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The Danube River basin currently lacks a comprehensive action plan for restoring its freshwater and transitional water ecosystems, despite some efforts to address continuum disruptions in upstream regions. The DANUBE4all project aims to address these challenges by identifying, selecting, and recommending implementation measures to increase the extent of free-flowing rivers throughout the entire basin. One of the specific objectives of the project involves identifying suitable habitats for both protected and invasive species, prioritizing conservation actions. To accomplish this, we initially modeled the habitat suitability of the fish species that inhabit the Danube basin. Fishes were chosen because they are good indicators for longitudinal connectivity. This modeling process involved spatially explicit species distribution models, which were trained using environmental data and information on species occurrences. Following the habitat suitability modeling, we conducted a spatial conservation planning analysis. This analysis aimed to pinpoint regions across the Danube River basin that are of high priority for future conservation and monitoring efforts. Priority areas were identified based on the presence of suitable habitats for fish species and the facilitation of longitudinal connectivity within the river system. more...

Das Einzugsgebiet der 2.857 km langen Donau ist mit einer Gesamtfläche von 801.463 km² - rund 10% des europäischen Festlands - das zweitgrößte Flusseinzugsgebiet in Europa. Es erstreckt sich über 19 Länder und ist damit das internationalste Flusseinzugsgebiet der Welt. Über 100 Fischarten sind in der Donau nachgewiesen, darunter vier hochgradig gefährdete Störarten, die charakteristischen Flaggschiffarten der Donau (SCHIEMER ET AL. 2004). Die diadromen Donaufischarten (z. B. Störe (Acipenser spp.), Pontischer Maifisch (Alosa immaculata), Asowscher Maifisch (Alosa tanaica) und Schwarzmeerforelle (Salmo labrax)) sind zwingend darauf angewiesen ihren Lebenszyklus im Süß- und Salzwasser zu vollziehen. Einige Arten wandern bzw. wanderten dabei über sehr große Distanzen, beispielsweise der Beluga-Stör (Huso huso) vom Schwarzen Meer bis zu den Laichgründen >2.500 km ins Landesinnere (SCHMALL & FRIEDRICH 2014). Aber auch potamodrome Arten migrieren in der Donau über weite Strecken; für Döbel (Leuciscus cephalus), Barbe (Barbus barbus) und Nase (Chondrostoma nasus) sind z. B. Wanderungen über 169, 318 und 446 km nachgewiesen (STEINMANN ET AL. 1937, VAN TREECK ET AL. 2022). Die Fischartenzusammensetzung und der Fischbestand sind wichtige Indikatoren für die Gewässerqualität der Donau. Die Ergebnisse des jüngsten Joint Danube Survey 4 zeigen, dass die Fischartengemeinschaft entlang des gesamten Flusslaufs bedroht ist. Andererseits ist die Vielfalt der Fischtaxa immer noch auf einem Niveau, als dass wirksame Gewässerentwicklungsmaßnahmen dazu beitragen können den ökologischen Zustand bzw. das ökologische Potential zu verbessern und die Ziele der EG-WRRL zu erreichen (BĂNĂDUC ET AL. 2014, ICPDR 2021). more...

This study was conducted on individuals of White bream from commercial catches carried out between December 2014 and May 2015 at two locations in the Danube near Belgrade, Veliko ratno ostrvo (VRO) – the main canal of the Danube, with fast water flow and Jojkića Dunavac (JD) – an armlet of the Danube, with slow water flow. A total of 377 individuals were analysed. Total body length (L, cm) and body weight (W, g) of each sampled individual were measured, and Fulton's condition factor was calculated. Average TL of the fish individuals from the VRO and JD were 23.8±2.4 and 23.1±1.7, respectively, and average W were 201.0±73.0 and 164.4±42.2, respectively. In general, fish from location VRO were in better condition (K = 1.44±0.16) compared to sample from JD (K = 1.31±0.11). Individuals in the sample from VRO had a positive allometric growth (a = -2.22, b = 3.28, r² = 0.89), while those from JD had a negative allometric growth (a = -1.79, b = 2.93, r² = 0.85). Based on the results of this study, positive allometric growth (b > 3) and fish condition indicated that individuals from VRO increased body mass more than body length. The source of food, its availability, and better habitat conditions at VRO could be the reason for the differences in the growth and condition of the fish from the investigated locations. The presented results can be applied in fisheries management plans and sustainable exploitation of this fish species as it provides information on stock condition. more...

Pikeperch of age classes 3+ and 4+ were collected from the Garaši reservoir (Serbia) to analyze their bioindicator potential and compare their possible differences. Concentrations of 26 elements were determined in gills, muscles, and liver by inductively-coupled plasma optical emission spectrometry (ICP-OES) and of 17 organochlorine pesticides (OCPs), and six polychlorinated biphenyls (PCBs) in muscle by gas chromatography with mass spectrometric detection (GC-MS). Histopathological changes in the liver and gills were analyzed as biomarkers of general fish health. Only the concentrations of Cd, Na, and P in the muscles differed significantly. The OCPs and PCBs concentrations were below the detection limits, so fish meat consumption does not pose a risk concerning these substances. Hg and Cd exceeded the maximum allowed concentrations in some 4+ individuals, probably due to biomagnification. Gills were the most affected by metal exposure in both age classes. Histopathological changes and indices were minor and did not differ significantly between age classes, suggesting that pollution did not affect the morphology and structure of gills and liver. There were no significant correlations between elemental accumulation and fish condition or between histopathological scores. Therefore, both age classes can be used as bioindicators of pollution. more...

1. Black bullhead is among the most abundant and successful non-native fish species in European freshwaters. A number of studies have indicated that its physical removal could be a potential solution to minimize possible negative impacts that it may have on native fishes; however, so far there have been no field studies to confirm this. 2. This study quantified population dynamics of both native and non-native fishes in a small slow-running lowland river within the Ponjavica Nature Park in Serbia before and after the black bullhead removal with fyke-nets, which proved to be an efficient tool for this purpose. 3. The removal of black bullhead resulted in statistically significant changes in two native species abundance – an increase of rudd (Scardinius erythrophthalmus) (by 5.3 times), and a decline of bleak (Alburnus alburnus) (by 2.3 times). 4. Significant increase was observed in three non-native fish species: the abundances of topmouth gudgeon (Pseudorasbora parva), pumpkinseed (Lepomis gibbosus), and Prussian carp (Carassius gibelio) increased 25.5, 4.9, and 4.2 times, respectively. 5. There were also substantial changes in the diversity of the fish assemblage after the black bullhead removal, illustrated by changes in diversity indices: Shannon's index doubled, while the Simpson’s dominance index decreased threefold. 6. The catch-per-unit-effort and the biomass-per-unit-effort values indicated the dominance of the black bullhead in the fish assemblage. YOY/adult ratio did not vary in relation to abundance, which confirmed that black bullhead might not compensate for fishing mortality with the increased recruitment. 7. The results suggest that black bullhead plays a significant role in structuring the fish assemblage and that its removal may have both positive and negative effects on species abundance and diversity. These findings can contribute to the conservation of native fish species and improvement of future management programs. more...

In the sake of better understanding of the mechanisms that drive interactions between invasive species and their ecosystems, results of selective removal of the black bullhead (Ameiurus melas) in two different lentic systems were compared. Ponjavica Nature Park has characteristical watercourse of the plains with very slow flow and the coastal remains of wetlands. Markovačko reservoir was built for the needs of the irrigation system of the nearby agricultural land. Both systems suffer dominance of the black bullhead, characterized as a species of "globally high risk". Combining results of the mass removal, the effects on the native fish populations have been empirically demonstrated and quantified. Black bullhead selective removal in Ponjavica lasted from August - October 2018, April - September 2019, with 20,145 black bullhead individuals removed. It showed decreased abundance of bleak (Alburnus alburnus) 2.3 times, while the abundances of roach (Rutilus rutilus) and European perch (Perca fluviatilis) remained almost unchanged. A significant increase in abundance was recorded in rudd (Scardinius erythrophthalmus) (5.3 times). The abundances of topmouth gudgeon (Pseudorasbora parva), pumpkinseed (Lepomis gibbosus), and Prussian carp (Carassius gibelio) increased 25.5, 4.9, and 4.2 times, respectively. The mass removal of black bullhead on Markovačko Lake lasted from August - October 2020, April - September 2021, and 15,921 black bullhead specimens were removed. When the post removal state from Markovačko lake was determined, two species appeared in the sample for the first time: European perch and chub (Squalius cephalus). The abundance of bleak increased 3 times, abundance of Prussian carp reduced 8 and black bullhead 16 times. The abundance of roach decreased 11, rudd 10, pike-perch (Sander lucioperca) 4 and freshwater bream (Abramis brama) 2 times. The abundances of pumpkinseed increased 10, Monkey goby (Neogobius fluviatilis) 3 and topmouth gudgeon 2.5 times. The more...

Over 2850 km long, the Danube River is certainly the most important river in Europe, flowing through Germany (687 km), Austria (358 km), Slovakia (172 km), Hungary (417 km), Croatia (138 km), Serbia (587 km), Bulgaria (472 km), Romania (1075 km), Moldovia (<1 km) and Ukraine (54 km) in a west-east direction, and representing a “water backbone” for many European countries located in its basin. more...

White bream is an important species in commercial and sport fishing that is caught in nets throughout the year. The analyzed samples of white bream (n = 377) came from commercial catches carried out between December 2014 and May 2015 at two locations in the Danube near Belgrade, Jojkića Dunavac (JD) – an armlet of the Danube, with slow water flow and Veliko ratno ostrvo (VRO) – the main channel of the Danube, with fast water flow. Total body length (TL, cm) and body weight (BW, g) of each fish were measured, and Fulton's condition factor (K = W/L3 x 100) was calculated. Average TL of the fish samples from the JD and VRO were 23.1±1.7 and 23.8±2.4, respectively, and average BW were 164.4±42.2 and 201.0±73.0, respectively. In general, fish from VRO were in better condition (K=1.44±0.16) compared to sample from JD (K=1.31±0.11). Individuals in the sample from JD had a negative allometric growth (a = -1.79, b = 2.93, r² = 0.85), while those from VRO have a positive allometric growth (a = -2.22, b = 3.28, r² = 0.89). Based on the results of this study, positive allometric growth (b > 3) and fish condition indicated that individuals from VRO increased body mass more than body length. The source of food, its availability, and better habitat conditions at VRO could be the reason for the differences in the growth and condition of the fish from the investigated locations. more...

River infrastructures, such as hydropower plants Iron Gate I (IG; rkm 943) and II (rkm 863) represent major obstructions to fish migration in the Danube River. Knowledge about fish behaviour and movements in the vicinity of major river structures is required to build effective fish passages to protect migratory fish species, with acoustic telemetry being an useful method for observing such behaviour. From autumn 2019 to the spring 2021, the movement of 185 fish (barbel Barbus barbus, nase Chondrostoma nasus, vimba bream Vimba vimba, asp Leuciscus aspius, Pontic shad Alosa immaculata, and carp Cyprinus carpio) were monitored in the Danube River upstream and downstream of the IG II dam using acoustic telemetry. The movements of tagged fish were recorded by a combination of automatic tracking of fish passing receivers deployed in the river and manual tracking by boat. Of the 101 fish released downstream of IG II, 48% moved upstream from their release site and were detected close to IG II. The remaining 84 tagged fish were released in the reservoir between IG I and II, with 49% of fish moving further upstream in the reservoir and 18% reaching IG I, while 48% of the tagged fish moved in a downstream direction and were recorded below IG II. No fish released downstream of IG II were detected in the reservoir between two dams, which indicates that the ship locks on either side of the river do not represent viable routes for upstream migration around IG II. There was also no clear pattern in which side of the river tagged fish preferred to move along. To conserve migratory fish species, dam management strategies that take into account the behaviour of fish around such structures is necessary. Acoustic telemetry can be used to inform and guide towards construction of the safe fish passage or adapt structures to improve the movement and fish migration. more...

European rivers are obstructed by more than one million barriers that have resulted in excessive loss of river continuity. On the main course of the Danube River there are 83 longitudinal continuity interruptions, out of which 65 dams are used for hydropower (ICPDR 2022a). The Iron Gate Hydropower and Navigation System is one of the largest river engineering projects undertaken in Europe, with the dams mainly built to provide hydropower and flood protection, and to facilitate navigation along the Danube. These infrastructures represent introduced barriers to fish migration. Hence, ensuring passage opportunities for fish at the Iron Gate dams is considered to be of major importance for the conservation of migratory fish populations in the Danube River basin. Restoration of river continuity at these sites would reopen an additional 900 km for migration up to the Gabčikovo dam, providing suitable habitats and spawning grounds along the Danube and its tributaries. Knowledge about fish behavior and movements in the vicinity of these river infrastructures is required to build effective up- and downstream passage facilities to allow the migration of fish species. To gain insight in the approach routes and aggregation areas a refined approach to acoustic telemetry is employed to support migration facilitation. more...

In this study, the movements and behaviour of Wels catfish (Silurus glanis, Linnaeus, 1758) were monitored during the different seasons when the water level in the river changed significantly. Wels catfish was caught on the Danube River, rkm 863, and tagged with an ultrasonic transmitter. Deployed Vemco receivers recorded detections of spatial movement between years 2015 and 2017. Our telemetry data found relatively short movements within a maximum range (~12km), but as a territorial species most of the time it was recorded by the two receivers, close to the Iron Gate dam and location where it was caught. Circadian rhythm showed that in the summer period, nocturnal activity is evident while during winter Wels catfish stayed most of the time at the same depth under the water surface. Wels catfish changed depths during the autumn and spring when more activity was recorded. The last signal received was during the winter 2017, which was period with the low temperatures and ice cover on the Danube River. This research shows the value and importance of installing coded acoustic transmitters in fish and monitoring their movement using a series of autonomous receivers deployed in the Danube River. Research by telemetry can be used to better understand fish behaviour and movements and to help improve large river management measures. more...

The European eel (Anguilla anguilla), a catadromous, critically endangered species, was the subject of this study. The main goal was to determine the status of populations of European eel in the waters of the Republic of Serbia. The research included both fieldwork (27 sampling sites) and the literature data analysis for all three river basins in Serbia: Aegean, Adriatic, and Black Sea. The methodology of data collection and determination of European eel presence differed from basin to basin. The fish were identified, measured, noted and immediately returned to the water. The waters that belong to the Aegean basin in Serbia could not be considered anymore as a natural habitat for the European eel, although it inhabits the middle and lower reaches of the rivers that belong in Bulgaria, Greece and North Macedonia. The rivers of the Adriatic basin were not available for sampling; therefore, just literature data were collected. Insufficient literature data on the presence of European eels in waters of the Black Sea basin in the last decade imposed using of inquiry survey with commercial fishermen about occurrence of European eels in their catches. Total of 54 commercial fishermen were surveyed at 31 locations on the Danube, Sava and Tisza. Results showed presence of both silver and yellow stages. The survey showed that there is a linkage between the time and manner of occurrence of the life stages. The collected data were georeferenced and the area where European eels were recorded was defined. Based on the hypothetical projection, according to statistical data, annual catch reached 1352 kg in the Danube, Sava and Tisza. Recent data (2015 to 2019) are predominantly related to the Danube, which can be correlated to the connection between the Black and North Seas (Rhine-Main-Danube canal connection). This study shows that the appearance of the juvenile migration stages of European eels is not unimportant and deserves more research attention. more...

Stone crayfish, an endangered and protected species in Republic of Serbia, inhabits mountain areas of the country. The knowledge and attitude of children, from two primary schools (Pirot and Bosilegrad) towards this species was tested. Two surveys with the same questionnaire were conducted. The first one was held at the end of the 6th grade, and the second was conducted a year later. The second survey has shown a moderate increase in children's knowledge. To better protect and conserve rare and endangered taxa it is necessary to raise awareness of the public, particularly in the areas where these species are present. Attitudes, values, behavior, knowledge of citizens and especially young generations form a good basis for the protection and sustainable development planning in local community. more...

The Pan-European Aquatic Animal Tracking Network is a data management and partnership platform that aims to connect and share data across Europe. It presents a forum where researchers and laboratories can shape partnerships, develop and align their research, share ideas and experiences. Fish are the most researched group of organisms, as they travel far and wide and sharing of data about their movement across countries is essential. Moreover, development of coordinated, Pan-European conservation measures is the key for their conservation. The backbone of the ETN is therefore a central database in which telemetry (meta)data can be stored and shared. The ETN COST action was launched to connect more European telemetry scientists and offer opportunities for networking and cooperation. We will focus on presenting the benefits and opportunities that telemetry as a research tool can offer, especially in the scope of the European Tracking Network COST action. more...

Water temperature plays an important role in the fish life cycle, and have a direct impact over fish species movement behavior, migration, feeding and reproduction. The impact might be different between the rivers because of hydro morphological factors that are specific for each watercourse (sediments, water conductivity, turbidity, total suspended solids etc.). The study focuses on 3 fish species, Vimba bream (Vimba vimba), Common nase (Chondrostoma nasus), Common barbel (Barbus barbus). Total number of 43 specimens from these three fish species were caught, tagged and released in Danube River upstream and downstream the Iron Gates II dam and tracked using acoustic telemetry equipment. The fish movement was followed for eight months, from September 2019 to April 2020. In this time period, data from 26 Vimba bream, 13 Common nase and 4 Common barbel movement were collected. Acoustic telemetry data was used to evaluate fish movement in relation with the water temperature variation of the Danube River. In all three species studied, was revealed a decrease in the number of detections in the moment when the water temperature drop below 12 °C more...

North American black bullhead (Ameiurus melas) is an ictalurid species that has become widespread outside of its native range, causing undesirable ecological impacts. Numerous studies have suggested that its physical removal could be a way to reduce any potential detrimental effects of this species. This study measured the effects on population dynamics of both native and non-native fish species following the removal of 20,145 black bullheads from the Ponjavica Nature Park. The most significant changes between the zero-point state and the post-removal state have been recorded among the populations of non-native fish species: the abundances of topmouth gudgeon (Pseudorasbora parva), pumpkinseed (Lepomis gibbosus), and Prussian carp (Carassius gibelio) increased 25.5, 4.9, and 4.2 times, respectively. Previous research has shown that smaller black bullhead individuals enter into competitive relationships with the topmouth gudgeon, while larger individuals use the topmouth gudgeon as prey. By removing black bullhead individuals from the ecosystem, a part of the ecological niche used by both species was freed. Also, the predatory pressure on topmouth gudgeon decreased by removing larger black bullhead individuals. All these factors led to an increase in the abundance of topmouth gudgeon. Black bullhead and pumpkinseed have overlapping diets and are therefore considered competitors for food. Moreover, research on the black bullhead's feeding ecology showed that this species feeds on the pumpkinseed. When a greater number of black bullhead individuals were removed from the ecosystem, it led to an increase in the abundance of pumpkinseed. The abundance of Prussian carp also increased after the removal of the black bullhead. The Prussian carp and the black bullhead are quite similar in terms of diet habits, habitat preferences, and reproductive characteristics. Since these two species are in direct competition, the decline in the black bullhead population contributed to an more...

Allochthonous and invasive species are among the main factors leading to biodiversity loss which further threatens the ecosystem functioning, stability and resilience. A modern way of life and climate changes accelerated and increased the spread of invasive species. Although many ecosystems are facing this problem, the most endangered ones are slow-flowing/stagnant shallow waters. The black bullhead (Ameiurus melas) is recognized as one of the most successful non-native fish species in European freshwaters. Regarding its mitigation, selective mass removal is considered as an effective method to reduce the abundance of the local population. This biomanipulative measure undoubtedly affects other ecosystem components, so monitoring of organisms from different trophic levels is crucial for assessing the impact and success of the whole process. The aim of this study was to detect and examine the changes in phytoplankton structure and abundance, as a response to the mass removal of the black bullhead. Selective removal took place in the lowland Ponjavica River in the same-named Nature Park in Serbia with the domination of black bullhead and urgent need for biodiversity recovery. The removal project was conducted from June to October 2018 and April to October 2019. The removal process was conducted at three localities along the protected part of the Ponjavica River. Along with fish removal, phytoplankton samples for qualitative and quantitative analyses were collected by plankton net and Van Dorn bottle, respectively. The taxonomic literature was used for qualitative analysis, while the Utermöhl method was conducted for the assessment of phytoplankton abundance. More than 200 algal taxa were detected in Ponjavica phytoplankton. Phytoplankton abundance at each of the localities showed similar dynamics ranged from minimal 156914 cell/ml in June, to maximal 1038946 cell/ml in August 2018. Cyanobacteria were the dominant group with more than 98% in total cell number from Augus more...

Distributed throughout all temperate European inland waters, pikeperch (Sander lucioperca L.) is one of the most interesting fish species for angling and in high demand for human consumption. There is also a growing interest in pikeperch aquaculture. Pikeperch as a freshwater predator has high tendency to accumulate metals in its tissues. Eight individuals of 3+ age class and twelve 4+ individuals were caught at Garaši reservoir during summer of 2017. Concentrations of 26 elements (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) were determined in gills, liver and muscles. Metal pollution index (MPI) was used to record the total metal content in different tissues. Apart from this, histopathological lesions in gills and liver were also assessed. Correlation tests between fish condition and element concentration as well as between HP scores for gills and liver were conducted. Aim of the present study was to investigate whether there are differences between element concentrations and HP alterations in the age classes. Results showed that the gills were exposed to the highest pressure of metal pollution in both age classes. There were no significant differences in elemental accumulation and histopathological changes between 3+ and 4+ age classes, nor between the elemental accumulation and condition of fish and between HP indices. more...

Invasive alien fish species represent one of the greatest threats to the biodiversity and ecological status of freshwater ecosystems. Within their management, their application as bioindicators of pollution in monitoring programs should be considered. The aim of this study was to examine the use of black bullhead Ameiurus melas (Rafinesque, 1820), invasive alien fish in Serbia, as a bioindicator of water genotoxicity by alkaline comet assay. Sampling was performed from June to September 2021 on Markovačko Lake, which is exposed to diffuse pollution from the application of pesticides on the surrounding agricultural land. Monitoring also included the assessment of water quality by basic physical and chemical parameters, as well as microbiological indicators of faecal pollution. Alkaline comet assay was performed on fish erythrocytes, on ten specimens per month. The study also included ten control fish from the recirculating aquaculture system (RAS), which were transferred from Markovačko Lake for breeding, and treatment of their erythrocytes with H2O2 as a positive control. Scoring of comets was performed by CometScore 2.0 software. The lowest level of DNA damage was recorded in the control group and the highest in the positive control group. August was the month with the lowest level of DNA damage, and September with the highest. Statistically significant differences were found between all groups indicating a high sensitivity of the alkaline comet assay to discriminate fine differences in the genotoxic potential of water. Knowing that black bullhead is highly abundant in stagnant waters and relatively easy to sample, this study draws additional attention to its use as a bioindicator of genotoxicity. more...

Tokom četiri sezone (sredina leta, kraj leta, rana jesen i sredina jeseni) obavljeno je merenje koncentracije hlorofila-a duž vodenog stuba od 30 m (interval 2 m). Analizirano je variranje vrednosti kao i dubinska distribucija merenog parametra. Tokom perioda direktne stratifikacije akumulaciju odlikuje metalimnionski maksimum koncentracije hlorofila-a. Vrednosti TSI varirale su u opsegu 36,9 – 49,5 dajući indikaciju o oligotrofnom, odnosno mezotrofnom statusu akumulacije u zavisnosti od sezone., During 4 seasons (middle of summer, late summer, early autumn, middle of autumn) measurements of chlorophyll-a have been conducted, along a 30 m water column (2 m interval). Variability of chlorophyll-a concentrations and their vertical distribution were analyzed. During the thermal stratification period, maximal concentrations of measured parameter were recorded in the metalimnion layer. TSI values varied within 36.9 – 49.4, thus indicating oligotrophic and mesotrophic status of reservoir depending on season. more...

The dam’s construction without fish passes had a major impact, obstructing migratory fish populations from moving between different parts of the river systems and utilizing their key habitats. Fish species and fish populations are depending on long migrations are most seriously affected by river fragmentation. Building well-functioning fish passage systems for migratory fish species at Iron Gate I (rkm 943) and Iron Gate II (rkm 863), is crucial for strengthening and re-establishing Danube’s River migratory fish populations. Between March and May 2021, 112 fish specimens were captured downstream Iron Gate II dam. All the fish was previously tagged with 69 KHz ultrasonic transmitters and released upstream Iron Gate II dam reservoir (53 fish) and downstream Iron Gate II dam (59 fish). Some of the acoustic transmitters are equipped with depth sensors, which provide information of water depths used by fish. Fish movements were recorded by a network of 18 ultrasonic automatic Vemco VR2w receivers (10 downstream the Iron Gate II dam and Gogosu branch, 6 in the IG II lake and 2 receivers at the Iron Gate I dam) with a 15 month battery life, positioned in Danube River. Downloading and interpreting recorded data by these receivers will be an important starting point for "We Pass 2" project that will begin in fall of 2021, when will be realized high resolution recordings of 3D fish movements, for finding the best technical solution for their passing upstream or downstream of dams. more...

Wels catfish (Silurus glanis, Linnaeus, 1758) is one of the most targeted species for recreational and commercial fishing in the Danube River, even though studies of behavior and movement patterns of Wels catfish in the Danube are rare. Wels catfish was caught downstream of Iron Gate II hydropower dam and tagged with an ultrasonic transmitter (Vemco Ltd, V16TP). Nine autonomous receivers (Vemco Ltd, VR 2W) recorded detections of spatial movement downstream of Iron Gate II dam between Serbia and Romania for almost two years, between the years 2015 and 2017. Our telemetry data found that Wels catfish exhibit relatively short movements within a maximum range (≈ 12 km), but as a territorial species most of the time it was recorded by the two receivers, close to the Iron Gate dam and location where it was caught. The longest displacement from the preferable place under Iron Gate II dam was migration to Romanian ship lock and turbines located in the right arm of the Danube River. Location under the river dam is already recognized as a place of aggregation of the fish and thus preference of predatory catfish is strongly connected with food availability. Our data revealed that dam and ship lock blocked further migration of this fish. The last signal received was during the winter 2017, which was a period with extremely low temperature and ice cover on the Danube River. Considering the fact that the ice displaced whole receiver deployment downstream the dam, we might conclude that the tagged catfish disappeared because of ice movement during the winter season. Results can be used for management ensuring habitat requirements and developing of restoration and conservation strategies. more...

Gobioids (Gobiiformes: Gobioidei) are a large group of vocal fishes with four sound types documented during aggressive or reproductive interactions in 23 species. Most attention has been dedicated to sound production in Gobiidae and Gobionellidae, while acoustic communications in other phylogenetically distant gobioid groups have been neglected. Odontobutidae, a basal family within the gobioids, is a poorly studied fish assemblage, with sounds documented in only a single species. The goal of this study was to record and describe the acoustic signals produced by Perccottus glenii (Odontobutidae) under laboratory conditions, with particular focus on the reproductive phase (courtship and pre-spawning), and to provide insight into the anatomical basis of the sound emission mechanism. We recorded two acoustically different call types, thumps and tonal sounds. Thumps were low-frequency sounds (similar to 95 Hz) with an irregular waveform, produced by males during both the courtship and pre-spawning phases. Thumps were frequently organized in long trains, a thump burst, composed from approximately five thumps and lasting over 10 s. Tonal sounds were short vocalizations (similar to 90 ms) produced only during courtship interactions, characterized by a sinusoidal oscillogram and a single frequency peak (similar to 120 Hz). Additionally, anatomical examination focusing on the pectoral girdle identified the muscles that could be responsible for sound emission. The levator pectoralis muscle, originating on the neurocranium and attaching to the cleithral bone, is separated into three bundles: a pars lateralis superficialis, a pars lateralis profundus and a pars medialis. These results expand the knowledge about gobioid vocal behaviour and underline the importance of acoustic communication within this group of fish. Odontobutidae is a sister group to rest of the gobioids, and therefore, our results have significant impact for future comparative studies dealing with sound producti more...

The black bullhead is an invasive species that forms dense populations and has a negative impact on the native ichthyofauna. Recent studies indicate that it is one of the most dominant invasive fish species in Serbian waters. Feeding habits based on stomach contents of individuals caught in Lake Sava were analyzed as a first step towards evaluating its possible negative impact on the native fish fauna of the lake. The following indices for diet analysis were applied: vacuity index, frequency of occurrence, numerical abundance and prominence value. Trophic niche breadth and seasonal trophic diversity were calculated using the Shannon's index. The diet spectrum comprised 16 different prey categories from five groups: Mollusca, Crustacea, Insecta, Teleostei and plants. Fish were the main prey in all seasons, followed by aquatic invertebrates. Plant material and terrestrial insects were used as food in relatively small quantities. Predation on fish eggs was also detected. Our research confirmed that this species is an opportunistic generalist. An ontogenetic diet shift was also detected. The lowest value of trophic diversity was found in age 1+ individuals (H=1.39), while the highest was found in age 3+ individuals (H=2.00). The widest niche breadth was recorded in spring 2011 (H=2.12). more...

The aim of the paper is to contribute to the research on education for environmental citizenship in a comparative perspective. The central concept of education is the complex issue of knowledge. In the present paper, different knowledge forms, knowledge use, and types of knowledge production in environmental education are analysed for two EU countries, France and Hungary, together with two candidate countries, Serbia and Turkey. We review the most important theories and publications, the research questions and the methods considered to be examples for our present work. The second part of the paper presents the case studies according to the theoretical priorities. Evidence-based papers on cases in different European countries illustrating and discussing the evaluation of the types of knowledge used in environmental education and sustainability projects, as well as analysing the power-related components of knowledge use are reviewed. In the final part, case studies are compared and conclusions are drawn. more...

The giant European catfish, Silurus glanis (total length = 200 cm; total weight approximate to 80 kg) was caught downstream of Iron Gate II hydropower dam (Danube River, 863 rkm) and tagged with an ultrasonic transmitter (V16TP; Vemco Ltd.) equipped with depth and temperature sensors. Changes in catfish diving behavior and temperature exposure were monitored over a period of roughly 2 years. Transmitter detections were recorded by nine autonomous receivers (VR2W, installed in 2015 between Serbia and Romania, as well as near Romanian shiplock and upstream Romanian turbines). The first signals were recorded on April 28, 2015 and the last on February 13, 2017. Altogether 59,355 and 59,175 detections of the catfish depth and water temperature were recorded, respectively. The greatest number of signals were recorded by the two receivers closest to the location where the catfish was caught, 72.3% and 27.1%, while only 0.6% of signals were recorded by other receivers. The mean catfish depth was 8.4 m, while minimum and maximum depths were 1.2 and 16.2 m. Results obtained showed that this catfish exhibited high site fidelity, while changes in depth at certain periods are possibly related to its search for prey and upstream migration during the spawning period. Hydropower dam and shiplock were obstacles on its migration upstream and telemetry studies could ensure habitat requirements and meet the development of restoration and conservation strategies for the fish resources in the future. more...

Environmental Education is essential to promote awareness and facilitate the development of environmental citizens. To contribute to the enhancement of environmental awareness, Iceland, Serbia, Bosnia and Herzegovina, and Romania have collaborated in joint educational projects which aim at building capacities on sustainable development, delivering environmental teaching lectures, and developing open educational resources. This article presents past and ongoing collaborations between the mentioned countries, assesses the status of environmental education, and highlights the benefits of international collaboration. For this purpose, information on environmental courses in representative universities from each country was collected, SWOT analyses were performed in each country, and a survey among potential students was carried out. The presented analysis reveals that international collaboration raises environmental awareness and increases the likelihood of becoming environmental citizens. more...

The Danube River basin represents a hotspot for the European freshwater diversity. The Danube in Serbia is characterized by a significant level of fish diversity, as well as by economically important fish resources. However, the Danube fish fauna is facing a number of adverse anthropogenic impacts, such as unsustainable fishery, habitat loss and fragmentation, water pollution and non-native species invasions. In this chapter, the major adverse impacts on the Danube fish communities in Serbia are presented, and the critical management measures are discussed, such as those related to supportive stocking and other conservation efforts. In order to ensure adequate protection and sustainable management of fish resources in the Danube in Serbia, it will be critical to introduce effective monitoring system, to establish and enforce adequate management measures, and to intensify research efforts on critical issues related to fish management and conservation. more...