ongoing increase in invasive species has heightened scientific and policy-maker awareness, as such introductions can lead to population declines and even extinctions of native fish. In response to this growing concern, various risk assessment tools have been developed to evaluate the potential hazards posed by non-native species, both those already established and those likely to be introduced. These tools are critical for informing policy decisions and managing biological invasions effectively. In the current study, a new tool, the Hellenic Risk Assessment (HeRA), is proposed. Unlike its predecessors, HeRA places greater emphasis on assessing the biological traits of introduced species and incorporates region-specific considerations tailored to the Mediterranean basin. Its scoring system evaluates both the likelihood of a species establishing itself and its potential environmental impact, making it a valuable resource for stakeholders in prioritizing management actions and making informed decisions regarding the import of live fish species. Full article

Introduction: River connectivity is a fundamental component of lotic ecosystems, frequently disrupted by anthropogenic barriers. Fishways are critical mitigation tools for restoring this connectivity; however, their temporal use by fish is often assumed to be restricted to specific seasonal windows (mainly spawning season). Understanding the fine-scale temporal dynamics of fishway use by native species such as the common barbel (Luciobarbus bocagei) is essential for effective, long-term river management and the conservation of Iberian freshwater biodiversity. Objective: This study aims to evaluate the daily and seasonal patterns of use of pool-type fishways by L. bocagei, in order to improve the determination of their temporal period of use and provide data-driven recommendations for their management. Methodology: The study was conducted in the middle reach of the Duero River (Burgos province). Over a multi-year period, more than 1000 individual barbels were captured, tagged with Passive Integrated Transponder (PIT) tags, and released. Movements were continuously monitored across two pool-type fishways. Telemetry detection data were analyzed to evaluate daily rhythms and seasonal use, as well as to estimate the start and end dates of the movement periods. Results: Our analysis revealed a highly marked daily pattern in fishway use, showing a clear increase during daylight hours, with more pronounced peaks at dawn and dusk. This daily activity dynamically adjusts throughout the year in response to the solar cycle. Furthermore, we successfully determined that the seasonal activity extends from March to November, a pattern that remained consistent throughout the different study years. Crucially, the telemetry data empirically demonstrated that L. bocagei utilizes fishways for a substantial portion of the year, indicating relevant non-reproductive movements. Conclusions: The extended temporal use of these fishways indicates their potential ecological functions throughout much of the year. This must be reflected in management and maintenance protocols that ensure sufficient flow conditions, cleaning, and active vigilance during most of the year. Additionally, this predictability reinforces the value of fishways as strategic biological monitoring stations for endemic populations. Full article

Introduction: The circum-Mediterranean region is a global biodiversity hotspot, hosting a highly distinctive freshwater fauna with a high degree of endemism and conservation concern. However, these ecosystems are increasingly threatened by biological invasions, particularly by non-native fish species, which represent a major driver of biodiversity loss. Objective: This study aims to compile a comprehensive and updated inventory of non-native inland fish species across the circum-Mediterranean region and to identify the main taxonomic, biogeographical, and socio-environmental drivers shaping their distribution. Methodology: We conducted an extensive review of the scientific literature, online databases (including EASIN, GISD, and CABI), and technical reports to compile records of non-native fish species across inland and transitional waters of Mediterranean-climate basins. Analyses focused on species composition, taxonomic representativeness, introduction pathways, native regions, and the relationship between species richness and selected environmental and socio-economic variables. Results: A total of 151 non-native fish species were recorded across the study area. Italy, Spain, Bosnia and Herzegovina, France, and Croatia exhibited the highest numbers of established species. Taxonomic representation was uneven, with Salmoniformes and Esociformes overrepresented among established non-native species, while Siluriformes and Characiformes were underrepresented. Most introductions originated from Europe, Asia, and North America, primarily through intentional releases and escape events. Non-native species richness was positively correlated with gross domestic product, precipitation, and the number of dams, highlighting the role of economic development and habitat modification in facilitating invasions. Conclusions: Biological invasions by non-native fishes are widespread across the Mediterranean basin and are strongly driven by human activities and environmental conditions. The high invasion levels observed in this biodiversity hotspot pose a significant threat to endemic freshwater faunas. These findings underscore the need for coordinated transnational management strategies, stricter regulation of introduction pathways, and prioritization of high-risk species to mitigate further impacts. Full article

Introduction: The global ornamental fish trade is a rapidly expanding sector and a major pathway for the introduction of non-native species, particularly in freshwater ecosystems in developed countries. The introduction of non-native species can result in a range of ecological impacts, including predation, competition, hybridization, and disease transmission, often leading to ecosystem degradation and biotic homogenization. Therefore, it represents a clear ecological risk, especially serious in freshwater systems with a high endemism rate, such as the Iberian Peninsula. The occurrence of ornamental non-native species in the Iberian Peninsula has been common, yet little has been done to describe the overall ornamental fish trade as a first step to evaluate invasion risk. Objective: This study characterizes the import dynamics of ornamental freshwater fish in Portugal between 2020 and 2024 and evaluates its potential role as a pathway for species introductions. Methodology: Data were obtained from the Institute for Nature Conservation and Forests database, including information on species composition, quantities, sizes, prices, and countries of origin. A total of 431 records were analyzed, resulting in 27,689 validated entries of imported freshwater fish, which were taxonomically verified and filtered to retain only freshwater species. Results: A total of 666 species from 88 families were identified, with an average of 380 species imported annually, reflecting high taxonomic diversity. Import volumes increased from approximately 1.25 million individuals in 2020 to 1.75 million in 2024, while total import value nearly doubled from €300,000 to €600,000. Imports were predominantly from five Southeast Asian countries, particularly Indonesia and Vietnam, and largely supported by aquaculture production (88%). A stable core of highly traded species, including Carassius auratus, Poecilia reticulata, and Paracheirodon innesi, suggests a sustained and very high propagule pressure, while some species variability was observed on yearly basis, suggesting the importance of monitoring programs on actual imports. Conclusions: Overall, the ornamental fish trade represents a significant and growing pathway for biological invasions in Portugal. The combination of increasing trade volume, high species diversity, and persistent dominance of key taxa highlights the need for improved monitoring, regulatory frameworks, and public awareness to mitigate ecological risks. Full article

Introduction: Freshwater habitats underpin global biodiversity and provide an array of essential ecosystem services to humans. However, threat hotspots like the Iberian Peninsula combine severe anthropogenic impacts (habitat degradation, climate change, and biological invasions, among others) with a high number of endemic range-restricted freshwater species. Despite the urgency, current conservation actions fall short of providing adequate protection. The irreplaceability index has been proposed as a useful assessment tool to focus limited efforts on areas that provide the highest benefit for threatened species. However, the transboundary nature of many rivers in the Iberian Peninsula can be a source of inefficiencies in protection if prioritisation efforts are conducted at a national rather than a peninsular scale. Objective: The aim of this study is to identify priority conservation basins for threatened native freshwater fish in the Iberian Peninsula and to evaluate the impact of national versus transboundary management strategies on the spatial protection afforded to these species. Methodology: The irreplaceability index was calculated for each basin by integrating basin richness, species rarity and their IUCN Red List conservation status. First, we modelled the species’ probability of presence using field observations recorded since 2000. Rarity was then calculated as the ratio between the modelled probability and the total number of basins within the species’ theoretical natural distribution. We then weighted each species’ rarity by its IUCN Red List conservation status, with higher weights to threatened species. We then calculated the basin irreplaceability index as the sum across all the species present in the basin of their conservation status-weighted rarity and ranked them according to this index. We replicated this approach considering Spain and Portugal independently, and both countries as one conservation planning unit. Results and Conclusions: The most irreplaceable basins were those harbouring a high density of threatened, narrow-range endemics. The priorities in each country differ depending on whether management strategies adopt a national or a broader geographical approach. Therefore, effective conservation requires transboundary planification to safeguard the shared biodiversity across countries. Full article

In the Iberian Peninsula, the rapid expansion of the invasive species Alburnus alburnus (bleak) has intensified its contact with several endemic cyprinid species, raising concerns about hybridization, introgression, and the loss of genetic diversity. Despite increasing evidence of hybridization, data remain limited for many Iberian River basins, where endemic species persist in fragmented and vulnerable habitats. The aim of this study is to assess the extent and spatial distribution of hybridization between the bleak and the following native cyprinid species, Anaecypris hispanica (jarabugo), Iberochondrostoma lemmingii (pardilla), Pseudochondrostoma willkommii (Guadiana nase), and Squalius alburnoides (calandino), across several rivers within the Guadalquivir Basin. To this end, Sanger sequencing will be performed on the mitochondrial cytochrome b gene (maternal lineage; approximately 1000 base pairs (bp)) and the nuclear β-actin gene (paternal lineage; approximately 950 bp) from individuals of all endemic species and the bleak. Parental species and putative hybrids were initially identified in the field using diagnostic morphological and meristic characters, including number of rays in the anal fin morphology, mouth position, and the number of lateral line scales. Molecular analyses will include haplotype network reconstruction and phylogenetic tree inference to evaluate relationships among individuals from different species and to assess lineage divergence. The results will allow us to: (1) detect hybrids between the bleak and endemic cyprinids, (2) identify hybridization events among endemic cyprinid species, and (3) evaluate the correspondence between diagnostic morphological and meristic traits and the molecular identification of hybrid individuals. Overall, these findings will provide key information for the conservation management of endangered Iberian freshwater fishes in the context of invasive species expansion and global change. Full article

Introduction: The Guadiana basin harbours one of the most threatened freshwater fish faunas in Europe, concentrating a high number of Iberian endemisms and species of high conservation interest. Among these, the Iberian minnowcarp (Anaecypris hispanica) and the Iberian Arched-Mouth Nase (Iberochondrostoma lemmingii) stand out as threatened species whose populations are in serious decline. Methodology: In March 2023, an obsolete river barrier, the Galaches weir, was removed from the Odeleite River (Guadiana basin), releasing an 8 km lotic stretch previously inaccessible to downstream fish fauna. This study aimed to evaluate the effects of weir removal on the composition and structure of the fish community, using a Before-After design with fish sampling conducted before (2022) and after (2024) weir removal. Fish sampling took place in early summer by means of electrofishing in two 150 m long river sites, one upstream and one downstream of the weir. Results: Before removal, both upstream and downstream sites were dominated by native leuciscids (A. hispanica, I. lemmingii, Squalius pyrenaicus, and Pseudochondrostoma willkommii) and cyprinids (Luciobarbus spp.), with non-natives Lepomis gibbosus and Australoheros facetus occurring in lower abundance. After removal, native species remained clearly dominant at both sites, while A. facetus was no longer detected and L. gibbosus did not increase in abundance, suggesting that barrier removal did not favour the spread of non-native fish. Species size–structure revealed the presence of multiple size classes, possibly supporting a regular recruitment of key native taxa: A. hispanica occurred almost exclusively with total lengths of 4 to 6 cm, whereas I. lemmingii and other native leuciscids displayed broader size ranges, spanning juveniles to adults, consistent with sustained reproduction and growth in the restored river stretch. Conclusions: These findings support the hypothesis that weir removal has improved the sustainability of native fish populations such as A. hispanica by improving habitat connectivity and increasing recruitment. The results highlight the importance of weir removal for the conservation of threatened species in Mediterranean river systems. Full article

Aquatic envenomations may cause severe tissue injury, neurologic morbidity, and even mortality among those whose leisure and/or occupational activities expose them to marine and freshwater animals. The Motoro ray, or Potamotrygon motoro (also known as an ocellate river stingray) is endemic to freshwater tributaries throughout Brazil, and is a frequent source of severe envenoming of local fisherman and those residing near waterways. Local wound management including immersion in warm water, wound cleaning and debridement, as well as antibiotics are mainstays of treatment, as are local anesthetics (e.g., nerve blocks) and systemic opioid analgesics; however, high-quality evidence supporting such interventions is lacking. We present a case of a Canadian who was envenomed by his pet Motoro ray, and describe his clinical presentation and evolution of symptoms over the subsequent months. With the ever-increasing trade of exotic wildlife, clinicians, public health authorities, and those within the broader wildlife regulatory ecosystem should be attuned for unanticipated adverse consequences, such as those described herein. We further situate this case within the existing published literature around this particular species of ray, which is not typically considered an ornamental fish. Full article

Introduction: Species Distribution Models (SDMs) are widely used to infer environmental drivers of freshwater fish distributions and to project biodiversity responses to climate and land-use change. However, freshwater ecosystems present specific conceptual and methodological challenges, including dendritic network structure, strong spatial autocorrelation, dispersal constraints, and scale mismatches between biological processes and environmental predictors that remain insufficiently addressed. At the same time, emerging data sources such as environmental DNA (eDNA) and high-resolution remote sensing offer new opportunities to improve data coverage and ecological realism in SDMs. Methodology: Focusing on Iberian systems as illustrative case studies, here, we synthesize the following recent advances and challenges in SDM applications to freshwater fishes: (i) the implications of using presence–absence versus abundance data; (ii) the integration of hydrological and connectivity metrics as predictors; (iii) approaches to explicitly account for spatial structure and biotic interactions; and (iv) the contribution of novel datasets, including eDNA and remote sensing. Furthermore, we examine the performance and transferability of correlative models under analogue and non-analogue climate conditions. Results: Our synthesis highlights the importance of incorporating network topology, seasonality, dispersal constraints, and novel data sources to improve ecological realism and predictive performance. The integration of emerging biodiversity and environmental data can substantially reduce data gaps and improve model calibration and validation, particularly in poorly sampled systems. Nonetheless, model transferability remains a challenge, particularly for endemic and range-restricted species. Advancing freshwater SDMs through the integration of hydrologically explicit frameworks and novel data sources will strengthen their capacity to support evidence-based management of freshwater fish assemblages facing accelerating environmental changes. Full article

Habitat alteration and biological invasions are two main drivers of biodiversity loss at the global scale. Eutrophication and invasive fish greatly disturb freshwater native communities. This is of particular conservation concern in the Iberian Peninsula (Portugal and Spain), where fish fauna display a high level of endemism. For this eco-region, there is a dearth of information on the interactions among water quality, physical condition and parasites of invasive fishes. Consequently, the aim of this study was to assess the effect of nutrient enrichment on health status and parasitological traits in the invasive mosquitofish Gambusia holbrooki inhabiting an Iberian river. Water (n = 18 replicates, three per site) and fish (n = 400 individuals, 33–34 ind. per site and year) samples were collected in September 2024 and 2025 along the River Bullaque (central Spain). Sampling effort was standardised among sites, with the following parameters consistent: seine and pond nets were used, deployed by wading; 10:00 solar time; 1.5 h duration; personnel (the same seven trained researchers); and weather/environmental conditions; ensuring methodological consistency and data comparability. Laboratory procedures were carried out near the sampling sites to minimise both fish stress and distortions to parasite communities. Morphological and parasitological parameters were compared between mesotrophic and eutrophic reaches (six sampling sites, three per reach). Body condition and health assessment index* were greater under eutrophic conditions. Fluctuating asymmetry (a measure of developmental instability) was significantly higher for eye diameter in the mesotrophic reach. Parasite taxonomic composition differed between reaches, with more digeneans and cestodes in the mesotrophic sites, whereas ciliates and monogeneans were more abundant in mosquitofish from the eutrophic reach. Parasite prevalence, abundance and index of life-cycle complexity (heteroxenous species) were lower in the eutrophic reach. These results strongly suggest that eutrophication can facilitate mosquitofish invasiveness. This is reflected in a variety of morphological and parasitological traits, such as better body condition, health status, developmental stability, parasite resistance and tolerance. Overall, these parameters indicate that mosquitofish is taking advantage of anthropogenic impacts to improve their level of establishment and subsequent spread throughout Iberian fresh waters. Full article

Introduction: The invasive European catfish (Silurus glanis) is actively spreading across Iberian freshwaters, with no effective management measures in place to control its growing abundance or prevent its establishment in new localities. It poses a severe threat to endemic and already endangered species, and is simultaneously a preferred target by few anglers who continuously promote its spread. The LIFE-PREDATOR project aims to stop the spread of European catfish in lentic systems in Portugal and Italy, particularly in protected areas. Objectives: This talk will present the mid-term results of the LIFE-PREDATOR in Portugal, and discuss the difficulties and future challenges to reduce the size of local populations of European catfish. Methodology: The LIFE-PREDATOR team developed several tasks in Portugal: (1) established the reference situation of fish communities in six reservoirs in the Tagus Basin, using scientific fishing, fish telemetry and eDNA-based tools; (2) determined the optimal protocols for sampling catfish; (3) implemented an early detection programme based on warning teams, data-mining and eDNA tools; (4) developed population control actions in four reservoirs; and (5) organised dissemination events for the general public, anglers, and students from kindergarten to university levels. Results: Overall, there is a grim view about recipient communities in the studied lentic systems, which tend to be dominated by invasive fish species, including common carp (Cyprinus carpio), gibel carp (Carassius gibelio), European catfish, pikeperch (Sander lucioperca), European perch (Perca fluviatilis) and largemouth bass (Micropterus nigricans). At least three new localities harbouring catfish were identified from online data-mining and warning teams. A total of 8 tons of catfish were removed by mid-June of 2025, mostly from the Natural Park of International Tagus. Outreach activities were conducted in nearly 60 schools, reaching more than 5000 students. Moreover, 67 general public events have reached more than 4500 people since the project started (September 2023). Conclusions: Despite its positive outcomes, the LIFE-PREDATOR team has encountered challenges in engaging key stakeholders such as anglers, involving local municipalities, and implementing catfish removal actions in remote areas. Difficulties and challenges in catfish management must therefore be debated in order to assure the after-LIFE implementation across Portuguese protected areas. Full article