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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.

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.

Accumulation of 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 analyzed in gills, liver, gonads, and muscle of European chub (Squalius cephalus), Cactus roach (Rutilus virgo), and pikeperch (Sander lucioperca) from Zlatar reservoir (Serbia) using inductively coupled plasma optical emission spectrometry (ICP-OES). The highest concentrations of Cu in liver as well as Ba, Ca, Fe, Mn, Na, P, and Sr in gills were detected in all fish species, while the lowest concentrations of Cu, Fe, Mn, Na, and Zn were detected in muscle. Pikeperch had significantly lower concentrations of Ba in all tissues compared to the other species, as well as Fe, P, and Sr in muscle, K, Mg, Mn, Sr, and Zn in gills, and Fe in gonads. European chub had significantly higher concentrations of Ca, Cu, and Zn in muscle, Cu in liver, and Cr and Cu in gonads compared to Cactus roach and pikeperch. Cd concentration in one individual of Cactus roach exceeded the maximum allowed concentration. The muscle was exposed to the lowest pressure of metal pollution in all species, and European chub accumulated more metals compared to the other species. There is no significant health risk due to consumption of investigated species. A major hazard index (HI) contributor in all species was Hg. According to the target carcinogenic risk factor (TR), target hazard quotient (THQ), and HI, men are under lower health risk compared to the women. The TR and THQ for As, Cr, Cu, Fe, Mn, Ni, and Zn as well as HI values were higher for European chub compared to the other species. On the other hand, THQ for Hg was highest for pikeperch.

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.

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.

The surface area of Montenegro’s portion of the Black Sea drainage basin is 7075 km2, or 0.9% of the entire basin, and is made up of the rivers Tara, Piva, Lim, Ćehotina and Ibar, and Lake Plav. The major polluters of watercourses are wastewaters and solid waste from inhabited settlements. According to water categorization regulations, the rivers of the Danube Basin in Montenegro are, based on the status quo, classified into four quality classes. Thus, the mid- and lower courses of the larger rivers fall within quality classes II and III. The water quality of the Lim, downstream of Berane, worsens at its exit from Montenegro and falls into quality class III. The Ibar profile downstream of Bać is largely out of a prescribed class. The Ćehotina downstream of Pljevlja is in water quality class III, and occasionally out of a prescribed class. The Tara belongs to the Durmitor National Park, but its water quality is class I only at its most upstream profile; its profiles downstream of Kolašin are from class II to class III. These findings are confirmed by analyses of their aquatic macroinvertebrate communities, i.e. Oligochaeta, as bioindicators of water quality. The ichthyofauna of the Danube Basin rivers in Montenegro comprises 20 fish species. Hydromorphological alterations of watercourses, such as dam construction, have a significant effect on fish populations. Thus, the dam on the Piva river has a negative effect on the fish population, presenting a barrier to migration routes, as is the case with huchen or Danube salmon (Hucho hucho).

The surface area of Montenegro’s portion of the Black Sea drainage basin is 7075 km2, or 0.9% of the entire basin, and is made up of the rivers Tara, Piva, Lim, Ćehotina and Ibar, and Lake Plav. The major polluters of watercourses are wastewaters and solid waste from inhabited settlements. According to water categorization regulations, the rivers of the Danube Basin in Montenegro are, based on the status quo, classified into four quality classes. Thus, the mid- and lower courses of the larger rivers fall within quality classes II and III. The water quality of the Lim, downstream of Berane, worsens at its exit from Montenegro and falls into quality class III. The Ibar profile downstream of Bać is largely out of a prescribed class. The Ćehotina downstream of Pljevlja is in water quality class III, and occasionally out of a prescribed class. The Tara belongs to the Durmitor National Park, but its water quality is class I only at its most upstream profile; its profiles downstream of Kolašin are from class II to class III. These findings are confirmed by analyses of their aquatic macroinvertebrate communities, i.e. Oligochaeta, as bioindicators of water quality. The ichthyofauna of the Danube Basin rivers in Montenegro comprises 20 fish species. Hydromorphological alterations of watercourses, such as dam construction, have a significant effect on fish populations. Thus, the dam on the Piva river has a negative effect on the fish population, presenting a barrier to migration routes, as is the case with huchen or Danube salmon (Hucho hucho).

The aim of this study was to describe biometric and feeding characteristics of highly in-vasive species Perccottus glenii in the investigated locality. A total of 85 fish were elec-trofished in the drainage channel located at the vicinity of Veliko Gradište (northeastern Serbia) and preserved in the alcohol solution. In the laboratory, fish were measured (TL, ± 0.01 mm; W, ± 0.01 g), otholits and digestive tracts were removed for age determination and dietary analysis (stereomicroscope). Biometric analysis included length-frequency distribution using 10 mm class intervals; determination of average length and weight for each age group; lenght-weigth relationship; Fulton’s condition factor. Ingested organisms were identified to the lowest reliable taxonomic level (mainly order) and counted. The respective ranges of TL and W of examined fish were 35-140.7 mm and 0.5-40 g. Length class 70.1-80.0 mm clearly dominated (24%). Four age groups were determined (0+-3+), and their descriptive statistics is presented. The value of allometric coefficient for the length-weight relationship (b= 3.068) indicated isometric growth. Fulton’s condition fac-tor did not differ between age groups. Empty digestive tract was found in 2 specimens. A total of 12 prey categories representing Ephemeroptera, Trichoptera, Odonata, Hemiptera, Chironomidae, Coleoptera, Gastropoda, Hirudinea, Oligochaeta, Gammaraidae, uniden-tified and terrestrial insects were identified in the diet. Generally, the diet is entirely com-posed of aquatic invertebrates, as only one terrestrial insect was found. Obtained results did not show clear difference in diet composition between age groups. However, analysis have shown that the most diverse diet characterize 2+ age. By frequency, the insect larvae were categories with highest participation regardless of age.

Ispitivana je ishrana potočne pastrmke iz tri vodotoka na području Specijalnog rezervata prirode „Uvac”: Mali Uvac (gornji deo toka Uvca); Tisovica i Zlošnica. Aparatom za elektroribolov ulovljeno je ukupno 29 primeraka pastrmke (14 iz Uvca, 11 iz Tisovice i 4 iz Zlošnice). Pregled crevnog sadržaja obuhvatio je identifikaciju konzumiranih kategorija plena i njihovu brojnu zastupljenost. Na osnovu dobijenih podataka izračunati su indeksi učestalosti, abundantnosti i značajnosti za svaku od utvrđenih kategorija plena. Utvrđeno je da pastrmke iz istraživanih voda, u pogledu diverziteta plena, odlikuje relativno širok spektar ishrane. Generalno, pastrmke iz ovih voda pretežno se hrane akvatičnim beskičmenjacima, pri čemu larve Trichoptera predstavljaju najznačajniji element ishrane. Kao vizuelni predator, pastrmka ispoljava jasan afinitet ka krupnijem i mobilnijem plenu. Dobijeni rezultati, budući da se radi o relativno malim uzorcima prikupljenim tokom jednog mesečnog izlaska (septembar), mogu se smatrati preliminarnim i iziskuju dalja istraživanja., The brown trout (Salmo trutta Linnaeus 1756) inhabits almost all rivers and streams running through the area of Special Natural Reserve «Uvac» (southwest of Serbia). In some of them it represents the only present fish species, and studies of its diet are important issue to understand its biology. Analysis of its diet provides information on its trophic requirements, interactions with other species, and habitat use in the investigated ecosystem (Oscoz et al., 2005; Ruginis, 2008). There are numerous studies concerning feeding of brown trout in European waters and elsewhere (Kara and Alp, 2005; Osoz et al., 2005; Montori et al., 2006; Ruginis, 2008; and references therein). On the contrary, such studies are scarce in Serbia and, to the best of our knowledge, in last 25 years only one paper concerning this matter was published (Skorić et al., 2012). The aim of this study is to describe diet composition of brown trout in the three rivers within the area of the Special Natural Reserve «Uvac».

Som je najveća primarno slatkovodna vrsta ihtiofaune Srbije i u staništima koja naseljava predstavlja vrhunskog predatora. Ova vrsta ne spada u nativnu ihtiofaunu u vodama Rezervata Uvac, a vreme introdukcije, količina i uzrasni sastav unetih riba su nepoznati. Generalno, podaci o biologiji prirodnih populacija soma u otvorenim vodama u Srbiji su siromašni i do sada ne postoje studije o populaciji u akumulaciji Uvac. Ciljevi ovog istraživanja su određivanje starosne i polne strukture populacije somova i njegove distribucije u akumulaciji. Definisane su tri zone akumulacije u kojima je vršeno uzorkovanje, i to: zona I (gornji kanjonski deo akumulacije), zona II (srednji deo akumulacije sa ulivima dve pritoke) i zona III (donji deo akumulacije u oblasti brane). Mrežarskim alatima ulovljeno je ukupno 20 somova. Među ulovljenim jedinkama 7 je bilo mužjaka, 9 ženki i kod 4 jedinke nije bilo moguće makroskopski odrediti pol. Dužina je varirala od 60-86 cm kod mužjaka; 66-113 cm kod ženki i 51-57.5 cm kod polno nezrelih jedinki. Težina ulovljenih primeraka kretala se u opsegu 993-4 000 g kod mužjaka; 1 520-9 000 g kod ženki; i 652-984 g kod polno nezrelih jedinki. Među mužjacima su dominirale jedinke starosti 3+, dok su kod ženki sve starosne klase bile jednako zastupljene (2+-7+). Sve polno nezrele jedinke su bile starosti 2+. Som u akumulaciji Uvac dominantno naseljava gornji (kanjonski) deo, a na osnovu starosne structure populacije pretpostavlja se da je som u akumulaciju introdukovan pre više od 10 godina.

Cilj rada je da se opiše dubinska distribucija odabranih parametara kvaliteta vode (temperatura, koncentracija rastvorenog kiseonika, pH, konduktivitet i koncentracija hlorofila-a) u vodi akumulacije „Uvac” tokom sezone sredina leta – rana jesen 2017. godine. Tokom posmatranog dela vegetacione sezone vodu ove akumulacije odlikuje direktna termička stratifikacija., The aim of the study was to describe the depth distribution of selected water quality parameters (temperature, dissolved oxygen content, pH, conductivity and chlorophyll – a concentration) in the "Uvac" reservoir during the middle of the summer to early autumn 2017. During observed part of the vegetation season, direct thermal stratification of water was recorded. Depth distribution of other water quality parameters closely followed the thermal stratification.

Ovaj rad ima za cilj da ustanovi koja je uloga zakona u dobrom upravljanju ribolovnim resursima. Zaštita i održivo korišćenje ribljeg fonda u Srbiji regulisano je istoimenim zakonom, a odvija se na 17 ribarskih područja i 29 ribarskih područja u zaštićenim prirodnim dobrima. Na 17 osnovnih ribarskih područja upravljaju „javna preduzeća“ ili privatne firme u statusu „doo“. Kod većih područja, posebno u Vojvodini, postoji više upravljača za jedno ribarsko područje. U zaštićenim prirodnim dobrima upravljači su ujedno i korisnici ribljeg fonda. U periodu od 2006. do 2017. godine Zakon o zaštiti i održivom korišćenju ribljeg fonda menjan je u dva navrata: 2009. i 2014. godine. Podzakonska akta su takođe podložna vrlo čestim promenama. U radu se prate efekti promene zakonske regulative na broj rekre ativnih i profesionalnih ribolovaca, broj ribočuvara i trendove u ulovima. Osnovni trendovi su da broj rekreativnih ribolovaca u navedenom periodu opada, broj profesionalnih riba ra stagnira, dok broj ribočuvara raste. Ulov ima tendenciju opadanja za sve vrste koje se statististički prate (šaran, som, smuđ i deverika od autohtonih vrsta, i babuška i tolstolobik od alohtonih). Odnos ulova u rekreativnom i komercijalnom ribolovu pokazuje značajne promene u poslednjih desetak godina: osim za tolstolobika, kod koga dominira komer cijalni ulov, kod ostalih vrsta je došlo do zamene u smislu da rekreativni ulov preuzima dominaciju u poslednjih nekoliko godina

The Iron Gate II HPP represents the first barrier for long migratory fish species (sturgeons, shads, eels) on their spawning migration from the Black Sea to the upstream parts of the Danube River. It was built in 1984 on rkm 864 while Iron Gate I HPP was built on rkm 943 in 1970, both without fish passages. The establishment of fish passages at the Iron Gate dams could provide access of migratory fish to the upstream 900 km long stretch of the Danube and its major tributaries. This study was performed as a part of activities in project "Fish behaviour preparatory study at Iron Gate Hydropower dams and reservoirs" financed by European Investment Bank with the main goal to test telemetry techniques in the vicinity of Iron Gate dams. Fish tagging was performed with Vemco V16 TP acoustic tags, equipped with temperature and depth sensors. Seven Vemco VR 2W receivers were installed on 7 - 8 April 2015 downstream the Iron Gate II HPP, along Serbian and Romanian banks. One catfish (Silurus glanis), with total length about 2 m and total weight about 100 kg, was tagged on April 28th 2015. Additionally, one specimen of barbel (Barbus barbus) and one specimen of asp (Aspius aspius) were tagged in the same year on November 6th and 11th, respectively. Asp and barbel were detected only in short period after releasing while catfish records lasted from 28 April, 2015 till 13 February, 2017. One beluga sturgeon, which was tagged in 2013 in Borcea branch (Danube rkm 300), was recorded on receivers in the vicinity of Iron Gate II during 2015. This research was the first attempt to investigate behavior of different fish species in the vicinity of Iron Gate II. It also point to problems of collecting reliable data for fish behavior in this area and need to solved them.

To shed light on thermoadaptive properties of Salmo trutta from lake Plav (Montenegro), we undertook kinetic studies of pyruvate reduction rates and thermal stability analyses of white muscle LDH. We compared these with the data obtained for trout of the same, confirmed by us, Danubian lineage living in rivers and streams of Serbia and Montenegro. We also tested the effect of acclimation in captivity at 4 and 14 A degrees C. The lake trout was of a typical smoltified phenotype (the size, the elongated silver colored body). At physiological substrate concentration, the breaks in the Arrhenius plots (critical temperature - T-c) correlated with acclimation temperatures or habitat water temperatures. Q(10) values for temperatures above T-c were close to one, in all cases except 4 A degrees C acclimated trout. At temperatures below T-c Q(10) was close to two, except in the case of 14 A degrees C acclimated trout. Lake trout had a highest Q(10) values at temperatures below T-c. It was conspicuous that within the entire range of tested temperatures the differences in Q(10) resulted from the effect of environmental temperature. Higher Q(10) values were obtained with LDH isolated from trout acclimated to 4 A degrees C compared with LDH acclimated to 14 A degrees C. E-a values were much lower at a temperature below T-c compared with temperatures above Tc. Thermal stability of muscle LDH was lower after acclimation to 14 compared to 4 A degrees C, while extremely high thermostability was obtained with the lake trout enzyme. Our data support the concept that T-c values have distinct physiological significance.

Several fish species in the family Salmonidae have evolved multiple life history forms that exploit different degrees of anadromy (McMillan, Pess, & Katz, 2007) and one of these is rainbow trout (Oncorhynchus mykiss). In some cases, anadromous O. mykiss undergo smoltification and migrate, however those migrations are completely within freshwater (Holecek, Scarnecchia, & Miller, 2012). Silvering of juvenile salmonids as a part of smoltification is a key determinant of migratory behavior (Haner, Faler, Schrock, Rondorf, & Maule, 1995). The silvering of the anadromous trout, rainbow trout and salmons, which functions as cryptic colorations in open water (Björnsson, Stefansson, & McCormick, 2011), is the change that occurs during the process of smoltification. However, biological changes that take place during smoltification do not preclude continued life in fresh water (Björnsson, Einarsdottir, & Power, 2012). Spawning of rainbow trout in Serbia has never been recorded. In recreational fishing, the rainbow trout has some significance only in those rivers where aquaculture facilities are located (Simonović, 2001). However, they are occasionally caught in the Danube (M. Nikčević, M., personal observation) and are assumed to be escapees from aquaculture. This study reports on the occurrence of smoltification in rainbow trout O. mykiss along the main bed of the Danube River in its Serbian section.

Temperature dependence of electroretinogram (ERG) was investigated in 3 fish species occupying different habitats - dogfish shark (Scyliorhinus canicula), Prussian carp (Carassius gibelio) and European eel (Anguilla anguilla). Acute cooling of the shark isolated eyecup from 23 degrees C down to 6 degrees C induced suppression of the electroretinographic b-wave - a complete degradation of this component was observed at 6 degrees C. On the other hand, photoreceptor component of the ERG, the negative late receptor potential was not affected by cooling. The fact that the suppression of the dogfish shark b-wave at low temperatures was as a rule irreversible testifies about breakdown of neural retinal function at cold temperature extremes. Although in vivo experiments on immobilized Prussian carps have never resulted in complete deterioration of the b-wave at low temperatures, significant suppression of this ERG component by cooling was detected. Suppressing the effect of low temperatures on Prussian carp ERG might be due to the fact that C. gibelio, as well as other cyprinids, can be characterized as a warmwater species preferring temperatures well above cold extremes. The ERG of the eel, the third examined species, exhibited the strongest resistance to extremely low temperatures. During acute cooling of in situ eyecup preparations of migrating silver eels from 30 degrees C down to 2 degrees C the form of ERG became wider, but the amplitude of the b-wave only slightly decreased. High tolerance of eel b-wave to cold extremes shown in our study complies with ecological data confirming eurythermia in migrating silver eels remarkably adapted to cold-water environment as well.

One of the purposes of this study was to examine whether b-wave measurements can be used in the evaluation of scotopic spectral sensitivity in Prussian carp measurements when the eyes were surgically deprived of cornea, lens, and most of the vitreous. Another goal was testing the new fitting procedure for A2-based photopigments. Using fitted amplitude-log intensity functions for threshold calculation, and two models for computer-assisted fitting of spectral sensitivity curves, no significant differences in lambda (max) were found between rod photopigments and b-wave-based spectral sensitivity.

The distribution and contents of organochlorine pesticides (OCPs) and congeners of polychlorinated biphenyls (PCBs) were analyzed in Bream (Blicca bjoerkna) and Barbel (Barbus barbus) from the Danube River, near Batajnica. The analysed compounds were 16 OCPs (α-Hexachlorocyclohexane (α-HCH), β-Hexachlorocyclohexane (β-HCH), Hexachlorobenzene (HCB), γ-Hexachlorocyclohexane (γ-HCH), δ-Hexachlorocyclohexane (δ-HCH), Heptachlor, Aldrin, cis-Heptachloroepoxide (cis-HCE), trans-Heptachloroepoxide (trans-HCE), γ-Chlordane, p,p'-Dichlorodiphenyldichloroethylene (p,p'-DDE), α-Chlordane, Dieldrin, Endrin, p,p'-Dichlorodiphenyldichloroethane (p,p'-DDD), p,p'-Dichlorodiphenyltri-chloroethane (p,p'-DDT)) and 7 PCB congeners (IUPAC numbers 28, 52, 101, 138, 153, 180, 118). Determination and quantification of OCPs and PCBs were performed by a GC-ECD method. The proximate composition of fish fillets was determined by applying standard SRPS ISO methods. The statistically significant difference (p lt 0.05) was found between the OCPs content in Bream and Barbel, as well as between PCBs content in the analyzed fish filets. Among all analyzed pesticides, both fish contained the highest amounts of ΣDDT (expressed as sum of p,p'-DDT + p,p'-DDE + p,p'-DDD), (13.8 ng/g fish - Bream, 2.6 ng/g fish - Barbel). The sum of PCB congeners in Bream filets (40.8 ng/g fish) was significantly higher than in Barbel filets (7.2 ng/g fish). Results of Student's t-test (p = 0.05) showed the differences in the content of lipids, moisture, ash and calculated energy value between the analyzed fish filets. Four times higher fat content in Bream (4.25%) than in Barbel (1.07%) is one of the main reasons for higher content of OCPs and PCBs in Bream compared to Barbel, which were taken from the same location (The Danube River, Batajnica)., U ovom radu prikazana je distribucija i sadržaj organohlornih pesticida (organochlorine pesticides, OCP) i polihlorovanih bifenila (polychlorinated biphenyls, PCB) u ribama krupatici (Blicca bjoerkna) i mreni (Barbus barbus) iz Dunava u blizini Batajnice. Ispitano je 16 organohlornih pesticida i 7 kongenera polihlorovanih bifenila. Anlizirana su sledeća jedinjenja: α-heksahlorocikloheksan (α-HCH), β-heksahlorocikloheksan (β-HCH), heksahlorobenzen (HCB), γ-heksahlorocikloheksan (γ-HCH), δ-heksahlorocikloheksan (δ-HCH), heptahlor, aldrin, cis-heptahloroepoksid (cis-HCE), trans-heptahloroepoksid (trans-HCE), γ-hlordan, α-hlordan, p,p'-dihlorodifenildihloroetilen (p,p'-DDE), dieldrin, endrin, p,p'-dihlorodifenildihloroetan (p,p'-DDD) i p,p'- dihlorodifeniltrihloroetan (p,p'-DDT) i PCB kongeneri označeni IUPAC brojevima 28, 52, 101, 138, 153, 180 i 118. Kvalitativna i kvanitativna ispitivanja ovih jedinjenja rađena su GC-ECD metodom. Sadržaj proteina, lipida, vlage i pepela u filetima riba određen je korišćenjem standardnih SRPS ISO metoda. Utvrđena je statistički značajna razlika (p lt 0,05) između sadržaja organohlornih pesticida u krupatici i mreni, kao i između sadržaja polihlorovanih bifenila u ispitanim ribama. Najveći sadržaj među ispitivanim organohlornim pesticidima, u obe vrste ribe utvrđen je za ΣDDT (pp'-DDT + pp'-DDE + pp'-DDD), (13,8 ng/g ribe - krupatica, 2,6 ng/g ribe - mrena). Ukupan sadržaj PCB jedinjenja u filetima krupatice (40,8 ng/g ribe) bio je značajno veći nego u filetima mrene (7,2 ng/g ribe). Na osnovu rezultata Studentovog t-testa (p = 0,05) utvrđeno je da postoji statistički značajna razlika u sadržaju masti, vlage, pepela i izračunate energetske vrednosti između fileta ispitanih riba. Četiri puta veći sadržaj masti u filetima krupatice (4,25%) u odnosu na filete mrene (1,07%) jedan je od glavih razloga većeg sadržaja organohlornih pesticida i polihlorovanih bifenila u krupatici nego u mreni, koje su uzete sa istog lokaliteta (Dunav, Batajnic

Anadromous fish could have intraspecific groups with different life histories; identification of these is very important for management and conservation. Geometric morphometrics represents a quick and cost-effective method to identify such intraspecific groups. In this study, geometric morphometrics of Pontic shad (Alosa immaculata) migrants from the Danube River were investigated, as was Fulton's condition factor (K), hepatosomatic index (HSI) and gonadosomatic index (GSI). Pontic shad specimens were collected during April and May of 2004 and 2006. The sample comprised four groups (65 males and 56 females in 2004; 110 males and 78 females in 2006). Geometric morphometrics revealed differences in shape that were statistically significant for both year (nested analysis of variance: F = 13.84; p lt 0.001) and sex (nested analysis of variance: sex nested in year, F = 1.71; p lt 0.01). The major differences between years were in head shape and position of fins. The most significant difference between females and males was in the dorsolateral expansion of the mid-body section with emphasis on the higher dorsal part of the body. Values for K in this work (0.650.70) were the lowest recorded for Pontic shad in the Danube River. Additional investigations involving both geometric morphometrics and molecular genetics are necessary to confirm the presence of races. This could be important information for conservation purposes as Pontic shad is listed as Vulnerable on the International Union for Conservation of Nature list.

The Danube River is 2,857 km long and navigable along the major part of its flow (2,411 km). Human activities have started to influence Danube River flow more significantly since the sixteenth century, through the flood prevention, navigation and hydropower plant construction activities. Two largest dams in the Danube, located at 943 river km ("Iron Gate I", constructed in 1970) and 863 river km ("Iron Gate II", constructed in 1984), have formed a large accumulation lake. These dams represent obstacles for migratory fish species, such as sturgeons and shads. Beside the negative impact of dams and the river flow regulation, common stocks of these species in the Lower Danube Region (LDR) are also impacted by unsustainable and illegal fishery and pollution. Major obstacle to an efficient common management of these fish stocks by LDR countries is a lack of management harmonization and coordination, as well as lack of common management plans that would be based on coordinated monitoring and research efforts in all LDR countries. Guiding principles for a good management plan for sturgeons and shads in the LDR should include efficient public and stakeholder participation, and a long-term vision that would be harmonized with the short-term social, cultural and economic needs. Availability of timely scientific information, provided through the broad and long-term monitoring and research activities, could determine the state of sturgeon and shad stocks and the efficiency of their current management.