Combined use of biomarkers to assess the impact of untreated wastewater from the Danube River, Serbia.

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.

Temporal variation of biomarkers in common bream Abramis brama (L., 1758) exposed to untreated municipal wastewater in the Danube River in Belgrade, Serbia.

This study was conducted on the Danube River locality Visnjica, exposed to the discharge of the largest wastewater collector in Serbia's capital, Belgrade. Concentrations of metals and metalloids (Al, Fe, Cr, As, Sr, Mn, Cd, Zn, Mo, Cu, Li, Ni, B, Co, Pb, and Ba) and histopathological alterations were investigated in different tissues of common bream during one representative month of each season in 2014. This is the first study in which these two biomarkers were assessed parallelly in common bream. The highest concentrations of examined elements were noticed in gills and the lowest in muscle. Statistically significant differences in element concentrations between different seasons were noticed only in gills for Al, Cu, and Fe. Concentrations of As and Pb in fish muscle were below the maximum acceptable concentrations (MAC). The histopathological index (HI) of the liver showed higher values in comparison to the HI of the gills. Histopathological index of the gills had a significantly higher score in November in comparison to August. The liver HI had the highest score in April, and the lowest in August, while the total histopathological index had the highest score in November, and the lowest in August, both without significant differences between the months. This study endorses gills and liver as reliable organs for studying accumulation and histopathology as biomarkers of environmental changes. A faster reaction of the gills was confirmed since seasonal variations of both biomarkers were observed in this organ. Common bream proved as a good indicator of the state of organisms in polluted environments.

Metal Accumulation in Muscle and Liver of the Common Nase (Chondrostoma nasus) and Vimba Bream (Vimbavimba) from the Danube River, Serbia: Bioindicative Aspects.

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.

Effects of mine tailing and mixed contamination on metals, trace elements accumulation and histopathology of the chub (Squalius cephalus) tissues: Evidence from three differently contaminated sites in Serbia.

Chub (Squalius cephalus) specimens were collected in Korenita River seven months after spillover from the waste water of antimony mine tailing pond and compared with chub living in Kruscica reservoir (intended for water supply) and Meduvrsje reservoir (influenced by intense emission of industrial, urban and rural wastewater). Concentrations of 15 elements (Al, As, B, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Si, Sr, Zn) were determined in muscle, liver and gills of chub by inductively coupled plasma optical spectrometry (ICP-OES) and histopathological alterations in liver and gills were assessed. Chub specimens from Korenita River had higher concentrations of As, Ba and Pb in all three investigated tissues as well as higher total histopathological index values than chub from reservoirs. Specimens from Meduvrsje reservoir were characterized by higher values for concentrations of Cu and Si in muscle tissue and higher values for regressive histopathological alterations in gills. Individuals of chub from Kruscica reservoir had the highest concentrations of Fe in liver, Hg in muscle and Sr and Zn in muscle while gills had the lowest value of total histopathological index. The results from the present study showed higher level of histopathological alterations as a result of mine tailing accident. As a result of mixed contamination on the Meduvrsje site, histopathological index values of gills were in line with the index value from Korenita River. Increased values for Fe and Sr in chub tissue from Kruscica reservoir could be explained by geological structure of the site which is characterized by magmatic rock rich in Cu, Fe and Ni as well as dominant carbonate sediment complex of marine origin with increased level of Sr.

Automatic High Frequency Monitoring for Improved Lake and Reservoir Management.

Recent technological developments have increased the number of variables being monitored in lakes and reservoirs using automatic high frequency monitoring (AHFM). However, design of AHFM systems and posterior data handling and interpretation are currently being developed on a site-by-site and issue-by-issue basis with minimal standardization of protocols or knowledge sharing. As a result, many deployments become short-lived or underutilized, and many new scientific developments that are potentially useful for water management and environmental legislation remain underexplored. This Critical Review bridges scientific uses of AHFM with their applications by providing an overview of the current AHFM capabilities, together with examples of successful applications. We review the use of AHFM for maximizing the provision of ecosystem services supplied by lakes and reservoirs (consumptive and non consumptive uses, food production, and recreation), and for reporting lake status in the EU Water Framework Directive. We also highlight critical issues to enhance the application of AHFM, and suggest the establishment of appropriate networks to facilitate knowledge sharing and technological transfer between potential users. Finally, we give advice on how modern sensor technology can successfully be applied on a larger scale to the management of lakes and reservoirs and maximize the ecosystem services they provide.

Use of histopathology and elemental accumulation in different organs of two benthophagous fish species as indicators of river pollution.

The bottom feeding fish species have a good potential to be used for assessments of pollution, as they are under pressure from pollutants from both water and sediments. In this study, the level of similarity of histopathological responses to pollution in gills and liver between barbel (Barbus barbus) and sterlet (Acipenser ruthenus) from the Danube River was assessed, and compared with elemental concentrations in their gills, liver, and muscle. Results indicate that the detected metal concentrations were likely cause of different tissue responses in gills and liver of the two investigated fish species. Statistical analysis indicated a clear differentiation of the two species based on elemental concentrations and the level of histopathological changes in gills and liver. Metal concentrations exceeded maximum acceptable concentrations in a number of analyzed specimens, which indicates the importance of this type of monitoring. Results indicate that barbel is a better indicator for specific, rather narrow sites, whereas sterlet is a better indicator of larger (longer) water current segments. Obtained information could be of importance for both scientists and fishery and water management authorities working on the development of water monitoring programs.

Heavy metal and trace element bioaccumulation in target tissues of four edible fish species from the Danube River (Serbia).

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.

Quantitative monitoring of diverse fish communities on a large scale combining eDNA metabarcoding and qPCR.

Environmental DNA (eDNA) metabarcoding is an effective method for studying fish communities but allows only an estimation of relative species abundance (density/biomass). Here, we combine metabarcoding with an estimation of the total abundance of eDNA amplified by our universal marker (teleo) using a quantitative (q)PCR approach to infer the absolute abundance of fish species. We carried out a 2850-km eDNA survey within the Danube catchment using a spatial integrative sampling protocol coupled with traditional electrofishing for fish biomass and density estimation. Total fish eDNA concentrations and total fish abundance were highly correlated. The correlation between eDNA concentrations per taxon and absolute specific abundance was of comparable strength when all sites were pooled and remained significant when the sites were considered separately. Furthermore, a nonlinear mixed model showed that species richness was underestimated when the amount of teleo-DNA extracted from a sample was below a threshold of 0.65 × 106 copies of eDNA. This result, combined with the decrease in teleo-DNA concentration by several orders of magnitude with river size, highlights the need to increase sampling effort in large rivers. Our results provide a comprehensive description of longitudinal changes in fish communities and underline our combined metabarcoding/qPCR approach for biomonitoring and bioassessment surveys when a rough estimate of absolute species abundance is sufficient.

Accumulation of 20 elements in great cormorant (Phalacrocorax carbo) and its main prey, common carp (Cyprinus carpio) and Prussian carp (Carassius gibelio).

In this study, 20 heavy metals and trace elements (Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Mo, Ni, Pb, Si, Se, Sr and Zn) were analyzed in different tissues (muscle, liver, intestine, feather and bone) of the great cormorant (Phalacrocorax carbo) and in different tissues (muscle, liver, gills, kidney and gonad) of their main prey (common carp-Cyprinus carpio and Prussian carp-Carassius gibelio) during the nesting season. Cormorant and fish specimens were collected at the Ecka Fishing Farm (Serbia) and from the nearby river. Principal components analysis (PCA) showed that cormorant livers were differentiated from other four tissues by higher concentrations of Hg, Fe, Cu and Mo, feathers by higher concentrations of Al and Si, and bones by higher concentrations of Sr and Mg. Differentiation among the three age classes of cormorants was observed only with regard to elemental concentrations in their feathers: subadult cormorants were differentiated by higher Hg and Zn concentrations, while the adults were separated by higher concentrations of Fe. In comparison with their prey (common carp and Prussian carp) cormorants were differentiated by higher concentrations of Fe, Hg and Cu in the muscle. Toxic mercury concentrations above 4µgg(-1)dw were determined in the liver of juvenile cormorants, as well as in the liver and feathers of subadults. Hg concentrations were significantly correlated among all studied tissues. Cormorant had significantly higher concentrations of Fe and Hg in muscle and liver than two studied fish species.

Heavy metal accumulation and the genotoxicity in barbel (Barbus barbus) as indicators of the Danube river pollution.

The aim of this study was to analyze 16 trace elements (Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Pb, Sr, and Zn) in different barbel (Barbus barbus) tissues and to detect the presence of genotoxic effects in erythrocytes with the alkaline comet assay. Barbel specimens were collected in the Danube river near Belgrade, Serbia, where the discharge of untreated communal and industrial wastewaters is likely to produce negative effects on fish residing in this area. The highest concentrations of Sr, Mn, Fe, Ba, B, and Al were found in gills, Mo and Cu in liver, and As and Zn in gonads. Concentrations of Zn and Fe were above maximum acceptable concentrations (MACs) in a number of gonad, gill, and liver samples. Three-year-old barbel specimens had higher tail moment and Zn concentrations in gills (1.71 and 51.20 µg/g dw, resp.) than 5-year-old specimens (0.85 and 42.51 µg/g dw, resp.). Results indicate that the younger barbel specimens might be more suitable for the monitoring of environmental pollution.

Non-dioxin-like PCBs in ten different fish species from the Danube river in Serbia.

This work has been developed to examine the level of non-dioxin-like (ndl) PCBs (28, 52, 101, 138, 153 and 180) in (a) ten different freshwater fish species from the Danube river, (b) two sampling points: up and downstream of the industrial zone of the city of Pancevo (ecological hot spot in Serbia) and (c) two time points i.e., in 2001 and 2006. Obtained results would serve to analyse spatial, temporal and congener profile characteristics of ndl PCBs cumulated in fish tissues due to environmental pollution. Sixty-four samples of the following species were collected: wels (Silirus glanus), pike (Esox lucius), bream (Abramis brama), crucian carp (Carassius carassius), pike pearch (Stizostedion lucioperca), barbel (Barbus barbus), tench (Tinca tinca), sterlet (Acipenser ruthenus L.), common carp (Cyprinus carpio) and bighead carp (Hypophthalmichthys nobilis). Gas chromatography coupled with electron capture detector was used for analysis of ndl PCBs. Total ndl PCBs content in upstream samples ranged from 2.7 to 98.1 ng/g and from 4.9 to 68.3 ng/g in 2001 and 2006, respectively. During the 5 years, ndl PCBs content increased significantly in downstream samples i.e., ndl PCBs varied from 13.7 to 46.1 ng/g and from 14.4 to 107.2 ng/g in 2001 and 2006, respectively. PCBs 138 and 180 were predominant congeners in 2001, while in 2006 the most abundant PCB congeners were 138 and 153. In 2006, the presence of PCB 28 and PCB 52 has indicated a recent contamination event. Data on continual monitoring of PCBs in all relevant environmental compartments together with appropriate biomonitoring data are expected to give comprehensive insight into the fate and behaviour profile of these contaminants.

Seasonal variations of macro-, micro-, and toxic elements in tissues of vimba bream (Vimba vimba) from the Danube River near Belgrade, Serbia.

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.

Liver, gills, and skin histopathology and heavy metal content of the Danube sterlet (Acipenser ruthenus Linnaeus, 1758).

The sterlet (Acipenser ruthenus L.) is a bottom-feeding fish species with a direct exposure to contaminants from water and sediments. Although heavy metal pollution is believed to be one of the main threats to the sterlet population in the Danube River basin, there is a lack of knowledge of the exact impact of heavy metals on their survival. In the present study, effects of heavy metal pollution on sterlet in the Danube basin were assessed as well as the utility of different sterlet organs and tissues as indicators of heavy metal contamination. The sterlet were sampled at three different sites in the Danube basin, in Hungary and Serbia, isolated from each other by dams. Heavy metal analysis included measurement of Cd, As, Pb, Cr, Hg, Cu, Ni, Fe, Mn, and Zn concentrations in sterlet gills, muscle, liver, and intestine, and histopathological analyses comprised assessment and scoring of the extent and intensity of alterations in skin, gills, and liver tissue. Analysis revealed a significant presence of sublethal histopathological changes that were most pronounced in the liver and skin and increased accumulation of heavy metals, with the highest concentrations in the liver. Canonical discriminant analysis showed significant differentiation among the three studied localities, suggesting that the heavy metal concentrations in sterlet populations were site specific. The present study concludes that the accumulation of heavy metals is a response to the presence of these pollutants in the environment, and, together with other pollutants, it affects the vital organs of natural sterlet populations.

Impact of reservoir properties on elemental accumulation and histopathology of European perch (Perca fluviatilis).

This study was conducted on individuals of European perch from six reservoirs in Serbia with different properties, used for different purposes, and situated at different altitudes. Samples of muscle, gills, and liver, as well as water samples, were used for analysis of elemental accumulation. Histopathological (HP) analysis of gills and liver, and Fulton's condition factor (CF) were used as biomarkers. Analysis of Ag, Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Se, Si, Sr, and Zn was conducted by inductively-coupled plasma optical emission spectrometry (ICP-OES), and accordingly, metal pollution index and bioaccumulation factor (BAF) were calculated. Elemental accumulation varied considerably both among tissues and reservoirs. Reservoirs located on large low-altitude rivers were the most heavily polluted with metals (Meduvrsje, on the Zapadna Morava River, and Lake Sava, on the Sava River). Of three tissues analyzed, the gills were most affected by pollution. The levels of Hg in muscle decreased with an increase in reservoir altitude. Specimens sampled from the highest altitude reservoir were the least affected by HP alterations; however, HP differences between the reservoirs were not statistically significant, and the severity of HP changes was generally low. No significant correlations between the elemental accumulation or HP indices with CF were observed.

Risk assessment of using fish from different types of reservoirs as human food - A study on European perch (Perca fluviatilis).

Concentrations of As, Cd, Cr, Cu, Hg, Pb, and Zn in sediment samples and muscle tissue of the European perch were analyzed using inductively-coupled plasma optical emission spectrometry (ICP-OES), with the aim to assess the potential ecological (RI) and human health risk, and the degree of contamination (Cd) of three types of reservoirs in Serbia, based on their purpose: electricity generation (Vlasina, Perucac, Zaovine, and Meduvrsje), drinking water supply (Garasi), and recreation (Lake Sava). The concentrations of the studied elements were higher in sediments than in fish. However, the levels of Cd in fish caught in Vlasina, Zaovine, and Meduvrsje, Hg in Perucac and Garasi, and Pb in Lake Sava exceeded the maximum allowed concentrations. The pollution load index (PLI) indicated that sediments in all six reservoirs were contaminated, but Cd was low; a moderate contamination with Cd was observed in Vlasina, Perucac, and Zaovine, Cr in Zaovine and Meduvrsje, and Cu in Meduvrsje. A low RI was recorded for all studied reservoirs. Cd was found to be the primary contamination and ecological risk factor. Total target hazard quotient (THQ) and target carcinogenic risk factor (TR) were higher for fishers operating in these reservoirs than for the general population. Higher values of PLI, Cd, RI, and TR were observed in electricity generation reservoirs. Results indicated that this type of reservoirs suffer from higher anthropogenic pressure and/or have a worse pollution management policy compared with other types of reservoirs included in this study, especially the drinking water supply reservoir.

Seasonal variation in metal concentration in various tissues of the European chub (Squalius cephalus L.).

Due to the increasing industrialization, metals are discharged into all spheres of the environment, in particular, in river courses, which leads to the need for constant monitoring. Metals do not degrade into harmless end products; they are very persistent and have high potential for accumulation in biota. Metals in the fish body are accumulated in different amounts in the tissue specific matter. In relation to the biotic conditions and fish metabolism, the load of food, or the stage of the reproductive cycle, the seasonal variation of metal levels can be expected. Because of that, the objective of our present study was to analyze 15 metals and metalloids in liver, gills, muscle, and gonads of European chub (Squalius cephalus) throughout the 4 seasons, autumn, winter, spring, and summer. The specimens were collected from two rivers, Pestan and Beljanica at the Kolubara basin, and their concentrations were determined with inductively coupled plasma optical emission spectrometry (ICP-OES). Specimens from both rivers have shown similarities in metal accumulation like the highest accumulation of majority of elements in gills, lowest accumulation of majority of elements in muscle (except for Hg), and higher accumulation of some elements in summer (Cu, Fe, Zn). In addition, Cu and Fe showed affinity for liver, while Ba, Cr, Sr, and Zn were specific for gills. Also, Al, B, Fe, Ni, and Pb did not show significant differences in concentrations among different seasons in all investigated tissues.

An affordable and reliable assessment of aquatic decomposition: Tailoring the Tea Bag Index to surface waters.

Litter decomposition is a vital part of the global carbon cycle as it determines not only the amount of carbon to be sequestered, but also how fast carbon re-enters the cycle. Freshwater systems play an active role in the carbon cycle as it receives, and decomposes, terrestrial litter material alongside decomposing aquatic plant litter. Decomposition of organic matter in the aquatic environment is directly controlled by water temperature and nutrient availability, which are continuously affected by global change. We adapted the Tea Bag Index (TBI), a highly standardized methodology for determining soil decomposition, for lakes by incorporating a leaching factor. By placing Lipton pyramid tea bags in the aquatic environment for 3 h, we quantified the period of intense leaching which usually takes place prior to litter (tea) decomposition. Standard TBI methodology was followed after this step to determine how fast decomposition takes place (decomposition rate, k1) and how much of the material cannot be broken down and is thus sequestered (stabilization factor, S). A Citizen Science project was organized to test the aquatic TBI in 40 European lakes located in four climate zones, ranging from oligotrophic to hypereutrophic systems. We expected that warmer and/or eutrophic lakes would have a higher decomposition rate and a more efficient microbial community resulting in less tea material to be sequestered. The overall high decomposition rates (k1) found confirm the active role lakes play in the global carbon cycle. Across climate regions the lakes in the warmer temperate zone displayed a higher decomposition rate (k1) compared to the colder lakes in the continental and polar zones. Across trophic states, decomposition rates were higher in eutrophic lakes compared to oligotrophic lakes. Additionally, the eutrophic lakes showed a higher stabilization (S), thus a less efficient microbial community, compared to the oligotrophic lakes, although the variation within this group was high. Our results clearly show that the TBI can be used to adequately assess the decomposition process in aquatic systems. Using "alien standard litter" such as tea provides a powerful way to compare decomposition across climates, trophic states and ecosystems. By providing standardized protocols, a website, as well as face to face meetings, we also showed that collecting scientifically relevant data can go hand in hand with increasing scientific and environmental literacy in participants. Gathering process-based information about lake ecosystems gives managers the best tools to anticipate and react to future global change. Furthermore, combining this process-based information with citizen science, thus outreach, is in complete agreement with the Water Framework Directive goals as set in 2010.

Ecological risk assessment for different macrophytes and fish species in reservoirs using biota-sediment accumulation factors as a useful tool.

Metal content was evaluated in the sediment, macrophytes and fish in the Medjuvrsje reservoir (Western Serbia). Concentrations of 16 trace elements (Ag; Al; As; B; Ba; Cd; Co; Cr; Cu; Fe; Li; Mn; Ni; Pb; Sr; Zn) were analysed in the sediment, macrophytes and fish of an aquatic ecosystem. Five macrophyte species and three fish tissues (liver, muscle, gills) from five fish species (freshwater bream, common nase, Prussian carp, chub, wels catfish) were sampled and the metal content was analysed with ICP-OES. The sediment concentrations of Cu, Cd, and Zn exceeded the Canadian sediment quality guidelines while concentrations of Cr and Ni were above the Netherlands' target values. Bioaccumulation factors (BSAF) were calculated for analysed macrophytes and fish tissue. The BSAF had higher values for macrophytes for all investigated elements except for Cu and Zn; Cu had a higher value in the liver of the freshwater bream (0.823) and Zn had a higher value in the liver of freshwater bream (0.914) and chub (0.834) as well as in gills of Prussian carp (2.58) and chub (1.26). Potamogeton pectinatus, Ceratophylum demersum and the root of Phragmites communis showed higher accumulation of elements than Trapa natans and Potamogeton fluitans and the body of P. communis. The highest BSAF values for Ba, Mn, Sr and Ni were recorded in the gills. Cd and Cu had the highest BSAF values in the liver. Results confirmed that particular macrophyte and fish species could be a good indicator of reservoir water and sediment pollution.

The impact of multiple stressors on the biomarkers response in gills and liver of freshwater breams during different seasons.

Biomarkers attract increasing attention in environmental studies, as a tool for detection of exposure and effects of pollution, from both natural and anthropogenic sources. This study aims to assess the impact of multiple stressors during distinctive seasons, covering also extreme hydrological events (extensive flooding in the mid May 2014), on different levels of biological organization in the liver and gills of three closely related freshwater breams. Our previous study on DNA damage in blood cells of these specimens showed increased DNA damage in June 2014, one month after the flooding event. As a continuation of that research, the present study was conducted. As a biomarker of exposure DNA damage was measured by applying the alkaline comet assay, while histopathological alterations were monitored as a biomarker of effect. Additionally, concentrations of metals and metalloids in gills, liver and muscle were assessed. Sampling of fish tissues was performed in 2014, during winter (January and February), spring (March and early June) and summer (late June, July and August). Significant seasonal difference in DNA damage was observed for both tissues. During spring and summer the level of DNA damage in gills was significantly higher when compared to the liver. Histopathological analyses showed higher frequency of alterations in gills during spring, and in liver during summer, but without a significant seasonal difference. Gills had the highest concentration of metals and metalloids during the spring and summer, and liver during winter. Muscle was the least affected tissue during all three seasons. This study highlighted the importance of the multiple biomarker approach and the use of different fish tissues in assessment of surface water pollution.

Prediction of fish catch in the Danube River based on long-term variability in environmental parameters and catch statistics.

The effects of physical factors on fish catch in the Serbian part of the Danube River were studied for period of six decades. The data on total catch for the Danube River from river kilometre 845 to river kilometre 1433 were collected from Statistical Office of the Republic of Serbia, while water level and water temperature data were collected from 16 water gauge stations along the investigated part of the Danube River for the period 1948-2009. Cross-correlation functions have been used to analyse the functional connection between Danube water level, water temperature and fish catch while ARMA model which combines cyclic (deterministic) and random (stochastic) components of the analysed sequences was used for the forecasts. The cross-correlation function showed negative correlation between water level and temperature as well as between water temperature and catch and positive correlation between water level and catch. The Danube water level and catch were coherent at the periods of 2.06, 4.13, 6.2, 10.33, 20.66years, while the cross correlation function between these time series did not show phase lag. The results of reconstruction and forecast of water level, temperature, and catch of fish in the Danube River, obtained by summing the cyclic and stochastic components, was used for the forecast till 2029. In 2016, seven years after, the initial forecasts were made, validity of the model was checked by obtaining data for water temperature, water level and fish catch in the Danube River for the period 2010-2015. Model gave the best prediction for water temperature; average standard error was 1.6 times higher for predicted value than for model value while for fish catch and water level they were 1.96 and 4.97, respectively. Methods used in this work could be powerful tool for prediction of fish catch and serve as the basis for better fisheries management.