Odonates (damselflies and dragonflies) are constrained by their requirement for freshwater for reproduction, though adult stages may disperse over dry land. In this study, we tested whether odonate assemblages were more similar in closely located ponds than in more distant ponds, and whether ecological variables predicted pond assemblage structure. To evaluate this question, we collected odonates in both the adult and nymph stages at 16 ponds clustered in four groups in Ocala National Forest in the summer of 2021 and 2023. We collected adults with aerial nets and nymphs with dipnets. We also measured physical and biological characteristics of the ponds, including the presence of potential predators (fish, tadpoles, crayfish). The number of individuals collected varied widely with pond size, but species richness and diversity varied little between groups. Odonate assemblages were slightly more similar if they were within the same group, although this pattern was stronger for dragonflies than for damselflies. With respect to the ecological characteristics of the ponds, adult odonate species richness was related to the area of open water present at a pond. For the nymphs, damselfly abundance, species richness and diversity were related to pond depth, coverage with lilies and small fish presence, whereas dragonfly abundance, species richness and diversity were related to pond size, coverage with grasses and the presence of sunfish. These results suggest that both dispersal and the physical and biological conditions of the habitat determine odonate structure in Ocala ponds. Given the pressure on ecosystems due to development and the limited research on odonates in Florida, we hope that these results will contribute to the support of odonate diversity in Florida.
Wetlands around Kibale National Park support biodiversity, regulate water quality and sustain livelihoods but face increasing anthropogenic pressures. This study assessed wetland-use and cover change (between 2016 and 2025), macrozoobenthos diversity and physico-chemical water quality in Bigodi, Kahunge and Businge wetland systems within a 5 km buffer of Kibale National Park, Kamwenge District, Uganda. Sentinel imagery was classified to determine cover change. Sampling sites were classified as high quality, medium quality and low quality using the wetland rapid assessment procedure (WRAP). These categories represented a disturbance gradient based on ecological and anthropogenic characteristics of the wetland sites. Macrozoobenthos were sampled in dry ( January 2025) and wet (April 2025) seasons across all quality sites a scoop net, identified to family level and analyzed for diversity indices and average score per Taxon (ASPT). Physico-chemical parameters were measured in situ and in a laboratory. Wetland-use and wetland-cover (WUWC) change varied: Bigodi wetland system gained 1.17% wetland, Kahunge wetland system lost 3.58% and Businge wetland system lost 8.47% with +7.64% grassland increase. Macrozoobenthos abundance was highest in Bigodi (1189 individuals, 22 families), moderate in Kahunge (538, 21 families) and lowest in Businge (216, 21 families). Seasonal effects were significant in Kahunge (diversity p = 0.002) and Businge (diversity p = 0.033, Average Score Per Taxon p = 0.048), while ASPT differences across disturbance gradients were significant only in Businge (p = 0.004). Physico-chemical parameters generally met National Environment Management Authority standards, with minor nitrite exceedance in isolated low-quality sites. A principal component analysis showed system- and season-specific water chemistry: Businge dry-season linked to higher nitrates (mean = 0.413 ± 0.393 mg/L) and hardness (mean = 175 ± 144.3); Bigodi wet-season to higher Total dissolved solids (mean = 142.5 ± 80.6 ppm) and nitrates (mean = 0.675 ± 0.496 mg/L). Despite acceptable water quality, significant wetland loss, especially in Businge, threatens ecological integrity, warranting targeted habitat protection and stricter wetland-use controls.
This study provides an integrated ecological assessment of a mountain river by combining responses of fish and macroinvertebrate communities as biological quality elements (BQEs). Macroinvertebrates showed significantly higher taxa richness than fish, with cumulative richness increasing downstream, whereas fish species richness displayed no clear longitudinal pattern. Trichoptera, Ephemeroptera, Coleoptera and Diptera were the most diverse macroinvertebrate groups, with Brachycentrus subnubilis, Cheumatopsyche lepida and Serratella ignita as the most abundant taxa. Eight species typical of mountain rivers were recorded in the fish community. Diversity, evenness and dominance patterns highlighted differences between the two BQEs: macroinvertebrate communities showed high diversity with evenly distributed taxa, while fish communities exhibited moderate diversity and strong dominance of Alburnoides bipunctatus and Barbus balcanicus along the entire reach. Notably, two Balkan regional endemic macroinvertebrates (Dina dinarica and Gammarus balcanicus) and several protected fish species (Cottus gobio, Sabanejewia balcanica, Barbus balcanicus, Alburnoides bipunctatus, Salmo trutta and Squalius cephalus) were recorded. Both BQEs were consistent in indicating favorable ecological conditions. Spearman rank correlations between corresponding fish- and macroinvertebrate community metrics were not statistically significant. However, Wilcoxon signed-rank tests revealed consistent, although non-significant, directional differences, with higher diversity and evenness in macroinvertebrates and stronger dominance in fish. Although fish communities in upper mountain catchments are naturally species-poor and limited in standalone assessment power, their combined use with macroinvertebrates may provide a more comprehensive and ecologically meaningful evaluation. The results contribute to the evidence supporting of multi-BQE approaches in mountain river assessment, highlighting the complementary information provided by fish and macroinvertebrate communities.
Aquaculture plays an increasingly important role in global food security, particularly in East Africa, where cage culture of Nile tilapia (Oreochromis niloticus) in Lake Victoria has expanded rapidly over the past decade. However, the sustainability of this production system may be threatened by emerging fungal and oomycete diseases that remain poorly understood in the region. This review synthesizes current knowledge on fungal and oomycete infections potentially affecting cage-cultured Nile tilapia in Lake Victoria, with particular emphasis on five key pathogens: Aphanomyces, Saprolegnia, Branchiomyces, Fusarium, and Exophiala species. Following PRISMA guidelines, a systematic literature search of PubMed, Web of Science, Scopus, Google Scholar, and EMBASE databases covering the period 2000–2025 identified 1,200 records. After duplicate removal and eligibility screening, 85 full-text studies were included in the final review. Of these, only 15 studies (17.6%) specifically addressed Lake Victoria or its immediate basin, highlighting a substantial regional knowledge gap. Available evidence indicates that fungal and oomycete pathogens may contribute to fish morbidity and mortality, particularly under conditions of poor water quality, environmental degradation, high stocking densities, and other stressors common in intensive aquaculture systems. Reported clinical manifestations include skin ulceration, cotton-like lesions, gill necrosis, granulomatous inflammation, and respiratory impairment. Although Fusarium and Exophiala species are recognized as opportunistic pathogens of potential public health relevance, there is currently no direct evidence of fish-to-human transmission within the Lake Victoria region; occupational exposure through contaminated water, biofilms, and handling of infected fish remains the more plausible route of concern. This review further identifies major gaps in diagnostic capacity, fragmented transboundary disease surveillance across Tanzania, Kenya, and Uganda, and limited farmer awareness regarding disease recognition and affordable control measures. Overall, the findings emphasize the urgent need for baseline epidemiological studies, standardized diagnostic protocols, antifungal resistance monitoring, and integration of fungal disease surveillance into One Health frameworks to support sustainable aquaculture development in East Africa.
Reba carp, Cirrhinus reba, is an economically important endemic fish species in Bangladesh. A 758 bp fragment of the mitochondrial DNA control region (mtDNA) was analyzed to assess the genetic diversity, intraspecific genetic structure, and historical demography of C. reba from three wild populations in Bangladesh. Individual samples were collected from two rivers (the Padma and Karatoya) and one haor (Dingapota) basin in Bangladesh. A total of 38 haplotypes were detected among the 89 individuals analyzed, which included 56 substitutions. Analysis revealed that the haplotype diversity (h) of the Padma River population was high (0.961 ± 0.026), followed by the Karatoya River (0.749 ± 0.055) and Dingapota Haor (0.753 ± 0.059) populations. On the contrary, nucleotide diversity (π) was high in the Karatoya population (0.007 ± 0.004), followed by the Padma River (0.005 ± 0.003) and Dingapota Haor (0.003 ± 0.002) populations. Pairwise F ST comparisons and AMOVA results indicate that the Karatoya population was significantly different from the Padma and Dingapota Haor populations. However, a statistically insignificant difference was observed between the Padma River and Dingapota Haor populations. The minimum spanning tree showed two different clusters of haplotypes. Phylogenetic analysis also revealed two distinct clades, one of which was composed of haplotypes from Padma River and Dingapota Haor, and the other from the Karatoya River. Demographic analysis indicated that the Padma River and Dingapota Haor populations underwent recent population expansion, as evidenced by significantly negative Tajima's D and Fu's Fs values and mismatch distribution analyses. In contrast, the Karatoya River population exhibited signs of weaker expansion, indicated by a significant negative Tajima's D but a positive, non-significant Fu's Fs value. Evolutionary factors, species biology, and hydrological characteristics of water bodies can all contribute to the formation of a structured population. Present findings can provide baseline information for initiating management strategies for this commercially important species in Bangladesh.
Freshwater ecosystems such as rivers, streams, and lakes are biodiversity hotspot and are of global ecological importance but increased human population have exerted significant pressure on these unique resources. This study assessed the ecological health of Etswan River using integrated habitat quality, physicochemical characteristics and macroinvertebrate assemblages for eight months (July 2025 to February 2026). Four sampling stations were selected long the river reach and were investigated using standard ecological and statistical approaches. Qualitative Habitat Evaluation Index (QHEI) scores ranged from 54% to 68%, indicating an ecologically stressed but viable system. Most of the physicochemical parameters were spatially uniform indicating a relatively homogeneous environment except for dissolved oxygen, depth, and total hardness that showed significant difference (p < 0.05) between the sampling stations. A total of 659 macroinvertebrate individuals from 24 species were encountered and the most abundant group was Hemiptera, followed by Mollusca and Odonata. Diversity indices indicated that there was a moderate level of species diversity among the stations as station 4 recorded the highest (19 species) in term of number of species while station 3 recorded the lowest (16 species). Station 1 had the highest number of individuals (214) followed by station 3 (157), station 4 (151) and the lowest number of individuals (137) was observed in station 2. Canonical Correspondence Analysis (CCA) showed that the dissolved oxygen, depth and nutrient concentrations had a significant effect on the distribution of the macroinvertebrates (p < 0.05) with more than 85% of the total variation accounted. Our findings show that although the river still possesses certain ecological integrity, rising anthropogenic activities are gradually altering habitat structure, deterioration of water quality, changes in macroinvertebrate community structure, reduced biodiversity, and increased dominance of pollution-tolerant taxa, although there is need for continuous monitoring of the river for sustainable management of the ecosystem.
We experimentally tested whether lake sturgeon (Acipenser fulvescens), a native species of conservation concern, could use associative learning to detect and respond to predator odors and alarm cues from other species (kairomones) to reduce predation risk. Alarm cues emitted by round goby (Neogobius melanostomus), a historically geographically separated non-native species in the Great Lakes region and white sucker (Catostomus commersonii), a common native co-distributed species with lake sturgeon were used. Lake sturgeon larvae were experimentally exposed to odorants in four replicated experimental treatments (1) conspecific lake sturgeon alarm cue and predator rock bass (Ambloplites rupestris) odors, (2) historically geographically separated round goby alarm cue and predator rock bass odors, (3) historically geographically co-distributed white sucker alarm cue and predator rock bass odors, or (4) predator rock bass odor only with distilled water as a negative control. Larval lake sturgeon survival was highest in experimental trials where lake sturgeon larvae had prior exposure to lake sturgeon alarm cue and rock bass predator odors. Survival rates for larval lake sturgeon from odor treatment groups exposed to geographically separated round goby alarm cue and groups exposed to geographically co-distributed white sucker alarm cue were significantly higher than those that were exposed to rock bass predator odor alone (with no conspecific or heterospecific prey odorant exposure). Results demonstrate that the presence of hetero-specific alarm cues can have considerable influence on survival and population levels of recruitment of taxonomically diverse stream prey communities during highly vulnerable early life stages. Management efforts designed to increase survival of numerically depressed species during critical early life stages may benefit from managing river ecosystems to promote high abundance and recruitment of co-distributed prey taxa.
Background Mitochondrial DNA is widely used in comparative genomics, molecular taxonomy, and phylogenetic analysis because of its conserved structure, maternal inheritance, and informative sequence variation. In fishes, mitochondrial markers such as COX1 are especially useful for examining sequence divergence, codon usage bias, and evolutionary relationships.Methodology In this study, mitochondrial sequence data from five fish species, Danio rerio, Cyprinus carpio, Carassius auratus, Oncorhynchus mykiss, and Tachysurus vachellii, were retrieved from GenBank and analyzed using Geneious Prime (Version: 2025.0.2). Sequence length variation, nucleotide composition, COX1 multiple sequence alignment, amino acid distribution, codon usage bias, and phylogenetic relationships were assessed. Phylogenetic reconstruction was performed using the Neighbor-Joining method with 1,000 bootstrap replicates, and Bayesian inference was added to improve tree robustness.Results The analyzed sequence lengths ranged from 11,776 bp to 13,964 bp, with a mean ungapped length of 13,296.0 bp. Overall nucleotide statistics showed an AT-rich composition, with A + T content of 57.2% and GC content of 42.8%. The COX1 alignment produced a final length of 1,554 bp, with a mean pairwise identity of 48.5% and 16.0% identical sites. Codon usage analysis showed non-random codon preference, with leucine as the most abundant amino acid and GCC, CTA, ATT, AAA, CAA, and TGA as strongly preferred codons. The phylogenetic tree showed that Carassius auratus and Cyprinus carpio formed a moderately supported cluster, while Oncorhynchus mykiss grouped with this clade with stronger support.Conclusion The findings confirm that mitochondrial sequence analysis is useful for examining nucleotide bias, codon preference, COX1 variation, and evolutionary relatedness among fish species. The addition of Bayesian inference and clearer branch support improves the robustness of the phylogenetic interpretation.
Hurricanes have increased in frequency and magnitude due to anthropogenic climate change. These events can cause outbreaks of parasitic diseases in humans, but little is known about how they impact parasite abundances for wildlife hosts. The southeastern United States Gulf region has been affected by hundreds of hurricanes in the past 50 years, with frequency and intensity increasing through time. Prior studies have quantified the response of wildlife parasites to individual hurricanes, but have never systematically evaluated whether these effects are consistent across hurricanes or different from control conditions. From the Royal D. Suttkus Fish Collection at the Tulane University Biodiversity Research Institute, we selected and performed parasitological dissections of 1197 preserved fish across seven fish species collected between 1963 and 2005 from the Pearl River in Louisiana. We evaluated the effect of hurricanes on parasite abundance using generalized linear mixed models that contrasted responses of fish parasites to 24 hurricanes against control conditions. We found that change in parasite abundance in response to a hurricane was dependent upon parasite taxonomic group and transmission strategy, with direct life cycle parasites (copepods and monogeneans) negatively impacted by hurricanes on short time scales, while complex life cycle parasites (acanthocephalan, cestode, nematode, trematode adult and trematode metacercaria) were not affected by hurricanes. This investigation of hurricane impacts on parasitism in wildlife populations across a 42-year period identifies parasite traits that modulate resistance to hurricane conditions. Continued anthropogenic climate change will cause more frequent and intense hurricane events, which our research suggests could lead to decreased abundances of direct life cycle parasites, affecting riverine fish parasite community structure. Declines of parasites may signal broader ecosystem stress under increasing hurricane frequency, with cascading effects on fish hosts and other interacting species.
Man-made barriers, such as dams, alter the water flow dynamics of rivers, affecting fish communities and habitat connectivity. In 2011, flooding associated with Hurricane Irene caused the failure of the Cornwall Lower Reservoir dam, which subsequently altered the flow of Black Rock Brook in Black Rock Forest, New York. Fish diversity, abundance, and individual size were surveyed by electrofishing in 2010 before dam failure and again in 2017, providing a rare opportunity to compare fish assemblage and morphometrics following barrier loss and determine whether the observed patterns were localized above or below the former dam. Fish length and weight were compared between years using Welch’s two-sample t-tests, species diversity was evaluated using Shannon diversity indices, and richness and evenness were summarized using observed species counts, Pielou’s evenness, and rank-abundance curves. Blacknose dace captured in March 2017 were significantly shorter and lighter than those captured in April 2010 in both the downstream reach and the pooled upstream reaches. Observed species richness and Shannon diversity were also lower in 2017 at both locations, and rank–abundance patterns indicated greater dominance by a small number of taxa. The surveys differed in both year and seasonal timing, so the observed patterns cannot be attributed solely to dam failure and may also reflect broader temporal or environmental variation. Nevertheless, the findings highlight the value of pre-disturbance baseline data for documenting biological differences following barrier loss in small headwater streams. For stream managers, the results demonstrate the importance of long-term monitoring and repeated seasonal sampling for distinguishing dam-related responses from broader variation and informing management decisions.
Lake Malawi National Park (LMNP) was created in 1980 to safeguard the rich freshwater fish biodiversity in Lake Malawi. However, the park is increasingly affected by anthropogenic activities in the surrounding upland areas and by encroachment, which threaten its ecological integrity. Despite this, limited information exists on temporal changes in fish abundance, species richness, diversity and assemblage structure across multiple islands and depth gradients within the park. This study assessed variations in fish populations at Mumbo, Domwe and Thumbi West Islands using surveys conducted in 2021 and 2025. At each site, transects were established parallel to the shoreline at depths of 3, 12 and 20 m. Along each transect, 2 × 2 m quadrats were placed at predetermined intervals, and all the fish observed within each quadrat were identified, counted and recorded. Differences in species richness and diversity across years, sites and depths were analysed using three-factor analysis of variance (ANOVA). A negative binomial generalized linear model (GLM) was used to evaluate the effects of year, site and depth on species abundance. Multivariate analyses examined variations in the fish assemblages and dominant species. Fish counts declined significantly by 47% between 2021 and 2025 (p < 0.001); however, species richness or diversity remained stable. Likewise, fish abundance was significantly lower at Mumbo, whereas species richness remained relatively stable across sites but declined significantly with increasing depth. The fish assemblages differed significantly across years, sites and depths. A total of 134 species were recorded, the majority being cichlids, with 93 species classified as Least Concern and 13 requiring conservation attention. These findings highlight the importance of LMNP as a critical conservation refuge for Lake Malawi; however, the decline in fish abundance warrants further investigation into potential drivers and calls for continued monitoring and adaptive management.
This study adopted Generalized Dissimilarity Modeling (GDM) to analyze the effects of spatial and environmental factors on the total beta diversity of phytoplankton functional groups (FGs) across the Chishui River Basin on the Yunnan-Guizhou Plateau of China. Following Baselga’s partitioning framework, we decomposed beta diversity into turnover and nestedness components and calculated community dissimilarity using the Sørensen dissimilarity coefficient. A total of 16 phytoplankton functional groups were identified throughout the sampling period, including 14 groups detected in the wet season and 11 in the dry season. The total beta diversity of phytoplankton functional groups was markedly higher in the wet season than in the dry season, while no significant seasonal differences were observed in the relative contributions of turnover and nestedness. GDM outputs revealed that hydrodynamic and suspended sediment conditions dominated community variation during the wet season, with environmental filtering acting as the primary structuring driver. Suspended solids and flow velocity constituted the key regulators of wet-season beta diversity, whereas total phosphorus was the dominant limiting factor in the dry season. Additionally, spatial factors exerted weaker explanatory power over beta diversity in the wet season relative to the dry season. This research provides fundamental data support for aquatic ecological health assessment and targeted watershed management planning for the Chishui River Basin.
Riverine fish diversity and community composition are strongly influenced by environmental conditions, yet such information from southern Malawi remains limited despite its usefulness in determining the health status of the river. This study assessed fish abundance, diversity and community composition in the Ruo River and Lichenya River and examined key environmental drivers influencing fish assemblages. Fish were sampled using a 1.5-mm mesh seine net. Physicochemical parameters, including temperature, dissolved oxygen (DO) and pH, were measured in situ, while total dissolved solids (TDS), total suspended solids (TSS), nitrate, nitrite, ammonia, total phosphorus and chlorophyll-a (Chl-a) were analyzed in the laboratory. Fish diversity, abundance and community composition between the two rivers were compared using an independent t-test, while multivariate analyses were used to examine differences in fish assemblages and identify environmental drivers. Results showed significantly higher fish diversity and abundance in the Ruo River compared to Lichenya (p < 0.05), and fish assemblages differed significantly between the two rivers (R = 0.62, p < 0.001). Environmental variables, including TDS and phosphorus, were identified as key predictors of fish community structure (p < 0.05). These findings demonstrate that physicochemical conditions play an important role in shaping fish diversity and assemblage patterns in riverine ecosystems. Continued monitoring of environmental drivers is therefore essential for informing sustainable management and conservation of riverine fisheries.
River systems in the Japanese archipelago feature steep gradients and narrow valleys, creating a tight spatial linkage between aquatic habitats and riparian forests' vertical structure. However, how adult aquatic insects utilize the lateral and height (2D) space within these topographically constrained ecosystems remains largely unexplored. This study quantified the spatial distribution of adult Ephemeroptera, Plecoptera, and Trichoptera in a mountain area in Kumamoto, Japan, by considering both lateral distance from the water and vertical height above the ground. The abundance patterns of the dominant taxa were determined using sticky traps deployed at varying lateral distances (0-95.7 m) and vertical heights (0.04-9.89 m). Our results revealed most adult insects were laterally concentrated on the water surface and at the water edge, whereas they were not restricted to lower strata. Moreover, an increase in the abundance of Heptageniidae (Ephemeroptera) toward higher strata is demonstrated. However, Rhyacophilidae (Trichoptera) were strongly concentrated near the channel and at low heights. Perlodidae (Plecoptera) showed no significant responses to spatial variables. These findings demonstrate differences among taxa in their spatial distribution patterns ranging from above the water surface to within riparian forests, even in steep mountain areas. Consequently, biodiversity conservation in these environments requires maintaining habitat heterogeneity, including riparian vegetation-provided 2D structures, rather than focusing solely on lateral buffer zones.
Western Grebe (Aechmophorus occidentalis) and Clark's Grebe (Aechmophorus clarkii) populations have declined across their range, and they are species of high conservation concern. Cascade Reservoir in central Idaho supports one of the largest breeding colonies of Aechmophorus grebes in North America (and the largest in Idaho), but few offspring are produced from the colony in most years. Low fecundity and little natal recruitment may be the proximate cause of Aechmophorus grebe population declines, but the ultimate cause of low recruitment is not known. One hypothesis for the low fecundity at Cascade Reservoir (and at other grebe colonies in the region) is that waves on freshwater breeding lakes inundate nests and cause pairs to abandon their nests. We tested that hypothesis by examining whether nest survival was negatively associated with changes in daily water level, daily peak wind speed and daily peak wind direction (i.e. winds that push water into the breeding colony). We also included daily mean temperature and daily total precipitation to evaluate a more general hypothesis that weather events caused nest failures. We used aerial imagery obtained from repeated drone flights to create encounter histories for 3888 Aechmophorus grebe nests to then estimate daily nest survival and evaluate whether daily water level, daily peak wind speed and daily peak wind direction (as predicted by the wind-driven wave hypothesis) were important causes of nest failure relative to other factors that commonly affect daily nest survival in birds. Nesting success was alarmingly low and we found some support for the wave inundation hypothesis; the results suggest that nesting attempts are more likely to fail on days with precipitation combined with winds blowing into the colony. Our results are the first to show that wind and precipitation affect the nest fate of Aechmophorus grebes.
Shovelnose sturgeon (Scaphirhynchus platorynchus) and related endangered pallid sturgeon (S. albus) are species of interest in the highly modified Missouri River. Scaphirhynchus sturgeon require long distances of riverine habitat for the development of drifting free embryos along with suitable foraging habitat during the subsequent transition to exogenous feeding. Working with specimens collected by the US Army Corps of Engineers and Nebraska Game and Parks Commission, we examined diet composition of age-0 (<12 cm) sturgeon at four reaches in the lower Missouri River to examine the potential role of prey acquisition at this vulnerable life stage. In general, Ephemeroptera were more represented at reaches further upstream in the lower Missouri River, whereas Diptera larvae were the dominant prey item in reaches downstream. Body condition, as measured by total lipid content and length-weight regressions, exhibited spatial differences in 2016 but not in 2017. Even with differences in prey frequencies and numbers consumed, percent consumption regardless of prey type remained consistent among reaches within years, but was overall higher in 2016 when river discharge was greater. Although temporal and spatial differences were observed in condition, comparisons using previous data from 2014 and 2015 suggest that these condition results were not driven by the longitudinal variability in prey composition as the reaches below Kansas city yielded relatively high and low lipid values despite the limited consumption of ephemeropteran prey relative to upstream reaches. Although it is unknown if any of the observed differences affected survival, our results, coupled with previous work, suggest that age-0 sturgeon can opportunistically forage in the lower Missouri River.
Understanding the ecological characteristics of freshwater fishes and quantifying their habitat requirements are important for effective restoration and management of freshwater ecosystems. Habitat suitability indices (HSIs) have been widely developed to estimate environmental flows and optimal habitats for freshwater fishes in South Korea. However, there still remains a demand for more comprehensive HSIs that represent species-specific habitat selection using a robust statistical approach. Here, we developed HSIs for 14 freshwater fish species using a large dataset collected from 195 study sites between 2007 and 2024. Based on regional- and local-scale environmental variables, the study sites were classified into two stream types with distinct environmental characteristics: sand-bed and gravel-bed streams. We then developed generalized (global) and habitat type-specific (group) HSIs using a resource selection function (RSF) approach fitted with a generalized linear mixed model (GLMM). The developed HSIs captured the ecological characteristics of 14 fish species, including both broadly distributed species and species mainly associated with gravel-bed streams. Three HSIs (global, sand-bed, and gravel-bed) were developed for seven species that occurred across a broad range of habitats, whereas the other seven species observed rarely in sand-bed streams were represented by the global and gravel-bed HSIs only. This study provides comprehensive and stream habitat-specific HSIs that contribute to better estimations of suitable habitats and environmental flows. Although these results only focused on stream fishes in South Korea, the RSF-GLMM framework and stream type classification approach may be applicable to other systems with comparable hydrological, geomorphic and ecological gradients.
Heavy rainfall significantly affects aquatic environments in urban lakes. To investigate the changes in the underwater light environment of shallow urban lakes under heavy rainfall disturbances, this study examined two heavy rainfall events in May 2023 at Qingshan Lake, a typical urban lake in the middle reaches of the Yangtze River. Spatiotemporal patterns of the water-quality indicators and light-environment parameters were analyzed before and after rainfall. Results indicate that: (1) Heavy rainfall significantly altered the water quality and eutrophication status. Near combined sewer outfalls, water pollution inputs were more direct, with higher total nitrogen, total phosphorus (TP) and chlorophyll a (Chl-a), permanganate index (CODMn), suspended solid (SS) and the comprehensive trophic-level index (TLI(Sigma)) values, but lower water transparency (SD). All indicators showed unimodal variations, with faster responses near discharge points. (2) Underwater light environment near shoreline discharge points responded more sensitively. After rainfall, light conditions deteriorated significantly, while the lake center showed stronger lag effects. (3) Submerged light radiation exhibited exponential attenuation with band selectivity: UV-A and near-infrared light decayed the fastest, while green-to-red (500-700 nm) decayed slowest. The euphotic-zone depth (Z(eu)) and the photosynthetically active radiation attenuation coefficient (K-d [PAR]) were significantly affected by the eutrophication status. (4) Influencing factors varied spatially. Near discharge points, Chl-a and CODMn dominated, while at the lake center, TP and SS dominated. Most factors showed significant positive correlation with K-d and negative correlation with Z(eu). (5) In the study area, light environment gradually returned to pre-rain levels 24 to 36 hours after rainfall. However, external pollutant input from combined storm-sewage systems near the shoreline has markedly accelerated the degradation of the light environment. This study reveals patterns and driving mechanisms of urban lake light environments under heavy rainfall, providing theoretical support for ecological restoration and precise light-environment regulation in shallow urban lakes.
Erythrocyte nuclear abnormalities (ENA) serve as sensitive biomarkers of genotoxic and physiological stress in fish. However, little is known about the extent to which age influences the frequency of ENA in species with different life-history traits. In this study, we investigated age-dependent ENA frequency in the peripheral blood of six freshwater fish species (C. carassius, S. erythrophthalmus, A. alburnus, R. rutilus, A. brama, and P. fluviatilis) collected from two sites of the Styr River (Ukraine). Fish age was determined from scale annuli, while ENA were assessed using the micronucleus test. To quantify the relationship between age and ENA frequency, we applied generalized linear models (GLMs) with a Poisson error structure. Statistically significant positive effects of age were observed in S. erythrophthalmus, A. alburnus, and A. brama, indicating cumulative erythrocytic damage with advancing age. By contrast, no significant trends were detected in R. rutilus, C. carassius, and P. fluviatilis, suggesting species-specific protective mechanisms. The combined GLM further confirmed an overall increase in ENA with age. These findings highlight interspecific variability in erythrocyte nuclear integrity among freshwater fish across their lifespan and support the use of ENA data for ecological monitoring.
Monopisthocotylans were examined from the gills of 336 specimens of 12 species of madtoms within the ictalurid catfish genus Noturus from western drainages of the Mississippi River in Arkansas, Kansas, Nebraska, and Oklahoma, U.S.A., as follows: 63 N. flavus of the subgenus Noturus; 39 N. exilis, 28 N. gyrinus, 22 N. lachneri, and 47 N. nocturnus of the subgenus Schilbeodes; and 26 N. albater, 18 N. eleutherus, 40 N. flavater, 2 N. maydeni, 23 N. miurus, 11 N. placidus, and 17 N. taylori of the subgenus Rabida. Ligictaluridus pricei (Mueller, 1936) was found on specimens of four of the 12 (33%) species of madtoms: N. exilis, 13 of 39 (33%); N. gyrinus, two of 28 (7%); N. nocturnus, two of 47 (4%); and N. maydeni, two of 2 (100%). Noturus nocturnus and N. maydeni represent new host records for L. pricei. A contingency table analysis indicated significantly less prevalence of infection (X2 = 12.3, P = 0.0004) of L. pricei on species of Rabida (two of 137 [1%]) than Schilbeodes (18 of 136 [13%]). The common occurrence of un-infested species of Rabida residing among syntopic Ameiurus and Schilbeodes potentially serving as reservoir hosts for L. pricei suggests that genetic susceptibility may be involved in its absence in most species of Rabida compared to Schilbeodes, although factors such as host size and microhabitat may also substantially influence prevalence. A single specimen of Crinocleidus crinicirrus (Kritsky and Leiby 1973), previously found only on the centrarchid Lepomis megalotis, was found on N. flavater. These records from N. maydeni and N. flavater represent the first monopisthocotylans reported from the subgenus Rabida, although N. flavater is probably an accidental host for C. crinicirrus.
