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R E S E A R C H Open Access
Comparison of the metal accumulation capacity
between the acanthocephalan Pomphorhynchus
laevis and larval nematodes of the genus
Eustrongylides sp. infecting barbel (Barbus barbus)
Milen Nachev
*
, Gerhard Schertzinger and Bernd Sures
Abstract
Background: Metal uptake and accumulation in fish parasites largely depends on the parasite group with
acanthocephalans showing the highest accumulation rates. Additionally, developmental stage (larvae or adult) as
well as parasite location in the host are suggested to be decisive factors for metal bioconcentration in parasites. By
using barbel (Barbus barbus) simultaneously infected with nematode larvae in the body cavity and adult
acanthocephalans in the intestine, the relative importance of all of these factors was compared in the same host.
Methods: Eleven elements Arsenic (As), Cadmium (Cd), Cobalt (Co), Copper (Cu), Iron (Fe), Manganese (Mn), Lead
(Pb), Selenium (Se), Tin (Sn), Vanadium (V) and Zinc (Zn) were analyzed in barbel tissues (muscle, intestine, liver) as
well as in their acanthocephalan parasites Pomphorhynchus laevis and the larval nematode Eustrongylides sp. (L4)
using inductively coupled plasma mass spectrometry (ICP-MS).
Results: Nine elements were detected in significantly higher levels in the parasites compared to host tissues. The
element composition among parasites was found to be strongly dependent on parasite taxa/developmental stage
and localization within the host. Intestinal acanthocephalans accumulated mainly toxic elements (As, Cd, Pb),
whereas the intraperitoneal nematodes bioconcentrated essential elements (Co, Cu, Fe, Se, Zn).
Conclusion: Our results suggest that in addition to acanthocephalans, nematodes such as Eustrongylides sp. can
also be applied as bioindicators for metal pollution. Using both parasite taxa simultaneously levels of a wide variety
of elements (essential and non essential) can easily be obtained. Therefore this host-parasite system can be
suggested as an appropriate tool for future metal monitoring studies, if double infected fish hosts are available.
Keywords: Pomphorhynchus laevis,Eustrongylides sp., Heavy metals, Pollution, Bioindication
Background
Different endohelminths of fish were suggested as sentinel
organisms to detect metal pollution in aquatic habitats
[1]. Most of the available papers emphasize adult intestinal
parasites such as acanthocephalans (e.g. Pomphorhynchus
laevis, Acanthocephalus lucii), which have a remarkable
capacity to accumulate heavy metals [1,2] at concentra-
tions many hundred to a thousand times higher than their
host tissues and the aqueous environment [3,4]. With the
use of these parasites even low levels of environmental
pollution can be detected [5], which is often impossible
using conventional analytical methods and/or free living
sentinels such as mussels [6]. Their excellent accumula-
tion capacity was found to be related to the acanthocepha-
lans’anatomy, metabolism/physiology and localization in
the host [4,7].
Metal accumulation in parasitic nematodes appears to
be more variable than in acanthocephalans with usually
only slightly higher concentrations of a few elements in
adult Philometra cyprinirutili,P. ovata,Anisakis simplex
and Anguillicola crassus in comparison to their fish host
tissues [8-12]. Less information is available on metal
* Correspondence: Milen.Nachev@uni-due.de
Aquatische Ökologie (Aquatic ecology) and Zentrum für Wasser- und
Umweltforschung (ZWU), Universität Duisburg-Essen, Universitätsstraße 5,
D-45141, Essen, Germany
© 2013 Nachev et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Nachev et al. Parasites & Vectors 2013, 6:21
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accumulation rates in larval fish nematodes. It could
be expected, however, that each developmental stage
shows different metal accumulation profiles as e.g. larval
stages have a different metabolic activity. Moreover,
nematode larvae are often encapsulated in host tissues,
which could restrict uptake of nutrients and pollutants.
The microhabitat preference (localization in the fish
host) could also affect metal accumulation, due to an
organ-specific availability of metals. As suggested by
Sures & Siddall [7] the major route of metal uptake in
the fish occurs in the gills. Subsequently, metals are
transported by the circulatory system into the fish liver
where they are bound in bile complexes and excreted
into the intestine. Here, they become available for the
parasites located in the intestine. Accordingly, intestinal
parasites should have a better access to metals than
parasites dwelling in the body cavity. This assumption
was tested in laboratory exposure experiments with the
acanthocephalan P. laevis [13]. Individuals which pene-
trated the intestinal wall and which were found in the
cavity of fish accumulated significantly less lead than the
acanthocephalans in the intestinal lumen.
The aim of the present study was to evaluate metal accu-
mulation of different fish helminths inhabiting different
microhabitats within the same host. As a suitable fish host
barbel, Barbus barbus, infected with larval nematodes of
the genus Eustrongylides sp. and the adult acanthocephalan
P. laevis were investigated. Barbel serves as second inter-
mediate or paratenic host for the nematodes that were
located in the anterior part of the body cavity, mainly on
the serosa of the intestine and in the liver tissue. In most
cases, the nematodes were surrounded by a capsule, form-
ing a spiral granuloma, as described by Mihalca et al. [14].
Simultaneously, free moving nematodes were found, which
appeared to cause massive histological damage such as
penetrations of the cavity wall and disruptions of inner
organs. The adult acanthocephalans were located in the
lumen of the small intestine and were therefore directly
exposed to bile fluids and the food acquired by the fish
host. This system of one host infected with two different
parasites is well suited to comparatively assess the relevance
of the parasite’s taxonomic position, developmental stage
and the location within its host for metal accumulation.
Methods
Fish samples
Fish infected simultaneously with P. laevis and larval
nematodes of the genus Eustrongylides sp. were identi-
fied during a four years sampling of barbel from the Bul-
garian part of the river Danube (for details see [15]).
Due to lower prevalence of the nematodes (between
17 and 24%) compared to 98 –100% prevalence for
P. laevis, 16 double infected barbel were selected. From
these fish, samples of muscle (anterior part of body),
intestine (medial section of intestinal tract) and liver as
well as the parasites were taken and frozen at –20°C
until further processing for metal analysis.
Metal analysis
The preparation of samples for metal analysis was per-
formed according to the procedure described earlier
[16,17]. After thawing, 150 to 340 mg (wet weight) of
the homogenized fish tissues and up to 110 mg of para-
sites was weighed into reaction vessels. The larval nema-
todes were previously extracted from the cysts, if they
were encapsulated. A mixture of 1.3 ml nitric acid (65%
HNO
3
, suprapure) and 2.5 ml hydrogen peroxide
(30% H
2
O
2
, suprapure) was added and the vessels were
heated for 90 min at about 170 °C using the microwave
digestion system MARS 5 (CEM GmbH, Kamp-Lintfort,
Germany). After digestion the clear sample solution was
brought to 5 ml volume with deionised water (MiliPore)
in a volumetric glass flask. Subsequently, the concentra-
tions of As, Cd, Co, Cu, Fe, Mn, Pb, Sn, Se, V, Zn were
analyzed using inductively coupled plasma mass spec-
trometry (ICP-MS, Perkin Elmer, Elan 5000; details on
instrumental settings, calibration and sample measure-
ments are given in [17]).
For validation of the analytical procedure a standard
reference material (DORM-3, National Research Council,
Canada) was digested and analyzed in the same way as the
fish samples and the certified values of 7 elements were
compared (Table 1). Detection limits (DL) for all elements
were determined following standard procedures.
Data analyses and statistical treatment
In order to express the accumulation capacity of para-
sites the ratios C
[parasite]
/C
[host tissue]
(Bioconcentration
factors - BCF) were calculated according to Sures et al.
[18]. Additionally, the concentration ratio between
Eustrongylides sp. and P. laevis was determined. In order
to test for significant differences between tissues and
parasites Friedman’s ANOVA and Wilcoxon matched
pair tests were applied. Spearman rank correlation was
calculated to check for possible relationship/interactions
between element concentrations in different organs and
parasites. All statistic methods were performed with
STATISTICA 9.0.
Results
Analytical procedure
The accuracy of certified elements in DORM3 as well as
the detection limits of each element are listed in Table 1.
The accuracy varied between 87% and 106%, which can
be considered a reliable analysis. The detection limits
calculated for essential metals (e.g. Cu, Fe, Mn and Zn)
were higher than those for non-essential ones (see
Table 1) due to their higher natural occurrence.
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Element concentrations in the host-parasite system
The distribution of elements in the host-parasite system
is displayed in Figure 1. Nine of eleven elements were
found in significantly higher concentrations in the para-
sites (either in P. laevis or in Eustrongylides sp.) com-
pared to their host tissues (Friedman’sANOVA,p<
0.05). The concentrations of the toxic elements (e.g. As,
Cd, Pb) in fish tissues were below 0.5 mg/kg (Figure 1b),
whereas essential elements in some cases exceeded con-
centrations of 50 mg/kg (e.g. Cu). The acanthocephalans
showed significantly higher levels of As, Cd, Cu, Mn, Pb
and Zn compared to all host tissues (Wilcoxon test, p ≤
0.01; Table 2) with bioconcentration factors of up to 340
(Table 3). Correlation analyses between element concen-
trations in host tissues and acanthocephalan showed
some significant associations for the elements Co, Mn,
Pb, Se and V (Table 4). Interestingly, positive correla-
tions were found between the parasites and the intestine
or liver (e.g. Co, Mn, Pb and V), respectively. The only
negative relationship was obtained for Se concentrations
between P. laevis and host muscle (r = −0.51; p < 0.05).
Comparisons of element concentrations between larval
Eustrongylides sp. and fish tissues showed that almost all
essential elements (Co, Cu, Fe, Se and Zn) were signifi-
cantly higher accumulated in the nematodes (Wilcoxon
test, p < 0.01; see Table 2). According to the bioconcentra-
tion factors the nematodes showed the highest accumula-
tion rates for Cu and Co followed by, Fe, Se and Zn
(Table 3). The accumulation of toxic elements, however,
showed some differences. The concentrations of Pb in
Eustrongylides sp. were significantly higher (Wicoxon test,
p≤0.01) compared to muscle and liver, but its concentra-
tions remained similar to those in the intestine. The levels
of Cd in the nematodes were significantly lower or similar
to those in the host tissues in contrast to Sn, which was
accumulated to a higher degree in the parasite (Wicoxon
test, p < 0.05; Table 2). The mean BCFs for the latter were
55, 22 and 9 for muscle, intestine and liver, respectively
(Table 3). Correlation analyses between element concentra-
tions in nematodes and fish organs showed more significant
associations in comparison to acanthocephalans. The levels
of eight metals (Co, Cd, Fe, Mn, Pb, Se, Sn and V) in organs
correlated with those in Eustrongylides sp., from which
most of them (Cd, Fe, Pb, Se, Sn) showed significant asso-
ciations with the concentrations in muscle. The levels of
toxic elements like Cd and Pb in larval nematodes were posi-
tively correlated with those in muscle and liver (see Table 4).
The only negative associations were obtained for the ele-
ments Se (r = −0.69; p < 0.01) and Sn (r = −0.72; p < 0.01)
between concentrations in the nematode and muscle tissue.
The comparisons of element concentrations between
both parasite taxa revealed clear differences. Essential
elements like Co, Cu, Fe, Se, Sn and V were found in
significantly higher concentrations in the larval Eustron-
gylides sp., whereas the adult P. laevis accumulated the
elements As, Cd, Mn and Pb to a significantly higher de-
gree (Table 2 and Table 3, Figure 1). Accordingly, the
ratios (C
[Eustrongylides sp.]
/C
[P. laevis]
) for most essential
elements were higher than 1, with the following values
in decreasing order: Cu > Co > Fe > Se > V > Zn. In con-
trast, the concentrations for As, Cd, Mn and Pb, were
between 1.7 to 25 times higher in P. laevis (Table 3)
compared to Eustrongylides sp. Correlation analyses be-
tween element concentrations in acanthocephalans and
nematodes revealed significant associations only for the
elements Co, Mn, Pb and V, (Table 4).
Discussion
Our field metal monitoring compares and highlights the
accumulation potential of different fish helminths. Nine
Table 1 Trace metal concentrations in certified reference material (DORM-3) as well as accuracy and detection limits
determined by ICP-MS analyses
Element DORM-3 values DORM-3 analyzed Accuracy Detection limit Detection limit (mg/kg)
± SD (mg/kg) ± SD (mg/kg) (%) (μg/L) for 200 mg (FW) sample
As 6.88 ± 0.30 6.30 ± 0.40 92% 0.008 0.001
Cd 0.290 ± 0.020 0.27 ± 0.02 94% 0.01 0.001
Co n.c. - - 0.009 0.001
Cu 15.5 ± 0.63 16.35 ± 0.93 105% 0.19 0.078
Fe 347 ± 20 346.95 ± 28.24 100% 2.76 0.354
Mn n.c. - - 0.1 0.251
Pb 0.395 ± 0.050 0.417 ± 0.043 106% 0.26 0.003
Se n.c - - 0.14 0.008
Sn 0.066 ± 0.012 0.0067 ± 0.010 102% 0.01 0.005
V n.c. - - 0.01 0.002
Zn 51.3 ± 3.1 44.4 ± 3.2 87% 2.77 0.161
FW: fresh weight.
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Table 2 Differences between element concentrations in barbel organs and parasites, and between Pomphorhynchus
laevis and Eustrongylides sp
P. laevis Eustrongylides sp. P.laevis vs Eustrongylides sp.
Element P.l. ↔MP.l. ↔IP.l. ↔LE↔ME↔IE↔LE↔P.l.
As P.l. ** P.l. ** P.l. ** E* n.s. n.s. P.l.**
Cd P.l. ** P.l. ** P.l. ** n.s. I** L** P.l.*
Co P.l.** n.s. P.l.* E** E** E** E**
Cu P.l. ** P.l. ** P.l. ** E** E** E** E**
Fe P.l.** n.s. L** E** E** E** E**
Mn P.l. ** P.l. ** P.l. ** n.s. I** n.s. P.l.**
Pb P.l. ** P.l. ** P.l. ** E** n.s. E** P.l.**
Se P.l.** n.s. n.s. E** E** E** E**
Sn M
1
I
1
L
1
E* n.s. E* E
**
V P.l.** I** L** E** n.s. L** E**
Zn P.l. ** P.l. ** P.l. ** E** E** E** n.s.
M: muscle; I: intestine; L: liver; P.l.: Pomphorhynchus laevis;E:Eustrongylides sp.
*: significant at p ≤0.05 (Wilcoxon matched pair test).
**: significan t at p ≤0.01 (Wilcoxon matched pair test).
1
: not statistically tested as concentrations in Pomphorhynchus laevis were below the detection limit.
n.s.: not significantly different (Wilcoxon matched pair test).
In case of significant difference, the site for higher concentration is given in each case.
Figure 1 Mean (±S.D.) element concentrations (a–d) in organs of barbels and in its parasites Pomphorhynchus laevis and Eustrongylides
sp. *Concentrations are not displayed, as they were below the detection limit.
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of eleven elements were found in significantly higher con-
centrations in the parasites in comparison to the host tis-
sues. However, the range of elements in parasites differed
between parasite taxa. The acanthocephalans accumulated
primarily elements which are known for their toxicity to
many organisms such as As, Cd and Pb [19]. In contrast,
the larval nematodes mainly bioconcentrated elements
which are part of several enzymes and other macro-
molecules and which are therefore considered as essential
elements (Co, Cu, Fe, Se, Zn) for many organisms [19].
Different authors reported high accumulation rates of
heavy metals in acanthocephalans and demonstrated that
they can be successfully used for monitoring purposes
(summarized by [2,20]). As expected, our study confirmed
these results for the acanthocephalan P. laevis, which is
probably the most intensively investigated fish acantho-
cephalan regarding metal accumulation [4]. Our data cor-
responded to field data published from the Danube River
[17,21,22] and showed some parallels with the metal up-
take experiments performed under controlled laboratory
conditions [7,13,23]. Again, concentrations of As, Cd, Cu,
Mn, Pb and Zn in P. laevis exceeded the levels in the fish
host, which confirms the use of acanthocephalans as indi-
cators for metal pollution.
Metal monitoring studies performed with the help of
parasitic nematodes are comparatively scarce. Most of the
available nematode papers focus on the accumulation po-
tential of adult parasites, while larval nematodes are less in-
tensively investigated and information about their
accumulation capacity is missing. Our study focused on
fourth stage larvae, which were able to accumulate a large
number of elements, especially essential ones (Co, Cu, Fe,
Se, Zn). This demonstrates that metal uptake already starts
during an early stage of development. In contrast, the
Table 3 Bioconcentration factors C
[parasite]
/C
[barbel tissue]
for Pomphorhynchus laevis and Eustrongylides sp. calculated
with respect to different host tissues and ratios C
[Eustrongylides sp.]
/C
[P. laevis]
P. laevis C
[P.laevis]
/C
[Organ]
±SD Eustrongylides sp. C
[Eustrongylides sp.]
/C
[Organ]
±SD C
[Eustrongylides sp.]
/C
[P. laevis]
±SD
Muscle Intestine Liver Muscle Intestine Liver
As 7.6 (± 7.4) 3.3 (± 3.6) 4.5 (± 4.9) 3.0 (± 2.1) 1.0 (± 0.6) 2.0 (± 2.2) 0.6 (± 0.6)
Cd 90.3 (± 121.6) 15. 6 (± 13.3) 14.1 (± 10.7) 1.3 (± 0.8) 0.3 (± 0.2) 0.3 (± 0.2) 0.04 (± 0.04)
Co 5.3 (± 3.8) 1.2 (± 0.7) 1.6 (± 0.8) 24.1 (± 12.1) 6.6 (± 5.2) 8.3 (± 2.9) 5.8 (± 3.8)
Cu 26.0 (± 26.5) 11.0 (± 10.2) 4.5 (± 6.5) 122.9 (± 71.0) 48.3 (± 22.6) 20.7 (± 17.8) 6.9 (± 5.2)
Fe 3.3 (± 2.8) 0.8 (± 0.4) 0.7 (± 0.6) 14.3 (± 7.7) 3.8 (± 2.1) 2.9 (± 1.7) 4.8 (± 2.0)
Mn 20.6 (± 18.5) 3.9 (± 4.5) 7.1 (± 4.1) 2.2 (± 1.3) 0.4 (± 0.3) 1.0 (± 0.7) 0.2 (± 0.1)
Pb 337 (± 401) 36.8 (± 27.6) 142 (± 133) 9.4 (± 12.5) 1.4 (± 1.8) 4.5 (± 4.6) 0.04 (± 0.03)
Se 2.5 (± 1.5) 1.2 (± 0.5) 0.8 (± 0.4) 7.1 (± 4.9) 3.4 (± 1.9) 2.1 (± 1.0) 2.9 (± 1.2)
Sn n.d. n.d. n.d. 54.5 (± 93.4) 22.1 (± 23.3) 9.1 (± 8.5) n.d.
V 2.0 (± 1.7) 0.6 (± 0.3) 0.3 (± 0.2) 3.6 (± 3.1) 1.0 (± 0.6) 0.5 (± 0.3) 1.8 (± 1.1)
Zn 10.3 (± 4.7) 4.0 (± 1.8) 3.6 (± 2.6) 11.6 (± 6.1) 4.5 (± 1.7) 3.6 (± 2.7) 1.2 (± 0.6)
n.d. : not determined as the concentration in the parasite was below or around the detection limit.
Table 4 Spearman correlation coefficients (r) for the
significant relationships between element concentrations
in parasites and fish tissues
Element Parasite versus organ/parasite R p
Co Eustrongylides sp. ↔intestine 0.53 < 0.05
Eustrongylides sp. ↔liver 0.51 < 0.05
Eustrongylides sp. ↔P. laevis 0.53 < 0.05
P. laevis ↔intestine 0.78 < 0.01
P. laevis ↔liver 0.74 < 0.01
Cd Eustrongylides sp. ↔muscle 0.79 < 0.01
Eustrongylides sp. ↔liver 0.66 < 0.05
Fe Eustrongylides sp. ↔muscle 0.57 < 0.05
Eustrongylides sp. ↔liver 0.62 < 0.05
Mn Eustrongylides sp. ↔intestine 0.69 < 0.01
Eustrongylides sp. ↔P. laevis 0.69 < 0.01
P. laevis ↔intestine 0.53 < 0.05
P. laevis ↔liver 0.71 < 0.01
Pb Eustrongylides sp. ↔muscle 0.53 < 0.05
Eustrongylides sp. ↔liver 0.74 < 0.01
Eustrongylides sp. ↔P. laevis 0.68 < 0.01
P. laevis ↔liver 0.55 < 0.05
Se Eustrongylides sp. ↔muscle −0.69 < 0.01
P. laevis ↔muscle −0.51 < 0.05
Sn Eustrongylides sp. ↔muscle −0.72 < 0.01
VEustrongylides sp. ↔intestine 0.68 < 0.01
Eustrongylides sp. ↔liver 0.56 < 0.05
Eustrongylides sp. ↔P. laevis 0.57 < 0.05
P. laevis ↔intestine 0.69 < 0.01
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accumulation capacity of larval acanthocephalans (cysta-
canths) was found to be very low and the metal uptake
starts in the intestinal lumen of their definitive host [24-26].
The higher levels of essential elements in the nema-
todes could be related to their biology and morphology.
After the fish acquires the infection, the larva migrates
through the intestinal wall into the body cavity, where it
starts feeding on blood and tissues prior to encapsula-
tion. Similar to adult nematodes, the fourth stage larvae
have a completely developed digestive system [27],
which suggests that they can accumulate metals by in-
gestion of food. Research on microstructure and proper-
ties of the nematode’s cuticle revealed that the cuticle of
larvae is not as complex as that of adults [28,29]. There-
fore, larval nematodes are also able to adsorb nutrients
and metals through their body surface. Taken together it
appears that fourth stage nematodes exhibit an even bet-
ter accumulation capacity than adult stages because of
different uptake routes. This was probably one of the
reasons why essential metals like Cu, Fe, Zn as well as
Co and Se were predominantly accumulated. These
macro and micro elements are important structural and
functional factors, as they are involved in the architec-
ture of many enzymes and other complex molecules
[19]. For example, elements like Fe were adsorbed or
ingested most likely with host blood, as Fe is an essential
part of the blood pigment hemoglobin. Therefore, its
levels in host muscle and liver tissues correlated with
the levels in the nematodes, (see Table 4). Similar uptake
sources may also exist for the elements Co, Cu and Zn
due to the fact that these elements are highly abundant
in organisms as co-factors of various enzymes. Correl-
ation analyses between Co levels in nematodes and host
liver or intestine for example revealed positive associa-
tions, which again underlines that the parasites profit
from high levels in the host and were not able to nega-
tively affect the balance of microelements in their host.
Higher metal concentrations in the larval lung nema-
tode Pseudalius inflexus were reported [29] not only for
essential elements but also for toxic ones. The authors
suggested that L4 larvae accumulated metals mainly
from the food (blood and host tissues) via their digestive
system. However, this nematode was not encapsulated,
as was the case for Eustrongylides sp., therefore element
uptake will not only occur via food, but also via the cu-
ticle. This assumption is supported by the fact that levels
of toxic elements such as As, Cd and Pb in the parasite
were similar to those in the host tissues. More specific-
ally, the concentrations of Cd and Pb in nematodes were
positively correlated with those in muscle and liver, indi-
cating that these metals were taken up from the tissues
in which the parasites were located (for details see
Table 4). Obviously, the specific microhabitat prefer-
ences of Eustrongylides sp. play a decisive role, as the
availability of toxic elements within the fish host differs
profoundly from those of the essential ones. With refer-
ence to this, high levels of Cd and Pb in larval nema-
todes of the genus Hysterothylacium sp. collected from
the intestinal lumen and from mesenteries of the fish
host have been reported recently [30]. It seems that both
metals were available to a high degree in the digestive
tract which therefore results in metal accumulation rates
similar to acanthocephalans.
Higher concentrations of various elements were also
found in the adult nematodes Philometra ciprinirutili and
P. ovata inhabiting the body cavity of fish [10,12]. Interest-
ingly, the authors reported higher levels of non-essential
elements like Cd and Pb in the parasites in contrast to the
results obtained in the present study. Mean ratios of Cd
and Pb between P. ovata and host muscle ranged between
20 and 25 [12], which indicates a much higher accumula-
tion capacity of Philometrids in comparison to Eustrongy-
lides sp. On the other hand, the respective bioaccumulation
rates for Cu (123) and Zn (12) in our study were much
higher than those reported for P. ovata [12] with only 22
and 3, respectively. These differences suggest that larval
nematodesprobablyhaveahigheraffinitytoaccumulate
essential elements whereas the adult Philometrids demon-
strated a higher accumulation capacity for toxic metals.
Explanations for these differences could be the relative im-
portance of different element uptake routes between the
developmental stages of the nematodes or competition be-
tween Eustrongylides sp. and P. laevis in the double
infected fish. The nematode larvae were encapsulated and
thus were unable to feed actively in contrast to the adult
stage. As the larval stages have to grow fast during their de-
velopment they rely on the uptake of essential elements
probably via uptake processes through their cuticle. Adult
nematodes actively feed on host tissues and thereby take
up and accumulate toxic metals like Cd and Pb.
An alternative explanation for the relatively low levels
of toxic elements in Eustrongylides sp. could be competi-
tion between acanthocephalans and nematodes. It is sug-
gested that acanthocephalans dwelling in the intestine
compete for nutrients and metals with the host tissues
[31] probably via interruption of the enterohepatic elem-
ent cycle [7]. Metals bound in bile complexes excreted
in the small intestine are taken up by acanthocephalans
and thus are not available for reabsorption by the host
intestine. Therefore, toxic elements might become un-
available for the host target tissues and simultaneously
occurring in parasites. In our study, the concentrations
of Pb in Eustrongylides sp. were significantly higher in
comparison to the muscle and liver tissues, but not
higher than those in the intestine, which supports the
assumption, that some heavy metals are predominantly
available for intestinal parasites. In mass infection cases
with P. laevis, which are common for barbel [15,32],
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metal distribution in the host tissues might be signifi-
cantly changed by the acanthocephalans.
Conclusions
Due to the taxa specific localization in the host and
differences in the development stage, the nematodes
and acanthocephalans exhibited different accumulation
profiles. Larval Eustrongylides sp. accumulated mainly
essential elements, whereas the adult P. laevis showed
a higher affinity to take up non-essential (toxic) ele-
ments. Our results suggest that larval nematodes can
also be applied as sensitive indicators for metal pollu-
tion. It could be even advantageous if they are taken
as sentinels in addition to acanthocephalans due to their
complementary accumulation profile. Using this host-
parasite system a large number of elements could be ana-
lyzed, therefore it represents an appropriate tool for future
metal monitoring surveys if low environmental levels have
to be detected.
Abbreviations
BCF: Bioconcentration factors.
Competing interests
The authors declare that they have no competing interests.
Authors’contributions
MN was involved in sampling, parasitological investigations, metal analyses
and in the data processing and evaluation as well as in writing of the
manuscript. GS contributed to the analytical work (element analysis) and
data processing. BS played a substantial role in the writing process by
corrections and critical comments and in the conception and guidance of
the study. All authors read and approved the final version of the manuscript.
Received: 11 December 2012 Accepted: 15 January 2013
Published: 18 January 2013
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Cite this article as: Nachev et al.:Comparison of the metal accumulation
capacity between the acanthocephalan Pomphorhynchus laevis and
larval nematodes of the genus Eustrongylides sp. infecting barbel
(Barbus barbus). Parasites & Vectors 2013 6:21.
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