Zoodiversity_01_2021.indb


UDC 594.141(282.243.7:477)

FRESHWATER MUSSELS (MOLLUSCA, BIVALVIA, UNIONIDAE) 
OF THE DANUBE RIVER BASIN OF UKRAINE

L. Shevchuk1*, L. Vasilyeva1, M. Taradajnyk2, S. Mezhzherin3

1Department of Zoology, Biological Monitoring and Nature Conservation, 
Zhytomyr Ivan Franko State University, Velyka Berdychivska, 40, Zhytomyr, 10004 Ukraine
2Department of Medical and Biological Bases of Physical Education and Sport, 
Zhytomyr Ivan Franko State University, Velyka Berdychivska, 40, Zhytomyr, 10004 Ukraine
3Schmalhausen Institute of Zoology NAS of Ukraine, vul. B. Khmelnyskogo, 15, Kyiv, 01030 Ukraine
*Corresponding author
E-mail: shevchuk.biol@gmail.com

L. Shevchuk (https://orcid.org/0000-0003-4164-514X)
L. Vasilyeva (https://orcid.org/0000-0003-0661-927X)
M. Taradajnyk (https://orcid.org/0000-0003-3993-1243)
S. Mezhzherin (https://orcid.org/0000-0003-2905-5235)

Freshwater Mussels (Mollusca, Bivalvia, Unionidae) of the Danube River Basin of Ukraine. 
Shevhuk,  L., Vasilyeva, L., Taradajnyk, M., Mezhzherin, S. — During 2009–2011, 50 points of the Danube 
River Basin were surveyed. In 23 of them, seven species of Unionidae were recorded: U.  pictorum, 
U. tumidus, U. crassus sensu lato, A. anatina, A. cygnea, P.  сomplanatа and S.  woodiana, which is an 
invasive species. Th e index of occurrence of freshwater mussels in general was 100 % in the Lower Danube 
River (5 study areas), 42 % in Tisa River (31 study areas), 33.3 % in Seret River (3 study areas), 36 % in 
Prut River (11 study areas). Th e index of occurrence of species was rather low: 24 % of A. anatina, 22 % of 
U.   tumidus, 22 % of U. crassus,  16 % of U. pictorum, 14 % of P. complanata, 14 % of S. woodiana, and 2 % 
of A. cygnea. U. crassus was not found in the Lower Danube river, while A. cygnea was found there only 
outside the main watercourse. Th e invasive species S. woodiana occurred in the Lower Danube River and 
in the sub-basin of Tisa River with 83 % and 20 % frequency, respectively. Th e mean values of population 
densities ranged from 1.00 (A. cygnea) to 6.14 ind./m2 (S. woodiana), and the mean biomass varied from 
1.14 (P. сomplanatа) to 797.54 g/m2  (S. woodiana). 
K e y  w o r d s :  Unionidae, Danube River Basin, Ukraine, species composition, abundance (population size 
and density), biomass.

Th e Danube is the longest European river that inspires signifi cant scientifi c interest in studying various 
aspects of its functioning. As early as 2001, a team of researchers established by ICPDR (International Commis-
sion for the Protection of the Danube River) has begun the studies along the whole river (http://www.icpdr.org/
main/activities-projects/joint-danube-survey-1). 

In Ukraine, the Danube River Basin covers 5.3 % of the territory and occupies the southern and south-
eastern slopes of the Eastern Carpathians, Transcarpathia and the southwestern outskirts of the Black Sea Low-
lands. It includes the rivers of Tisa, Seret, and Prut basins (the Ukrainian sections of these rivers amount to 
7.3 % of the total fl ow of the Danube), as well as several rivers that fl ow into the Danube or the Danube lakes 
below the mouth of the Prut River. Th e water resources of the Danube River in Ukraine belong mostly (73 %) 

Zoodiversity, 55(1): 41–50, 2021
DOI 10.15407/zoo2021.01.041



42 L. Shevchuk, L. Vasilyeva, M. Taradajnyk, S. Mezhzherin

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43Freshwater Mussels (Mollusca, Bivalvia, Unionidae) of the Danube River Basin of Ukraine

to the basin of the Tisa River, which is the Danube’s largest tributary. Th e Ukrainian part of the Danube River 
is 174 km long, from Reni city to river’s mouth. Although that is a small part of the Lower Danube, the local 
hydrobionts were studied extensively. However, there have been no specifi c studies of freshwater mussels (Mol-
lusca, Bivalvia, Unionidae). Th ese mussels have been studied in other Ukrainian water bodies and watercourse 
of the Danube River Basin in the second half of XX century (Markovsky, 1955; Zdun, 1960; Shnarevich and 
Ivanchik, 1963; Ivanchik, 1967, 1968; Dedyu and Mushchinsky, 1969; Polishchuk, 1974, 1977; Stadnichenko, 
1984) and in Transcarpathians, only Unionidae of the Uzh were studied (Stadnichenko, 1984). Th e bivalve mol-
lusks are natural fi lters and thus they are important components of self-sustaining purifi cation of water bodies. 
A large body of scientifi c research indicates the importance of studying that animal group in water bodies and 
watercourses of the Danube River Basin in various countries of Europe (Popa, 2005; Bódis, 2008; Sîrbu, 2006; 
Sîrbu et al., 2010; Bódis et al., 2011; Tomović et al., 2014). Th e studies of Unionidae of the Ukrainian part of the 
Danube River will result in better data on their systematic and chorological characteristics in diff erent areas of 
the basin, will help  to concentrate on the main problems of the biodiversity conservation.

Th ere are six species of aboriginal freshwater mussels (Unionidae) of Ukraine: Unio pictorum Linnaeus, 
1758, U.  tumidus Philіpsson, 1788, U. crassus Philipsson, 1788 (considered sensu lato in present study 
(Mezhzherin et al., 2013)), Anodonta  anatina Linnaeus, 1758, A. cygnea Linnaeus, 1758 and P.  сomplanatа 
Rossmassler, 1835. Th e same species are found in the Danube River Basin. Moreover, the invasive species 
Sinanodonta woodiana Lea, 1834 was found in the Lower Danube River Basin in 1999 (Yurishinets and 
Kornyushin, 2001). 

Hence, only the water bodies and watercourse of the Danube River Basin in Ukraine contain 7 Unionidae 
species (fi g. 1). Th e studies of distribution, frequency of occurrence, specifi cs of population structure of those 
essential species of fi lter animals are of signifi cant interest.

Material and methods

Th e samples were collected manually according to standard methods in warm seasons of 2009–2011. Th e 
material is described in tables 1 and 2.

T a b l e  2 .  Sampling areas where the mollusks were not found

No Sampling area Settlement Sampling coordinates(Lat/Long)
Sub-basin of Tisa River

1 Borzhava River Velyki Kom’yaty 48°14'46''/22°59'36''
2 Latorytsa River Pidpolozzia 48°44'58''/23°0'48''
3 Latorytsa River Svaliava 48°33'11''/22°58'48''
4 Drainage system of

Latorytsa River Solomonove 48°26'48''/22°9'38''
5 Latorytsa River Tyshiv 48°48'16''/23°4'47''
6 Channel, connected to Latorytsa River Gat’ 48°18'51''/22°38'20''
7 Uzh River Kam’anytsa 48°41'22''/22°25'25''
8 Uzh River Nevytske 48°40'49''/22°24'7''
9 Chorni lake Uzhhorod 48°37'46''/22°15'23''
10 Tisa River Teresva 47°59'37''/23°42'17''
11 Tisa River Khust 48°10'9''/23°16'33''
12 Tereblia River Bushtyno 48°2'29''/23°29'26''
13 Teresva River Teresva 48°0'0''/23°40'36''
14 Teresva River Teresva 47°59'12''/23°40'24''
15 Roman River Dun’kovytsa 48°19'7''/22°53'48''
16 Babachka water reservoir Sofi ya 44°22'55''/22°48'48''
17 Babachka channel Zaluzhzhia 48°21'47''/22°51'8''
18 pond Sokyrnytsa 48°7'33''/23°22'3''

Sub-basin of Seret River
19 Mykhydra River Stara Zhadova 48°12'34''/25°30'7''
20 pond Nedoboyivtsi 48°26'8''/26°21'42''

Sub-basin of Prut River
21 Ryngach River Marshyntsi 48°12'19''/26°19'14''
22 Prut River Chernivtsi 48°18'42''/22°55'3''
23 Kotyliv River Koteleve 48°17'28''/26°22'31''
24 Rokytna River Novoselytsa 48°13'5''/26°16'18''
25 pond Novoselytsa 48°13'43''/26°17'12''
26 Siret River (old riverbed) Stary Vovchynets 48°0'51''/25°58'0''
27 Siret River Storozhynets 48°9'32''/25°43'0''



44 L. Shevchuk, L. Vasilyeva, M. Taradajnyk, S. Mezhzherin

Results and discussion
In 2009–2011, 50 sampling points were examined in the Danube River Basin. Unioni-

dae mussels were found only in 23 of them (46 %) (tables 1, 2). Th e frequency of occurrence 
of Unionidae mussels (our data) was compared to data of other researchers on these mus-
sels of other water basins of Ukraine (table 3). Th e state of Unionidae populations in the 
studied basin is not encouraging.

Th e obtained results showed (table 4) that 16 sampling areas which contained mussels 
were in rivers, 5 in channels and 2 in ponds. Unionidae populations were absent in rivers 
(54 %), in all water reservoirs and lakes (100 %), in the majority of ponds (60 %) and in a 
number of channels (37.5 %).

1
2

3
4

5 6

7
8

Fig. 1. Shells (left  side): 1 — U. tumidus (the Stalineshty River, Mamalyga); 2 — U. pictorum (the Stalineshty 
River, Mamalyga); 3 — U. crassus (the Borzhava River, Vilkhivka); 4 — A. anatina (PMK channel, Vylkove); 
5 — A. cygnea (PMK canal, Vylkove); 6 — P. complanata (the Danube River, Lisky); 7 — S. woodiana (the 
Danube River, Vylkove); 8 — S. woodiana (the Latorytsa River, Solomonove). Scale 10 mm.



45Freshwater Mussels (Mollusca, Bivalvia, Unionidae) of the Danube River Basin of Ukraine

Notably, the frequency of oc-
currence of freshwater mussels 
varied in diff erent parts of the 
Danube River Basin. Th is was re-
fl ected in the ratio of study areas 
where the mollusks were found 
to all study areas. Th us, this pa-
rameter was 100 % for the Lower 
Danube (5 study areas in total), 
42 % for the sub-basin of the Tisa 
River (31 study areas in total), 
33.3  % for the sub-basin of the 
Seret (3 study areas in total), 36 % 
for the sub-basin of the Prut (11 
study areas in total). Previously, the populations of freshwater mussels were observed at the 
whole riverbed (Bartosh, 1938; Sarkany-Kiss, 1997). Th is is infrequent now.

Species richness (table 1) is an important characteristic of a community. Th us, 6 spe-
cies of mollusks (U. pictorum, U. tumidus, U. crassus, A. anatina, P. complanata, S. woodi-
ana) were found in 1 biotope (the Latorytsa River, Chabanivka village, Zakarpattia Region 
of Ukraine), 5 species in 2 biotopes (the Danube River and PMK channel, Vylkove, Odesa 
Region of Ukraine), and 4 species in 5 biotopes (the Borzhava River, Vary village, Zakar-
pattia Region; Latorytsa River (old and new riverbed), Solomonove village, Zakarpattia Re-
gion; Stalineshty River, Mamalyga village, Chernivtsi Region; Bazarchuk channel, Vylkove, 
Odesa Region). 2 species, (U. tumidus and A. anatina) were found in a pond of Orichovytsa 
village, Zakarpattia Region, and in the Danube River, Lisky village, Odesa Region (U. tumi-
dus and P.  complanata). 11 communities were monospecifi c, 8 of them in rivers: 6 of river 
communities were composed of U. crassus, 4 communities were of A. anatina, and 1 was of 
S. woodiana. Th e species composition of Unionidae in the rivers of the Danube River Basin 
was the most various compared to those of other river basins (Yanovych, 2013).

T a b l e  3 . Frequency of occurrence of Unionidae in river basins 
of Ukraine

River basins Frequency of occurrence, %
Danube 46
Dniester 39
Western Bug 28
Southern Bug 47
Prypyat 84
Desna 79
Dnipro 74
Siversky Donets 67
Pryazovia 0
Crimea 17

T a b l e  4 .  Frequency of occurrence of Unionidae freshwater mussels in Danube River Basin and number 
of species in study area

Type of water 
body

Number of 
study areas

Study areas with 
Unionidae

Study areas with the noted number of mollusk 
species

6 5 4 3 2 1 0
River 35 16 1 1 4 1 1 8 19
Water reservoir 1 0 – – – – – – 1
Lake 1 0 – – – – – – 1
Pond 5 2 – – – – 1 1 3
Channel 8 5 – 1 1 1 – 2 3

T a b l e  5 .  Frequency of occurrence (%) of freshwater mussels in various parts of the Danube River Basin 

Species 
of mollusk

Lower 
Danube River

Sub-basin 
of Tisa River

Sub-basin 
 of Seret River

Sub-basin 
of Prut River

U. pictorum 40 33 – 25
U. tumidus 83 40 – –
U. crassus – 73 – 50
A. anatina 67 33 100 75
A. cygnea 17 – – –
P. complanata 50 20 – 25
S. woodiana 83 20 – –



46 L. Shevchuk, L. Vasilyeva, M. Taradajnyk, S. Mezhzherin

Th e frequency of occurrence of some freshwater mussel species and their abundance 
are of particular interest in the Danube River Basin (table 5).

Overall the frequency of occurrence of Unionidae was low in the Danube River Basin: 
16 % for U. pictorum, 22 % for U.  tumidus, 22 % for U. crassus, 24 % for A. anatina, 2 % for 
A. cygnea, 14 % for P. complanata and for S. woodiana. Interestingly, the index was rather 
high for U. crassus and very low for A. cygnea. 

Th us, according to literature, U. pictorum has already been recorded in the Danube 
watercourse (Markovsky, 1955; Zdun, 1960; Shnarevich and Ivanchik, 1963; Ivanchik, 
1967, 1968; Dedyu and Mushchinsky, 1969; Polishchuk, 1974, 1977; Stadnichenko, 1984). It 
was found in various areas of the watercourse. According to our data, the frequency of 
occurrence of that species was 16 %. However that parameter varied in diff erent areas of 
the Danube River Basin. Th us, the species was found in 2 of 5 study areas (frequency of 
occurrence 40 %) in the Lower Danube River, in 5 of 15 study areas (33 %) in the sub-basin 
of the Tisa River, in 1 of 4 study areas (25 %) in the sub-basin of the Prut River. It was 
absent in the single study area in the sub-basin of the Seret River.

U. tumidus has also been considered a common species of Unionidae in Ukraine, be-
cause it occurred in all natural geographical zones and was numerous (Stadnichenko, 1984). 
It has been found in the Danube River Basin, too (Gaidash, 1971; Markovsky, 1955; Ivanchik, 
1964, 1967, 1968; Polishchuk, 1974, 1977; Kornyushin and Lyashenko, 2004). In present study, 
it was found in the Lower Danube and sub-basin of the Tisa River, with 83 and 40 % fre-
quency of occurrence, respectively.

U. crassus has been previously recorded in rivers Tisa, Prut, Uzh, and in the estuaries of 
the Danube Delta (Zhadin, 1938; Markovsky, 1955; Cheremisina and Ivanchik, 1955; Ivanchik, 
1967, 1968; Polishchuk, 1977; Stadnichenko, 1984; Kornyushin and Lyashenko, 2004). However, 
the fi ndings in the Danube Delta are rather controversial, because they have not been con-
fi rmed by the numerous surveys conducted by other authors in this region. We did not fi nd 
this species in the Lower Danube. In the sub-basin of the Tisa River its frequency of occur-
rence was 73 %, and in the sub-basin of the Prut River it was 50 %.

А. anatina is also a common mollusk species in Ukraine. It has been observed in the 
Lower Danube River Basin and in Transcarpathia rivers (Markovsky, 1955; Zdun, 1960; 
Ivanchik, 1968; Polishchuk, 1977). We found it in water bodies and watercourse of the Low-
er Danube (frequency of occurrence 67 %), and in sub-basins of the Tisa (33 %), Seret 
(100  %), and Prut (75 %).

А. cygnea prefers the lakes and fl oodplain water bodies with clean water. It has not 
been recorded previously in the Danube River Basin in Ukraine. We found that species in 
a single study area in the Lower Danube (17 % frequency of occurrence). Th e unevenness 
of distribution of this species has been noted by other researchers. Th e species is frequently 
absent in samples, or present as hollow shells (Popa, 2005; Sîrbu et al., 2010; Tomović et al., 
2014; Bódis et al., 2015).

P. complanata was rather common in Ukraine until 1970s–1980s, though with low 
abundance. It has been observed in the basin of the Lower Danube River and Transcar-
pathia rivers (Markovsky, 1955; Zdun, 1960; Ivanchik, 1967; Polishchuk, 1974, 1977). We 
found it in the Lower Danube (50  % frequency of occurrence) and the sub-basins of the 
Tisa (20 %) and Prut (25 %).

In 2001, invasion of S. woodiana has been reported in the aquatic coenoses of Ukraine, 
in the Lower Danube Basin (Yurishinets and Kornyushin, 2001). We have found it in the 
Lower Danube River and in watercourses of Transcarpathia, particularly in the old river-
bed of the Latorytsa River in 2010 (Pampura and Yanovich, 2012). In 2011, that species was 
found not only in the main riverbed of the Latorytsa River (Solomonove and Chabanivka 
villages) but also in its system of channels (Demechi village). S. woodiana was found in 7 
study areas, 3 of them were rivers 4 were channels. It was the only species in the channel, 
connected to the Latorytsa River (Demechi village, Zakarpattia Region). In other areas, 



47Freshwater Mussels (Mollusca, Bivalvia, Unionidae) of the Danube River Basin of Ukraine

it co-existed with U. pictorum (in 5 biotopes), U. tumidus (6), U. crassus (1), P. compla-
nata (3), A.  anatina (5), and A.  cygnea (1) mollusks. Th e invasive species had the total 
frequency of occurrence of 83 % in the Lower Danube River, and 20 % in the sub-basin 
of the Tisa River.

Various species of freshwater mussels had diff erent population density and biomass in 
the water bodies and watercourses of the Danube River Basin (table 6).

Th e analysis of density of U. pictorum populations showed that the mean density was 
4.5 ind./m2, ranging from 1 to 8 ind./m2. Th e highest population density of that species, 
7 and 8 ind./m2 was recorded in the sub-basin of the Tisa River (the Latorytsa River, the 
new and old riverbeds, respectively), in Solomonove village, Zakarpattia Region. In the 
same region, the lowest population density was observed for that species too. In the Lower 
Danube River, that parameter was 2–3 ind./m2 (the Bazarchuk channel in Vylkove, Odesa 
Region, and the Danube River also in Vylkove, respectively). Th e biomass of mollusks per 
1 m2 of biotope was not high either, the mean biomass was 186.05 ± 44.16 g/m2 in the 
Lower Danube River Basin.

Th e population density of U.  tumidus did not signifi cantly diff er from the above-
mentioned, although the frequency of occurrence was higher. Th e mean density was only 
5.27 ind./m2, in the range of 1–10 ind./m2. Th e maximum population density (7–10 ind./m2) 
was recorded in the sub-basin of the Tisa River, namely in the Latorytsa River. In the Lower 
Danube, that parameter ranged from 3 to 5 ind./m2. Notably, in the second half of XX cen-
tury, the density of U.  tumidus population has been 80 ind./m2 in the Danube River Ba-
sin (Prut River) (Ivanchik, 1968). Th e species was able to sustain enormous populations 
of 850 ind./m2 (the Siret River) (Ivanchik, 1968), or even 2680 ind./m2 (the Vovcha River) 
(Gaidash, 1971). Currently the mean biomass of the species was 132.90 ± 23.34 g/m2 in the 
river basin.

Th e population density of U. crassus was 25–416 ind./m2 in the Prut River Basin in 
the middle of XX century (Ivanchik, 1959). Now, it became one of the lowest among the 
Unionidae species in Ukraine (Shevchuk (Yanovych) et al., 2019). According to our data, 
the highest density was recorded in the Danube River Basin (4.82 ± 1.48 ind./m2). Th e 
maximum population density (15 ind./m2) was recorded only in 1 study area in the sub-
basin of the Tisa River (the Borzhava River, Vilkhivka village, Zakarpattia Region). In two 
areas at the Latovytsa River (Stare Davydkove and Solomonove villages of Zakarpattia 

T a b l e  6 . Mean (M), standard deviation (m) and range (min–max) of population density and 
biomass of Unionidae in the Danube River Basin 

Species of mollusk Number of samples

Population density of mollusks, 
ind./m2

Biomass of mollusks, 
g/m2

М ± m 
(min–max)

М ± m 
(min – max)

U. pictorum 8 4.50 ± 0.98
(1–8)

186.05 ± 44.16
(60.24–292.70)

U. tumidus 11 5.27 ± 0.94
(1 – 10)

132.90 ± 23.34
(16.86 – 249.34)

U. crassus 11 4.82 ± 1.48
(1 – 15)

130.89 ± 25.50
(39.86 – 234.23)

A. anatina 12 4.50 ± 1.20
(1 – 15)

417.51 ± 52.15
(23.98 – 1531.92)

A. cygnea 1 1.00
(1)

–

P. complanata 7 1.14 ± 0.14
(1 – 2)

39.12 ± 8.69
(4.98 – 59.57)

S. woodiana 7 6.14 ± 0.705
(5 – 10)

797.54 ± 303.04
(378.28 – 2001.550)



48 L. Shevchuk, L. Vasilyeva, M. Taradajnyk, S. Mezhzherin

Region), 9–11 individuals of the species were recorded per 1 m2, which is one of the highest 
indices for Ukraine. Th e mean biomass of U. crassus individuals was 130.89 ± 25.50 g/m2 
in the Danube River Basin. 

Although A.anatina is one of the most common species of Unionidae in the Da-
nube River Basin, its mean population density is low, 4.50±1.20 ind./m2. Th e maximum 
density was only 15 ind./m2, recorded in a single study area in the sub-basin of the Tisa 
River (a pond, Orikhovytsa village, Zakarpattia Region). Th e biomass of individuals was 
417.51±52.15 g/m2 in the river basin, which is the highest for Ukraine (Yanovych, 2013)). 
Th e highest biomass was recorded in a study area in the sub-basin of the Prut River, namely 
in the Stalineshty River, Mamalyga village of Chernivtsi Region (1531.92 g/m2). Th e bio-
mass of A. anatina mollusks has been 1400 g/m2 in the Prut River basin in the middle of 
XX century (Ivanchik, 1964).

А. сygnea was one of the rarest species under study, with the lowest frequency of oc-
currence and population density among the Unionidae of the Danube River. We found 
only 1 individual of this species in the Lower Danube River (PMK channel, Vylkove town, 
Odesa Region). Th at mollusk’s population density has been as high as 48 ind./m2 in the wa-
tercourses of the Ukrainian Carpathians in the second half of XX century (Ivanchik, 1967).

P. complanata was a species with the lowest population density among the freshwater 
mussels in Ukraine and in the Danube River Basin particularly. We observed its maximum 
population density (2 ind./m2) only in the Danube River (Lisky village, Odesa Region). In 
other study areas the parameter was 1 ind./m2. Th e mean biomass in the Danube River 
Basin was 39.12 ± 8.69 g/m2. Overall, the low abundance in populations of all European 
Unionidae species in other waterbodies of the Danube River has been noted by other 
researchers (Bódis et al., 2015).

In contrast, we found the maximum population density of S.  woodiana, 10 ind./m2, 
in a study area in the sub-basin of the Tisa River (the Latorytsa River, Chabanivka village, 
Zakarpattia Region). In 2 other study areas (one of them also in the sub-basin of the Tisa 
River, one in the Lower Danube River), 6 and 7 individuals per 1 m2 were found, respec-
tively. Th e mean biomass of invasive species S.  woodiana was the highest of all recorded 
values, 797.54 ± 303.04 g/m2). Th e biomass in a single study area was also the highest re-
corded (2001.55 g/m2) in the Latorytsa River (Solomonove village, Zakarpattia Region), 
with the low density of 5 ind./m2. However, the biomass of 25 kg/m2 was observed in the 
Konin lakes, Poland (Kraszewski, Zdanowski, 2001).

Conclusions
According to our results, Unio nidae mollusks were found in 23 of 50 study areas 

(46  %) during the survey of the Danube River Basin in 2009–2011. Th e frequency of oc-
currence was 100 % in the Lower Danube River (5 study areas), 42 % in the sub-basin of 
the Tisa River (31 study areas), 33.3 % in the sub-basin of Seret (3 study areas), 36 % in the 
sub-basin of the Prut (11 study areas). 

Th e Danube River Basin is the only river basin of Ukraine populated by 7 species 
of freshwater mussels: U.  pictorum, U. tumidus, U. crassus (here, sensu lato), A. anatina, 
A. cygnea, P. сomplanatа and S. woodiana. Th e latter species is invasive.

Th e frequency of occurrence of freshwater mussels is low in the Danube River Basin: 
U.  pictorum, 16 %; U.  tumidus, 22  %; U.  crassus, 22 %; A.  anatina, 24 %; A.  cygnea, 2 %, 
P. complanata, 14 %, and S. woodiana, 14 %. U. crassus is not found in the Lower Danube, 
and A. cygnea is found only there. S. woodiana is found both in the Lower Danube and in 
the sub-basin of the Tisa River (the frequency of occurrence is 83 and 20 %, respectively).

Th e mean values of population density of the studied species range from 1.00 
(A. cygnea) to 6.14 ind./m2 (S. woodiana). Th e mean values of biomass ranged from 1.14 
(P. сomplanatа) to 797.54 g/m2 (S. woodiana). Th us, maximum values of those parameters 
are characteristic for the invasive species, the Chinese pond mussel.



49Freshwater Mussels (Mollusca, Bivalvia, Unionidae) of the Danube River Basin of Ukraine

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Received 14 September 2020
Accepted 5 January 2021