North American freshwater mussels (Order Unionida, Families Margaritiferidae and Unionidae) are a diverse group of invertebrates with many species threatened by extirpation or extinction. A deeper understanding of freshwater mussel ecology will enhance the effectiveness of conservation strategies. While older life stages of fishes have been studied as hosts for the parasitic life stage of unionids, larval fishes have received little attention. The aims of this study were to: (1) determine if larval Yellow Perch (Perca flavescens) support metamorphosis of Fatmucket (Lampsilis siliquoidea) larvae (glochidia) in the laboratory, and (2) measure the natural glochidia infection frequency on wild-caught stream and river larval fishes. Using standard methods (laboratory infection in a bath of suspended glochidia), we determined that metalarval Perca flavescens support Lampsilis siliquoidea glochidia metamorphosis, and describe low natural glochidia infection frequency among larval fishes living in Rice Creek and the St. Croix River. This study and others across three continents have demonstrated that larval fish can be naturally parasitized by glochidia; however, this study documents glochidial metamorphosis. These results suggest that fish larvae may be an important resource for unionid recruitment because larval fishes are much more abundant than older life stages in some habitats during the spring. Our observation of glochidia metamorphosis on metalarval fish shows that early life stages of fishes are not necessarily a ‘parasite sink’ or ‘ecological trap’ for glochidia. Larval fishes may be an unsuspected—but possibly not underutilized—host. As unionids are distributed globally, interactions between the young life stages of fishes and mussels may occur on a worldwide scale. Although the scope of our study is limited, the importance of larval fishes to unionid recruitment is unclear and should be studied further.

Fish are highly diverse aquatic organisms that are integral to global food systems and have been extensively scientific investigation. The region of Dir and Malakand Khyber Pakhtunkhwa was examined for the first time, expanding the cytochrome c oxidase I (COI) gene as a DNA barcoding tool for accurate species documentation in conjunction with traditional morphological diagnostic techniques. Fish specimens were collected from three distinct local streams including, River Panjkora, the Gumbat Khwar River and the Shogram Khwar River in Malakand Division, Khyber Pakhtunkhwa (KP), Pakistan. A total of fourteen species (Barilius vagra, Garra gotyla, Channa punctata, Channa marulius, Crossocheilus diplocheilus, Pethia conchonius, Carassius auratus, Schizothorax plagiostomus, Glyptothorax cavia, Glyptosternon reticulatum, Paraschistura cristata, Paraschistura abdolii, Mastacembelus armatus and Acanthocobitis botia) belonging to 13 genera, five families and four orders were identified by using morphological and COI based analysis. The diversity indices indicated rich ichthyofauna, with a Simpson index of 0.92 and a Shannon–Wiener index of 0.80. S. plagiostomus showed the highest relative density, while A. botia was the least abundant. COI sequencing produced a 594 bp fragment with an overall GC content of 46.37%, containing 41% variable sites and a transition/transversion ratio of 1.5. The mean genetic divergence was 0.24%, supporting clear species-level differentiation. Furthermore, phylogenetic analysis of each family was performed to validate the usefulness of the COI in species identification and their evolutionary relationship. This study demonstrates the effectiveness of the integration of molecular analysis with a traditional morphological taxonomic method to identify fish robustly and reliably as well as the need to have advanced techniques such as mitochondrial genome methods and the use of a broader geographical region.

The introduction of invasive mollusc to non-native habitats can have adverse impacts on native species. This successful introduction is facilitated by habitat degradation linked to human activities. The hypothesis that it had been introduced through the importation of exotic plants was suggested after the first scientific report of Melanoides tuberculata in Reservoir No.3 of Ouagadougou. However, to date, information on the current status of its invasion and the factors favoring its establishment and dispersal in Centre Region remains unknown. This study aimed : (1) to assess Reservoir No.3 and the changes in factors that could impact the establishment of M. tuberculata at the site, (2) map the current distribution of M. tuberculata in Centre Region of Burkina Faso, and (3) identify the key environmental and anthropogenic factors driving its establishment and spread. We surveyed 12 sites from November 2020 to September 2021. At each site, molluscs were collected and physicochemical parameters were measured. We assessed the anthropogenic impacts and environmental conditions at each site. Collected molluscs were taken to the laboratory for identification and counting. The relationships between species occurrence and variables were analysed using the random forest algorithm. The findings indicate that from 1993 to 2021, temperature, precipitation, and conductivity have increased, while dissolved oxygen has decreased significantly in the reservoir. We found that M. tuberculata has successfully colonised 10 out of the 12 surveyed sites since 2017. Its occurrence was significantly associated with habitat type, specific richness, substrate type, atmospheric temperature, and fishing activities. Furthermore, M. tuberculata demonstrated tolerance to a range of abiotic stressors. Our findings suggest that habitat type, anthropogenic activities, and connectivity play a more important role in the spread of M. tuberculata in Centre Region than physicochemical parameters. This study provides a critical baseline for monitoring and managing the invasive species in this region.

ABSTRACT Human activities have put considerable pressure on the dynamics and overall health of dominant fish species in aquatic ecosystems. In this study, we investigated the influence of habitat structures on fish abundance and diversity in Wanzum River, a rural River within the North Central eco-region of Nigeria. We selected four sampling stations along the river that represent various levels of anthropogenic activities. The samples were collected for a period of twelve (12) months (December 2021–November 2022) and were analysed using standard methods and procedures. A total of 1,470 individual fish belonging to 19 species, 14 families and 9 orders were recorded. Cichlidae was the most abundant family, represented by Oreochromis niloticus (22.99%), Tilapia zillii (20.27%) and Hemichromis fasciatus (3.94%). Clariidae was the second most dominant family, with Clarias gariepinus (15.71%) and Clarias anguillaris (8.29%). The diversity indices revealed the highest species richness at Station 1 (18 species) and the lowest richness at Station 3 (14 species). The Shannon–Weiner index values ranged from 2.012 (Station 3) to 2.317 (Station 1), while Simpson’s index indicated relatively high diversity across stations (0.813–0.865). Canonical correspondence analysis showed that fish distribution was influenced by depth, dissolved oxygen, biochemical oxygen demand, pH, and electrical conductivity, though the relationships were not statistically significant (p > 0.05). These findings highlight that fish abundance and diversity in the Wanzum River are shaped by habitat structures and anthropogenic pressures. Effective management of habitat quality is therefore critical for sustaining fish biodiversity and ensuring the ecological health of rural rivers in North Central Nigeria.

ABSTRACT To evaluate whether photosynthesis-induced calcium‒phosphorus (Ca‒P) coprecipitation in Hydrilla verticillata can be harnessed for eutrophic freshwater phytoremediation, we conducted controlled light incubator experiments to determine how key environmental factors regulate this process. We manipulated four drivers—light intensity (66 vs. 110 μmol m⁻² s⁻¹), inorganic carbon (HCO₃−: 0 vs. 50 mg L⁻¹ = 0.82 mM), calcium (CaCl₂: 0 vs. 50 mg L⁻¹) and phosphorus (K₂HPO₄: 0 vs. 1 mg L⁻¹)—and quantified the responses in dry weight total phosphorus (DWTP), total ash phosphorus (TAP) and its fractions: water-soluble H₂O-P, organic NaOH-P and calcium-bound HCl-P. The key results revealed that a higher light intensity (110 vs. 66 μmol m⁻²​​​​​​ s⁻¹) exerted a stronger influence on H₂O-P and HCl-P fractions (by percentage) than on NaOH-P or DWTP in the light‒phosphorus interaction experiments. This suggests that enhanced photosynthesis under high light boosted P adsorption and promoted coprecipitation with supersaturated CaCO₃. For the inorganic carbon × phosphorus interactions, TAP and H₂O-P peaked under high inorganic carbon and high P conditions. Inorganic carbon contributed more to H₂O-P (45.13%) than did P (35.33%), indicating that inorganic carbon-enhanced photosynthesis primarily drove P adsorption. In the calcium‒phosphorus experiments, the maximum HCl-P and TAP occurred under high Ca (50 mg L⁻¹) and high P conditions. Calcium contributed more to HCl-P than did P, identifying Ca as the primary driver of Ca-P coprecipitation in H. verticillata. In summary, photosynthesis-induced Ca-P coprecipitation in H. verticillata is a synergistic, multifactor process—highlighting Ca as a key regulator of remediation efficiency. Ecologically, H. verticillata is particularly effective at reducing P bioavailability via Ca-P coprecipitation in calcium-replete waters, while in calcium-limited systems, P removal relies more on adsorptive/absorptive pathways. These findings highlight the need to integrate nutrient availability and plant physiological processes for optimizing phytoremediation of eutrophic freshwater.

ABSTRACT Quantifying how wetlands regulate the magnitude, variability, and responsiveness of water temperature is essential to understanding their ecological functions and informing climate-adaptive management. To investigate the mechanisms underlying wetlands’ thermal influence, we monitored groundwater, open water, channel, and outlet temperatures across seven palustrine wetlands in Oregon’s forested Cascades in summer 2024. We identified early- and late-summer thermal phases based on water temperature shifts and used principal component analysis to define site-level thermal gradients. Generalized least squares modeling and multivariate dispersion analysis further identified landscape drivers and unexplained within-site temperature variability, respectively. We compared this variability with the Oregon Rapid Wetland Assessment Protocol (ORWAP) indicators of thermoregulation. This analytical approach explores how spatial scales influence distinct aspects of thermal regimes, with broad-scale factors such as elevation and air temperature shaping overall temperature magnitude, while site-level features such as vegetation structure and hydrology regulate day-to-day variability and thermal stability. Large wetlands with ponded surface water generally stabilized outflow temperatures despite relative warming compared to smaller wetlands with relatively more permanently saturated vegetated zones, which exhibited cooler but more variable atmospherically-driven changes. Within-site sub-seasonal shifts between early and late summer were minor relative to differences across sites. While comparing rapid-assessment scores to water temperature variability resulted in low explanatory power, vegetation structure indicating shade most consistently associated with lower temperature variability. These findings highlight both merits and limitations of ORWAP, and restoration trade-offs between creating open-water habitat and sustaining cool-water conditions in headwater systems.

ABSTRACT Macrophyte dynamics in rivers are expressed through spatiotemporal gradients that reflect the functioning of freshwater ecosystems. In Mediterranean rivers, characterized by irregular low-flow periods and sudden floods, these gradients strongly influence the distribution and structure of aquatic vegetation. In Morocco, however, the ecology and distribution of aquatic macrophytes remain poorly documented, particularly in the Upper Oum Er-Rbia Basin. This study analyzes the spatiotemporal dynamics of macrophyte diversity along this basin using thirteen monthly surveys (June 2018–June 2019) conducted at fourteen sites in five rivers spanning spring-fed, perennial, and temporary streams. Macrophyte diversity and evenness were quantified using Shannon–Weaver (H′) and Pielou’s (J′) indices and evaluated with a multivariate framework: PERMANOVA and NMDS to test community differentiation between rivers and months, PCA to summarize hydrochemical and hydromorphological gradients, and CCA to relate species composition to environmental drivers. The results reveal marked spatial structuring, with upstream–downstream organization and strong river-specific assemblages. Geographic position within the basin emerges as a key determinant of macrophyte diversity, while hydrochemical status and hydromorphological conditions—including flow velocity, water depth, channel substrate, and disturbance pulses associated with floods and low-flow phases—shape within-river trajectories of composition and cover. This work provides the first basin-scale ecological assessment of macrophyte distribution in the Upper Oum Er-Rbia and highlights the importance of integrating spatial and temporal processes when diagnosing and managing Mediterranean river ecosystems.

Springs and other groundwater-dependent ecosystems have received much less attention than rivers, lakes, and wetlands. Among freshwater springs, those that flow directly into oceans have been studied even less than those that flow into freshwater systems, the former being less common. The goal of this study was to document the fish assemblages of several springs that flow into the Gulf of Mexico and to compare these assemblages with those of springs that flow into rivers prior to flowing into the Gulf. To describe the fish assemblages, I deployed GoPro cameras along the first 650 m of each of 24 springs, five with a terminus in the Gulf and 19 that had a terminus in a river. On the 12-min footage from each camera, I counted the maximum number of individuals of each species that occurred in a frame together. From these counts, I calculated the total number of fish, species richness, and diversity. Across the geographic range of the study, springs varied in conductivity by more than an order of magnitude, but for any given spring, the conductivity was related more to the proximity of the spring head to saltwater than to a marine or riverine terminus. The total number of fish, species richness, and diversity of the springs did not differ between the two categories of springs; instead, species richness and diversity were related more to the size of the spring, the temperature (which is influenced by latitude), and the percent substrate coverage by primary producers. However, the composition of fish assemblages differed, with the addition of euryhaline species and some loss of sunfish (Lepomis sp.) in springs with more saline water. In addition, the springs in the most urban area had relatively high abundances and species richness of nonnative fishes. Therefore, the physical, chemical, and biological characteristics of springs, and the potential for human-caused disturbance, may be more important than the springs' exact terminus in predicting the composition of the fish assemblage. In particular, connection to saltwater and high salinity is important for migration of euryhaline fish species into a spring, but this connection need not be direct.

ABSTRACT The present study investigated the monthly dynamics of algal diversity in relation to the physicochemical parameters of the Dor River, a key freshwater tributary of the Indus Basin in Khyber Pakhtunkhwa, Pakistan. Water and algal samples were collected monthly for one year from two hydrological distinct stretches of the river, extending from Barengali to Dhamtor (freshwater zone) and from Domail to Tarbela Dam. Standard limnological protocols and taxonomic microscopy were employed to identify Chlorophyta species, quantify their community structure, and evaluate the environmental influences on the algal distribution. A total of 23 algal species belonging to 3 classes, 8 orders and 14 families were recorded, with Chlorophyceae being the most dominant group. Diversity indices revealed the highest species richness and Shannon diversity during autumn and late winter, while monsoon months exhibited reduced diversity associated with increased turbidity, dilution, and ionic fluctuations. The physicochemical variables, such as pH (7.1–7.87), conductivity (254–444 μS/cm), turbidity, and nutrient levels, displayed clear seasonal patterns, significantly shaping the algal abundance, frequency, and importance value index (IVI). Chlorophycean taxa, including Scenedesmus bijuga, Ulothrix zonata and Oocystis borgei, showed strong ecological plasticity and served as indicators of stable water quality. Overall, the Dor River maintained a healthy ecological status with strong resilience to seasonal variations, although monsoon-driven disturbances temporarily altered the algal community structure. This study highlights the value of integrating algal bioassessment with water quality monitoring as an effective tool for evaluating freshwater ecosystem health and guiding conservation strategies for the Dor River.

Microplastics (<5 millimeters) are a prominent contaminant globally, negatively affecting terrestrial, freshwater, and saltwater systems. Virtually no research has investigated microplastic contamination in remote, forested headwater streams in Pennsylvania. At five streams in central Pennsylvania, we assessed microparticle/microplastic contamination across three trophic levels: tertiary consumers (Salvelinus fontinalis), secondary consumers (Rhinichthys atratulus), and primary consumers (Trichoptera, Plecoptera, Ephemeroptera, Odonata, and Megaloptera). From 100-meter unblocked reaches, fish (n = 46 total, n = 21 tertiary consumers, n = 25 secondary consumers) and benthic macroinvertebrates (n = 106 total, Trichoptera: n = 40, Plecoptera: n = 39, Ephemeroptera: n = 22, Odonata: n = 4, Megaloptera: n = 1) were collected using standard wadeable stream sampling procedures. Fish gastrointestinal (GI) tracts and macroinvertebrates were digested in 10% potassium hydroxide (KOH) solutions, and microparticles were identified after vacuum filtration and visualization with a dissecting microscope at 45× magnification. Microparticles were categorized as microplastics at two of our five sites using μFTIR spectroscopy on Salvelinus fontinalis, Rhinichthys atratulus, and Plecoptera. Our efforts resulted in the identification of 159 microparticles and 5 microplastics among all heterotrophs across all sites. Microparticle contamination was highest among secondary consumers with no heterotroph or site effect on microparticle count (p > 0.05). The distribution of microparticle morphology and color combinations varied significantly across the heterotroph groups, and there were negative correlations between brook trout morphological characteristics and microparticle count (e.g. total length: r = –0.62, p = 0.03; weight: r = –0.62, p = 0.03; gastrointestinal tract weight: r = –0.66, p = 0.02). Negative relationships between size characteristics among all fish and microparticle count were expressed by δ15N analysis (r = –0.37, p = 0.03). We believe that the disparity in microparticle contamination by fish size and between trophic levels is driven by divergences in feeding strategies, ontogenetic shifts in feeding behavior, and contrasts in life histories. Overall, our data highlight the presence of microplastic/microparticle contamination in remote, forested headwater streams in Pennsylvania without any known upstream point-source pollution.