Trace metal accumulation is infrapopulation-dependent in acanthocephalans parasites of the white mullet (Mugil curema) from an estuarine environment of southeastern Brazil coast.

Here, in an estuarine canal in southeast Brazil, we evaluated the potential for trace metal accumulation of the acanthocephalan parasite Floridosentis mugilis, which infects the fish host Mugil curema. The quantities of the trace metals were quantified using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), which was used to analyze samples of the fish's muscle, intestine, and liver as well as the parasites. The parasites and the host's tissues had significantly different trace metal concentrations, according to our data. Furthermore, some metals have quite high bioconcentration factors, including Al, Cr, Ni, and Cd. We also found that the trace metal concentrations in the parasites were impacted by the sizes of the parasitic infrapopulations, with smaller infrapopulations tending to accumulate more metals. This study shows this acanthocephalan species' effective ability to store metals and is the first to investigate metal accumulation using it as a model.

Identification of antiparasitic drug targets using a multi-omics workflow in the acanthocephalan model.

BACKGROUND: With the expansion of animal production, parasitic helminths are gaining increasing economic importance. However, application of several established deworming agents can harm treated hosts and environment due to their low specificity. Furthermore, the number of parasite strains showing resistance is growing, while hardly any new anthelminthics are being developed. Here, we present a bioinformatics workflow designed to reduce the time and cost in the development of new strategies against parasites. The workflow includes quantitative transcriptomics and proteomics, 3D structure modeling, binding site prediction, and virtual ligand screening. Its use is demonstrated for Acanthocephala (thorny-headed worms) which are an emerging pest in fish aquaculture. We included three acanthocephalans (Pomphorhynchus laevis, Neoechinorhynchus agilis, Neoechinorhynchus buttnerae) from four fish species (common barbel, European eel, thinlip mullet, tambaqui). RESULTS: The workflow led to eleven highly specific candidate targets in acanthocephalans. The candidate targets showed constant and elevated transcript abundances across definitive and accidental hosts, suggestive of constitutive expression and functional importance. Hence, the impairment of the corresponding proteins should enable specific and effective killing of acanthocephalans. Candidate targets were also highly abundant in the acanthocephalan body wall, through which these gutless parasites take up nutrients. Thus, the candidate targets are likely to be accessible to compounds that are orally administered to fish. Virtual ligand screening led to ten compounds, of which five appeared to be especially promising according to ADMET, GHS, and RO5 criteria: tadalafil, pranazepide, piketoprofen, heliomycin, and the nematicide derquantel. CONCLUSIONS: The combination of genomics, transcriptomics, and proteomics led to a broadly applicable procedure for the cost- and time-saving identification of candidate target proteins in parasites. The ligands predicted to bind can now be further evaluated for their suitability in the control of acanthocephalans. The workflow has been deposited at the Galaxy workflow server under the URL tinyurl.com/yx72rda7 .

Cavisoma magnum (Cavisomidae), a unique Pacific acanthocephalan redescribed from an unusual host, Mugil cephalus (Mugilidae), in the Arabian Gulf, with notes on histopathology and metal analysis.

Cavisoma magnum (Southwell, 1927) Van Cleave, 1931 was originally described from a sea bass, Serranus sp. and spotted surgeonfish, Ctenochaetus strigosus (Perciformes) off Sri Lanka before its more recent redescription from milkfish in the Philippines in 1995. These reports were based on only light infections of their host fishes. Of the few flathead grey mullets, Mugil cephalus (Mugilidae), that we examined in the Arabian Gulf, one fish was infected with 1,450 worms. One milkfish, Chanos chanos (Chanidae), from the same location in the Arabian Gulf, was also heavily infected with specimens of C. magnum. The descriptions of this unique large worm are revised and for the first time, we provide SEM images, new systematic observations, metal analysis of hooks showing extremely high levels of sulfur, and histopathology in the mullet intestinal tissue. Adjustments and corrections of previous descriptive accounts are made. The histopathology studies show extensive damage to the host intestinal tissue including epithelial necrosis, hemorrhaging and worm encapsulation. There is an extensive amount of host connective tissue surrounding the worm. Results of x-ray analysis displayed high levels of sulfur in proboscis hooks, especially at the tips and edges of these attachment structures.

Neoandracantha peruensis n. gen. n. sp. (Acanthocephala, Polymorphidae) described from cystacanths infecting the ghost crab Ocypode gaudichaudii on the Peruvian coast.

The cystacanths of Neoandracantha peruensis n. gen. n. sp. are described from the ghost crab Ocypode gaudichaudii collected from the Pacific coast of Peru. While it is uncommon to describe acanthocephalan taxa from immature stages, the presence of clear-cut distinguishing features separating the present material from its nearest congeneric taxa, and the absence of adults, justifies the erection N. peruensis. The new genus is distinguished by having three separate fields of trunk spines. Specimens of N. peruensis have a slender trunk with two anterior swellings, 3 separate fields of spines on the foretrunk swelling, and no genital spines on the hindtrunk. The proboscis of the new species is heavily armored with 21-22 longitudinal rows of 22 hooks each. Hook no. 14 is more robust ventrally than dorsally. Cystacanths of N. peruensis also have a long tubular hindtrunk and the males have diagonal testes in the midtrunk swelling. Specimens of the closely related Andracantha Schmidt, 1975 have anteriorly enlarged pear-shaped Corynosoma-like trunks, only two fields of anterior trunk spines with occasional genital spines, and bilateral or tandem testes. Proboscides of species of Andracantha have considerably fewer hooks that gradually decrease in size posteriorly. The taxonomic component of this work is amplified by metal analysis of hooks and spines that shows a marked amount of magnesium (Mg) in hooks but not in spines. The highest level of sulfur (S) was found in the outer layer of hooks and anterior spines. The metal footprint of hooks and spines varies in different species of acanthocephalans and has an interspecific diagnostic value.

Description of a New Quadrigyrid Acanthocephalan from Kashmir, with Notes on Metal Analysis and Histopathology, and a Key to Species of the Subgenus Acanthosentis from the Indian Subcontinent.

Acanthogyrus (Acanthosentis) kashmirensis n. sp. is described from recently collected acanthocephalan specimens in the Jhelum River in northern Kashmir that are conspecific with Neoechinorhynchus kashmirensis Fotedar and Dhar, 1977 originally described in a Ph.D. thesis in 1972 from 4 species of cyprinid fishes: Tor tor Hamilton, Bangana diplostoma (Heckel) (syn. Labeo diplostoma Heckel), Labeo rohita Hamilton, and Ptychobarbus sp. Steindachner. The poor unpublished diagnosis was followed by 1 uninformative abstract in a scientific meeting in 1977. The acanthocephalan was later designated as invalid because of the lack of a formal published description and absence of information on deposited type or voucher specimens. Recent collections of specimens of the same species were made from 2 other cyprinid species of cyprinid fishes, Schizothorax plagiostomus Heckel and Schizothorax labiatus (McClelland) from the Sandran River, a tributary of the Jhelum River, in southern Kashmir. It is now possible to provide a full description of these specimens and reassign them in the subgenus Acanthosentis Verma and Datta, 1929 based on the finding of circles of vestigial spines at the anterior end of the trunk of male and female specimens. These vestigial spines are barely visible and easy to miss with optical microscopy. The new species is also characterized by having (1) a para-receptacle structure in males and females, (2) unique double Saefftigen's pouches, (3) large round single-nucleated cells in the proboscis, and (4) the lemnisci being either equal or distinctly unequal with no intermediate states. A key to the species of Acanthosentis of the Indian subcontinent is provided. Histopathological sections show extensive damage to the host intestine with subsequent blood loss, cell necrosis, and attempted encapsulation. Results of the energy dispersive X-ray analysis (EDAX) study show hollow hooks high in sulfur but with limited calcium ions. Hooks of most acanthocephalans studied with X-ray scans are solid with high calcium and low sulfur ions.

Rhadinorhynchus oligospinosus n. sp. (Acanthocephala, Rhadinorhynchidae) from mackerels in the Pacific Ocean off Peru and related rhadinorhynchids in the Pacific, with notes on metal analysis.

Specimens of a new species of Rhadinorhynchus Lühe, 1911 are described from the chub mackerel Scomber japonicus (Scombridae) and the Chilean Jack mackerel Trachurus murphyi (Carangidae) (possibly a subspecies of Trachurus symmetricus) from the Pacific Ocean off the Peruvian coast at the Port of Chicama, La Libertad. Specimens of Rhadinorhynchus oligospinosus n. sp. are somewhat small having 11-14 rows of alternating proboscis hooks with 20-22 hooks each with posteriormost hooks in a continuous ring. Ventral hooks are robust with prominent roots but dorsal hooks are slender and shorter with discoid roots. Trunk spines are in two zones separated by a non-spiny region. Anterior trunk spines are in 2-3 complete circles but posterior spines are only ventral and lateral, and do not extend posterior to the level of the posterior end of the proboscis receptacle in both sexes. The new species is closest to Rhadinorhynchus seriolae (Yamaguti, 1963) Golvan, 1969 found in Japanese and Australian waters, but not as close to 19 other species found in the same Pacific waters off Australia, Japan, and Vietnam. In R. seriolae, posterior trunk spines extend well past the receptacle in females, among other diagnostic differences. Proboscis hooks of the new species were analyzed for chemical elements using X-ray in conjunction with EDAX (energy-dispersive analysis for X-ray) software; sulfur had a higher concentration at the edge than the middle of cut hooks.

Ultrastructure and chemical composition of the proboscis hooks of Acanthocephalus lucii (Müller, 1776) (Acanthocephala: Palaeacanthocephala) using X-ray elemental analysis.

The ultrastructure and chemical composition of the proboscis hooks and surrounding tegument of Acanthocephalus lucii (Müller, 1776), a parasite of European perch, Perca fluviatilis Linnaeus, were examined using scanning (SEM) and transmission (TEM) electron microscopy and X-ray microanalysis (EDXA). The blade of middle hooks consists of three layers: an outer homogeneous layer, an inner heterogeneous layer and a central core. TEM observation revealed the presence of hollow tubes, which spaced the central core; fibrous inner hook layer surrounded by an electron-dense margin and the basal tegumental layer filled with electron-dense bodies and outer layer. We found for the first time that the so-called 'epidermal covering' surrounding of the exposed hook blade (outer hook layer) is a modified striped portion of the tegumental layer and there are no special contact sites between these two morphologically different structures, i.e. striped layer of the syncytial tegument and following proper outer hook layer, which is a homogeneous, moderately electron-dense layer of -0.3 µm in thickness. The hook root is embedded into subtegumental fibrous layer. X-ray microanalysis of both the surface and internal parts of A. lucii hooks demonstrated the presence of calcium, magnesium, phosphorus and sulphur. The highest concentration of sulphur was recorded at the tip of hooks, whereas the middle part of the hooks was most rich in calcium, phosphorus and magnesium. The proximal part of the hooks contained lower concentrations of sulphur, calcium and phosphorus. In the proboscis tegument, only two elements, calcium and silicon, were found. The differences observed in the chemical composition of the hook 'epidermal covering' and the proboscis tegument support our ultrastructural findings that the hook tegumental covering is a modified structure compared with that of the general proboscis tegument.

Effect of acanthocephalan infection on metal, total protein and metallothionein concentrations in European chub from a Sava River section with low metal contamination.

In the present study, the importance of considering fish intestinal parasites i.e. the acanthocephalans in metal exposure assessment was estimated under low metal contamination conditions. Two acanthocephalan species, Pomphorhynchus laevis and Acanthocephalus anguillae were examined in 59 specimens of European chub (Squalius cephalus L.) sampled at 5 locations along the Sava River, Croatia. Concentrations of essential (Cu, Mn) and non-essential (Ag, Cd, Pb) metals were higher in intestinal parasites than chub gastrointestinal tissue, but levels of essential metals Fe and Zn were comparable or lower in parasites, respectively. The highest accumulation in both acanthocephalan species was found for non-essential metals and followed the order: Ag>Pb>Cd. Higher infection intensity with P. laevis allowed us to present their spatial metal distribution and evaluate the influence of P. laevis on metal levels and sub-cellular biological responses (total protein and metallothionein levels) in the host infected with P. laevis. Even in the river section with low metal contamination, parasitism affected metal levels, resulting in lower Cu, Cd and Pb concentrations in chub infected with P. laevis than in uninfected chub. Although total protein and metallothionein levels remained constant in infected and uninfected chub, acanthocephalans should be considered a potential confounding factor in metal exposure assessments. Moreover, P. laevis-chub system can be suggested as an appropriate tool in biomonitoring, since in both species increased Cu and Cd concentrations towards the downstream locations were found. Higher Cu and Cd levels in P. laevis suggest acanthocephalans to be sensitive bioindicators if low metal levels have to be detected.

Does the carotenoid-based colouration of Polymorphus minutus facilitate its trophic transmission to definitive hosts?

Freshwater gammarids infected with the acanthocephalan parasite Polymorphus minutus show behavioural alterations but also differ from uninfected individuals in their appearance because of the carotenoid-based colouration of the parasite visible through the cuticle. However, it's not clear whether this phenotypic alteration is an adaptation favouring parasite transmission to the definitive host. To test this hypothesis, we investigated the selective preference of mallard towards two prey types: uninfected gammarids on which we applied a dot of inconspicuous brown paint, and uninfected gammarids on which we applied a dot of bright orange paint to mimic the change in appearance due to P. minutus without changes in host behaviour. Mallards showed a significant preference for orange-painted gammarids regardless of how gammarids were distributed (isolated or aggregated). This suggests that parasite's colouration may play a role in enhanced transmission to definitive avian hosts. The role of P. minutus' colouration in the conspicuousness of gammarids has however to be balanced by the extent to which mallards use visual cues to forage in the field. From the perspective of a multidimensional manipulation, this study suggests that the change in appearance may act synergistically with the changes in behaviour to promote transmission to waterbirds.

Comparison of the metal accumulation capacity between the acanthocephalan Pomphorhynchus laevis and larval nematodes of the genus Eustrongylides sp. infecting barbel (Barbus barbus).

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.

Perch and its parasites as heavy metal biomonitors in a freshwater environment: the case study of the Ruzín water reservoir, Slovakia.

Heavy metal concentrations were determined in 43 perches (Perca fluviatilis) and in two of its most common parasites, the acanthocephalan Acanthocephalus lucii and the cestode Proteocephalus percae, collected in the period 2009-2010 from Ruzín, a seriously polluted water reservoir in Slovakia. Samples of muscle, liver, kidney, brain, male and female reproductive organs and adipose tissue of fish and both parasites were analyzed for As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn, by ICP-MS. Mean concentrations of individual heavy metals in all fish samples decreased in the order zinc > copper > manganese > mercury > arsenic > chromium > cadmium > nickel > lead. Zinc was found to be the dominant element and its antagonistic interaction with copper was confirmed. The kidney was a key target organ receiving the highest mean concentrations of all analyzed metals, but some metals showed specific affinity for particular tissues. In terms of human health, concentration of Hg in fish muscle, which exceeded more than two-times its maximum level admitted in foodstuffs in European countries, is of great importance and should be taken into account. Bioaccumulation factors (C([parasite])/C([fish tissue])) calculated for all elements indicated much higher detection skills of A. lucii and P. percae parasites than fish organs and hence, present results allow proposing both parasite models as useful tools to monitor aquatic environmental quality. Acanthocephalans, however, seem to be superior for heavy metal monitoring, also demonstrated under experimental conditions. Present results also indicate the decreasing heavy metal burden of the reservoir and its gradual recovery in the course of time.

Concentrations of Zn, Mn, Cu and Cd in different tissues of perch (Perca fluviatilis) and in perch intestinal parasite (Acanthocephalus lucii) from the stream near Prague (Czech Republic).

We monitored concentrations of Cd, Cu, Mn and Zn in acantocephalan parasites (Acanthocephalus lucii) and its final host (Perca fluviatilis). The concentrations in parasites were found to be significantly higher than those found in the muscle, gonads and liver of fish host. The bioaccumulation factor values (BF=C(parasite)/C(host muscle)) were 194, 24.4, 2.2 and 4.7 for Cd, Cu, Mn and Zn, respectively. This suggests a benefit for the host due to the high accumulation of toxic cadmium.

Interspecific differences in carotenoid content and sensitivity to UVB radiation in three acanthocephalan parasites exploiting a common intermediate host.

Few endoparasite species are pigmented. Acanthocephalans are an exception however, with several species being characterised by yellow to orange colouration both at the immature (cystacanth) and adult stages. However, the functional and adaptive significance of carotenoid-based colourations in acanthocephalans remains unclear. One possibility is that the carotenoid content of acanthocephalan cystacanths acts as a protective device against ultra-violet radiation (UVR) passing through the translucent cuticle of their crustacean hosts. Indeed, acanthocephalans often bring about behavioural changes in their aquatic intermediate hosts that can increase their exposure to light. Carotenoid composition and damage due to ultra-violet - B (UVB) radiation were investigated in three acanthocephalan parasite species that induce contrasting behavioural alterations in their common intermediate host, the crustacean amphipod Gammarus pulex. The fish acanthocephalans Pomphorhynchus laevis and Pomphorhynchus tereticollis both induce a positive phototaxis in gammarids, such that infected hosts spend more time out of shelters, while remaining benthic. The bird acanthocephalan Polymorphus minutus, on the other hand, induces a negative geotaxis, such that infected hosts typically swim close to the water surface, becoming more exposed to UV radiation. We show that differences in cystacanth colouration between acanthocephalan species directly reflect important differences in carotenoid content. The two fish parasites exhibit a contrasting pattern, with P. tereticollis harbouring a large diversity of carotenoid pigments, whereas P. laevis is characterised by a lower carotenoid content consisting mainly of lutein and astaxanthin. The highest carotenoid content is found in the bright orange P.minutus, with a predominance of esterified forms of astaxanthin. Exposure to UVB radiation revealed a higher susceptibility in P. laevis larvae compared with P. tereticollis and P. minutus, in terms of sublethality (decreased evagination rate) and of damage to DNA (increased cyclobutane pyrimidine dimers production). Although we found important and correlated interspecific differences in carotenoid composition and tolerance to high UVB radiation, our results do not fully support the hypothesis of adaptive carotenoid-based colourations in relation to UV protection. An alternative scenario for the evolution of carotenoid accumulation in acanthocephalan parasites is discussed.

Is metal accumulation in Pomphorhynchus laevis dependent on parasite sex or infrapopulation size?

Concentrations of the elements As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, Sn, V, Zn were analysed by inductively coupled plasma mass spectrometry (ICP-MS) in the acanthocephalan Pomphorhynchus laevis and its fish host Barbus barbus. A total of 27 barbels were collected from the Danube River in autumn 2006 close to the town Kozloduy (685 river kilometer) on the Bulgarian river bank. Fish were divided into 3 groups. According to their P. laevis infrapopulation size hosts were considered as heavily infected (>100 worms per fish) and lightly infected (<20 worms per fish). The third group was used to compare heavy metal concentrations between male and female P. laevis. The 5 elements As, Cd, Cu, Pb and Zn were detected in significantly higher concentrations in parasites compared to host tissues (muscle, intestine, liver). According to the calculated mean bioconcentration factors, 3 more elements (Co, Mn, V) showed usually higher concentrations in P. laevis. Comparisons between heavily and lightly infected fish revealed significant differences only for V with higher concentrations for the heavily infected group. Concerning sex-specific metal accumulation V and Zn showed significant differences (V, at P<0.05; Zn, at P=0.05), with higher levels of both metals in females of P. laevis. Our results suggest that - for the metals analysed - the size of the parasite infrapopulation plays no role in the degree of metal accumulation. Similarly, parasite sex seems not to be a crucial factor for metal accumulation in the parasites. Thus, for metal monitoring purposes there is no need to take these aspects into account, which makes the use of parasites as bioindicators more applicable.

Carotenoids of two freshwater amphipod species (Gammarus pulex and G. roeseli) and their common acanthocephalan parasite Polymorphus minutus.

Carotenoid compositions of two freshwater Gammarus species (Crustacea: Amphipoda) and of their common acanthocephalan parasite Polymorphus minutus were characterized. The effect of carotenoid uptake by the parasite was addressed by comparing the carotenoid content of uninfected and infected female hosts. Using high-pressure liquid chromatography (HPLC), co-chromatography of reference pigments and electron ionization mass spectrometry of collected HPLC fractions (EI-MS), several xanthophylls and non-polar compounds were identified. Seven kinds of carotenoids, mainly xanthophylls, were identified in gammarids. Astaxanthin was predominant, amounting to 40 wt.% of total carotenoid in both uninfected G. pulex and G. roeseli. By contrast, we found only non-polar compounds with a predominance of esterified forms of astaxanthin in P. minutus larvae. No significant effect of infection on carotenoid content was evidenced in G. pulex and G. roeseli females. Our study highlights the use of a Matrix Solid Phase Dispersion as an efficient extraction method of both xanthophylls and non-polar pigments in small samples, including lipid-rich ones as P. minutus parasite. We discuss on the presumptive pathway leading to the formation of free astaxanthin in gammarids via hydroxy compounds, and on the accumulation of esters of astaxanthin in parasites.

The intestinal parasite Pomphorhynchus laevis (Acanthocephala) from barbel as a bioindicator for metal pollution in the Danube River near Budapest, Hungary.

Concentrations of As, Al, Ag, Ba, Bi, Cd, Co, Cr, Cu, Fe, Ga, Mg, Mn, Ni, Pb, Sb, Sn, Sr, Tl, V and Zn were analyzed by inductively coupled mass spectrometry (ICP-MS) in the intestinal helminth Pomphorhynchus laevis and its host Barbus barbus. The fish were caught in the Danube river downstream of the city of Budapest (Hungary). Ten out of twenty one elements analyzed were found at higher concentrations in the acanthocephalan than in different tissues (muscle, intestine, liver and kidney) of barbel. Considering the fish tissues, most of the elements were present at highest concentrations in liver, followed by kidney, intestine and muscle. Spearman correlation analyses indicate that there is competition for metals between the parasites and the host. The negative relationships between parasite number and metal levels in organs of the barbel support this hypothesis. The bioconcentration factors for Ag, As, Ba, Bi, Cu, Ga, Mn, Pb, Sr, Tl, and Zn showed that the parasites concentrated metals to a higher degree than the fish tissues. They accumulated the metals As, Cd, Cu, Fe, Ni, Pb, Sr and Zn even better than established bioindicators such as the mussel Dreissena polymorpha as revealed by data from the literature. The results presented here emphasize that acanthocephalans of fish are very useful as sentinels for metal pollution in aquatic ecosystems. Ratio of metal concentrations in the parasites and the host tissues provide additional information. Not including acanthocephalans in accumulation bioindication studies with fishes (as still customarily done) may lead to false results.

Fish acanthocephalans of the genus Pomphorhynchus sp. as globally applicable bioindicators for metal pollution in the aquatic environment?

Intestinal helminths of fish, especially the acanthocephalans, have become increasingly interesting as potential bioindicators for heavy metal contamination in aquatic habitats. Pomphorhynchus laevis from chub and barbel has been investigated frequently for its ability to take up and bioconcentrate metals within its body. This papers summarizes the present knowledge on P. laevis and its metal bioaccumulation properties in order to evaluate the applicability of species of the Pomphorhynchus genus as promising sentinels for heavy metals on a global scale.

Accumulation of heavy metals by intestinal helminths in fish: an overview and perspective.

Intestinal helminths of fish are of increasing interest as potential bioindicators for heavy metal contamination in aquatic habitats. Among these parasites cestodes and acanthocephalans in particular have an enormous heavy metal accumulation capacity exceeding that of established free living sentinels. Metal concentrations several thousand times higher in acanthocephalans than in host tissues were described from field and laboratory studies. Whereas larval stages inside their intermediate hosts are not able to take up high quantities of metals, young worms begin to take up metals immediately after infection of the final host. After four to five weeks of exposure, the parasites reach a steady-state concentration orders of magnitude higher than the ambient water level. Thus, acanthocephalans are not only very effective in taking up metals, but they can also respond very rapidly to changes in environmental exposure. The mechanism which enable acanthocephalans to take up metals from the intestinal lumen of the host appears to be based on the presence of bile acids, which form organo-metallic complexes that are easily absorbed by the worms due to their lipophilicity. Investigations of the environmental conditions affecting metal uptake have shown that the parasites are more consistent and reliable indicators for metal pollution than the host tissues as metal levels of the latter are much more dependent on the water chemistry. Thus, after some years of research on the uptake of metals by acanthocephalans and on the factors affecting metal accumulation in intestinal parasites it should be asked if acanthocephalans meet the criteria commonly accepted for sentinels. If parasites can be considered as promising sentinels, we need reasons for the establishment of 'new' indicators. Therefore, this review summarises the present knowledge about parasites as bioindicators and compares the accumulation properties of parasites and established free living indicators. Finally, this review presents possible answers to the question why it could be advantageous to have new and even more sensitive indicators for environmental monitoring purposes.

Fish macroparasites as indicators of heavy metal pollution in river sites in Austria.

This paper describes two approaches to evaluate the use of fish macroparasites as bioindicators of heavy metal pollution at selected river stretches in Austria. Firstly changes in the diversity and richness of endoparasites of the cyprinid barbel, Barbrus barbuls (L.), were tested in relation to heavy metal contents in the aquatic system. Secondly, the bioaccumulation potential of cadmium, lead and zinc was assessed in the acanthocephalan, Pomphorhynchus laevis (Miller, 1776), and compared with that in the muscle, liver and intestine of its barbel host. The present results indicated that in order to validate the role of parasite community patterns related to heavy metal pollution, more investigations on food web dynamics, interelationships between parasites and the presence/absence of intermediate hosts will be essential. Heavy metal concentrations differed significantly between the organs of barbel and P. laevis (P=0.001) with levels up to 2860 fold in the parasite. The high level of heavy metal accumulation in P. laevis compared with that in its barbel host, suggests that despite variability in the parasite infrapopulation, host mobility and feeding behaviour, P. laevis is a most sensitive indicator of heavy metals in aquatic ecosystems.

The acanthocephalan Paratenuisentis ambiguus as a sensitive indicator of the precious metals Pt and Rh from automobile catalytic converters.

Recent studies revealed that intestinal acanthocephalans of fish can accumulate heavy metals to concentrations orders of magnitude higher than those in the host tissues or the aquatic environment. This significant heavy metal accumulation by acanthocephalans, even surpassing that of established free living accumulation bioindicators, encouraged us to study the bioavailability of the platinum-group-metals (PGM) Pt and Rh for parasites. These precious metals are used in catalytic converters of cars for exhaust gas purification in Europe since the early 1980s. In addition to the beneficial effect in reducing the emission of CHx, CO and NOx of cars there is an increasing emission of these metals. However, it still remains unclear if these elements become accumulated in the biosphere and whether they affect the health of organisms. The present study reveals that in European eels (Anguilla anguilla) naturally infected with the eoacanthocephalan parasite Paratenuisentis ambiguus and experimentally exposed to ground catalytic converter material, the parasites take up and accumulate the catalytic active metals Pt and Rh whereas in the examined host tissues we found no metal uptake. Compared with the PGM concentrations in the water the worms contained 1600 times higher Rh and 50 times higher Pt concentrations. Thus, the parasites can be used as sentinel organisms reflecting even very low levels of precious metals.