After becoming extinct in the second half of the 20th century, the European beaver (Castor fiber L., 1758) was successfully reintroduced from Bavaria into Serbia during 2004-2005. In the necropsy of an adult female beaver (found dead in December of 2007), we discovered some parasites identified as Stichorchis subtriquetrus in the colon and peritoneal area. This is the first occurrence of the given specific parasite of beavers in Serbia. Decoding of a subcutaneous implanted microchip has confirmed that our specimen was one of the released beavers. We therefore conclude that the parasite in question was reintroduced into Serbia with the beavers originating from Bavaria.Nakon nestanka u drugoj polovini XX veka, evropski dabar (Castor fiber L. 1758) je tokom 2004-2005. godine, uspešno reintrodukovan sa područja Bavarske u Srbiju. Tokom obdukcije jedne adultne ženke(pronađena mrtva u decembru 2006) pronašli smo parazite u želucu koji su identifikovani kao Stichorchis subtriquetrus. To je prvi nalaz ovog specifičnog parazita dabra u Srbiji. Dekodiranjem subkutano implantiranog mikročipa, potvrđeno je da pronađena ženka jedna od 20 jedinki koje su decembra 2004. godine naseljene na području Specijalnog rezervata prirode Obedska bara. Ova činjenica nam sugeriše da je parazit neželjeno reintrodukovan u Srbiju zajedno sa dabrovima koji su poreklom iz Bavarske naseljavani u Srbiju.Projekat ministarstva br. TR 2001

Ivetić, V.

Milenković, M.

Pavlović, I.

Radović, I.

Savić, B.

Ćirović, Duško

English

 Digital Repository of Archived Publications - Institute for Biological Research Sinisa Stankovic (RADaR)

INTRODUCTION
The European beaver (Castor fiber L., 1758) is a 
semi-aquatic species that used to be widely distrib-
uted in the past. It formerly inhabited almost the 
whole Eurasian region, excluding the southeastern 
and central desert parts of Asia and the mountain 
massif of the Himalayas. Excessive hunting has led 
to the almost complete disappearance of this species 
from its natural area of distribution, so that at the 
beginning of the 20th century there were only eight 
surviving relict populations in the whole range. It 
was estimated that these relict beaver populations 
included only about 1200 individuals (Halley and 
Rosell, 2002). These relict populations served as the 
source of individuals for numerous reintroductions 
realized throughout the continent in the last 80 
years, when this species was returned to the territo-
ries of most European countries (McDonald et al., 
1995; Halley and Rosell, 2002).
An identical destiny affected the European bea-
ver in Serbia. As in the other parts of its range, 
excessive hunting led to the disappearance of this 
species. According to written documents, the last 
beavers were recorded in the second half of the 19th 
century; however, according to a non-documented 
source, the last beaver was shot on the Danube in 
the vicinity of Belgrade at the very beginning of the 
last century. At that point, the given species became 
extinct not only in Serbia, but also along the whole 
course of the Danube and all its tributaries. At the 
same time, these were the last beaver extinctions in 
Europe (Ćirović et al., 2003, 2007).
Almost a century later, in 1999, an acciden-
tally shot beaver was reported from Northern Serbia 
(Vojvodina, Bačka region). This was an immigrant, 
an individual that had been reintroduced from 
Bavaria into Hungary (vicinity of Baja). The record 
in question initiated a national beaver reintroduc-
tion program in Serbia (Ćirović et al., 2001, 2003).
In the period of 2004-2005, there were four 
reintroductions into the Obedska Bara and Zasavica 
Special Reserves, Serbia, that included 75 beavers 
REINTRODUCTION OF THE EUROPEAN BEAVER (CASTOR FIBER L.) INTO SERBIA
AND RETURN OF ITS PARASITE: THE CASE OF STICHORCHIS SUBTRIQUETRUS
D. ĆIROVIĆ1, I. PAVLOVIĆ2, V. IVETIĆ2, M. MILENkOVIĆ3, I. RADOVIĆ4, and B. SAVIĆ2
1Faculty of Biology, University of Belgrade, 11000 Belgrade, Serbia
2Scientific Veterinary Institute of Serbia, 11000 Belgrade, Serbia
3Siniša Stanković Institute for Biological Research, 11060 Belgrade, Serbia
4Faculty of Security Studies, University of Belgrade, 11040 Belgrade, Serbia
Abstract — After becoming extinct in the second half of the 20th century, the European beaver (Castor fiber L., 1758) 
was successfully reintroduced from Bavaria into Serbia during 2004-2005. In the necropsy of an adult female beaver 
(found dead in December of 2007), we discovered some parasites identified as Stichorchis subtriquetrus in the colon and 
peritoneal area. This is the first occurrence of the given specific parasite of beavers in Serbia. Decoding of a subcutaneous 
implanted microchip has confirmed that our specimen was one of the released beavers. We therefore conclude that the 
parasite in question was reintroduced into Serbia with the beavers originating from Bavaria.
Key words: European beaver, reintroduction, Stichorchis subtriquetrus, parasite, Bavaria, Serbia
UDC 599.322.3(4)(497.11):616.993
141
Arch. Biol. Sci., Belgrade, 61 (1), 141-145, 2009                  DOI:10.2298/ABS0901141C
D. ĆIROVIĆ ET AL.142
from Bavaria. In order to facilitate further monitor-
ing, all the introduced animals were marked with 
subcutaneously implanted microchips (Ćirović et 
al., 2007).
Disappearance of beavers entailed the disappear-
ance of specific beaver parasites such as Stichorchis 
from the same area (Sprent, 1992; Stork and Lyal, 
1993). Later, after the beavers were reintroduced, it 
was possible that the parasites were reintroduced as 
well. For this reason, simultaneously with monitor-
ing the increase in population numbers of beavers 
in Serbia, their parasite fauna was also studied. In 
this paper, we discuss the beaver’s return and record 
the first occurrence in Serbia of Stichorchis subtri-
quetrus, which is a specific parasite of European 
beavers.
MATERIAL AND METHODS
Within monitoring activities started after the rein-
troduction of beavers into Serbia, one of the main 
goals was to establish the causes of mortality of 
this species. In the period 2004-2008, post-mortem 
analysis was performed on eight beaver carcasses. 
Only beavers dying in accidents (traffic accidents, 
drowning, etc.) were excluded from the post-mor-
tem analysis procedure.
All collected carcasses were immediately trans-
ported to the Scientific Veterinary Institute of Serbia 
in Belgrade and subjected to post-mortem examina-
tion. For parasitological examination, we used the 
method of total dissection of all individual organs. 
The intestine and other organs were slit open and 
visible parasites removed. The contents and wash 
water were passed through a gauze sieve under a jet 
of tap water, and the remaining material was exam-
ined in small quantities at a time in a large enamel 
tray.
The necropsy revealed 56 Paramphistomum-like 
parasites in the stomach. For further determina-
tion, the parasites were fixed in 10% formaldehyde, 
embedded in paraffin, cut into 5-6–µm mediosagit-
tal sections, and stained with aceto alum carmine 
and HEA.
All 56 collected parasites were also morpho-
metrically analyzed, and body length and width 
were measured in all specimens. Basic statistics (X, 
min, max, sd, CV) were established for the cited 
morphometric parameters. In addition, length and 
width of the acetabulum were measured in five dis-
sected specimens. For these parameters, only the 
mean value is presented.
RESULTS
Out of eight beavers subjected to post-mortem 
analysis, adult parasites were recorded in the stom-
ach of only one adult female, which was found dead 
on December 7th, 2006 in a suburb of Šabac (West 
Serbia, N 44° 54.202', E 019° 38.664'). There were 
56 adult parasites in the sample. The female beaver 
was identified through decoding of the subcutane-
ously implanted microchip (ID No. 342635) of the 
type used to mark all the beavers reintroduced into 
Serbia. This female beaver found in the vicinity 
of Šabac was one of the 20 beavers released in the 
Obedska Bara Reserve in December of 2004.
After microscopic analysis of 56 adult helminths, 
the parasites were identified as belonging to the spe-
cies Stichorchis subtriquetrus Rudolphi, 1814 (syn. 
Paramphistomum castori) (Fig. 1). This record rep-
resents the first information on the presence of the 
given species within the territory of Serbia and in-
dicates that the beaver-specific parasite in question 
was returned together with its host.
All the collected parasites were measured. The 
average body length of adult individuals varied from 
0.69 to 1.25 cm (on average 0.97 cm), while the width 
ranged from 0.51 to 0.75 cm (on average 0.69 cm) 
(Table 1). 
Structure of the dorsal part of acetabulum (AC) 
is characteristic of this species (Fig. 2). Muscles of 
the dorsal circular layer have two parts – dorsal ex-
ternal part 1 (De 1) and dorsal external part 2 (De 
2), and these are diagnostic characteristics of the 
family Paramphistomidae (Fig. 2). The De 1 part was 
strongly developed, and together with the ventral 
external circular layer protruded at the dorsal and 
ventral joints of the acetabulum (forming a strong 
sphincter). Average dimensions of the acetabulum 
reintroduction of the european beaver into serbia and return of its parasite 143
were 0.78 mm (width) and 1.37 mm (length). The 
shape, position, and dimension ratios of the radial 
layer, external longitudinal layer, and muscle of the 
acetabulum were within the normal range for S. sub-
triquetrus.
The life cycle of S. subtriquetrus is generally simi-
lar to that of all other trematodes. The development 
cycle includes intermediate hosts – either aquatic 
snails (Planorbis vortex, Bythinia tentaculata, and 
Lymnea ovata) or the terrestrial snail Suvccinea pu-
tris (Skrjabin, 1949). The parasite is transferred to 
the beaver via infected vegetation, as beavers are 
specialized herbivores with a high ratio of aquatic 
macrophytes in their diet, leading to the risk of infec-
tion with S. subtriquetrus (Romashov, 1976a, 1976b; 
McMaster and McMaster, 2001).
DISCUSSION
Stichorchis subtriquetrus is a highly specialized para-
site recorded in both species of beavers – European 
beaver (C. fiber) and Canadian beaver (C. canaden-
sis) (Romashov, 1976a, 1976b; koubkova et al., 
2002). The parasites usually occur in the coecum 
(Romashov and Safonov, 1965; Merkushava, 1978; 
Mckown et al., 1995; koubkova et al., 2002). In cases 
of mass infections, adult parasites were also recorded 
in the intestines (colon), causing progressive weight 
loss, anemia, intoxication, and even death (Romashov 
and Safonov, 1965; Drozdz et al., 2004).
Infestation with S. subtriquetrus is the most fre-
quently recorded infection transmitted through an 
intermediate host into beaver populations. There 
are numerous papers regarding those infections. 
Most of these studies were performed in Europe. 
Romashov (1966), Romashov and Safonov (1965), 
and kozhukhov (1978) examined the helminth 
fauna of beavers and found S. subtriquetrus in vari-
ous parts of Russia. Stichorchis subtriquetrus was re-
corded in beavers in Belarus by Merkushava (1978) 
and Samusenko (1980), in Ukraine by Sharpilo and 
Panov (1976), and in Norway by Bakke (1978). 
koubkova et al. (2002) studied these parasites of 
beavers in the Czech Republic, and Mažeika et al. 
(2003) in Lithuania. Joszt (1964) and Drozdz et al. 
(2004) found them in Poland, and Sager et al. (2005) 
Fig. 1. Stichorchis subtriquetrus – ventral view.
Fig. 2. Mediosagittal section of acetabulum.
Table 1. Morphometric parameters of Stichorchis subtriquetrus.
 N x Min Max sd CV
Length (cm) 56 0.97 0.69 1.25 0.1573 16.2178
Width (cm) 56 0.69 0.51 0.79 0.0503 7.2910
D. ĆIROVIĆ ET AL.144
in Croatia. These parasites have been found world-
wide and also occurred in Canadian beavers in the 
USA – in Texas (Fedynich et al., 1986) and kansas 
(Mckown, 1995).
Besides being widely distributed, S. subtriquetrus 
is also the most common parasite in both European 
and Canadian beavers. In most parasitological stud-
ies after beaver reintroductions, this parasite was 
recorded within a relatively short interval of time 
after the introduction or first appearance in an area 
(Mažeika et al., 2003; Sager et al., 2005). Most au-
thors agree that the parasite arrived directly with the 
introduced individuals (Drozdz et al., 2004; Sager et 
al., 2005).
Explaining the origin of S. subtriquetrus in a 
beaver in Serbia, other authors maintain that the 
parasite was accidentally reintroduced in the adult 
stage together with its host from natural habitats 
in Bavaria. The arguments supporting this hypoth-
esis stem from the fact that the dead female was 
one of 75 beavers reintroduced into Serbia from 
Bavaria (Ćirović et al., 2007). This also agrees with 
statements by other authors that the parasite was 
returned together with beavers elsewhere (Mažeika 
et al., 2003; Drozdz et al., 2004; Sager et al., 2005). 
The time interval from introduction of the infected 
female to its death was only two years. The complex 
development cycle includes various snail species as 
intermediate hosts (Skrjabin, 1949). It is therefore 
unlikely that the parasite arrived with another indi-
vidual, completed the whole life cycle, and infected 
another beaver on the territory of Serbia.
The first record of S. subtriquetrus in beavers 
in Serbia has ecological-epidemiological impor-
tance, focusing attention on the need for continuous 
parasitological studies of this mammalian species. 
Parasitological monitoring is extremely important 
because individual beaver dispersions may reach 
120 km (McDonald et al., 1995), making possible 
rapid spreading of this parasite specific for beavers, 
not only in our country, but also in the broader 
region around the Sava River.
Acknowledgments — The authors wish to express their grati-
tude to all persons involved in the collection of information 
connected with monitoring of the beaver population in Serbia: 
Slobodan Simić, Slađan Papić, and Mihajlo Stanković (Zasavica 
Special Nature Reserve); and Vladimir Radaković (Šabac). 
This study was supported by the Ministry of Science and 
Technological Development of the Republic of Serbia (Contract 
TR 20019).
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РЕИНТРОДУКЦИЈА ЕВРОПСКОГ ДАБРА (CASTOR FIBER L.) У СРБИЈУ
И ПОВРАТАК ЊЕГОВОГ ПАРАЗИТА: СЛУЧАЈ STICHORCHIS SUBTRIQUETRUS
Д. ЋировиЋ1, и. ПавловиЋ2, в. иветиЋ2, М. МиленковиЋ3, и. раДовиЋ4 и Б. СавиЋ2
1Биолошки факултет Универзитета у Београду, 11000 Београд, Србија
2Научни институт за ветеринарство Србије, 11000 Београд, Србија
3Институт за биолошка истраживања “Синиша Станковић”, 11000 Београд, Србија
4Факултет безбедности Универзитета у Београду, 11040 Београд, Србија
На­кон не­ста­нка­ у другој полови­ни­ XX ве­ка­, 
е­вропски­ да­ба­р (Ca­stor fi­ber L. 1758) је­ током 
2004-2005. годи­не­, успе­шно ре­и­нтродукова­н са­ 
подруч­ја­ Ба­ва­рске­ у Срби­ју. Током обдукци­је­ је­д-
не­ а­дултне­ же­нке­ (прона­ђе­на­ мртва­ у де­це­мбру 
2006) прона­шли­ смо па­ра­зи­те­ у же­луцу који­ су 
и­де­нти­фи­кова­ни­ ка­о Sti­c­horc­hi­s subtri­quetrus. То 
је­ први­ на­ла­з овог спе­ци­фи­ч­ног па­ра­зи­та­ да­бра­ у 
Срби­ји­. Де­коди­ра­ње­м субкута­но и­мпла­нти­ра­ног 
ми­кроч­и­па­, потврђе­но је­ да­ прона­ђе­на­ же­нка­ је­д-
на­ од 20 је­ди­нки­ које­ су де­це­мбра­ 2004. годи­не­ 
на­се­ље­не­ на­ подруч­ју Спе­ци­ја­лног ре­зе­рва­та­ при­-
роде­ Обе­дска­ ба­ра­. Ова­ ч­и­ње­ни­ца­ на­м суге­ри­ше­ 
да­ је­ па­ра­зи­т не­же­ље­но ре­и­нтродукова­н у Срби­ју 
за­је­дно са­ да­брови­ма­ који­ су поре­клом и­з Ба­ва­р-
ске­ на­се­ља­ва­ни­ у Срби­ју.


Reintroduction of the European beaver (Castor fiber L.) into Serbia and return of its parasite: The case of Stichorchis subtriquetrus

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Reintroduction of the European beaver (Castor fiber L.) into Serbia and return of its parasite: The case of Stichorchis subtriquetrus

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