Aims Limnology and Freshwater Biology is an international peer reviewed open access journal that publishes original articles, reviews, and short communications in the interdisciplinary area of limnology. It links several scientific disciplines including hydrobiology, ichthyology, microbiology, sanitary microbiology, cellular and molecular biology, ecology, genetics, geology, physics and chemistry in an integrated fashion, to address critical issues related to freshwater ecosystems of lakes, rivers, wetlands and reservoirs. Scope hydrological, hydrochemical and geochemical aspects of aquatic ecosystems; molecular and classical biology of ecosystem research; systematics and ecology of aquatic ecosystems; natural and anthropogenic impacts on water systems and resources; paleolimnology and history of the environmental development; field and laboratory studies, and modelling.
This work is distributed under the Creative Commons Attribution-NonCommercial 4.0 International License.
Paleohydrology of the Manych Strait in the Khvalynian basin of the Caspian Sea during the Late Pleistocene
The paper discusses controversial issues of the paleohydrology of the Manych Strait—a key element in the water exchange system between the Khvalynian basin of the Caspian Sea and the Neoeuxinian basin of the Black Sea during the Late Pleistocene. Special attention is paid to two parameters: the maximum level of the Khvalynian transgression and the height of the spillway threshold through the Manych depression. Geological-geomorphological analysis, digital terrain modelling, and hydraulic modelling in the HEC-RAS system allowed reconstructing scenarios of Caspian water discharge through the Manych valley. The modelling results indicate that the most probable maximum level of the Caspian Sea during the Early Khvalynian transgression was approximately 40 m a.s.l. with a spillway threshold at 31 m a.s.l. Hypothetical limits of the discharge capacity of the Manych Strait channel of the Khvalynian Caspian basin were also calculated. The results can be used in further research.
Copyright (c) 2026 Limnology and Freshwater Biology https://creativecommons.org/licenses/by-nc/4.0
Problems of biological invasions in the fish fauna of southern Vietnam: the example of the Dong Nai River basin
Biological invasions of fish are among the key drivers of transformation in freshwater ecosystems, particularly in regions with intensive aquaculture development and high anthropogenic pressure. The aim of this study was to assess the extent of introduction and degree of naturalization of non-native fish species in the Dong Nai River basin (southern Vietnam), as well as to identify patterns of their spatial distribution and main pathways of introduction. Ichthyological sampling was conducted in April–May 2025 at 56 stations in the upper and middle reaches of the Dong Nai River, including the Da Nhim and Da Dang rivers, their tributaries, and lentic water bodies in Dong Nai and Lam Dong provinces. A total of 17 non-native fish species were recorded across 13 of the 17 surveyed areas. The highest diversity of introduced species was observed in large water bodies subjected to significant anthropogenic impact, particularly in Tri An Lake (11 species), as well as in the middle reaches of the Da Nhim River and the Dai Ninh Reservoir (6 species each). In contrast, the number of non-native species was considerably lower in highland areas of the Central Highlands (1–3 species), while no alien species were recorded in water bodies within Cat Tien National Park. Most species exhibited low to moderate occurrence frequency; however, two species—guppy (Poecilia reticulata Peters, 1859) and Nile tilapia (Oreochromis niloticus (Linnaeus, 1758))—showed very high prevalence. The results indicate a substantial scale of biological invasions in the Dong Nai River basin. Aquaculture and the aquarium trade are identified as the primary sources of non-native fish introductions, while their spatial distribution is strongly associated with the level of anthropogenic impact and the type of water body.
Functional digestive morphology and feeding intensity of the halfbeak Zenarchopterus clarus (Hemiramphidae) in a tropical estuarine habitats, southern Vietnam
This study examines the functional digestive morphology and feeding intensity of the halfbeak Zenarchopterus clarus (Hemiramphidae) in a tropical estuarine habitats of southern Vietnam. A total of 892 specimens were collected monthly from August 2024 to July 2025 at two estuarine sites. The species exhibited a superior mouth with an elongated lower jaw, dense conical dentition, well-developed pharyngeal tooth plates, and numerous gill rakers. The digestive tract consisted of a muscular esophagus and a short intestine, lacking a clearly differentiated stomach, indicating rapid processing of soft prey. Feeding intensity was evaluated using the gut-somatic index (GI) and analyzed with generalized linear mixed models. The model indicated significant variation in GI (p < 0.001). The GI differed significantly between sexes and sampling locations, with higher values in females and at Dam Doi. Although the season had no significant main effect, a significant sex × season interaction indicated contrasting seasonal feeding patterns between males and females. Morphological traits and GI collectively suggest that Z. clarus is adapted for surface-oriented feeding on small, mobile prey in dynamic estuarine environments. However, the feeding strategy was inferred from morphological traits and GI, as diet composition was not directly examined. These findings provide baseline insights into the digestive morphology and feeding ecology of an estuarine hemiramphid fish.
A decade of Philippine freshwater goby research (2010–2022): a systematic review and meta‑analysis of ichthyofaunal surveys
Freshwater goby (Family Gobiidae) is one of the diverse and widespread fish species in rivers and lakes, with economic values ranging from ornamental and subsistence provisions. Several ichthyofaunal surveys have been conducted in the Philippines; however, no systematic review and meta-analysis was performed to analyze freshwater goby species richness over fish species richness. Following the PRISMA Protocol, twenty–three (23) studies were assessed and statistically analyzed using JASP Version 0.18.3. Each paper was reviewed to identify study sites, goby genera, diversity indices (Shannon, Pielou’s evenness, and Simpson), and physicochemical parameters, with correlations analyzed across fish species, goby species richness, and diversity indices. Results revealed that most freshwater goby studies take place in Luzon, and the genus Glossogobius is the prevalent goby species at most study sites. The diversity index for introduced fish species ranged from low to medium, as indicated by the enriched biodiversity index score from Guerrero (2014). In terms of physicochemical parameters, all values generally met the standards set by DAO 2016-08. However, the forest plot revealed that the effect size was entirely on the positive side of zero, with a combined effect size of 0.46, suggesting a moderate impact. The funnel plot indicated an asymmetrical pattern among studies, suggesting potential publication bias. Analysis suggests that goby diversity in the Philippines is high in terms of species richness, with a moderate effect size when compared to overall fish species richness based on the collated studies. Taking into account the high publication bias observed, we recommend including more studies from Southeast Asian countries. Researchers are encouraged to prioritize biodiversity studies in the Visayas and Mindanao regions to mitigate study bias. A comparative analysis of native and introduced fish species richness would also be beneficial in determining their potential impact on the overall effect size of species richness.
Assessment of water quality and zooplankton community structure in the Gambhiri River (Chittorgarh, Rajasthan, India)
This study examines water quality parameters and zooplankton community structure in the Gambhiri River, Chittorgarh district of Rajasthan, India, to assess the ecological health and trophic state of this vital freshwater ecosystem. Seasonal sampling was conducted from January to December 2023 at six sampling sites to observe spatial and temporal variations in physicochemical parameters and zooplankton communities. Key water quality parameters, including water temperature, pH, total dissolved solids, turbidity, electrical conductivity, total hardness, chloride, alkalinity, dissolved oxygen, and biological oxygen demand, were measured using standard analytical techniques. Zooplankton samples were collected with a plankton net, preserved, and identified to the lowest possible taxonomic level, following standard keys. In the study period, 65 species of zooplankton were analyzed, of which 26 species of Rotifera, 25 species of Cladocera, 8 species of Copepoda, and 6 species of Ostracoda were recorded. Cladocera appeared as the dominant group of zooplankton with a higher density (38.67%), followed by Rotifera (35.72%), Copepoda (18.57%), and Ostracoda (7.03%). The season-wise zooplankton analysis revealed that Cladocera and Rotifera were the dominant groups across all seasons, while Copepoda and Ostracoda contributed comparatively less to the total density. Cladocera showed higher density than Rotifera during summer and post-monsoon seasons, whereas during monsoon and winter, Rotifera slightly dominated over Cladocera. Copepoda consistently remained the third dominant group in all seasons, while Ostracoda recorded the lowest density throughout the study period. The study highlights the importance of zooplankton as sensitive bioindicators for evaluating the health of freshwater ecosystems and recommends routine monitoring and pollution control measures to preserve the ecological integrity of this crucial water resource in Rajasthan’s semi-arid region.
Seasonal dynamics of rotifer community in relation to water quality at Pravara-Godavari river confluence (Ahmednagar, MS, India)
This study reports the diversity, abundance, and seasonal dynamics of the rotifer community in the Pravara-Godavari river confluence, Ahmednagar, throughout a year, from November 2024 to October 2025. Seasonal sampling was conducted to assess rotifer species composition and density, and to measure key physicochemical water parameters, including temperature, pH, dissolved oxygen, turbidity, alkalinity, hardness, and chloride. A total of 19 rotifer species, representing 4 genera and 3 families, were recorded in the study area. Strong temporal variation in population structure was indicated by the rotifer community’s noticeable seasonal variations in both species richness and density. The summer period recorded the highest rotifer diversity and abundance. At the same time, the monsoon season had the lowest values, perhaps due to a dilution effect, increased water turbulence, and altered habitat stability. Furthermore, correlation analysis showed that important physicochemical parameters such as pH, water temperature, turbidity, alkalinity, total hardness, chloride concentration, and dissolved oxygen had a significant impact on rotifer species richness. These results demonstrate that even small changes in water quality can significantly impact the composition of rotifer communities. Overall, the study highlights rotifers’ sensitivity to environmental factors and underscores their value as reliable bioindicators for evaluating freshwater ecosystems.
Morphological and genetic features of crustaceans Artemia parthenogenetica and A. tibetiana (Crustacea, Anostraca) in different-type hypersaline lakes in the south of Western Siberia
We studied modern morphological features of parthenogenetic and bisexual Artemia populations from 10 different-type hypersaline lakes in the south of Western Siberia (Altai Krai). DNA barcoding of these populations revealed two Artemia species: Artemia parthenogenetica Barigozzi, 1974 and A. tibetiana (Abatzopoulos et al., 1998). The studies were conducted monthly from July to September 2025. Principal component analysis indicated differences in the hydrochemical composition of brine (water) of lakes inhabited by parthenogenetic and bisexual Artemia populations. Comparative analysis of morphological features suggested that females of A. parthenogenetica and A. tibetiana significantly differed in mean values (14 of 16 traits). Cluster analysis of 12 plastic and 4 meristic characters of A. parthenogenetica females demonstrated splitting of its population into three groups with different structural features of the furca: length (fl), number (sf), and length of setae (sl). The Spearman correlation index establishes significant statistical correlations between the morphological features of A. parthenogenetica and A. tibetiana and main environmental factors, i.e. salinity and water temperature.
Features of polychlorinated biphenyls accumulation in Baikal fishes (initial results)
A detailed systematic analysis of the content of polychlorinated biphenyls (PCBs) in various Baikal fish species was conducted for the first time. Accumulation levels of indicator and dioxin-like PCBs were determined in the muscles of five species of Baikal sculpins of the family Cottidae: Abyssocottus pallidus, Abyssocottus godlewskii, Abyssocottus platycephalus, Leocottus kesslerii and Cottocomephorus comephoroides, and of two species of the family Coregonidae: Coregonus baicalensis and Coregonus migratorius. The features of pollutants accumulation by various fish species depending on habitat specificity and feeding ecology are revealed. The total toxic equivalents of dioxin-like PCBs were calculated despite their extremely low concentrations in the water of Lake Baikal.
Copyright (c) 2025 Limnology and Freshwater Biology https://creativecommons.org/licenses/by-nc/4.0
Vertical distributions of dissolved methane into bottom sediments from background areas of Lake Baikal
Vertical distributions of dissolved methane and this flux into bottom sediments (up to 3 m thickness) from background (undisturbed sedimentation) areas of the Southern, Middle and Northern basins of Lake Baikal were obtained and characterized. Vertical methane profiles at all stations are similar characteristics: low concentrations in the near-surface layers (≤ 1–2 µM) and a steady increase with depth. The highest concentrations of methane into sedimentary were observed in the Middle basin, followed by somewhat lower levels in the Southern, and concentrations an order of magnitude lower in in the Northern basin. The exponential decrease in methane concentrations toward to the bottom–water interface to equally low values, regardless of its content within the sediment, indicates its significant oxidation and consequently minimal influence on methane concentrations at the near-bottom water interface. The obtained results fill a gap in knowledge concerning the vertical distribution of methane into baikalian bottom sediments and are important for assessing the stability and functioning of hydrocarbon systems in a cold and deep freshwater reservoir.
The complete chloroplast genome of Chlorella vulgaris strain BAC9706 isolated from Lake Baikal
We report here the complete chloroplast genome sequence of the strain BAC9706 of green microalga Chlorella vulgaris isolated from Lake Baikal. The chloroplast genome is a circular DNA molecule of 161,721 bp and contains 78 protein-coding genes, 33 tRNA genes, and 3 rRNA genes. Comparative analysis revealed a high level of conservation of gene content and gene order among other C. vulgaris strains with minor differences mainly associated with introns and non-coding regions. Phylogenetic analysis based on concatenated chloroplast protein-coding genes showed that strain BAC9706 clusters within the C. vulgaris clade with high bootstrap support. These results indicate that strain BAC9706 represents a Baikal ecotype of C. vulgaris rather than a new species.
Methodological aspects of estimating natural mortality coefficients for the baikal omul: a case study of The selenga population
This scientific article presents a critical analysis of methods for estimating the instantaneous natural mortality coefficient (M) of the Baikal omul, Coregonus migratorius (Georgi, 1775), in the context of managing its commercial stock. The von Bertalanffy growth equation was parameterized based on growth and age structure data. A comparative analysis of existing M estimates used in the Total Allowable Catch (TAC) materials for 2017–2025 revealed their significant variability, leading to threefold discrepancies in the calculated population biomass under equal recruitment. An important factor determining the dynamics of cohort abundance and biomass is the extremely high post-spawning mortality (>90%) in the Selenga population. The applicability of theoretical models based on life history invariants for calculating average M values (Jensen, 1996) is justified using the concept of maximum age (Shibaev, 2023). The resulting estimate based on maximum age, Mavg=0.19 yr⁻¹, and the ratio M/K≈1.5 yield more realistic projections consistent with historical fishery data. The reliability criterion for any M estimation method should be its consistency with key population indicators, taking into account the spatial heterogeneity of the stock.
Unification of geological and geophysical characteristics of gas hydrate-bearing structures in Lake Baikal
We carried out the unification of the geological and geophysical characteristics of the gas hydrate-bearing structures of Lake Baikal. For this purpose, we conducted a comprehensive compilation and analysis of all currently available primary and processed data. The study included a detailed examination of >400 seismic and acoustic profiles, 50 sonograms of side-view sonar, 60 bathymetric schemes of multipath echo sounder, and >1,000 primary descriptions of sediment cores. This resulted in the identification of six reference (model and typical) gas hydrate-bearing structures (two mud volcanoes, two hydrate mounds, and two seeps), which most fully characterize each of the listed types. Unification of characteristics of hydrate-bearing structures of Lake Baikal and allocation of supporting structures facilitates the research of already known ones and will help in the search for new places with near-surface gas hydrates in bottom sediments.
Identification and comprehensive characterization of a new soil strain of carotenogenic microalgae Chlorosarcinopsis sp. VKM Al-296 (Chlorophyta)
We conducted a complex study of the new green microalgae strain VKM Al-296, isolated from arable soil and identified as Chlorosarcinopsis sp. (Chlamydomonadales, Chlorophyta), using molecular phylogenetic analysis (18S rDNA and ITS2 sequences) and light and scanning electron microscopy. The strain’s morphology, growth, and carotenogenesis during two-stage batch cultivation were studied. In a liquid medium, the cells occurred singly or in packages surrounded by extracellular mucilage, with cell sizes of 3-6 µm. By the end of the “green” stage (vegetative growth) lutein was the predominant pigment, accounting for >60% of the total carotenoids. Other primary carotenoids were also present: beta-carotene (14.6%), neoxanthin (11.1%), and antheraxanthin (7.1%). At the end of the “red” (secondary carotenogenesis) stage, the culture’s dry biomass content was 1.92±0.04 g/L, with carotenoids accounting for 0.3% of the dry biomass. The pigment profile was dominated by ketocarotenoids: astaxanthin (mono- and diesters), canthaxanthin, and adonixanthin monoesters (35%, 21% and 20% of the total carotenoid content, respectively). Over the entire cultivation period (17 days), the average biomass productivity and total carotenoid productivity were 0.10 g/L/day and 0.2 mg/L/day, respectively. Chlorosarcinopsis sp. VKM Al-296 may be a perspective object of further research aimed at optimizing cultivation conditions as a source of lutein at the “green” stage, as well as canthaxanthin and esters of astaxanthin and adonixanthin at the “red” stage.
Nanoplastics as a substrate for fungal growth Lecanicillium coprophilum (Cordycipitaceae, Hypocreales)
Anthropogenic pollution of the environment by plastic waste represents one of the most serious environmental problems. Nanoplastics, particles smaller than 1000 nm, pose a particular danger, as their small size and high specific surface area result in high bioavailability and toxicity for a wide range of aquatic organisms. Fungi are promising candidates for cleaning contaminated ecosystems due to their metabolic capabilities for breaking down complex molecules. In this study, for the first time, we experimentally investigated the ability of the micromycete, Lecanicillium coprophilum, to use nanoparticles of synthetic polymers–polyvinyl chloride (PVC), polystyrene (PS), and polymethyl methacrylate (PMMA)–as a growth substrate. Fluorescence microscopy and measurements of polymer concentrations in the medium proved that this fungus can not only adsorb nanoplastics on the surface of its hyphae but also metabolize them. Non-parametric analysis of variance (Kruskal-Wallis test) revealed statistically significant differences in mycelial biomass accumulation in media containing different plastics at 10°C. PS was the most favorable substrate for the growth of L. coprophilum. The median mycelial biomass values demonstrated a consistent ranking of polymers by favorability: PS > PMMA > PVC, which remained across different cultivation temperatures. This paper also discusses the enzymatic activity of L. coprophilum and the potential contribution of enzymes, particularly lipases, to the biodegradation of nanoplastics by this fungal species.
Coumarin-based dye for vital staining of cell cultures
Fluorescent dyes are widely used in modern biochemical and biological research to assess, in particular, the functional state of cells, cellular components, tissues, and organisms. Blue fluorescent dyes offer the advantage of not interfering with the autofluorescence of biological media in the green-red spectrum. This study aims to design a new affordable blue fluorescent dye capable of penetrating living cells. The structure of prepared dye (ZS-833) combines the blue fluorophore 7-(diethylamino)coumarin with the dimethyl-2-butenedioate moiety. The utility potential of ZS-833 was tested with staining heterotrophic as well as naturally pigmented cells (the Saccharomyces cerevisiae yeast and Gymnodinium corollarium dinoflagellate). ZS-833 penetrates readily both types of living cells, making them bright fluorescent in the blue and green spectral ranges but leaving dead cells unstained. These data suggest ZS-833 as a promising agent for intravital cell culture staining and visualization of cellular components, especially nonpolar ones.
Genomic basis of Baikal sponge tissue degradation caused by a free-living Flavobacterium with host-glycan-targeting polysaccharide utilization loci
Here we present the complete genome sequence of the Flavobacterium sp. strain PLB03 isolated from the primmorphs cell culture of the Lubomirskia baikalensis sponge and compare it with pathogenic free-living members of the genus Flavobacterium. Strain Flavobacterium sp. PLB03 exhibits pronounced lytic activity towards sponge cells and causes death of symbiotic microalgae (the Trebouxiophyceae). The Flavobacterium sp. PLB03 genome has 5,925,828 bp and a GC content of 34.3%. An average nucleotide identity (ANI) of 98.9% revealed that strain Flavobacterium sp. PLB03 has the highest similarity to Flavobacterium CSZ. Comparative genomic analysis of the strain and phylogenetically related Flavobacterium indicated that Flavobacterium sp. PLB03 has a large genome size characteristic of the environmental genus Flavobacterium, and the peptidase (PEP) to glycoside hydrolase (GH) gene ratio is 1.8, suggesting that strain PLB03 exhibits characteristics similar to nonpathogenic strains.
Weakly basic fluorescent dye for vital staining of calcium structures in living organisms
Vital dyes capable of staining developing skeletal elements made of carbonate or calcium phosphate contain carboxyl groups that can interact with calcium ions. These dyes are in demand both in research of the biomineralization mechanisms and in the tagging of fish and mollusks in ecological and aquaculture experiments. At the same time, negatively charged dye molecules such as calcein do not penetrate cell membranes well. This necessitates the use of high concentrations, which can cause toxic effects and non-specific staining. This article describes an effective method for synthesizing a new fluorescent dye, QE2, containing a weakly basic amino group and two carboxyl groups in the form of methyl esters capable of hydrolysis in a weakly alkaline environment or under the action of enzymes. The fluorescence of QE2 and its hydrolysis product significantly depends on the polarity of the environment, intensifying in a nonpolar environment with a simultaneous shift in emission from the green-blue to the blue region. The dye is able to easily penetrate living cells, as shown by the example of dinoflagellate culture. Growing organisms with calcium skeletons (gastropods, fish) in the presence of QE2 leads to fluorescent staining of growth areas (gastropod shell aperture, fish spine and fin elements). The QE2 dye can be used to track areas of calcium mineralization, assess the polarity of cell organelles, introduce markers into fish for experiments in ecology and aquaculture, and stain cell cultures and skeletal elements for confocal microscopy studies.
Morphometric analysis of selected claw traits in Tubuca forcipata (Ocypodidae) from Southern Vietnam
A total of 233 specimens of the fiddler crab Tubuca forcipata (189 males and 44 females) were collected monthly from intertidal mudflats in Dam Doi and Hoa Binh, Ca Mau Province, Southern Vietnam, from July to October 2025. Selected morphometric traits, comprising the carapace width left-to-right (CWL–R), the carapace width right-to-left (CWR–L), the manus widths (MW2 and MW3), the pollex width (PW5), and the dactyl width (DW7), were measured to 0.01 mm. Generalized linear models with a gamma distribution and log link were used for trait comparisons; cheliped traits were analyzed with sex and the carapace width (CWL–R or CWR–L) as predictors. The carapace width did not differ by sex (p > 0.05), whereas MW2, MW3, PW5, and DW7 were significantly larger in males after adjusting for the carapace width (βsex = 0.156–0.257; rate ratios (RR) = 1.17–1.29; p < 0.001). The carapace width had strong positive effects on all cheliped traits (βCW = 0.054–0.070; RR ≈ 1.06–1.07; p < 0.001). Model diagnostics showed χ²/df < 1, indicating no overdispersion. These results demonstrate pronounced sex-linked functional dimorphism in the chelae of T. forcipata despite similar overall body size, providing a quantitative morphometric baseline for ecological and evolutionary studies of mangrove crabs in the Mekong Delta.
The effect of sample volume and number of reads on the sequencing result of a microeukaryotic community from an oligotrophic lake
Microeukaryotes are an important component in aquatic ecosystems and can be used as an indicator of environmental conditions. Changes in their abundance or diversity can indicate changes in the habitat. In the last decade to addition to light microscopy method, DNA metabarcoding is used a monitoring of microeukaryote community. In order to optimise the metabarcoding method, it is important to determine the necessary sample volume and sequencing depth. This study compared samples with different filtered water volumes (50, 10 and 1.2 L) and sequencing depths to determine their impact on the diversity and taxonomic composition of the unicellular microeukaryotic community in Lake Baikal. ANOSIM analysis revealed similarity among samples with different filtered volumes. This suggests that a small filtered sample volume (1.2 L) is sufficient to reveal a high diversity of taxa in an oligotrophic reservoir, comparable to that obtained with a larger filter volume (50 L). Ciliophora species were detected the highest number of reads by metabarcoding at the large volume of filtered sample (50 L), while diatoms and green algae were better read in smaller volumes (10 and 1.2 L). It is seems that samples volumes in 10 and 1.2 L are sufficient for microalgae monitoring. Samples with different sequencing depths produced similar results in the characterisation of dominant species. Differences were observed in minor taxa, some of which were only detected with a higher number of reads. These results are important for improving the monitoring of oligotrophic bodies using metabarcoding.
Influence of sex and body size on selected morphometric traits of Metopograpsus frontalis (Miers, 1880) from Southern Vietnam
A total of 167 specimens of Metopograpsus frontalis (105 males and 62 females) were collected monthly from intertidal mudflats in Ganh Hao, Ca Mau Province, Southern Vietnam, from July to October 2025. Selected morphometric traits, including carapace width from left to right (CWL–R), carapace width from right to left (CWR–L), manus width (MW2, MW3), pollex width (PW5), and dactyl width (DW7), were measured with a 0.01-mm vernier caliper. Generalized linear models were fitted to evaluate the effects of sex and body size, using Gaussian models for CW and Gamma models with a log link for MW, PW, and DW. We found no significant sex-related differences in CWL–R and CWR–L (p > 0.05), whereas MW2, MW3, PW5, and DW7 were significantly larger in males (p<0.001). Sex coefficients (β=0.156–0.257) corresponded to rate ratios (RR) of 1.17–1.29, indicating that male claws were 17–29% larger after adjusting for CWL–R and CWR–L. Both CW variables had strong positive effects (β=0.054–0.070; RR=1.06–1.07; and p<0.001). All Gamma models showed χ²/df<1, confirming good model fit without overdispersion. These results provide quantitative evidence of sex-related variation in morphometric traits of M. frontalis and establish a morphometric baseline for future ecological and evolutionary studies of mangrove crabs in the Mekong Delta.
Biodiversity and structure of zooplankton communities in the Yantarnyi water-flooded quarry (Kaliningrad region, Russia)
To study the biodiversity and quantitative development of zooplankton, in vestigations were conducted in the Yantarnyi water-flooded quarry in Kaliningrad region in 2011 and 2023–2024. Due to its quarry origin, this water body has a relatively large surface area and high depth. The study included hydrochemical analysis of the water, determination of the taxonomic composition of zooplankton communities, their quantitative indicators, and calculation of the Shannon diversity index for areas with macrophytes and for open water. It was established that Cladocera dominate the quarry in terms of the number of species found, abundance, and biomass. Despite the small projective cover of aquatic vegetation, species diversity is higher in macrophyte stands due to a greater number of Rotifera species and species characteristic of these biotopes. Low mortality rates of zooplankton were recorded in the Yantarnyi water-flooded quarry, indicating favorable conditions for planktonic communities. This is confirmed by the results of hydrochemical analysis, which classify this water body as oligosaprobic.
Organic matter and nutrients in Lake Glubokoe (Moscow region, Russia)
According to monitoring data from 2019-2025, the current regime of organic matter and nutrient elements in the water of Lake Glubokoe is assessed. The lake is located in a nature reserve within the Moscow region and can be considered as a natural (background) water body for the region (the maximum nitrogen and phosphorus content is several times lower than in the Mozhaysk Reservoir and dozens of times lower than in Lake Beloe in Moscow). Significant interannual variability in the ecological state of the lake was observed: in years with incomplete spring circulation, intensity of summer anoxia is the strongest, and approximately twice as much mineral nitrogen, phosphorus, and colored iron compounds accumulate at the bottom than in other years. At the same time, no monotonous trend is observed in the regime of nutrient elements throughout the history of research, and no long-term changes occur in the organic matter content since the 1960s, when its content in the lake decreased by about half as a result of reclamation work in the catchment area. This calls into question the existing hypothesis of gradual eutrophication of Lake Glubokoe.
Assessing the effects of dietary and waterborne commercial salt on the performance and welfare of common carp
This study investigated the effects of salt additives in water and diet on the physiological and health parameters of common carp (Cyprinus carpio L.). Fingerlings (~50 g) were divided into seven groups: a control group (G1), three water treatment groups (G2A–C; 4, 8, and 12 g L⁻¹ salt), and three diet treatment groups (G3A–C; 5, 10, and 15 g kg⁻¹ dietary salt). All fish were fed a standard diet containing 28% crude protein at 3% body weight per day. Results revealed that G1 had the highest values for lymphocyte and monocyte counts, mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), cholesterol, triglycerides, low-density lipoprotein cholesterol (LDL), albumin, total protein, and several somatic indices. G2B exhibited significantly higher potassium and sodium levels, while G3A showed elevated white blood cell (WBC), granulocytes, liver enzyme activities (Alanine aminotransferase activity (ALT), aspartate aminotransferase activity (AST)), creatinine, glucose, chloride, and various somatic indices. G2A and G2B groups had increased red blood cells (RBC), hemoglobin, hematocrit, and body weight index. The findings indicate that using 12 g L⁻¹ salt in rearing water and 15 g kg⁻¹ salt in the diet can enhance growth and health performance in Cyprinus carpio. This study provides important insights into salt-induced physiological responses in carp and offers practical recommendations for aquaculture practices.
Trophic structure and functional feeding groups of macroinvertebrates in a section of the Gallinazo tropical stream
Aquatic macroinvertebrates play crucial roles in ecosystem processes such as grazing, decomposition, and mineralization. Classifying these organisms into functional feeding groups (FFGs) enables a more comprehensive understanding of energy and matter flow through trait-based approaches, complementing traditional taxonomic methods. The study analyzed the trophic structure and FFG variation of aquatic macroinvertebrates in a section of a tropical stream, located in the municipality of Aguachica, Colombia. Sampling was carried out during the rainy season in May and the dry season in July 2024, during which the composition and abundance of macroinvertebrate feeding groups were analyzed. Physical and chemical parameters were measured both in situ and ex situ at strategically selected stations based on accessibility and location. Macroinvertebrates were collected using Surber and D-type nets and identified to the family level. They were then assigned to functional feeding groups. Ecological indices and multivariate statistical analyses were applied to evaluate ecosystem attributes. Results revealed seasonal variations in water parameters, including lower dissolved oxygen and higher chemical oxygen demand during the dry season, suggesting potential organic pollution. Macroinvertebrate richness was higher during the dry season, with Caenis sp. and Tanypodinae sp. being dominant, while Drepanotrema sp. and Physa sp. were more abundant during the rainy season, reflecting eutrophic conditions. The P/R index indicated heterotrophic dominance, and low CPOM/FPOM ratios pointed to limited riparian cover. These findings underscore the importance of implementing conservation strategies to mitigate anthropogenic pressures and preserve the ecological integrity of freshwater ecosystems.
Variability of Coregonus peled (Gmelin, 1789) fecundity in the middle part of the Ob River (Western Siberia, Russia) and the influence of environmental temperature on it
The peled, Coregonus peled, is a widespread species of the Coregonidae in Northern Eurasia. Its numbers remain relatively high throughout the Ob River basin. This species is environmentally plastic. Its fecundity varies widely, both across different water bodies and within the same water body during different observation periods. Hydrological conditions influence the reproductive capacity of peled, with higher fecundity in high-water years. This study aimed to analyze the fecundity of peled migrating upstream to the middle part of the Ob River for natural reproduction and detection the relationship between its fluctuations and environmental temperature. We identified that peled, which comes to spawn in the middle part of the Ob River, reaches sexual maturity at the age of three years. However, individuals aged five to six years form the basis of the spawning stock, comprising up to 70% of the total. The reproductive capacity of peled is highly variable. Individual absolute fecundity ranges from 11.3 to 58.0 thousand eggs, increasing with age, standard length, total weight, body weight, and Fulton and Clark indexes. Individual absolute fecundity ranges from 36 to 103 eggs per gram of body weight and correlates with total weight and Fulton indexes. Peled reproductive capacity indicators vary significantly between years. Overall, the individual relative fecundity of this species in age groups of 5+ years and older has decreased by 41–47% compared to the mid-20th century. There was a relationship between the reproductive capacity of peled migrating to the middle part of the Ob River for spawning and the environmental temperature in the lower part of the Ob River, where fish were feeding before the spawning migration begins: relatively high July temperatures are associated with lower individual absolute fecundity indicators for the most numerous age groups. Thus, global warming may have a negative impact on the reproductive capacity of peled in the Ob River basin.
Nanozinc as an emerging nanopollutant: sublethal effects on the invasive freshwater bivalve Limnoperna fortunei (Dunker, 1857)
Zinc oxide nanoparticles (ZnONP) are among the most widely produced nanomaterials worldwide given their unique properties, despite their nanotoxicity has been poorly addressed. In parallel, environmental concern has risen because of increasing amounts of them reaching the environmental matrices, whereas the aquatic ones are one of the main final sinks. As key non-target species, we aimed to expose the invasive freshwater bivalve Limnoperna fortunei to sublethal concentrations of ZnONP (0, 0.025, 0.25, and 2.5 mg/L) to evaluate tissue damage and oxidative stress-related markers in the soft tissue. After a 96 h-exposure, the alkaline phosphatase enzyme activity increased after 0.025 mg/L, and the alanine aminotransferase activity decreased at 2.5 mg/L. Aspartate aminotransferase enzyme activity also decreased at 0.25 and 2.5 mg/L. In terms of oxidative stress, only superoxide dismutase activity increased after exposure to the lowest nanozinc concentration. We concluded that nanozinc may pose a threat to the aquatic biota in a context that lacks proper regulation and control for nanopollutants, and that the toxicity mechanisms in this species are mainly related to tissue damage, even at environmentally relevant concentrations, as the lowest one tested.
Modelling of melt using simple and enhanced temperature-index models: testing for the Sygyktinsky Glacier, the Kodar Range (northern Transbaikalia, Russia)
Modelling snow and ice melt in drainage basins can significantly improve the forecasting of hydrological processes at local and regional scales. Melt rates on the surface of the Sygyktinsky Glacier were measured using an ultrasonic ranger and calculated by the physically based surface energy-balance (SEB) model with a 30-minute resolution for the period from 7 July to 23 August 2021. Two temperature-index models, simple (TM) and enhanced (ETM), were tested to calculate melt rates. All models used 30-minute meteorological data from automatic weather station installed in the central part of the glacier at the mean equilibrium line altitude (2561 m a.s.l.). The performance of the temperature-index models was assessed by comparing 30-minute melt rates with the physically based SEB model. The TM model used air temperature as a predictor, explaining up to 30% of the variability of melt rates. Meanwhile, the ETM model, taking into account incoming shortwave radiation and albedo besides air temperature, demonstrated significantly better performance. The model explained up to 90% of variance in the 30-minute melt rates. The advantages of the enhanced model can be used for future studies of spatial variability of melt rates on the Kodar glaciers.
Thermohydrodynamic processes in Lake Ladoga
The results of adapting a three-dimensional mathematical model of the hydrodynamics of an inland sea to the conditions of Lake Ladoga are presented, followed by its verification using field and remote measurements. During adaptation, a spherical B-type computational grid with a spatial resolution of 1 km × 1 km was constructed. The equation of state for seawater was replaced by an equation for weakly mineralized water with a maximum density at a temperature close to 4 °C. A procedure was implemented to calculate the inflow of heat and dissolved substances into the lake through liquid boundaries with the waters of tributaries. The flow of the Neva River was taken into account. Atmospheric forcing from NCEP/NCAR reanalysis with a spatial resolution of 2.5°×2.5° has been replaced with the European equivalent ERA5 with a resolution of 0.25°×0.25°. Verification of the new model version was performed for three areas of the lake: the southern shallow area (≤ 40 m), the central area (~50 m), and the northern deep area with depths up to 230 m. To assess the impact of climate change on thermohydrodynamic processes, calculations were performed from 1990 to 2020. Both contact measurements from the Institute of Limnology of the Russian Academy of Sciences and images from NOAA and MODIS Terra/Aqua satellites were used for verification. The verification results showed that the model adequately reproduces the main features of thermohydrodynamic processes in Lake Ladoga, namely: the vertical thermal structure of the lake’s water mass, the beginning of the formation and spread of the vertical frontal zone - the thermobar. Accounting for inflow waters allows tracking their further distribution in the lake. Replacing atmospheric forcing has led to a significant improvement in calculations of ice conditions in the lake. The results of verification of the new version of the model should be considered satisfactory. Some shortcomings of the model have also been noted.
Spatial and temporary differences in the development of Ulnaria danica, Ulnaria acus, and Fragilaria radians in Lake Baikal
The assessment of phytoplankton diversity in freshwater bodies strongly depends on the methods used for taxonomic identification. Araphid diatoms of the genera Ulnaria (Kützing) Compère and Fragilaria Kützing are often dominate the phytoplankton composition of freshwater ecosystems. To use of an integrated approach, including metabarcoding using analysis of fragments of the V3-V4 region of 18S rRNA, light and scanning electron microscopy, made it possible to assess the differences of these species. It was shown that in 2017, a gradual change of the studied species occurred in the Southern and Middle parts of Lake Baikal, which is due to the fact that the high development of Fragilaria radians is early then ones of Ulnaria acus. Thus, during the hydrological spring in the pelagic zone of the lake in these areas, and in the Chivyrkuisky and Barguzinsky Bays, U. acus dominated among diatoms. The population development in the Northern part of the lake did not correspond to the revealed trends, according to which a high number of both species should be expected here in the late spring, but it did not exceed 3% of the total number. In the summer, the number of U. acus decreased significantly and reached its minimum in the autumn. Ulnaria danica was present in the phytoplankton of large bays throughout the entire study period.
Bioactivities of freshwater sponges and their associated bacteria: a review
This review aims to provide an overview of the biological activities of freshwater sponges and their microbes associated with them. Freshwater sponges, despite their ecological significance and potential as reservoirs of bioactive compounds, remain underexplored compared to their marine counterparts. This review highlights the bioactivities of eight freshwater sponge extracts, among them being Ochridaspongia rotunda (Arndt,1937), Ephydatia fluviatilis (Linnaeus,1759), Oncosclera asiatica (Manconi & Ruengsawan,2012), Metania reticulata (Bowerbank,1863), Drulia browni (Bowerbank,1863), Drulia cristata (Weltner,1895), Drulia uruguayensis (Bonetto & Ezcurra de Drago,1969), and Eunapius carteri (Bowerbank,1863).Various extracts, including those obtained using methanol, acetone, aqueous, ethyl acetate, and methylene chloride, were employed in previous studies to evaluate a range of bioactivities. Observed bioactivities include antibacterial, antifungal, anti-quorum sensing, antiplasmodial, acetylcholinesterase inhibition, and anticancer properties, which are determined either from the crude extracts of the sponges themselves or by their associated microbes.