This study investigates the ecological and morphological traits of invasive pumpkinseed (Lepomis gibbosus) in five lowland reservoirs in Serbia. A total of 434 specimens were collected in October 2020 and analyzed for population structure and growth parameters, body shape, condition, and diet. The population consisted of seven age classes, with three distinct age structures identified across the analyzed reservoirs. The highest growth increment occurred during the first year of life. Compared to other European populations, this cohort exhibited the slowest overall growth, characterized by the lowest k values. However, the specimens maintained a robust body condition (K>1) and displayed positive allometric growth (b>3). The autumn diet included 14 prey categories, with Chironomidae larvae being the most prominent. Mean dietary similarity between reservoirs was 75.7%, indicating significant dietary niche overlap. Niche breadth analysis showed greater dietary specialization in Topola and Kudre & ccaron; 2, and lower specialization in Jatagan, where prey diversity was highest. These findings offer valuable insights into the adaptive potential and ecological impact of this invasive species and can support future management and monitoring strategies.

Microplastics (MPs) are an emerging environmental concern due to their persistence, ability to act as carriers of contaminants and microorganisms, and potential impacts on aquatic ecosystems and human health. This study presents the first comprehensive assessment of MPs in common bream (Abramis brama; Linnaeus, 1758) from the Danube River that integrates both visual characterization and qualitative polymer identification using μFTIR. The presence, abundance, morphology, size, color, and polymer composition of MPs were investigated in the gastrointestinal tract of common bream collected from the Danube River in Belgrade, a river section exposed to pronounced anthropogenic pressure. Particles were detected in all analyzed specimens. In total, 88 particles were extracted from 15 fish, corresponding to a mean abundance of 5.87 ± 3.29 particles per individual (range: 2-15). Particle lengths ranged from 39 to 10,223 μm, with an average length of 1146 ± 1499 μm. Morphological analysis revealed a strong dominance of fibers (97.70%), while only two fragments were recorded. Most fibers were smaller than 2000 μm and were predominantly blue, brown, and grey in color. Chemical characterization was performed on 37 particles (∼42% of the total) using μFTIR. Cellulosic fibers represented 40.50% of identified particles, followed by polyester (27.00%) and acrylic (10.80%), while nylon, polyvinyl chloride and polypropylene were detected less frequently. These results indicate that urban river sections are important MPs hotspots, with common bream representing a species that can effectively reflect contamination in these areas. Future studies should extend spatial coverage along the Danube River and apply harmonized methodologies to improve comparability of results and strengthen assessments of MPs distribution across different riverine conditions, alongside integration of data from other biotic and abiotic compartments for a more comprehensive evaluation of riverine pollution.

Rapid urbanization and increased anthropogenic activities have led to the release of an increasing number of pollutants, including metals, into freshwater ecosystems, posing a significant threat to aquatic life. In this study, the bioaccumulation of metals and hepatic enzyme activities in northern pike (Esox lucius) from two contrasting freshwater ecosystems in Serbia, the lotic Tisza River and the lentic Bela Crkva Reservoirs, were investigated. A total of 22 specimens (11 per site) were sampled in autumn 2024. The liver tissue was analyzed for the concentrations of 11 metals (As, Cd, Cr, Co, Cu, Pb, Li, Fe, Zn, Mn, Ni) and the activities of the liver enzymes (ALT, AST, AP, GGT). The results showed ecosystem-specific patterns of metal accumulation, with the northern pike in the rivers showing significantly higher Cu and Fe levels, while the fish in the reservoirs showed increased Zn concentrations. Enzymatic biomarkers showed different responses between ecosystems, with river fish showing increased ALT and AST activities, indicating hepatocellular stress, while reservoir fish showed increased GGT, indicating enhanced detoxification processes. The body condition factor was negatively correlated with liver Mn and Zn concentrations, emphasizing its utility as an integrative bioindicator of metal-induced stress. No significant sex-specific differences in metal or enzyme levels were found. These results suggest the suitability of northern pike as a sentinel species for environmental monitoring in freshwaters and highlight the different physiological adaptations to local metal stress in lentic and lotic habitats.

This study assessed the impact of untreated wastewater discharge in the Danube River on four native fish species: barbel (Barbus barbus), vimba bream (Vimba vimba), perch (Perca fluviatilis), and white bream (Blicca bjoerkna). Biomarkers of exposure and effect were evaluated, including metal and metalloid bioaccumulation in gills, liver, and gonads, DNA damage (comet assay), chromosomal abnormalities (micronucleus assay), liver enzyme activities (ALT, AST), and erythrocyte maturation. White bream showed the highest genotoxic damage (TI% = 22.57), particularly in liver tissue, indicating high sensitivity to pollution. Perch had elevated DNA damage in blood (TI% = 22.69) and strong biomarker responses, likely due to its predatory behavior. Barbel displayed notable DNA damage in gills (TI% = 30.67) and liver (TI% = 20.35), aligning with sediment exposure due to its benthic habits. Vimba bream had the lowest responses, possibly reflecting reduced exposure or resilience. Element accumulation varied across tissues and species, with perch showing the highest overall levels. Hepatic enzyme activities (highest values: ALT = 105.69 in barbel; AST = 91.25 in white bream) and changes in erythrocyte profiles supported evidence of physiological stress. Integrated Biomarker Response (IBR) analysis identified white bream as the most sensitive species, followed by perch and barbel. These results emphasize the value of multi-species biomonitoring and the importance of species-specific traits in freshwater ecotoxicology.

Bats reflect environmental quality in diverse habitats, from cities to forests. This study aimed to reveal element bioaccumulation and DNA damage in the long-fingered bat (Myotis capaccinii) using non-lethal methods. Twenty-four hair samples and 15 blood samples were taken from bats caught at two locations in Eastern Serbia between July and September of 2024. Hair analysis by inductively coupled plasma-optical emission spectrometry (ICP-OES) detected As, Cr, Fe, Li, Mn, Ni, and Zn, while Cd, Co, Cu and, Pb were below detection limits. The degree of DNA damage in peripheral blood was determined using the alkaline comet assay. In M. capaccinii, there was a significant difference in element concentrations between sexes, with females having higher concentrations of Cr, Fe, and Mn, and between seasons, with samples from summer having higher concentrations of Ni and Mn. A significant difference in zinc concentration was observed between adults and juveniles. DNA damage was higher in the summer season. Significant correlations were confirmed between element concentrations in hair (Cr-Fe, Cr-Zn, Cr-Mn, Fe-Zn, and Fe-Mn) and between Cr and Zn concentrations and DNA damage in blood cells. The Cr-DNA damage link highlights hair as a marker for sustained environmental exposure. Every significant correlation that included Zn was negative. This is the first genotoxic study of bats in Serbia and of M. capaccinii globally, laying the groundwork for future research in other bat species and the wider Central Balkans. It marks an initial step toward using bats as bioindicators for noninvasive pollution monitoring.

Individuals of common nase were sampled from three waterbodies (Kačer river, Zaovine, and Medjuvršje reservoirs) with different characteristics, types, and levels of anthropogenic pressure. The aims of this study were to determine the concentrations of 26 elements in gills, liver, and muscle using inductively coupled plasma optical emission spectrometry (ICP-OES); determine the concentrations of 17 organochlorine pesticides (OCPs) in muscle tissue using gas chromatography with mass spectrometric detection (GC–MS); compare these findings with fish condition (CF); and conduct human health risk and benefit assessments due to consumption of fish meat using target hazard quotient, target carcinogenic risk factor, Se:Hg molar ratio, Na:K and Ca:Mg ratios, and contribution of elements to human diet. Results indicated that in addition to the fact that the type of ecosystem (lentic vs. lotic) plays an important role in the fate and kinetics of pollutants, the degree of anthropogenic pressure is one of the most important factors of environmental pollution — Zaovine and Medjuvršje reservoirs (both lentic ecosystems) had the lowest and the highest levels of pollution, respectively. CF did not reflect the differences in accumulation of all analyzed elements in nase tissues. None of the 17 analyzed OCPs were detected due to the absence of recent use. Fish muscle was the least affected by metal pollution at all studied localities and could be safely used for consumption. We recorded several benefits for human health when using the nase meat in human diet.

The aim of this study was to determine the concentrations of 28 elements in the liver, kidney, muscle, and heart of a small Indian mongoose from Montenegro. Element concentrations were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Significant differences in elemental concentrations between analyzed tissues were observed for Ag, Al, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, P, S, Se, and Zn. The concentrations of Ag, Fe, Mo, and S were significantly different between all analyzed tissues. Muscle tissue is characterised by higher concentrations of some macroelements (K, Mg, S) and liver tissue by higher concentrations of some trace elements (Fe, Mn, Mo, and Zn). Cardiac tissue could be the target organ for bioaccumulation of Ag and Se. The molar ratio Se:Hg was higher than 1 in all studied tissues. There were few significant differences between element concentrations in mongooses from three analyzed (Airport, Saline, Inland) groups. Significantly higher concentrations of Ag and Se were found in liver tissue of Inland mongooses compared to animals from Airport and Saline. There were few significant differences (Zn in liver and muscle, Fe in muscle) in element concentrations between females and males.

In this study a battery of bioassays, both in vivo (metals and metalloids concentrations, erythrocyte morphometry, comet assay, micronucleus assay, and histopathological analyses) on vimba bream Vimba vimba (L., 1758) and white bream Blicca bjoerkna (L., 1758), and in vitro (treatment of HepG2 cells with native water samples) was applied to assess the harmful potential of untreated wastewater. Faecal indicator bacteria were quantified to assess the microbiological water quality. Vimba bream had significantly higher Fe concentrations in both liver and muscle, while white bream had higher Ca and Cu concentrations in liver. Vimba bream had a significantly higher level of DNA damage in both liver and blood cells, in comparison to white bream. Low levels of micronucleus and nuclear abnormalities were observed in both species. Erythrocytes morphometry did not show significant interspecific differences. Histopathological analyses revealed a similar response of the studied species, with a significantly higher presence of ceroid pigments in the liver of vimba bream. Treatment of HepG2 cells revealed the high genotoxic potential of water downstream of the discharge point. The results of this study clearly demonstrate the importance of effect-based monitoring, in order to enforce more efficient management of natural resources and implementation of wastewater treatment systems.

Vimba bream (Vimba vimba) individuals were collected from the Danube River near Belgrade, from May 2016 to May 2017. Samples of muscle and liver tissue were analyzed for concentrations of 25 elements (macro-, micro-, and toxic elements) using inductively coupled plasma optical emission spectrometry (ICP-OES). For both tissues, the highest concentrations of most elements were observed in late spring/early summer (months of May and June). Majority of statistically significant correlations between elements were positive in both tissues. Contributions of Ca, K, and Mg to human diet were in a similar range. The lowest contribution of all macroelements was observed for Na, while the contribution of Se was well above the recommended dietary allowance for this element. Levels of detected elements were well below MAC values prescribed by national and international regulations. The highest value of Hg liver/muscle index (>1) was observed in August, which could indicate a higher contamination of the sampling location in that month. Se:Hg molar ratio never drops below 1, which could indicate that Hg toxicity is prevented. THQ values showed little variation thought the year and were well below the threshold of 1, with the exception of THQ for Al in May (0.92). This element also strongly affects the hazard index.

Vimba bream individuals (n = 157), obtained from commercial catches in 2016 and 2017 near Belgrade. were analysed to obtain information on growth and condition of this species. The total body length of sampled fish ranged from 248 to 440 mm, while the body weight ranged from 139 to 889 g. Five age classes (from 4+ to 8+) were present in the sample, with predominance of individuals aged 6+. Back-calculated annual length growth was the highest in the first year of life. The total body length defined according to the parameters of the von Bertalanffy growth curve could be calculated at any given time t using 75.07 x (1-e(-0.06x(t+1.73))), and the length-weight relationship - using LogW = 0.010 + 3.02 x logTL. The asymptotic standard body length was SL infinity = 63.86 cm and the phi-prime growth performance index was phi'= 2.53. The highest mean values of Fulton's condition factor were observed in spring of 2016, followed by spring of 2017, and in individuals aged 7+. The seasonal and age-related differences in condition were statistically significant. The lack of data, the degree of endangerment in some European countries, the status of important species for the river continuity restoration and commercial exploitation of this species, emphasise the need for future research.

Fish erythrocytes released from erythropoietic sites are immature. During circulation, they increase their own surface, while the cell body and nuclei begin to become more elliptical and less spherical during maturation. The relative abundance of different developmental stages represents an erythron profile which could be a more sensitive indicator of contamination than classic hematological indices. In this study, we analyzed blood smears of the common nase ( Chondrostoma nasus ) and vimba bream ( Vimba vimba ) with the main goal to identify the determinants of the developmental stage of erythrocytes. Based on parameters developmental stages, erythrocytes are categorized into immature, intermediate or mature. In this investigation we have used four classification methods: the Two Step Cluster analysis, the K-Means Cluster analysis, and Neural Networks–Multilayer Perceptron and an Ordinal Regression model. Our findings clearly justify that Multilayers Perceptron and OLR models are appropriate to classify the developmental stage of fish erythrocytes in both species.

Prey preference and seasonal variation in the diet of the Eurasian otter, Lutra lutra (Linnaeus, 1758), were examined by the analysis of 789 spraint samples collected along a 10-km section of a small lowland salmonid river in Serbia, with a trout farm situated in its lower part, from June 2009 to March 2012. Of particular interest was any possible impact of the otter on brown trout, which is important to investigate for preventing and managing any potential conflicts with fishers and fish farmers. Fish were by far the most important otter prey, followed by crayfish. Cottus gobio Linnaeus, 1758 (the European bullhead) was the most common prey species, probably because of the combination of its abundance and easy catchability. Other prey contributed very little to the diet of the otters. Of 11 fish species present in the river, five were found in the otter diet: the European bullhead, Salmo trutta Linnaeus, 1758 (brown trout), Squalius cephalus (Linnaeus, 1758) (chub), Barbus balcanicus Kotlik, Tsigenopoulos, Rab & Berrebi, 2002 (the Danube barbel), and Phoxinus phoxinus (Linnaeus, 1758) (the Eurasian minnow). The bullhead was the only positively selected species, however. The share of fish prey in the otter diet was stable throughout the year, except for a decrease noticed during the summer. The results suggest that otters on the River Gradac target smaller, sedentary, and less nutritious prey. Owing to a small percentage of brown trout in otter spraints, we surmise that otters do not represent a major biological or economic threat, either to the native trout population in the river or to the trout from the nearby fish farm. Although there are no reports of otters causing damage to the trout population in the local fish farm, it is advisable to establish mechanisms for the compensation of fish farmers in case such damage does occur. The data presented in this paper can be used to contribute to the conservation of the otter in stream habitats, especially because there are no published studies on the dietary requirements of otter in Serbia.

Accumulation of 17 elements in muscle and liver of common nase and vimba bream, caught between February and May 2016 in the Danube River (1173 river kilometer), were assessed by ICP-OES. The principal component analysis grouped muscle and liver samples based on element concentrations (muscle grouped by higher Ba and Sr values, and liver grouped by higher Al, B, Cd, Cr, Cu, Fe, Mn, and Zn values), but no grouping between the two species was observed. Concentrations of Ba, Cu, Fe, and Zn were significantly higher in muscle, and concentrations of Ba, Cd, Cu, and Mn in liver of common nase, while vimba bream had significantly higher concentrations of Cr and Fe in liver. Common nase has a higher affinity for bioaccumulation of Cu, Fe, and Zn in muscle, while vimba bream has a higher affinity for Al, Cd, and Cr in muscle.

46 ———————– * University of Belgrade, Faculty of Biology, Studentski trg 16, 11000 Belgrade, Serbia, e-mail: ssubotic@bio.bg.ac.rs, jkrpo@bio.bg.ac.rs ** University of Belgrade, Institute for Multidisciplinary Research, Kneza Višeslava 1, 11030 Belgrade, Serbia, e-mail: zvisnjic@imsi.rs *** University of Belgrade, Institute for Biological Research Siniša Stanković, Bulevar despota Stefana 142, 11060 Belgrade, Serbia, e-mail: lenhardt@ibiss.bg.ac.rs AGE, GROWTH, AND LENGTH-WEIGHT RELATIONSHIP OF COMMON NASE (CHONDROSTOMA NASUS) IN THE DANUBE RIVER NEAR BELGRADE (SERBIA)

The grey wolf (Canis lupus) is a large carnivore species and a top predator in the ecosystems that it inhabits. Considering its role in food webs, wolves may be exposed to high concentrations of potentially harmful elements. Therefore liver samples from 28 legally hunted wolves were analyzed for concentrations of 16 elements using inductively coupled plasma optical emission spectrometry. The Mann–Whitney U test showed a significant difference between the genders only for Li, and there were no differences between individuals caught in different years. The majority of statistically significant correlations between element levels were positive, except for three cases. Compliance with several criteria for suitable bioindicator organisms imply that wolves may serve for monitoring environmental contamination.

The analysis of 18 elements in muscle, liver, gills, and gonads of sichel (Pelecus cultratus), ruffe (Gymnocephalus cernua), and European perch (Perca fluviatilis), caught at a polluted segment of the Danube River near Belgrade, was carried out with the aim to expand the knowledge about the ecotoxicology of these species for monitoring purposes and the possible impact on human health. Generally, the elemental concentration significantly differed between species and tissues (p < 0.0001), and a statistical interaction between these two factors was observed (p < 0.0001). In muscle and liver, concentrations of Hg and Se were statistically higher in ruffe than in sichel and European perch. In gills, statistically highest concentrations of Mn, Sr, and Zn were found in sichel, and of Fe in European perch. In gonads, statistically highest concentrations of As were detected in sichel, of Zn in ruffe, and of Mn and Mo in European perch. The highest number of coefficients of partial correlations between fish weight and element levels was found in sichel (11 in total). Of all analyzed elements, Al and B had the highest number of partial correlations in tissues. The levels of Hg exceeded the maximum acceptable concentration (0.5 mg kg−1) in all muscle samples, which can pose a risk for human consumption. Different diet preferences of the investigated fish species resulted in a different accumulation of elements in tissues, and ruffe (as a species that consume mainly benthic macroinvertebrates) accumulated the highest level of Hg, which makes it suitable for monitoring of this element in water bodies.

Pikeperch (Sander lucioperca), European catfish (Silurus glanis), burbot (Lota lota), and common carp (Cyprinus carpio) were collected from the Danube River (Belgrade section, Serbia), and samples of liver, muscle, and gills were analyzed for Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Hg, Li, Mn, Mo, Ni, Pb, Se, Sr, and Zn using inductively coupled plasma optical emission spectrometry (ICP-OES) to highlight the importance of species and tissue selection in monitoring research, contaminant studies, and human health research. The Kruskal–Wallis test revealed significant differences between fish species in regard to metal levels in liver, muscle, and gills. The principal component analysis (PCA) indicated that the studied fish species could be grouped on the basis of the level of analyzed elements in liver and gills. The Mann–Whitney test showed two subsets (one comprising two piscivorous species, pikeperch and catfish, and the other, two polyphagous species, burbot and carp) in regard to Cr and Hg levels in liver (higher levels in piscivorous species), as well as B, Fe, and Hg in gills (B and Fe with higher levels in polyphagous and Hg in piscivorous species), and As in muscle (higher levels in polyphagous species). Carp had distinctly higher levels of Cd, Cu, and Zn in liver in comparison to other three species. None of the elements exceeded the maximum acceptable concentrations (MAC). However, since Hg levels are close to the prescribed MAC levels, the consumption of these fishes can be potentially hazardous for humans.

Pikeperch (Sander lucioperca), European catfish (Silurus glanis), common carp (Cyprinus carpio), and gobies (Neogobius gymnotrachelus, Neogobius melanostomus) were collected from the Danube River (Belgrade section), and samples of liver, muscle, or whole-body composites (in the case of gobies) were analyzed for As, Cu, Fe, Hg, Mn, and Zn with inductively coupled plasma optical spectrometry to find out if there was a correlation between accumulation of these elements in predatory and prey species, as well as in pairs of species with overlapping diets. Concentrations of all analyzed elements were either higher (Cu, Fe, Mn, Zn) in liver than in muscle, or equal (As, Hg), except for Hg in carp, which was higher in muscle. Mercury concentration in liver and muscle of predators (catfish, pikeperch) was significantly (<10−4) higher than in prey fishes (carp and gobies). The results indicate that Hg concentration was biomagnified through the food chain. Concentrations of As, Fe, and Hg in carp liver and gobies whole-body composite were similar, but carp had significantly (<10−4) higher values of Zn and Cu in liver. The regression analysis and trendline equations indicate that the concentrations of all tested elements, except for As in liver, and Mn and Fe in muscle, were similar in predatory fish (pikeperch and catfish), on one hand, and in prey fish (carp and gobies), on the other hand. Distinctly high Zn concentration in carp is very common in this species due to its physiology. Concentrations of Hg and Zn were higher than the maximum acceptable concentration due to the high pollution level in this section of the Danube River, accordingly posing a risk for the human consumption of these fish species.