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The circulation of the contents of Cu, Cd, and As was traced in the system of Chondrostoma nasus – Pomphorhynchus laevis – Contracaecum sp. – water – sediments from the Danube River in the Kudelin biotope. New data on the content of the elements examined are presented. The concentrations of the three elements in the materials studied, which included tissues, organs, and parasites of common nase, and water and sediments from the Kudelin biotope, were higher than the limits set forth in Bulgarian and international legislative documents. The bioindicator role of the tissues, organs, and parasites examined was revealed, and the liver of common nase and Contracaecum sp. were good bioindicators for Cd content, while P. laevis was a good bioindicator for As content.

The results of research on biological diversity in a section of the Chepelarska River and the territories adjacent to it, subjected to anthropogenic pressure, are presented. The studied area (water body code BG3MA500R103, river type R5Semi-mountainous type in Ecoregion 7 Eastern Balkans) falls entirely within protected area BG0000194 "Chaya River". It is located along the lower section of the river before it flows into the Maritsa River (Eastern White Sea Basin). The types of natural habitats and their ecological status are presented. Regarding the registered 45 species of higher plants and 22 animal species, the nature protection status and the species with resource importance have been determined. The results from the ecological monitoring of the freshwater ecosystem based on physicochemical elements (dissolved O2, pH, electrical conductivity, Ptotal, N-NH4, N-NO2, N-NO3, P-orthoPO4, Zn, Cu, Pb, Cd) and ecological quality element macrozoobenthos, after applying the established standards are discussed. Measures to improve the ecological condition of the studied area are indicated. [ABSTRACT FROM AUTHOR]

During the period 2019-2021, the helminth fauna of two species of freshwater fish of the family Cyprinidae, genus Ballerus Heckel, 1843 - white-eye bream (Ballerus sapa (Pallas, 1814)) and zope (Ballerus ballerus (Linnaeus, 1758)) were examined. Six specimens of white-eye bream and one specimen of zope were collected from a total of three biotopes located in the Bulgarian section of the Danube River between 845 and 807 river km. Three species of helminths were found - 2 species of the class Trematoda (Asymphylodora imitans (Mühling, 1898) Looss, 1899; Nicolla skrjabini (Iwanitzky, 1928) Dollfus, 1960)) and 1 species of the class Nematoda (Contracaecum sp. (larvae)). The present study aims to provide new data on the species composition and helminth ecological indices of the two examined fish species. B. sapa is reported as a new host record for the three helminth species in Bulgaria. Koshava biotope is a new habitat for the established helminths in the white-eye bream. [ABSTRACT FROM AUTHOR]

Twelve specimens of northern pike (Esox lucius (Linnaeus, 1758)) were caught from the Maritsa River during 2020- 2021 and examined for parasites. Helminth parasites were found in 50% of the examined northern pikes (6 specimens) from the Maritsa River. Two species of parasites were fixed: one trematode species (Bunodera luciopercae (Müller, 1776)) and one nematode species (Raphidascaris acus (Bloch, 1779)). The dominant structure of the established species is represented at the level of component communities and infracommunities. R. acus is a core species for the component community of Esox lucius from the Maritsa River. B. luciopercae is an accidental parasite species for northern pike helminth communities. The data for the infracommunities were used to determine the basic biotic indices. The bioindicator significance of the established parasite species was discussed for an ecological assessment of the studied river ecosystem. As a result of the conducted research, new data on the parasite fauna of E. lucius from the Maritsa River have been presented. [ABSTRACT FROM AUTHOR]

The study presents for the first time the Cherna River, southern Bulgaria, Aegean water basin, the results of research on the biological diversity and helminth communities of the Round-scaled barbell Barbus cyclolepis Heckel, 1837. 30 specimens of B. cyclolepis are studied. Infection by 5 species of helminths are found (Allocreadium isoporum (Loos, 1894); Bathybothrium rectangulum (Bloch, 1782); Caryophyllaeus laticeps (Pallas, 1781); Capillaria petruschewskii Zeder, 1800; Neoechinorhynchus rutili (Müller, 1780)). The infection indices and the dominant structure of helminth communities are presented. Basic biotic indices are determined. Helminth communities are analyzed at two levels: infracommunity and component community. All established parasite species are autogenous for the helminth communities of the Round-scaled barbell from the freshwater ecosystem of the Cherna River. New data for helminths and helminth communities of B. cyclolepis are presented. The bioindicator significance of helminths and helminth communities are discussed. [ABSTRACT FROM AUTHOR]

During 2019-2021, six specimens of pontic shad (Alosa immaculata Bennett, 1835); family Clupeidae were examined for parasites. The specimens were collected from three biotopes (Kudelin, Yasen, and Koshava) located in the section of the Danube River in the northwestern part of Bulgaria. Infection with 3 species of helminths was found - 1 species of the class Trematoda (Lecithaster confusus Odhner, 1905); 1 species of the class Acanthocephala (Pomphorhynchus laevis (Zoega in Müller, 1776) Porta, 1908) and 1 species of the class Nematoda (Hysterothylacium gadi aduncum (Rudolphi, 1802) Deardorff et Overstreet, 1981 (larvae)). Ecological indices of the found helminth species were examined. The purpose of the study is to provide new data on the helminth fauna of the pontic shad from the freshwater ecosystem of the Danube River in Bulgaria. Al. immaculata is a new host for one endohelminth species (L. confusus). Two of the investigated biotopes (Koshava and Yasen) are new habitats for the found endohelminths in pontic shad. [ABSTRACT FROM AUTHOR]

For the period 2019-2021, an ecoparasitological study of six fish species - grass carp (Ctenopharyngodon idella Valenciennes, 1844); silver carp (Hypophthalmichthys molitrix Valenciennes, 1844); pumpkinseed (Lepomis gibbosus Linnaeus, 1758); Prussian carp (Carassius gibelio Bloch, 1782); gudgeon (Gobio gobio Linnaeus, 1758); European bitterling (Rhodeus amarus Bloch, 1782) was conducted. The fish were caught from 3 biotopes (Koshava, Kudelin, Novo selo) from the upper section of the Danube River in Bulgaria. A total of two parasite species (Pomphorhynchus laevis Zoega in Müller, 1776) Porta, 1908 and Contracaecum sp. (larvae) were found in two of the investigated fish species. Four fish species were not infected. The ecological indices (mean intensity; mean abundance; prevalence) of parasites were calculated. Kudelin and Koshava biotopes are new habitats for the found helminth species of the infected fish species. [ABSTRACT FROM AUTHOR]

For the period 2019-2021, three fish species of the family Cobitidae, caught from the upper section of the Danube River in Bulgaria, were subjected to ecologohelminthological investigation. Four specimens of Cobitis elongata Heckel & Kner, 1858 (two specimens from Kudelin biotope and two from Koshava biotope); six specimens of spined loach (Cobitis taenia Linnaeus, 1758) (from Koshava biotope) and one specimen of Sabanejewia bulgarica Drensky, 1928 (from Kudelin biotope) are objects of research. The trematode Asymphylodora tincae (Modeer, 1790) Lühe, 1909 was reported for the first time as a helminth of S. bulgarica. The nematode Pseudocapillaria tomentosa (Dujardin, 1845) Moravec, 1987 was reported for the first time as a helminth of C. elongat?. Kudelin and Koshava biotopes are new habitats for the found helminth species. During the helminthological examination of C. taenia, infection with helminths was not found. The study provides new data on helminth fauna and ecological indices (MI, MA, and P%) in the helminth communities of C. elongat? and S. bulgarica. [ABSTRACT FROM AUTHOR]

As a result of the study of 10 specimens Perca fluviatilis Linnaeus, 1758 and 10 specimens Vimba melanops (Heckel, 1837) from the Maritsa River, Aegean water basin, Bulgaria, infection with 5 helminth species are presented (Allocreadium isoporum (Loos, 1894); Proteocephalus percae (Müller, 1780); Caryophyllaeus laticeps (Pallas, 1781); Contracaecum sp., larvae and Acanthocephalus lucii (Müller, 1776)). All identified parasite species are autogenous to the parasite communities of the perch and Macedonian vimba, except Contracaecum sp., which is an allogeneic species. Infection indices are discussed and pathways of helminth flux circulation are traced. The dominant structure of the helminth communities was analyzed. New data on the helminths and their communities in the two species of freshwater fish, as well as on the ecological status of the studied biotopes of the freshwater ecosystem are presented. [ABSTRACT FROM AUTHOR]

This study is the first to reveal the helminth fauna and helminth community's structure of Prussian carp (Carassius gibelio) from Maritsa River, Bulgaria. In 2022, ten Prussian carp specimens were collected from the Maritsa River and examined for parasites. 90% of the studied hosts harbour parasites. Two species of helminths were fixed: one from class Acanthocephala (Acanthocephalus anguillae Muller, 1780) and one from class Nematoda (Pseudocapillaria tomentosa Dujardin, 1843). The established nematode species is distinguished with high prevalence. Carassius gibelio is reported for the first time as a host for Pseudocapillaria tomentosa in Bulgaria. The river ecosystem of Maritsa is a new locality record for Pseudocapillaria tomentosa in Bulgaria. [ABSTRACT FROM AUTHOR]

In 2021, ecologoparasitological research was done based on the helminths and helminth communities of Prussian carp (Carassius gibelio (Bloch, 1782)) from the freshwater ecosystem of the Tundzha River, Aegean Water Basin. As a result of the examined twenty-one specimens of Prussian carp, three taxa of helminths were found: Nicolla skrjabini (Iwanitzky, 1928) Dollfus, 1960; Pomphorhynchus laevis (Müller, 1776) Porta, 1908; Contracaecum sp. The dominant structure of the helminth communities was determined. N. skrjabini is a core species for helminth communities of C. gibelio (P% = 23.81). New data on the helminth communities of the Prussian carp from the studied area of the freshwater ecosystem are presented. The basic ecological indices of the helminth populations and communities were determined. The bioindication role of the established helminth species as well as an assessment of the ecological status of the studied biocenoses was presented. [ABSTRACT FROM AUTHOR]

Ecologoparasitological research was done based on the helminths and helminth communities of the Prussian carp (Carassius gibelio (Bloch, 1782)) from the freshwater ecosystem of the Panicheri Reservoir, Aegean Water Basin, Bulgaria. As a result of the examined nine specimens of the Prussian carp, two species of helminths were found: Ligula intestinalis (Linnaeus, 1758), larvae and Pomphorhynchus laevis (Müller, 1776). The dominant structure of the helminth communities was determined. The Panicheri Reservoir is a new habitat in Bulgaria of P. laevis and L. intestinalis from C. gibelio. C. gibelio is a new host record for L. intestinalis in Bulgaria. The two helminth species are core species for the helminth communities of the examined species of the freshwater fish. P. laevis was distinguished with higher prevalence and mean intensity (P%=33.34; MI=1.34) than L. intestinalis (P%=22.23; MI=1.0). The circulatory pathways of the helminth flow were traced. [ABSTRACT FROM AUTHOR]

In the spring of 2020, ecoparasitological studies were conducted on 30 specimens of common nase (Chondrostoma nasus (Linnaeus, 1758)) from the freshwater ecosystem Danube River near Kudelin village, northwestern Bulgaria. Two parasite species were determined. One species - Proteocephalus torulosus (Batsch, 1786), juvenile, belongs to the class Cestoda. The other one - Contracaecum sp., larvae, belongs to the class Nematoda. C. nasus is a new host for P. torulosus in the studied area. In the study, Contracaecum sp., larvae was a core parasite species (P% = 90.00) in the component community of C. nasus from the Danube River (Kudelin). For Contracaecum sp. larvae, the highest mean intensity (MI = 18.15) and the highest mean abundance (MA = 16.33) were found. [ABSTRACT FROM AUTHOR]

In 2020, 30 specimens of common nase (Chondrostoma nasus Linnaeus, 1758) were caught. A total of 6 samples of water and sediments were collected from the Danube River, near the Kudelin village, north western Bulgaria. Tissues and organs of common nase, water and sediments from the Danube River ecosystem for cadmium (Cd) content were studied. In the samples of tissues and organs of common nase, the highest concentrations of Cd were found in the liver (CCd = 1.21 ± 0.39 mg.kg-1 wet weight). The concentrations of cadmium decrease in the order: liver > skin > muscles. The study presented the bioconcentration factor and the linear correlation coefficient of Spearman. The study compared the norms specified in national and international documents with obtained concentrations for cadmium in tissues and organs of common nase and water and sediments. [ABSTRACT FROM AUTHOR]

During the ecological study of 19 specimens of Prussian carp (Carassius gibelio, Bloch, 1782) from Tundja River, by applying standard techniques for parasites, an infestation was found with the acanthocephalan species Acanthocephalus anguillae (Müller, 1780). Helminth parasites were recorded in 5 Prussian carp specimens (26.32%). The established helminth species is autogenic species, matured in fish. In the component community of Carassius gibelio from Tundja River A. anguillae is core species. This study is the first that presents the Prussian carp's endohelminth species biodiversity from Tundja River, Bulgaria. The established in this study parasite species is discussed and compared with previous researches of parasite communities of C. gibelio from Bulgaria. This is the first report of Acanthocephalus anguillae for the helminth communities of Prussian carp for river related to Aegian Basin in Bulgaria. [ABSTRACT FROM AUTHOR]

In 2020, 30 specimens of bleak (Alburnus alburnus Linnaeus, 1758), 3 samples of water and 3 samples of sediments were collected from the Danube River (Kudelin) in the northwestern part of the Republic of Bulgaria. Samples of water and sediments, of tissues/ organs (liver, skin and muscles) of bleak were investigated for the presence of cadmium (Cd). The concentrations of Cd in the studied tissues/ organs of Alburnus alburnus decreased as follows: liver (CCd = 1.38 ± 0.55 mg.kg-1 wet weight) > skin (CCd = 0.50 ± 0.18 mg.kg-1 wet weight) > muscles (CCd = 0.09 ± 0.05 mg.kg-1 wet weight). The reported concentrations of Cd in water samples are CCd = 0.008 ± 0.006 mg.l-1, and in sediments samples CCd = 1.55 ± 2.35 mg.kg-1 dry weight. [ABSTRACT FROM AUTHOR]

In 2020, 37 specimens of vimba bream (Vimba vimba Linnaeus, 1758) from the Danube River near the village of Kudelin were examined for parasites. Four parasite species were established: Nicolla skrjabini (Iwanitzky, 1928) and Posthodiplostomum cuticola (von Nordmann, 1832) (Trematoda); Pomphorhynchus laevis (Zoega in Müller, 1776) (Acanthocephala) and Philometra rischta Skrjabin, 1917 (Nematoda). The study aims to provide new data on parasites and parasite communities of Vimba vimba from the Danube River’s freshwater ecosystem near the village of Kudelin in northwestern Bulgaria. In the study, the prevalence (P%), mean intensity (MI), mean abundance (MA) and the Brillouin’s diversity index (HB) were presented and discussed. [ABSTRACT FROM AUTHOR]

Ecologoparasitological research was done based on the helminths and helminth communities of wels catfish (Silurus glanis Linnaeus, 1758) from the freshwater ecosystem of the Tundja, Aegean Water Basin. As a result of the examined seven specimens of wels catfish, three taxa of helminths were found. The dominant structure of the helminth communities was determined. Eustrongylides excisus Jägersiöld, 1909, larvae is a core species for helminth communities of S. glanis (P% = 42.86). S. glanis from the river ecosystem is a new host record for E. excisus. The basic ecological indices of the parasitic populations and communities were determined. The bioindication role of the established parasitic complexes was studied. An assessment of the ecological status of the studied biocenoses was carried out. [ABSTRACT FROM AUTHOR]

During the summer of 2017, 10 specimens of freshwater bream (Abramis brama (Linnaeus, 1758)) from the Bulgarian part of the Lower Danube River were examined with standard techniques for parasites. Helminth parasites were recorded in 9 freshwater bream specimens (90.00%) from the Danube River. Five species of parasites were identified: one cestode species Caryophyllaeus laticeps (Pallas, 1781), two trematode species from family Monorchiidae (Asymphylodora imitans (Mühling, 1898); Palaeorchis incognitus (Szidat, 1943)), one acanthocephalan Pomphorhynchus laevis (Zoega in Müller, 1776) and one nematode species Rhabdochona denudata (Dujardin, 1845). All established helminth species are autogenic species, matured in fish. In the component community of Abramis brama from Danube River P. laevis, P. incognitus and R. denudata are core species. A. imitans and C. laticeps are component parasite species for the helminth communities of A. brama. The established in this study parasite species are discussed and compared with previous researches of parasite communities of A. brama from River Danube in Bulgaria. As a result of this study is presented new data for helminths and helminth communities of A. brama. [ABSTRACT FROM AUTHOR]

During 2018, 22 specimens of the round-scale barbell from the Tamrashka River (Bulgaria) were examined for helminths. B. cyclolepis is an endemic fish species of the Maritsa River Water Collection. Five parasite species (Allocreadium isoporum Ergens & Lom, 1970; Caryophyllaeides fennica (Schneider, 1902) Nybelin, 1922; Pomphorhynchus laevis (Müller, 1776); Rhabdochona hellichi (Šramek, 1901) Chitwood, 1933; Rhabdochona gnedini Skrjabin, 1948) belonging to four classes and four families were fixed. The Tamrashka River is a new habitat for All. isoporum, C. fennica, P. laevis, Rh. hellichi and Rh. gnedini of B. cyclolepis in Bulgaria. The dominant structure of the parasite communities was discussed based on the level of the component community. The bioindicator role of the studied parasite populations and communities are presented. [ABSTRACT FROM AUTHOR]

In 2019, studies on the parasites and parasite communities of Chondrostoma nasus (Linnaeus, 1758) from the Danube River, Bulgaria (Koshava and Kudelin villages, Vidin region) were conducted. After ecoparasitological studies of a total of 155 specimens of C. nasus from the two biotopes, eight species of parasites were found: two species of the class Trematoda (Allocreadium isoporum (Looss, 1894), Sphaerostomum bramae (Müller, 1776)), one species of the class Cestoda (Bothriocephalus acheilognathi (Yamaguti, 1934, immature specimens)), one species from the class Acanthocephala (Pomphorhynchus laevis (Müller, 1776)) and four species from the class Nematoda (Raphidascaris acus (Bloch, 1779), larvae; Contracaecum sp., larvae; Hysterothylacium sp., larvae; Pseudocapillaria tomentosa (Dujardin, 1843)). The majority of parasite species (seven species) were detected during the spring from biotope Kudelin. The dominant parasite species in all three seasons was the nematode Contracaecum sp. C. nasus was reported as a new host for A. isoporum, S. bramae, B. acheilognathi, R. acus, Contracaecum sp., Hysterothylacium sp., P. tomentosa from the Bulgarian section of the Danube River. New data on the structure of parasite communities of the river freshwater ecosystem were presented. [ABSTRACT FROM AUTHOR]

The study aimed to present the results of investigations on the content of heavy metals/metalloids (Cu, Cd and As) in tissues and organs (liver, skin and muscles) of Alburnus alburnus (Linnaeus, 1758), and in waters and sediments of the Danube River (Kudelin, Vidin), Bulgaria. The highest Cd contents were found in liver samples (0.80 ± 0.56 mg.kg-1), followed by contents in skin samples (0.21 ± 0.15 mg.kg-1) and muscle (0.08 ± 0.07 mg.kg-1). The highest As contents were found in liver (28.14 ± 10.98 mg.kg-1) and skin (14.36 ± 11.45 mg.kg-1), and the lowest in muscle (2.14 ± 0.64 mg.kg-1). The highest content of Cu was established in liver samples (7.32 ± 2.39 mg.kg-1), followed by this in the skin (3.78 ± 2.24 mg.kg-1) and muscles (1.29 ± 1.03 mg.kg-1). The highest values for As contents (0.07 ± 0.05 mg.l-1) were determined in surface waters, and the highest values for Cu contents were determined in sediments (204.09 ± 121.05 mg.kg-1). The results of studies on the circulation of the studied elements in the water-sediment-tissue and organs of A. alburnus system were analysed. [ABSTRACT FROM AUTHOR]

During the ecological study of 31 specimens of freshwater bream (Abramis brama (Linnaeus, 1758)) from Danube River, by applying standard techniques for parasites, an infestation was found with two acanthocephalan species -- Pomphorhynchus laevis and Acanthocephalus lucii. The content of arsenic in water, sediments, parasites, tissues and organs of Abramis brama (infected and uninfected) were establishedin the present study. P. laevis showed 42-170 times higher content of arsenic than its host tissues and organs. The content of arsenic in A. lucii was 37-205 times higher than the content of arsenic in its host tissues and organs. The highest concentration of arsenic in uninfected specimens of A. brama was found in liver (1.35±1.29 mg.kg-1 ). The highest concentration of arsenic for the infected with P. laevis specimens of freshwater bream was established for muscles (0.68±0.08mg.kg-1 ), while for the infected with A. lucii specimens of fish, the highest concentration of arsenic was established for skin (1.75±1.32 mg.kg-1 ). A highly significant correlation (p<0.01) was fixed for the relationship between CAs/P. laevis--CAs/Muscles. [ABSTRACT FROM AUTHOR]

In the spring, summer and autumn of 2019, ecoparasitological studies were conducted on 165 specimens of Alburnus alburnus (Linnaeus, 1758) from the Danube River (Koshava, Kudelin and Novo selo villages, Vidin region). The species diversity of parasites of the bleak was determined. Seven species of parasites were identified: 4 species of Trematoda (Nicolla skrjabini (Iwanitzky, 1928), Allocreadium isoporum (Looss, 1894), Posthodiplostomum cuticola (von Nordmann, 1832), Sphaerostomum bramae (Müller, 1776)), one species of Cestoda (Neogryporhynchus cheilancristrotus (Wedl, 1855), larvae), one species of Acanthocephala (Pomphorhynchus laevis (Müller, 1776)) and one species of Nematoda (Contracaecum sp., larvae). In the spring the dominant species was the trematode A. isoporum, detected in 9 specimens of A. alburnus from the Koshava biotope. The dominant parasite species in summer and autumn was the trematode P. cuticola. A. alburnus is a new host for S. bramae and N. cheilancristrotus, from the studied river ecosystem. The structure of the parasite communities of the bleak from the investigated section of the freshwater ecosystem of the Danube River was presented. [ABSTRACT FROM AUTHOR]

Ecoparasitological examinations of brown trout from the Tamrashka River, Aegean Water Basin, Bulgaria were carried out. Five species of helminths, one Trematoda species (Nicolla skryabini (Iwanitzky, 1928) Ślusarski, 1972) and four Nematoda species (Rhabdochona hellichi (Šramek, 1901) Chitwood, 1933; Raphidascaris acus (Bloch, 1779); Salmonema ephemeridarum (Linstow, 1872) Moravec, Santos et Brasil-Sato, 2008; Schulmanela petruschewskii (Shulman, 1948) Ivashkin, 1964) are determined. S. phemeridarum was distinguished with the highest prevalence (50%). It is a core species for the helminth communities of the brown trout from the studied river ecosystem. Sch. petruschewskii is a new parasite species of brown trout and S. t. fario is a new host record for Sch. petruschewskii in Bulgaria. The Tamrashka River is a new habitat for N. skryabini, Rh. hellichi, R. ?cus, S. ?phemeridarum and Sch. petruschewskii as parasites of the brown trout in Bulgaria. [ABSTRACT FROM AUTHOR]

This study presents the result of investigations of heavy metals (Cu, Cd) and metalloids (As) in the liver, skin and muscles of Chondrostoma nasus (Linnaeus, 1758), as well as in waters and sediments of the Danube River (Kudelin village, Vidin region), Bulgaria. The highest levels of Cu (23.05 ± 16.14 mg.kg-1), Cd (0.08 ± 0.04 mg.kg-1) and As (9.24 ± 4.79 mg.kg-1) was found in samples of liver. The content of the studied elements decreased in the following order: liver>skin>muscle. The highest values for As content (0.07 ± 0.05 mg.l-1) were found in surface waters, while the highest values for Cu content (204.09 ± 121.05 mg.kg-1) were found in sediments. The circulation of the studied elements in the freshwater ecosystem was investigated. The excesses in the values of the obtained results were analyzed against regulated national and international standards. [ABSTRACT FROM AUTHOR]

During summer 2019, 15 specimens of round-scaled barbell (Barbus cyclolepis Heckel, 1837) and 12 specimens of Orpheus dace (Squalius orpheus Kottelat & Economidis, 2006) from Topolnitsa River were collected and examined with standard techniques for parasites. Helminth parasites were recorded in 9round-scaled barbell specimens (60%) and 7 Orpheus dace specimens (58.33%) from Topolnitsa River. Only one parasite species was identified in both cyprinid fishes -the acanthocephalan species Pomphorhynchus laevis (Zoega in Müller, 1776). Bioindicator significance of established parasite species was discussed for ecological evaluation of the state of the studied freshwater ecosystem. New data for the helminths of round-scaled barbell and Orpheus dace from Topolnitsa River are presented. [ABSTRACT FROM AUTHOR]

During 2018, studies on the biodiversity and biomonitoring by the biological elements for environmental quality: Squalius orpheus (endemic of Balkan Peninsula) and its helminths and helminth communities were carried out. In 59 specimens of Sq.orpheus, four specimens of intestinal helminths are fixed (Allocreadium isoporum (Kowal et Kulakowskaja, 1957); Caryophyllaeus brachycollis (Janiszewska, 1951); Pomphorhynchus laevis (Müller, 1776); Rhabdochona denudata (Dujardin, 1845)). P. laevis is distinguished with the highest prevalence and mean intensity (66.10% and 1.85, respectively). A. isoporum, P. laevis and Rh. denudata are core species for the helminth communities of Orpheus dace, while C. brachycollis is a component species. The eutrophication effects on the pathways of the parasitic flow and the structure of the helminth communities were traced. The bioindicator significance of the parasitic complexes was discussed. [ABSTRACT FROM AUTHOR]

During 2018, biomonitoring of the Luda Yana River ecosystem was carried out by examining the biological elements of quality: the freshwater fish species common roach (Rutilus rutilus (Linnaeus, 1753)) and its endohelmiths and endohelminth communities as bioindicators. 45 specimens of common roach are examined for parasites and three species of endohelmiths (Caryophyllaeides fennica (Schneider, 1902) Nybelin, 1922; Acanthocephalus lucii (Mueller, 1776); Rhabdochona denudatа (Dujardin, 1845) Raillet, 1916) are fixed. New host and locality records are reported. The analysis of the dominant structure of the established intestinal parasite complex was presented to the level of the component community. For an ecological estimation of the freshwater ecosystem, principal biotic indexes are fixed. The bioindicator significance of the identified parasitе populations and communities are discussed. [ABSTRACT FROM AUTHOR]

This study is the first that presents the rudd's (Scardinius erythrophthalmus (Linnaeus, 1758)) endohelminth species and structure of helminth communities from Maritsa River, Bulgaria. During 2018, 13 specimens of Scardinius erythrophthalmus were collected and examined with standard techniques for parasites from Maritsa River. Helminth parasites were recorded in all 13rudd specimens (100%) from Maritsa River. Three species of parasites were identified: one cestode species (Ligula intestinalis (Linnaeus, 1758)), one acantocephalan species (Pomphorhynchus laevis (Müller, 1776)) and one nematode species (Rhabdochona denudatа (Dujardin, 1845, Raillet, 1916).The analysis of the dominant structure of the found parasite species is presented to the component level. All established parasite species are core for the component community of Scardinius erythrophthalmus from Maritsa River. The infracommunities data was used to be fixed principal biotic indices. Bioindicator significance of established parasite species was discussed for ecological evaluation of the state of the studied freshwater ecosystem. [ABSTRACT FROM AUTHOR]

During summer 2018, 29 specimens of bleak (Alburnus alburnus (Linnaeus, 1758)) from Maritsa River were collected and examined with standard techniques for parasites. Helminth parasites were recorded in 24 bleak specimens (82.75%) from Maritsa River. Five species of parasites were identified: one trematode species (Allocreadium isoporum (Looss, 1984)), two cestode species (Caryophyllaeus brachycollis Janiszewska, 1951, Ligula intestinalis (Linnaeus, 1758)); one acantocephalan species (Pomphorhynchus laevis (Müller, 1776)) and one nematode species (Rhabdochona denudatа (Dujardin, 1845; Raillet, 1916). The analysis of the dominant structure of the found parasite species is presented to the component and infracommunities level. In the component community of Alburnus alburnus from Maritsa River C. brachycollis, P. laevis and, R. denudatа are corespecies. L. intestinalisis component parasite species and A. isoporum is accidental parasite species for the helminth communities of bleak. The infracommunities data was used to be fixed principal biotic indices. Bioindicator significance of established parasite species was discussed for ecological evaluation of the state of the studied freshwater ecosystem. New data for the helminths and helminth communities of bleak from Maritsa River are presented. [ABSTRACT FROM AUTHOR]

Maritsa River is related to the Aegean water collecting region. During 2015, a total amount of 23 specimens of perch (Perca fluviatilis Linnaeus, 1758) are investigated. Identified two species of helminths (Proteocephalus percae (Müller, 1780) and Acantocephalus lucii (Müller, 1776)) are reported for the first time as intestinal parasites of perch from the freshwater ecosystem of the Maritsa River. They are core and authogenic species for the helminth communities of P. fluviatilis. Analyses of the helminth communities were carried out at both levels: infracommunity and component community. Basic ecological characteristics and biotic indices were determined to evaluate ecosystem condition of the river. The results of these studies attest to the importance of perch's helminths and helminth communities as sensitive bioindicators. [ABSTRACT FROM AUTHOR]

During 2018, the first ecologoparasitologycal study of Squalius cephalus from Osym River, a tributary of Danube River, Bulgaria was made. In 20 specimens of examined common chub, 3 species of endohelminths are established (Ichtyocotylurus pileatus (Rudolphi, 1802) Dubois, 1937 Metacercaria; Caryophyllaeus brachycollis Janiszewska, 1951; Rhabdochona denudatа (Dujardin, 1845) Raillet, 1916). C. brachycollis and Rh. denudatа are autogenic species, whereas I. pileatus isallogenic species. I. pileatus is reported for the first time for the freshwater fish fauna of Osym River. Sq. cephalusis a new host record for I. pileatus in Bulgaria. The basic ecological characteristics and biotic indices of the parasite populations and communities are determined. The dominant structure of the endohelminth communities is presented on the level of the component community. [ABSTRACT FROM AUTHOR]

During the summer of 2015, 13 specimens of barbel (Barbus barbus (Linnaeus, 1758)) were examined by standard techniques for parasites. All the examined barbels (100%) were infected with the acantocephalan Pomphorhynchus tereticollis.The study of the intestinal content and fishfood fixed the presence mainly of Unionidae molluscs.The swollen river mussel (Unio tumidus Philipsson, 1788; Mollusca, Unionidae) is one of the most common Unionidae in the studied habitat (Biotope Vetren, the DanubeRiver). The aim of the research wass to study the lead content in samples of sediments, Unio tumidus, Pomphorhynchus tereticollis, skin, muscles and liver of B. barbus from the Danube River. From the tissues and organs of the studied fish specimens Barbus barbus, the lowest concentrations of lead were found in the muscles. The content of lead in the samples of liver is higher than in the skin and muscles. The alteration was in the following order: Pbliver>Pbskin>Pbmuscles. P. tereticolliss howed significantly higher content of lead than its host tissues and organs. The content of lead in Unio tumidus was higher than the content of lead in the tissues and organs of B. barbus. A highly significant correlation (p<0.01) was fixed for the relationships between the Pb content in the acanthocephalan and mollusks (CP. tereticollisPb-C U.tumidusPb) and between that in the acanthocephalan and the skin of the fish (CP. tereticollisPb-CskinPb). [ABSTRACT FROM AUTHOR]

During the ecological study of 45 specimens of freshwater bream (Abramis brama (Linnaeus, 1758)) by applying standard techniques for parasites, an infestation with the acantocephalan Pomphorhynchus tereticollis was found. The aim of the present study is to establish the content of nickelin the water, sediments, parasites, tissues and organs of A. brama and its parasite Pomphorhynchus tereticollis, and the possibilities of accumulation and circulation in the freshwater ecosystem of the Danube River. From the tissues and organs of the studied specimens Abramis brama, the content of nickel in the skin samples was higher than in the liver and muscles and ranged as follows: Niskin>Niliver>Nimuscles (in both infected and uninfected specimens). The obtained values for nickel content in the liver and skin of the uninfected A. brama were found to be higher than the obtained values for nickel content in the liver and skin of A. brama infected with P. tereticollis. In contrast to that, the nickel content in the muscles of the infected A. Brama was higher than the nickel content in the muscles of the uninfected specimens of freshwater bream. The acanthocephalan Pomphorhynchus tereticollis showed significantly higher content of nickel than its host tissues and organs. Significant correlations (p<0.05) were fixed for relationships between СP. tereticollisNi - СliverNi, СP. tereticollisNi- СmuscleNi и СP. tereticollisNi - СskinNi. [ABSTRACT FROM AUTHOR]

The aim of the study was to reveal the helminth diversity and the parameters of infection of white bream (Blicca bjoerkna) from Srebarna Biosphere Reserve, North-East Bulgaria. This is the first study of helminth fauna of white bream from Srebarna lake. The hosts were examined by standard techniques. Five species of helminths were found: trematodes (metacercariae of Diplostomum paraspathaceum, Diplostomum pseudospathaceum, Posthodiplostomum cuticola, Tylodelphys clavata) and monogenean (Paradiplozoon homoion). All helminth species identified in the present study are new host-records for the white bream in the Srebarna Lake. Blicca bjoerkna was reported as a new host record for digeneans, namely Diplostomum paraspathaceum, D. pseudospathaceum, T. clavata and T. monogenean, P. homoion from the territory of Bulgaria. Blicca bjoerkna was reported as a new host record for D. paraspathaceum, D. pseudospathaceum and monogenean P. homoion from Balkan Peninsula. In the present study, was reported for the first time the trematodes for D. paraspathaceum, D. pseudospathaceum as parasite of white bream from Basin of Danube River. [ABSTRACT FROM AUTHOR]

During 2016, 45 specimens of freshwater bream (Abramis brama (Linnaeus, 1758)) are collected and examined from the Danube River. Helminth parasites are recorded in 29 freshwater bream specimens (64.44%) from the Danube River. Five species of parasites were identified: one trematode species (Asymphylodora imitans (Mühling, 1898)), three acantocephalans (Acanthocephalus lucii (Müller, 1776), Acanthocephalus anguillae (Müller, 1780), Pomphorhynchus tereticollis (Rudolphi, 1809)) and one nematode species (Raphidascaris acus, (Bloch, 1779), larvae). In the component community of Abramis brama from Danube River A. imitans and A. lucii are core species. P. tereticollis is component parasite species for the helminth communities of freshwater bream. A. lucii and R. acus are accidental parasite species for the helminth communities of A. brama. New data for the lead contents in sediments, parasites, tissues and organs of freshwater bream from the Danube River are presented. From the tissues and organs of the studied fish specimens Abramis brama, the lowest concentrations of lead were found in the muscles. The content of lead in the samples of skin and liver are higher than in the muscles. The acanthocephalan Pomphorhynchus tereticollis showed significantly higher content of lead than its host organs. Bioconcentration factor for lead (Pb) in the tissues and organs of freshwater bream were presented and discussed with respect to their content in sediments. Very significant correlation (p<0.001) was fixed for relationship between P. tereticollis Pb -Sediments Pb. [ABSTRACT FROM AUTHOR]

During 2016, 45 specimens of barbel (Barbus barbus (Linnaeus, 1758)) and 45 specimens of bleak (Alburnus alburnus (Linnaeus, 1758)) are collected and examined from the Danube River. The aim of the study is to analyse the lead content in sediments, tissues and organs of two fishes that inhabit different water levels and in their common parasite - P. tereticollis from the Bulgarian section of River Danube. New data for the lead contents in sediments, parasites, tissues and organs of barbel and bleak from the Danube River are presented. From the tissues and organs of the studied fish specimen B. barbus, the lowest concentrations of lead were found in skin, while in A. alburnus the lowest concentrations of lead were found in muscles. The acanthocephalan Pomphorhynchus tereticollis showed significantly higher content of lead than its hosts tissues and organs. Bioconcentration factor for lead (Pb) in the tissues and organs of barbel and bleak and their common parasite Pomphorhynchus tereticollis were presented and discussed with respect to their content in sediments. Highly significant correlation (p<0.01) was fixed for relationship between P. tereticollis Pb-Skin Pb for Barbus barbus. Highly significant correlation (p<0.01) was also fixed for relationship between P. tereticollis Pb-Sediments Pb for Alburnus alburnus. [ABSTRACT FROM AUTHOR]

During 2015, 76 specimens of freshwater bream (Abramis brama (Linnaeus, 1758)) were examined by means of standard techniques for parasites. Seven species of parasites (Paradiplozoon homoion (Bychowsky & Nagibina, 1959), Dactylogyrus yinwenyingae (Gusev, 1962), Asymphylodora tincae (Modeer, 1790), Caryophyllaeus fimbriceps (Annenkova-Khlopina, 1919), Acanthocephalus lucii (Miiller, 1776), Acanthocephalus anguillae (Müller, 1780), Contracaecum microcephalum (Stossich, 1890), larvae) were fixed. New parasite and host records were determined. The analysis of the dominant structure of the found parasite taxa were presented to the level of the component communities. All fixed parasite species were component for the parasite communities of examined fish with the exception of A. lucii and A. anguillae. A. lucii is a core parasite species and A. anguillae is an accidental parasite species for the helminth communities of freshwater bream. New data for the lead content in sediments, tissues and organs of bream from the Danube River are presented. From the tissues and organs of the studied fish specimens of A. brama, the lowest concentrations of lead were found in the muscles. [ABSTRACT FROM AUTHOR]

Concentration of heavy metals in Scardinius erythrophthalmus (L., 1758) found in Biosphere Reserve "Srebarna" (Northeastern Bulgaria) was examined in 25 fish individuals from every age group and season. The concentration of heavy metals was investigated by mineralization and subsequent atomic absorption spectrophotometry (according to the requirements of the methodology of the pollutants). To ensure the comparability of results the following standards were complied: 1. Sample collection and storage - ISO 5667-3/4:1995; etc. Fish sampling and analysis were carried out in compliance with National Program for Biomonitoring of Bulgaria (MEW, 1999). Particular the concentrations of Pb in Scardinius erythrophthalmus, Ceratophyllum demersum (L.), sediments and water were studied. Bioconcentration factor (BCF=C fish tissues;macrophytes/C water;sediments) for Pb in the tissues of fish and macrophytes were estimated and discussed. Biomagnification factors (BMF=C fish tissues/C macrophites) for Pb in the tissues of fish were estimated and discussed. The chemical analysis showed accumulation of Pb mainly in the fish bones as compared to the accumulation of the respective metal in the fish muscles. Biomagnification factors of Pb in Scardinius erythrophthalmus compared to Ceratophyllum demersum were evaluated. The mean concentration of Pb in the muscles of Scardinius erythrophthalmus was established to greatly exceed the reference values for lead in fish meat from Regulation No 31 of 29 July 2004 on the maximum levels of pollutants in food. [ABSTRACT FROM AUTHOR]