Understanding how abiotic conditions interact with species interactions to shape outcomes of secondary contact remains a central challenge in evolutionary biology. Environmental stress may limit persistence through physiological constraints, but it can also alter competitive dynamics, determining whether closely related species can coexist. We investigated these mechanisms in two long-studied secondary contact zones between the darter species Etheostoma pulchellum and E. radiosum spp. in southeastern Oklahoma that have experienced different fates: long-term coexistence in the spring-fed Blue River versus the disappearance of E. pulchellum from Little Glasses Creek in the warmer, more variable Washita River drainage. Using critical thermal maximum (CTmax) assays, field temperature records, and standardized feeding trials in parental species, we tested whether contrasting outcomes in these systems are better explained by differences in physiological tolerance or by temperature-mediated shifts in competitive interactions. Although CTmax varied among rivers, we found no consistent species-level differences in thermal tolerance across drainages. In contrast, exploitative competition was strongly temperature dependent, with E. pulchellum dominating under cooler conditions characteristic of the Blue River, whereas E. radiosum spp. outcompeted E. pulchellum under elevated temperatures matching summer conditions in Little Glasses Creek. These results show that warming can flip competitive hierarchies, providing a mechanistic explanation for contrasting secondary contact zone trajectories and underscoring how environmental variability shapes species persistence following secondary contact.

ABSTRACTPhylogeographical patterns in North American freshwater fish are linked to the evolution of drainage configurations and have been shaped by the Pleistocene glaciations, especially throughout the Mississippi River drainage and eastern North America. This study investigated the recent phylogeographical history of Rhinichthys obtusus, Western Blacknose Dace, by integrating mitochondrial genomic DNA phylogenetics with geologic and paleoclimate data. This monophyletic species, recently determined to be genetically distinct from its sister species Rhinichthys atratulus, represents an important model to study the phylogeographic history of a North American stream fish in depth. Maximum‐Likelihood and Bayesian analysis trees based on full consensus mitochondrial genomes resolved three major clades of R. obtusus: An Eastern Great Lakes clade, a Southeast clade, and an Upper Midwest clade. Our phylogenetic analyses suggested these three clades diverged 2–1.5 million years ago during the Pre‐Illinoian glaciations, when the advancing ice sheet altered river systems and landscapes and broke up populations, constricting ancestral populations of R. obtusus to refugia in the Interior and Eastern Highland regions. Based on present and historical MaxEnt species distribution models as well as geologic evidence, recolonization into the Eastern Great Lakes and Upper Midwest regions may have primarily occurred from around 15 to 12 thousand years ago as glaciers retreated, habitat suitability increased, and river connections appeared. Our findings contribute to an understanding of the evolutionary history of Rhinichthys, and to a broader discussion of freshwater fish phylogeography in North America.

Aethycteron malleusodes n. sp. (Monopisthocotyla: Dactylogyridae) is described from the gills of the federally threatened leopard darter, Percina pantherina (Moore & Reeves) (Perciformes: Percidae), from the Cossatot River (Little River Drainage of the Red River System) in the Ouachita Mountains of Arkansas, USA. Aethycteron malleusodes n. sp. is morphologically most similar to Aethycteron malleus (Mueller (1938) by possessing a ventral bar with a posterior medial protuberance, a relatively straight male copulatory organ (MCO) with a distal spiraling sheath, and tip of the MCO with a pronounced flange. The body size and sclerites are generally smaller in A. malleusodes n. sp. and the spiraling sheath wraps around the MCO 2.5-3 times, compared to 3-4 times in A. malleus. We document the first helminth described from this threatened fish species. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:232173AF-D776-48BD-9A8E 660C1764C006.

Taxonomic studies of freshwater fish reveal that intraspecific morphological variation highlights cryptic species complexes. Here, we describe Laubuka sittaungensis, a new species of the family Danionidae, based on 23 specimens collected from a tributary of the Sittaung River drainage in Myanmar. The new species can be distinguished from the congeners by a combination of the following characters: (1) an unbranched pelvic-fin ray reaching the anus, (2) the presence of vertical bars along the side of the body in preserved specimens, (3) predorsal scales 18-20, (4) branched anal-fin rays 17½-20½, (5) precaudal+caudal vertebrae 15-16 + 18-20, and (6) smooth lower jaw. The molecular phylogenetic analyses based on mitochondrial cytochrome c oxidase I (COI) and cytochrome b (Cytb) gene sequences confirm that it is a distinct species, closely related to Laubuka tenella.

Abstract Drainage reorganization is a fundamental process shaping landscapes and redistributing continental water resources. On the eastern Tibetan Plateau, geomorphic evidence indicates that the drainage divide between China's two longest rivers, the Yangtze and Yellow Rivers, is migrating northwestward, implying that the Yangtze is capturing the Yellow River's headwaters. We test this hypothesis through integrated analysis of topography, drainage network morphology, channel steepness, and knickpoint dating using a calibrated stream‐power model. Results demonstrate that a series of river capture events between ∼1.7 and 0.8 Ma systematically transferred at least ∼30,000 km 2 of drainage area from the headwaters of the Yellow River to the Yangtze River. We attribute this reorganization to Quaternary climate change, which amplified the erosional advantage of the steeper, high‐relief Yangtze basin, triggering headward erosion. This ongoing process has reduced the long‐term average runoff of the upper Yellow River by ∼5 billion m 3 /yr, a volume that exceeds the designed annual diversion capacity of the first phase of the nearby South‐to‐North Water Diversion Project. Our findings underscore that landscape evolution exerts a first‐order, geological‐timescale control over water resource distribution, providing an important framework for assessing large‐scale water management strategies.

Freshwater gastropods are among the most imperiled organisms globally, and taxonomic uncertainty remains a major obstacle to their conservation. Elimia melanoides (Conrad, 1834), previously presumed extinct, was rediscovered in the Black Warrior River drainage of Alabama, prompting renewed interest in its conservation status. However, persistent taxonomic uncertainty has hindered listing under the U.S. Endangered Species Act. We used integrative taxonomy-including extensive field sampling, 3RAD-based phylogenomics, and morphological analysis of museum specimens-to resolve the taxonomy of E. melanoides sensu lato. Our molecular phylogenetic analyses revealed that E. melanoides, as currently conceived, comprises three distinct lineages: E. melanoides sensu stricto, Elimia hydeii (Conrad, 1834) (in part), and Elimia turgida (Haldeman, 1840), which we restore from synonymy. Comparison to historical museum specimens indicates that the extant lineage currently identified as E. melanoides is not conspecific with the taxon described as Anculosa melanoides by Conrad. We propose to follow prevailing usage and retain the name E. melanoides for the extinct taxon described by Conrad. There is no available name for the extant taxon, which we describe here as Elimia mintoni n. sp. Population genomic analyses revealed high genetic structure in E. mintoni n. sp. and E. hydeii, especially in headwater populations, while E. turgida showed no structure across its narrow range but maintains high genetic diversity. These findings have urgent conservation implications: E. mintoni n. sp. and E. turgida are valid, range-restricted species with low redundancy and representation. Our study underscores the necessity of taxonomic resolution for accurate biodiversity assessments and effective conservation planning.

Pareuchiloglanis anteanalis belonging to the genus Pareuchiloglanis, within the family Sisoridae (order Siluriformes), is a group of small benthic-dwelling freshwater fishes adapted to alpine canyon environments characterized by steep slopes, rapid currents, and marked seasonal fluctuations in water discharge between dry and flood periods. This species is primarily distributed in the Jinsha River, Dadu River, and Bailong River, all located within the upper reaches of the Yangtze River drainage. In this research, through the integration of PacBio HiFi long read sequencing and Hi-C (high-throughput chromatin capture) technology, we generated a high-quality chromosome-level genome of the P. anteanalis. The assembly yielded a genome of 873.97 Mb, with a scaffold N50 length of 50.12 Mb, covering 98.59% of the contig-level genome, were accurately mapped onto 18 chromosomes by using Hi-C data. The BUSCO analysis indicated that the completeness of the genome assembly and the annotation both reached 93.3% and 93.4%, respectively. This high-quality genomic resource provides a solid foundation for deciphering genome architecture and functional elements, thereby enabling deeper investigations into the genetic mechanisms underlying adaptation in P. anteanalis. Moreover, it offers valuable support for resource conservation, artificial propagation, and selective breeding of this native species.

We describe Glyptothorax intonsus, a new species of sisorid catfish from the Nam Mang watershed in the Mekong River drainage of Laos. The new species is distinguished from all Mekong drainage Glyptothorax by a combination of its very long nasal barbels, head and body proportions, features of the thoracic adhesive apparatus and lateral line, colouration and body tuberculation.

The results of comprehensive geoecological studies of water bodies formed as a result of mining activities are presented. It was noted that newly formed water bodies are characterized by a wide range of physicochemical parameters and variability in the structural indicators of aquatic organisms. A wide range of pH values (3.83–9.33), total mineralization (106–8693 mg/L), concentrations of chemical elements, and variability of chemical composition were established. Groups of water bodies (quarry lakes, tailings ponds, dump lakes, a flooded pit in the river floodplain and drainage streams) were determined statistically reliably (PERMANOVA, p < 0.05), differing in a number of abiotic and biotic indicators. It was concluded that the obtained results will further serve as a basis for the typification of water bodies in technogenic zones of the Transbaikal Territory.

The karst ecosystem in southwestern China is a global hotspot for cavefish diversity research, yet the origins and evolutionary history of this diversity remain poorly understood. To elucidate their evolutionary origins and history, we analyzed 183 cavefish species and their close relatives from ten clades. Our findings indicate that freshwater fishes began colonizing caves ~44 million years ago (Ma). Speciation was driven by in situ diversification, starting around 43.2 Ma, increasing sharply by ~35 Ma and 18 Ma, and peaking at ~8.3 Ma, 2.5 Ma, and 1.5 Ma. Distinct hydrological basins exhibited divergent diversification patterns. Dispersal between the Pearl and Yangtze River basins began by ~24.1 Ma, accelerated around 21 Ma, 13 Ma, and 9.6 Ma, and peaked at ~13 Ma, 5 Ma, and 2 Ma. We propose that river drainages in southwestern China developed stepwise from the late Eocene to early Pleistocene, with connectivity between the Pearl and Yangtze basins established by the late Oligocene ( ~ 26 Ma). The origin and diversification of cavefishes are closely linked to the evolution of karst landscapes, shaped by orogeny and monsoon-driven climate changes since the late Eocene. These insights are crucial for informing conservation strategies for these unique habitats under ongoing climate change.

A single quillback Carpiodes cyprinus was collected with a boat electrofisher during May 2022 from the Verdigris River, Wagoner County, Oklahoma, USA. Its gills, gall bladder, fins, integument, musculature, and other major organs were macroscopically examined for myxosporeans. The gill rakers and gill lamellae were each infected with a new myxosporean, Myxobolus arkansasense sp. n., and Myxobolus verdigrisense sp. n., respectively. Qualitative and quantitative morphological data were obtained from fresh myxospores. Molecular data consisted of a 772 base pair sequence of the partial small subunit (SSU) ribosomal RNA gene for M. arkansasense sp. n. and a 1700 base pair sequence for M. verdigrisense sp. n. Phylogenetic analysis grouped Myxobolus arkansasense sp. n. and Myxobolus verdigrisense sp. n. with myxosporeans primarily known to infect North American catostomid fishes. To date, M. arkansasense sp. n is the only member of the genus known to infect the gill rakers of C. cyprinus.

Akysis poecilurus, a new species of catfish, is described from the Lenya River drainage in southern Myanmar. It is distinguished from congeners in Myanmar by the color pattern of the body and caudal fin, as well as morphometry. Akysis poecilurus differs from congeners outside of Myanmar by pectoral-spine morphology and the color pattern of the body. This represents the eighth species of Akysis recorded from Myanmar.

Four new species of the small-sized armoured catfish genus Pareiorhina are described from mountain ranges in the Grande River drainage, upper Paraná River basin, based on morphological and molecular species delimitation methods. Molecular analyses based on the cytochrome oxidase subunit I (COI) marker recovered Pareiorhina as polyphyletic, with none of the 11 nominal species, including the 4 newly described, forming a clade with the type species Pareiorhina rudolphi. Instead, two sister clades were recovered outside P. rudolphi: one comprising species with a postdorsal ridge and unicuspid teeth, and another lacking the ridge and bearing bicuspid teeth. The four new species resemble Pareiorhina carrancas and Pareiorhina hyptiorhachis, both readily distinguished by the presence of a postdorsal ridge and simple teeth, and differ from all congeners by unique combinations of body colouration, abdominal plating, vertebral counts, pelvic girdle morphology and morphometric traits. These results underscore the underestimated diversity of the upper Paraná River basin and reinforce the need for continued ichthyofaunal surveys. Furthermore, they highlight the importance of integrating morphological and molecular data to unravel species diversity and distribution patterns of small-sized fish species inhabiting southeastern Brazilian headwaters.

Aquatic food webs typically include highly coupled fast, ‘green’ energy pathways driven by algae or phytoplankton and slower, ‘brown’ energy channels driven by detritus and terrestrial plants. Quantifying how much energy biological communities obtain from each of these pathways is essential, particularly across multiple interconnected food webs over large areas, because energy dynamics are known to influence ecosystem structure and function. Despite their importance, few studies track variance in energy channel contributions to food webs across interconnected habitats during distinct hydrologic seasons. In this study, we used tri-isotope Bayesian mixing models to quantify seasonal contributions of energy pathways to consumers in nine aquatic food webs across two river drainages in the Florida coastal Everglades. Sites span an ecosystem gradient from freshwater marshes to estuarine riverine mangroves and marine seagrass habitats. We found that green energy channels were the dominant pathway for consumers in 12 of 18 seasonal food webs, with the remaining 6 being more reliant on detrital energy channels. There were contrasting spatiotemporal trends between river networks. Shark River Slough food webs showed a clearer pattern of greener marsh food webs upstream switching to browner food webs more heavily reliant on mangrove detritus downstream. In contrast, Taylor Slough food webs showed the opposite pattern of browner marsh food webs upstream switching to greener food webs downriver and in marine seagrass habitats. Seasonal switching of the dominant energy channel was less common than expected, with 2 of 9 food webs shifting from green to brown dominance between the dry and wet season. Seasonal shifts disrupted spatial gradients in energy channel use, but the seasonal dynamics quantified in this single year study require further contextualization. Our findings provide a short but dynamic view of energy pathways in aquatic communities across the Everglades, but continued research will allow us to better predict how species, food webs, and ecological networks may respond to environmental drivers under future global change.

Two new species of the genus Sineuchiloglanis are described from two tributaries of the upper Yangtze River, China. These two new species can be distinguished from all congeners by morphological comparisons and phylogenetic analysis. Sineuchiloglanischishuiensissp. nov. can be distinguished from its congeners by the combination of the following characters: eye enlarged, with diameter 6.8–9.1% of head length (HL); interorbital width 24.1–24.8% of HL; maxillary barbel length 67.1–84.4% of HL; caudal-peduncle depth 27.1–40.3% of caudal-peduncle length; dorsal-fin rays i, 51/2; anal-fin rays i, 41/2; caudal-fin rays i, 7+8, i; gill opening extending to the base of second to third pectoral-fin elements; tip of nasal barbel not reaching anterior orbital margin; pelvic-fin tip reaching or extending beyond anus; and the abdomen slightly convex in profile. Sineuchiloglanisbaishuiensissp. nov. can be distinguished from its congeners by the combination of the following characters: head depth 42–48.4% of HL; maxillary barbel length 65.9–82.1% of HL; caudal-peduncle depth 25.9–40.6% of caudal-peduncle length; dorsal-fin rays i, 51/2; anal-fin rays i, 41/2; caudal-fin rays i, 7+8, i; gill opening extending to the base of the fourth to fifth pectoral-fin elements; tip of maxillary barbel not reaching the lower corner of the gill opening; tip of nasal barbel not reaching anterior orbital margin; and the abdomen flattened in profile. Molecular phylogenetic analysis inferred from mitochondrial Cytb gene sequences supported the validity of these two new species.

Northeastern Tibetan Plateau paleo-Yellow River drainage expansion at ~3 Ma linked to the East Asian summer monsoon intensification

Abstract Extracting coarse-resolution river drainage networks from fine-resolution DEM or DTM is essential for large-scale hydrological and environmental modeling. Flow direction upscaling methods are preferred for preserving drainage patterns, but they face significant computational challenges when handling massive fine-resolution datasets. This study introduces eCOTAT + , an enhanced version of the COTAT + algorithm, designed to improve computational performance through two key strategies: (i) tile-based domain partitioning to reduce memory usage by processing localized subsets of data sequentially, and (ii) OpenMP-based parallelization to accelerate execution using multi-core processors. The eCOTAT + was applied to a 1-m LiDAR-derived DTM covering a 40× 40 km region in northeastern Brazil (1.6 billion pixels) and upscaling it to 100 m resolution. Twelve tiling configurations and eleven parallelization schemes (1–20 cores) were tested. Results showed that intermediate tile sizes (~ 20 × 20 coarse-resolution cells) offered the best trade-off between runtime and memory demands. Tiny tiles lead to high overhead from frequent memory and file operations, while large tiles diminish the advantages of parallelization. Parallelization significantly reduced runtime up to 8–12 cores, beyond which performance declined. A novel runtime-memory elasticity metric was proposed to quantify the balance between execution time and memory use across configurations. The upscaled drainage networks retained hydrological realism compared to the fine-resolution reference, confirming that computational optimizations did not compromise output quality. The eCOTAT + algorithm enables fast and scalable flow direction upscaling for both macro- and microscale applications, facilitating the use of massive elevation datasets even in standard computing environments.

Abstract The Capibaribe and Ipojuca Rivers drain vital watersheds in the state of Pernambuco, northeastern Brazil, but are influenced by intense anthropogenic activities, particularly because they flow through municipalities in the region known as the Textile Triangle. To evaluate the spatial distributions, contamination levels, and sources of trace elements, surface sediments were collected from the two rivers and the concentrations of seven trace elements (As, Cr, Cu, Co, Ni, Pb, and Zn) were determined. Contamination levels were assessed using five indices: enrichment factor (EF), geoaccumulation index (I geo ), contamination factor (CF), pollution load index (PLI), and combined pollution index (CPI). For the Capibaribe River, Pb was considered to originate from natural sources, with the remaining trace elements presenting contamination levels ranging from low to moderate, primarily due to inputs associated with textile industry effluents and agricultural activities. For the Ipojuca River, Ni was derived from natural sources, while Cr, Cu, Pb, and Zn, at levels ranging from moderate to high, were from anthropogenic origins, especially sewage discharges. Multivariate statistical analysis was employed to distinguish the primary sources of trace element contamination, which was shown to increase in urban areas. Potential sources of contamination in both rivers also included contributions from vehicle emissions and rainwater leachate. These findings provide a comprehensive understanding of substantial contamination by trace elements and the impact of human activities in these watersheds, serving as a guide for the development of preventive and remediation policies aimed at minimizing risks to living species.

The Red River, which flows through several tectonic blocks in Southeast Asia, is considered to have formed in response to the Cenozoic tectonic reorganization of the SE Tibetan plateau. This study present new detrital zircon U-Pb geochronological data from Oligocene samples in the Red River subaqueous delta to constrain sediment provenance and paleo-drainage evolution. The U-Pb age patterns indicate that whereas the Yangtze and Cathaysia Blocks served as primary sediment sources for the Yinggehai Basin in the Late Oligocene, the Qiangtang Block contributed substantial distal detritus to the basin system. Comparative analysis with existing detrital zircon records from the Yinggehai Basin shows a notable absence of the 562 Ma age peak in Lower Miocene strata, which was prominent in the underlying Oligocene deposits. This stratigraphic discrepancy suggests a significant drainage reorganization within the Red River system, resulting from the loss of Qiangtang Block catchment areas. Middle Miocene sediments exhibit diminished 797 Ma and 970 Ma zircon age peaks relative to underlying units. This indicates reduced sediment flux from both the Yangtze and Cathaysia blocks to the Yinggehai Basin and consequent contraction of the Paleo-Red River’s drainage network. The Middle Miocene detrital zircon age spectra show remarkable consistency with modern Red River sediments, which shows that the present-day Red River drainage configuration had almost been established by this period. This source-to-sink system investigation on the northwestern corner of the South China Sea provides critical constraints on the paleogeographic evolution and drainage development of the southeastern Tibetan Plateau since the Late Oligocene.

Northern snakehead Channa argus (Cantor, 1842) is an aquatic invasive fish species in the United States with first documented occurrence in the wild in the 2000s.Management efforts to control their populations in the eastern United States are ongoing.In the Mississippi River basin, limited resources have been allocated to control its distribution, after initial detection and rapid response in Arkansas were unsuccessful.Northern snakehead distribution in the Mississippi River basin was limited to Arkansas and Mississippi until 2019 when a single northern snakehead was detected on the southern border of Missouri in the Saint Francis River drainage, the furthest northern detection.Described here are additional northern snakehead detections following public reports and subsequent monitoring in the Mingo basin of the Saint Francis River drainage, a historical braided channel and floodplain habitat of the Mississippi River with intermittently flooded bottomland hardwood forests and wetlands, and other consistent aquatic habitats.These increasing captures document the recent range expansion of northern snakehead.Most of the 11,300 ha Mingo basin consists of Mingo National Wildlife Refuge and Duck Creek Conservation Area; these areas are protected aquatic ecosystems possessing sensitive species and serve as a potential example of prioritized areas for northern snakehead control efforts.Additionally, we highlight the significance of these detections in the Mingo basin which is connected via the Castor River water-control structure to the Upper Mississippi River and may facilitate further range expansion.