Search Results (80)

Over 40% of freshwater fish species in Europe are currently at risk of extinction, highlighting the need for improved conservation planning. This study examines whether the threat status is associated with life-history and ecological traits across 580 autochthonous (native and endemic) freshwater fish species in European inland waters. Using data from FishBase and the IUCN Red List, we assessed associations between threat level and both categorical (e.g., migratory behavior, commercial importance, reproductive guild, and body shape) and numerical traits (e.g., maximum length, weight, age, growth parameters, and maturity traits). Significant, though modest, associations were identified between species threat level and migratory behavior and reproductive guild. Non-migratory species exhibited higher median threat levels, while amphidromous species showed a non-significant trend toward higher threat, suggesting that limited dispersal ability and dependence on fragmented freshwater networks may increase extinction vulnerability. Species with unclassified reproductive strategies also showed elevated threat levels, possibly reflecting both actual risk and underlying data gaps. In contrast, body shape and trophic level were not significantly associated with threat status. Critically Endangered species tend to be larger, heavier, and mature later—traits characteristic of slow life history strategies that limit population recovery. Although length at maturity and maximum age did not differ significantly among IUCN categories, age at maturity was significantly higher in more threatened species, and growth rate (K) was negatively correlated with threat level. Together, these patterns suggest that slower-growing, later-maturing species face elevated extinction risk. Overall, the findings underscore that the threat level in European freshwater fish is shaped by complex interactions between intrinsic biological traits and external pressures. Trait-based approaches can enhance extinction risk assessments and conservation prioritization, especially in data-deficient freshwater ecosystems facing multifaceted environmental challenges. Full article

Food-based environmental enrichment (EE) is a valuable strategy for stimulating foraging behaviour in fish under human care, as it increases the challenge of food acquisition and encourages prolonged engagement in this activity. Curimbas (Prochilodus argenteus) and pacus (Myleus micans) are fish species for which ex situ maintenance has become an important conservation measure. In this context, providing EE is essential to ensure high welfare standards. This study aimed to assess the effects of food enrichment on the behaviour of these two endemic species from the São Francisco River basin in Brazil. Behavioural data were collected across three experimental phases, including baseline, enrichment, and post-enrichment. Slow-dissolving food items known as “acorns” were introduced during the enrichment phase. Both species exhibited a marked reduction in inactivity throughout the study. For curimbas, the enrichment phase was associated with increased foraging, elevated agonistic interactions, and greater use of specific tank areas. Among pacus, inactivity significantly declined during the enrichment period. Additionally, the presence of visitors influenced behavioural patterns, promoting foraging activity while reducing inactivity and interactions with the enrichment device. These findings reinforce the value of incorporating environmental enrichment to promote the welfare of freshwater fish in public aquariums. Full article

Freshwater fish is facing a great crisis due to the looming threat of biodiversity loss. Certain important target areas are difficult to survey owing to their accessibility, making them susceptible to data deficiencies. In this study, we surveyed 52 sites using environmental DNA techniques to investigate fish biodiversity in the Chishui River Basin of the Yangtze River, China. A total of 96,031 valid fish sequences were read, resulting in the identification of 77 species belonging to six orders, 62 genera, and 18 families. The dominant orders were Cypriniformes, Siluriformes, and Perciformes. Among the identified fishes, 71 were native and six were exotic, with the native fishes including 16 endemic fishes from the upper reaches of the Yangtze River. The Shannon–Wiener and richness indices of the tributaries in the upstream section were significantly higher than those of the tributaries in the downstream section. The Datong River is the most diverse secondary tributary of the Chishui River. Among the environmental factors in the Chishui River Basin, altitude and electrical conductivity had the greatest influence on fish diversity (p < 0.01). Our findings highlight the application of environmental DNA technology to modern biodiversity surveys and illustrate that the Chishui River Basin is primarily affected by environmental factors at this stage. However, continuing efforts are needed to protect freshwater biodiversity, and additional research is required to better understand the complex interplay between human activity and environmental factors. Full article

Species belonging to the crustacean infraorder Astacoidea represent taxa of particular interest from a conservation point of view, such as the threatened European crayfish (i.e., Austropotamobius pallipes), and at the same time include invasive taxa having highly negative impacts where they are introduced. Among the latter, some freshwater-dwelling species seem to show some abilities to tolerate high salinity levels, such as Procambarus clarkii Girard, 1852. By using metadata and field observation, this review will investigate whether the alien P. clarkii can threaten coastal waters. Specifically, we will shed light on P. clarkii’s (1) invasiveness, (2) its dispersal pattern, (3) its tolerance to salinity, and (4) its ecological plasticity as an invasive species in relation to estuaries. This new habitat colonization is also possible as P. clarkii has been observed to survive up to 20 ppt of water salinity and a maximum of 30–35 ppt with its lifetime drastically reduced. As a result, P. clarkii colonizes different ecosystems globally, reaching estuarine and coastal ecosystems due to active and passive transport by human and animal vectors. Due to recent discoveries of alien crayfish in estuarine and coastal waters, monitoring activities have become mandatory to preserve coastal habitats and all the aquatic resources (e.g., limicolous birds, endemic fish, fishery and aquaculture activities) inhabiting therein. Full article

Background: Onychostoma virgulatum is an endemic freshwater fish in South China, first described as a new species in 2009. However, little is known about this species and no complete mitochondrial genomes of O. virgulatum has been reported to date. This study seeks to elucidate the characteristics of the mitochondrial genome of O. virgulatum and investigate the phylogenetic relationships within the Acrossocheilinae subfamily, particularly among the genera Onychostoma, Acrossocheilus, and Folifer. Methods: The mitochondrial genome of O. virgulatum was sequenced and assembled. We analyzed its sequence length, nucleotide composition, and evolutionary relationships within the Acrossocheilinae by incorporate data from 58 previously published mitochondrial genomes. Results: The complete circular sequence is 16,606 bp in length and contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a typical control region (D-loop), all arranged in a typical order. The genomic base composition is biased toward A+T content (56.5%), with 31.4% A, 25.1% T, 27.4% C, and 16.1% G. Among about 30 Acrossocheilina species, the nonsynonymous (Ka) to synonymous substitutions (Ks) for all 13 protein-coding genes (PCGs) are significantly less than 1, suggesting strong negative or purifying selection in these species. The phylogenetic trees inferred from the mitogenome and 13 PCGs of 58 Acrossocheilinae sequences consistently indicate that: (1) O. virgulatum shares the closest genetic relationship with Onychostoma barbatulum; (2) Acrossocheilinae species are clustered into three major clades, with neither Acrossocheilus nor Onychostoma forming monophyletic groups. Conclusions: This study provides new insights into the taxonomy and phylogenetic relationships of Acrossocheilinae, particularly O. virgulatum, contributing to a better understanding of the systematics, origin, and evolution of this subfamily. Full article

Determination of the ecological state of any water body is crucial for its adequate conservation and is, moreover, required by the Water Framework Directive. Employment of multimetric indices, which integrate various anthropogenic threats to water systems with the responses of different elements of fish communities, improve our understanding and allow us to monitor the ecological state of freshwater bodies. However, design of multimetric indices that describe the ecological state of water bodies based on fish communities has already proved difficult for the Mediterranean region for several reasons, including the frequent presence of species-poor and ecologically tolerant fish communities, high endemicity and a serious lack of localities with undisturbed fish communities. The development of an ecological state index for natural water bodies in Croatia based on fish as a biological element which we present in this paper was also hindered by similar obstacles, particularly due to exceptionally high endemicity present in rivers of the Adriatic watershed, the great number of distinct water types, and significant anthropogenic pressures. Nevertheless, based on comprehensive sampling of fish communities throughout Croatia and following appropriate statistical procedures, we were able to identify stressors acting on certain water bodies, as well as responses of fish communities to them, and, finally, describe the ecological state of natural water bodies throughout Croatia. We also propose measures that will most likely help in achieving improvement and/or maintenance of the ecological states of these water bodies. Full article

The genus Cyprinus encompasses economically vital freshwater fish species; yet the phylogenetic relationships and evolutionary history of many taxa within this genus remain unresolved. To address this knowledge gap, we reconstructed the molecular phylogenetic and estimated divergence times using complete mitochondrial cytochrome b (CYTB) sequences of 76 Cyprinidae specimens, within Cyprinidae, including 4 outgroup species. Phylogenetic trees were reconstructed using maximum likelihood (ML) and Bayesian inference (BI) methods, while divergence times were estimated using a Bayesian relaxed molecular clock approach. The results confirmed the monophyly of the genus Cyprinus. The relationships among C. (Cyprinus) multitaeniata, C. (C.) pellegrini, C. (C.) acutidorsalis, and three Erhai Lake species (C. (C.) longipectoralis, C. (C.) barbatus, and C. (C.) chilia) were resolved with strong support. Cyprinus (C.) multitaeniata is basal. The species in Erhai Lake form a monophyletic group, and C. (C.) acutidorsalis is at the top of the phylogenetic tree. The taxonomic delineation within the genus Cyprinus remains controversial, particularly regarding the proposed division into two subgenera (Cyprinus and Mesocyprinus), which has been historically constrained by limited specimen availability for Mesocyprinus. Our comprehensive phylogenetic analysis reveals significant evolutionary divergence patterns: The genus Cyprinus diverged from Carassius during the 56.9 Mya. Notably, the Erhai Lake radiation species (C. (C.) longipectoralis, C. (C.) barbatus, and C. (C.) chilia) originated during 2.03 Mya, while the Lake Biwa endemic C. (C.) haematopterus demonstrates 8.7 Mya. We identified a late Pleistocene speciation event (0.75 Mya) in C. (C.) acutidorsalis, coinciding with its adaptation to brackish water ecosystems. The native C. (C.) pellegrini of Xingyun Lake and Chilu Lake may have originated 4.8 Mya, when the ancient lake that its ancestral population inhabited became isolated. These findings provide robust molecular evidence supporting the recognition of two evolutionary distinct subgenera within Cyprinus. Full article

In recent years, microplastic pollution has become one of the major global concerns and represents a complex, multidimensional, and multisectoral reality. The considerable existing data relating to microplastic pollution in matrices such as water and soil suggests that microplastics are widespread globally, but there are several knowledge gaps regarding their actual distribution mostly in remote locations far from sources. In this review we examine current knowledge on microplastic pollution in the Antarctic continent. Antarctica, the unique continent not permanently anthropized, is the southernmost part of the planet but its geographic isolation does not protect against the harmful impact of human activities. This continent is characterized by limited internal pollution sources but high-burden external routes of contaminants and represents a unique natural laboratory to analyze how pollution can reach every part of the biosphere. This review reports the presence of microplastics in organic and inorganic matrices not only at marine level (water, sediments, benthic organisms, krill, and fish) but also in freshwater (lakes, rivers, snow, and glaciers) highlighting that microplastic contamination is endemic in the Antarctic environment. Microplastic pollution is of great environmental concern everywhere, but the characteristics of remote ecosystems suggest that they could be more sensitive to harm from this pollution. Full article

Simpsonaias ambigua (Salamander Mussel) is a freshwater mussel of the Family Unionidae endemic to North America, and it is considered endangered across most of its range. This species is unique among the Unionidae, because it uses the salamander, Necturus maculosus (Mudpuppy), as its larval host rather than fish like all other unionids. The overall goal of this study was to obtain baseline data on the current distribution and life history traits of S. ambigua in Ontario, Canada. These data are critical for future recovery efforts to protect, restore, or augment populations of S. ambigua across its range. Conventional survey methods were adapted to target S. ambigua, and an additional method was employed to detect this species: trapping N. maculosus and inspecting for signs of encysted glochidia. Both methods were successful at detecting S. ambigua when they were present. Furthermore, Simpsonaias ambigua’s life history traits were investigated, and more information is now available on the reproductive timing windows related to gonad and glochidia development and the host infestation period, as well as on longevity. Full article

Hydrological changes caused by dam construction are among the primary drivers of global freshwater biodiversity decline. To assess the current status of fish community diversity and examine the impacts of cascade hydropower development on fish diversity, this study employed environmental DNA (eDNA) technology from 2023 to 2024 to conduct seasonal surveys at 18 sampling sites across six river segments separated by five dams in the downstream section of the Fujiang River. The study aimed to uncover the temporal and spatial dynamics of fish diversity and community structure, as well as to analyze the influence of environmental factors on these patterns. The results identified 84 fish species spanning 60 genera, 19 families, and 7 orders, including 2 nationally protected species, 11 endemic species of the upper Yangtze River, and 13 alien species. The cascade dams were found to have significantly reduced fish diversity compared to historical records, with a marked decline in native species and a rise in alien species, contributing to the miniaturization and homogenization of fish communities. Environmental factor analysis revealed that chemical oxygen demand (COD), dissolved oxygen (DO), total dissolved solids (TDS), electrical conductivity (EC), and reservoir formation time were significant drivers of fish community structure and diversity. This study provides essential baseline data on fish diversity under the influence of cascade hydropower development in the Fujiang River. It also offers valuable insights into the current status of fish resources and supports efforts in fish conservation and aquatic ecosystem management in the region. Full article

Dioctophyme renale, also known as the giant red kidney worm, is a parasitic nematode that infects various mammalian hosts, including dogs, and is associated with an important renal pathology. This case report describes the first known D. renale parasitism in a 5-month-old puppy from Uruguay. The animal presented with hematuria and was diagnosed through abdominal ultrasonography, which revealed characteristic ring-like structures in the right kidney, and urine sedimentation, which confirmed the presence of D. renale eggs. The dog underwent nephrectomy to remove the adult female parasite. While D. renale is typically associated with a prepatent period of 3.5 to 6 months in canines, this case is notable for the early presence of a mature parasite in a young dog. This finding suggests the possibility of a shorter prepatent period or alternative transmission routes, such as transplacental or lactogenic transmission. The case highlights the importance of including dioctophymosis in the differential diagnosis of young puppies in endemic areas, especially near freshwater sources. Given the zoonotic potential of D. renale, this case emphasizes the need for surveillance of this parasite, particularly in regions where untreated water and fish consumption pose risks to both animals and humans. Full article

Endemic fish are important components of freshwater ecosystems because they contribute to biodiversity and provide vital ecological functions. The Carolina Madtom, Noturus furiosus, is a small catfish endemic to the Neuse and Tar river basins of North Carolina, USA. Three previous surveys over the past 60 years have shown declining occurrence and abundance in the basins, and as such, the species was listed as federally endangered in 2021. To provide critical information to guide Carolina Madtom conservation and recovery strategies, we surveyed 36 sites (75 locations) in both basins to (1) determine the current distribution of the Carolina Madtom, (2) develop occupancy models to estimate probability of detection and occurrence of the species throughout its range, and (3) determine its instream habitat use and suitability. We collected 59 Carolina Madtom during snorkel surveys in the Tar River basin and none from the Neuse River basin, indicating that Carolina Madtom populations are still declining in both occurrence and abundance throughout their historical and recent range, especially in the Neuse River basin. Occupancy modeling estimated low occupancy probability (0.35), while detection probability was high (0.81). Carolina Madtom occupied slow-to-moderate velocity water over sand and gravel substrate, using cobble and woody debris as cover. Habitat suitability distributions quantified the most suitable ranges of microhabitat parameters for Carolina Madtom occupancy. A comparison of available suitable habitat in the two river basins revealed that adequate suitable habitat was available in both basins, suggesting that other factors such as pollution or predation from the non-native Flathead Catfish Pylodictis olivaris, may be contributing to population declines. The application of our results will aid in management and recovery actions for the species. Full article

The fish fauna of Rio de Janeiro has been extensively studied, resulting in a comprehensive database of species collected over more than three centuries. This study aimed to provide a checklist of species, to identify patterns of diversity and the distribution of freshwater ichthyofauna, to delineate biogeographic units, and to explore changes in faunal composition among different areas. Analyzing data from ichthyological collections and the literature on original species descriptions revealed 206 freshwater fish species: 183 native and 23 allochthonous. The checklist includes updated species names. The sampling effort in Rio de Janeiro is extensive, especially in coastal lowlands. The findings indicate that inventory work is still needed in some areas, particularly within the Rio Paraíba do Sul basin. Seven bioregions of freshwater ichthyofauna were identified, including a major region of higher species richness and smaller areas with higher endemism of restricted-range species. This biogeographic assessment underscores the diverse and distinctive freshwater fish fauna in the basins of Rio de Janeiro, with well-defined biogeographic units. Full article

Some East Asian rivers experienced repeated rearrangements due to Indian–Asian Plates’ collisions and an uplift of the Tibetan Plateau. For the upper Changjiang (Yangtze/Jinsha River), its ancient south-flowing course and subsequent capture by the middle Changjiang at the First Bend (FB) remained controversial. The DNA of freshwater fishes possess novel evolutionary signals of these tectonic events. In this study, mtDNA Cyt b sequences of endemic Schizopygopsis fish belonging to a highly specialized grade of the Schizothoracinae from the eastern Tibetan Plateau were used to infer the palaeo-drainages connectivity history of the upper Changjiang system. Through phylogenetic reconstruction, a new clade D of Schizopygopsis with three genetic clusters and subclusters (DI, DII, DIIIa, and DIIIb) were identified from the upper Yalong, Changjiang, and Yellow Rivers; the Shuiluo River; the FB-upper Changjiang; and the Litang River; respectively. Ancient drainage connections and capture signals were indicated based on these cladogenesis events and ancestral origin inference: (1) the upper Yalong River likely acted as a dispersal origin of Schizopygopsis fish to the adjacent upper Yellow and Changjiang Rivers at ca. 0.34 Ma; (2) the Litang River seemed to have directly drained into the upper Changjiang/Yangtze/Jinsha River before its capture by the Yalong River at ca. 0.90 Ma; (3) the Shuiluo River likely flowed south along a course parallel to the upper Changjiang before their connection through Hutiao Gorge; (4) a palaeo-lake across the contemporary Shuiluo, Litang, and Yalong Rivers was inferred to have served as an ancestral origin of clade D of Schizopygopsis at 1.56 Ma. Therefore, this study sheds light on disentangling ambiguous palaeo-drainage history through integrating biological and geological evidence. Full article

Hydropower plants (HPPs) create barriers across rivers and fragment aquatic ecosystems, river reaches and habitats. The reservoirs they create slow the flowing water and convert the riverine into lacustrine ecosystems. The barriers created by HPPs interrupt the seasonal migrations of many fish species, while the reservoirs drive away fish species that are dependent on flowing water habitats. This paper assesses the distribution of fish species in the 3S rivers—Sekong, Sesan and Sre Pok, in Cambodia, Laos and Viet Nam—using IUCN Red List-assessed species distribution by HydroBasin Level 8 from the freshwater reports of the Integrated Biodiversity Assessment Tool (IBAT) and their connectivity with the Mekong. There are currently 61 commissioned dams in the 3S basins and a further 2 under construction, 23 of which are larger than the 30 MW installed capacity. A further 24 HPPs are proposed or planned in these basins. The changes in connectivity caused by the dams are measured by adapting the River Class Connectivity Index (RCI_CLASS); the original connectivity of the 3S basin taking into account the two major waterfalls in the Sesan and Sre Pok rivers was estimated at 80.9%. With existing dams, the connectivity has been reduced to 23.5%, and with all planned dams, it is reduced further to 10.9%. The resulting re-distribution of fish species occurring throughout the 3S basins is explored, by focusing on migratory guilds and threatened and endemic fish species. With all dams built, it is predicted that the total numbers of species in HydroBasins above the dams will be reduced by 40–50%. The Threatened Species Index is estimated to fall from over 30 near the confluence of the three rivers to less than 10 above the lowest dams on the 3S rivers. The analysis demonstrates how widely available global and regional datasets can be used to assess the impacts of dams on fish biodiversity in this region. Full article