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Acanthocephalans are parasites with complex lifecycles that are important components of aquatic systems and are often model species for parasite-mediated host manipulation. Genetic characterization has recently resurrectedPomphorhynchus tereticollisas a distinct species fromPomphorhynchus laevis, with potential implications for fisheries management and host manipulation research. Morphological and molecular examinations of parasites from 7 English rivers across 9 fish species revealed thatP. tereticolliswas the onlyPomphorhynchusparasite present in Britain, rather thanP. laevisas previously recorded. Molecular analyses included two non-overlapping regions of the mitochondrial gene – cytochrome oxidase and generated 62 sequences for the shorter fragment (295 bp) and 74 for the larger fragment (583 bp). These were combined with 61 and 13 sequences respectively, from Genbank. A phylogenetic analysis using the two genetic regions and all the DNA sequences available forP. tereticollisidentified two distinct genetic lineages in Britain. One lineage, possibly associated with cold water tolerant fish, potentially spread to the northern parts of Britain from the Baltic regionviaa northern route across the estuarine area of what is now the North Sea during the last Glaciation. The other lineage, associated with temperate freshwater fish, may have arrived laterviathe Rhine/Thames fluvial connection during the last glaciation or early Holocene when sea levels were low. These results raise important questions on this generalist parasite and its variously environmentally adapted hosts, and especially in relation to the consequences for parasite vicariance.

Adult specimens of Pomphorhynchus fuhaiensis were identified from common carp (Cyprinus carpio L.) in Ulungur Lake of northwest China, and acanthors, acanthellae, cystacanths dissected from Gammarus lacustris in a small tributary of Ulungur River for the first time. The acanthocephalans were also found in crucian carp (Carassius carassius L.), tench (Tinca tinca L.), oriental bream (Abramis brama orientalis Berg), and ide (Leuciscus idus L.) in the lake. This species is distinguished from other species in Pomphorhynchus by its large, spherical bulb and very long neck as well as by a cylindrical proboscis armed with 15-17 longitudinal rows of 9-12 hooks each. The anterior proboscis hooks are almost uniform in size and shape, the sixth hook in a short row and the seventh hook in long row decrease abruptly in size posteriorly with the last end hook being a little larger than the prebasal hook, and in a ring; posterior proboscis hooks much more widely spaced. Furthermore, the lemnisci are claviform. The mean neck:trunk ratio is about 0.5, which is larger than most other species in Pomphorhynchus. Females are larger than males. In males, the testes are in one-third to one-half of the trunk, equal, ovoid-spheroid, usually contiguous, and small relative to the body size, and there are 6 ovoid cement glands. Pomphorhynchus fuhaiensis is similar to Pomphorhynchus laevis but can be distinguished by the number of longitudinal rows of hooks. Pomphorhynchus laevis is armed with 18-20 longitudinal rows of 11-13 hooks, P. fuhaiensis is armed with 15-17 longitudinal rows of 9-12 hooks.

Parasites with complex life cycles often alter the phenotypic appearance of their intermediate hosts in order to facilitate ingestion by the final host. However, such manipulation can be costly as it might increase ingestion by less suitable or dead-end hosts as well. Species-specific parasitic manipulation is a way to enhance the transmission to suitable final hosts. Here, we experimentally show that the altered body colouration of the intermediate host Gammarus pulex caused by its acanthocephalan parasite Pomphorhynchus laevis differently affects predation by different fish species (barbel, perch, ruffe, brown trout and two populations of three-spined stickleback) depending on their suitability to act as final host. Species that were responsive to colour manipulation in a predation experiment were more susceptible to infection with P. laevis than unresponsive species. Furthermore, three-spined stickleback from different populations responded to parasite manipulation in opposite directions. Such increased ingestion of the intermediate host by preferred and suitable hosts suggests fine-tuned adaptive parasitic manipulation and sheds light on the ongoing evolutionary arms race between hosts and manipulative parasites.

This study evaluated efficacy and toxicity of the pyrazinoisoquinoline anthelmintic praziquantel (PZQ) in barbel infected with metacercariae of Diplostomum spathaceum and adult Pomphorhynchus laevis, and assessed antioxidant biomarkers and the lipid peroxidation response in juvenile barbel post-treatment. The estimated 96-hr LC50 of PZQ was 28.6 mg/L. For evaluation of efficacy, barbel naturally infected with D. spathaceum were exposed to a 10 and 20 mg/L PZQ 4-day bath treatment. Both concentrations were 100% effective against D. spathaceum and significantly (p < .01) affected the activity of catalase, superoxide dismutase, glutathione reductase and glutathione-S-transferase as well as levels of reduced glutathione in liver and muscle. The efficacy of orally administered PZQ was assessed in adult barbel naturally infected with P. laevis. Fish were administered 10, 30 and 50 mg/kg of body weight and examined via gut dissection after 6 days. The 50 mg/kg dose significantly decreased the intensity of infection. Praziquantel is a feasible bath treatment for barbel infected with D. spathaceum and has potential for oral treatment of broodfish infected with P. laevis.

DNA (meta)barcoding is applied to study biodiversity and is available for standardized biodiversity assessments. However, it suffers from PCR bias, which can lead to the loss of specific taxa. PCR-free techniques such as shotgun metagenomics are therefore thought to be more suited for biodiversity assessments, but are currently limited by incomplete reference libraries. The technique of “mitogenome-skimming” or “mitogenomics,” in which complete mitochondrial genomes are sequenced, is ideal to bridge the techniques of (meta)barcoding and metagenomics. However, without the enrichment of mitochondria, roughly 99% of all sequencing reads are of non-mitochondrial origin and mostly useless for common applications, e.g. species identification. Here, we present a simple centrifugation protocol that leads to an average 140-fold enrichment of mitochondrial DNA. By sequencing six ‘mock’-communities—comprising the freshwater taxa Corbicula fluminea, Gammarus roeselii and Hydropsyche exocellata each—we recovered whole mitochondrial genomes of these species and the acanthocephalan endoparasite Pomphorhynchus laevis. The enrichment protocol will speed up building reference libraries for whole mitochondrial genomes, as dozens of species can be sequenced on a single MiSeq run. Subsequently, it will also allow biodiversity assessments, using mitogenomics at greatly reduced costs in comparison to mitogenomic approaches without prior enrichment for mitochondria.

Occurrence of Pomphorhynchus laevis (Müller, 1776) in cage-reared rainbow trout Oncorhynchus mykiss (Walbaum, 1792) and the effects of parasitism on the fish condition were studied between July and November 2014 in Işıklı Spring. A total of 221 O. mykiss specimens were examined. In addition to P. laevis, three other parasite species; Trichodina sp., Ichthyophthirius multifiliis Fouquet, 1876 and Diplostomum sp. were also recorded. P. laevis was numerically the predominant species with the highest prevalence (77.8%), mean intensity (6.74), and mean abundance (5.24). In total 1160 P. laevis specimens were collected. The mean abundance of P. laevis increased over a period of months from 2.5 individual parasites per fish in July to 7.1 in November. The mean intensity of P. laevis increased with increasing fish host length from 1.5 in the 5.0–6.9 cm length class to 18.4 in the 25.0–26.9 cm length class. Although there was no statistically significant bias in the spatial distribution of P. laevis within the gut (p ˃ 0.05), the parasite tended to prefer the pyloric caeca (47.9%). The larval stage (cystacanth) of the acanthocephalan parasite were obtained from the haemocoel of Gammarus obnixus Karaman and Pinkster, 1977. The value of Fulton’s condition factor (K) ranged from 0.84 to 1.66., Ağ kafeslerde yetiştirilen gökkuşağı alabalığı Oncorhynchus mykiss (Walbaum, 1792)’nda Pomphorhynchus laevis (Müller, 1776) varlığı ve balık kondüsyonu üzerindeki paraziter etki Işıklı Kaynağı’nda Temmuz ve Kasım 2014 süresinde çalışıldı. Toplam 221 O. mykiss örneği incelendi. P. laevis den başka üç diğer parazit türü; Trichodina sp., Ichthyophthirius multifiliis Fouquet, 1876 ve Diplostomum sp. da kaydedildi. P. laevis yaygınlık (%77.8), ortalama yoğunluk (6.74) ve ortalama çokluk (5.24) ile sayısal olarak baskın parazitti. Toplamda 1160 P. laevis örneği toplandı. P. laevis ortalama çokluğu, aylık devrelerde Temmuz’da her balıkta 2.5 parazit bireyinden Kasım’da 7.1’e yükseldi. P. laevis ortalama yoğunluğu, artan balık uzunluğu ile 5.0-6.9 cm lik boy sınıfında 1.5’den 25.0-26.9 cm lik boy sınıfında 18.4’e yükseldi. Sindirim kanalında P. laevis’in uzamsal dağılımında istatistik olarak belirgin bir eğilim olmamasına karşın (p ˃ 0.05) parazit tercihi pilorik çekaya (%47.9) yönelik olmuştur. Acanthocephalan parazitin larval dönemi (cystacanth), Gammarus obnixus Karaman and Pinkster, 1977’ un vücut boşluğunda bulunmuştur. Fulton Kondisyon Faktörü değerleri (K), 0.84 ile 1.66 arasına yayılmıştır.

We suggest helminthological investigations of cod as a supplement to traditional biological and hydrographical methods for elucidation of ecological changes in the Baltic Sea. It is under discussion if oxygen deficit or seal abundance should explain the present critical situation of Baltic cod. A comparative investigation of endoparasitic helminths in Baltic cod (Gadus morhua), captured in the same marine habitat with an interval of 35 years (1983/2018) recorded 11 species of helminths comprising trematodes (Hemiurus luehei, Podocotyle atomon, Lepidapedon elongatum), nematodes (Contracaecum osculatum, Hysterothylacium aduncum, Capillaria gracilis, Cucullanus cirratus), cestodes (Bothriocephalus sp.) and acanthocephalans (Echinorhynchus gadi, Pomphorhynchus laevis, Corynosoma semerme). Significant prevalence and intensity increases were recorded for third-stage larvae of the nematode C. osculatum (liver location) and larvae of C. semerme (encapsulated in viscera). Both parasite species use grey seal as their final host, indicating the recent expansion of the Baltic seal population. A lower E. gadi intensity and an increased prevalence of L. elongatum of small cod (31–40 cm body length) suggest a lowered intake of amphipods (intermediate host) and elevated ingestion of polychaetes, respectively, but no significant changes were seen for other helminths.

Interspecific interactions between parasites sharing the same host are often antagonistic; the presence of one species decreases the number of individuals or negatively affects both the distribution and reproduction of the other species. Antagonistic interactions between co-infecting parasites may translate into direct competition or interactive segregation, but elements of both may be present. Potential interactions between two acanthocephalan species, Pomphorhynchus laevis and Acanthocephalus anguillae, were studied in the field in two of their natural fish definitive hosts. There was no evidence for competitive exclusion between P. laevis and A. anguillae. However, a negative interaction was found for the first time in the field between these two species. Based on the analysis of parasite abundance and total biomass using a static regression approach, I found that the abundance and total biomass of parasites was also limited by host characteristics. These results are consistent with previous laboratory studies on competition between P. laevis and A. anguillae.

Harvest quality rainbow trout (Oncorhynchus mykiss Walbaum, 1792) raised in an integrated multi-trophic aquaculture (IMTA) unit off the German coast in the Baltic Sea were studied for ectoparasites and endoparasites. One hundred five specimens were sampled between November 2013 and 2014. Four endoparasite taxa were found, while no zoonotic or fish pathogenic ectoparasites could be detected. Molecular identified metacercariae of Diplostomum baeri were recorded at a non-critical level (18.1% prevalence, 1–4 intensity), getting introduced into the Baltic Sea through the cultured rainbow trout from the freshwater-based hatchery. The isolated acanthocephalan Echinorhynchus truttae was of freshwater origin, too. Pomphorhynchus laevis (Acanthocephala) and Brachyphallus crenatus (Digenea) seem to be transmitted into the net cage from Baltic Sea intermediate hosts. The parasite fauna was compared with those of wild living sea trout, Salmo trutta trutta studied at the immediate area (Unger and Palm in Parasitol Res 115(1):165–174, 2016). Stomach content analyses demonstrated that the farmed pellet-fed fish also utilized natural resources, especially fouling organisms. A single escapee, caught from the wild in the vicinity of the cages, had a massive intestinal infection with Baltic Sea parasites, the acanthocephalans Echinorhynchus gadi, P. laevis and the nematode Hysterothylacium aduncum. The salinity (helminths) as well as the culture conditions (trichodinids) at this pilot facility prevent significant transfer of fish pathogenic and zoonotic parasites as well as ectoparasite establishment and reduce the parasite risk for maricultured rainbow trout. This sampled location is particularly suitable for healthy and environmentally friendly aquaculture farming in the Baltic Sea.

A parasitological study was carried out on 330 eelpouts from two fishing grounds of the Polish fishing zone off the Oder estuary (Pomeranian Bay and Dziwna Mouth). A total of 11 species and genera of parasites from six higher taxa were recorded: 1 monogenean, 1 digenean, 5 nematodes (eelpout was a new host for Ascarophis morhuae and Capillaria gracilis), 2 acanthocephalans, 1 mollusk and 1 protist (a fungus-related pathogen). A total of 4284 autogenic countable parasites were identified. These included parasites of eight species and two genera (six higher taxa) from Pomeranian Bay, and five species (two higher taxa) from the Dziwna Mouth. The abundance of parasites per host was higher in fish from the Dziwna Mouth, while the parasitic biodiversity index was almost two times lower than in Pomeranian Bay. Pomphorhynchus laevis dominated among the eelpout parasites in both fishing grounds, but the parasite communities from the Dziwna Mouth consisted of a larger number of dominating classes. The high intensity of infection of Hysterothylacium auctum and the relative density affect more the dimensions of the dominant parasite (P. laevis) in the Dziwna Mouth than the crowding of parasites. Infection by more abundant large parasites have an important influence on the value of Fulton’s coefficient.

A sub-population of 34 specimens of chub, Squalius cephalus, was sampled from the River Brenta (Northern Italy) and examined for ecto- and endo-parasites. Pomphorhynchus laevis (Acanthocephala) was the only enteric helminth encountered. Immunofluorescence and ultrastructural studies were conducted on the intestines of chub. Near the site of parasite's attachment, mucous cells, mast cells (MCs), neutrophils and rodlet cells (RCs) were found to co-occur within the intestinal epithelium. The numbers of mucous cells, MCs and neutrophils were significantly higher in infected fish (Mann-Whitney U test, p < 0.05). Dual immunofluorescence staining with the lectin Dolichos Biflorus Agglutinin (DBA) and the macrophage-specific MAC387 monoclonal antibody, with parallel transmission electron microscopy, revealed that epithelial MCs often made intimate contact with the mucous cells. Degranulation of a large number of MCs around the site of the acanthocephalan's attachment and in proximity to mucous cells was also documented. MCs and neutrophils were abundant in the submucosa. Immune cells of the intestinal epithelium have been described at the ultrastructural level and their possible functions and interactions are discussed.

During the ecological study of 28 specimens bleak (Alburnus alburnus (Linnaeus, 1758)) by applying standard techniques for parasites was found infestation with the acantocephalan Pomphorhynchus laevis (Müller, 1776). Aim of the present study is to establish the content of nickel in water, sediments, tissues and organs of A. alburnus and its parasite Pomphorhynchus laevis, and the possibilities of accumulation and circulation in the freshwater ecosystem of Danube River. From the tissues and organs of the studied specimens Alburnus alburnus, the content of nickel in samples of liver are higher than in the skin and muscles (in both infected and uninfected specimens). Differences were observed not only in nickel content, but also in the amendment of nickel content of infected (Ni Liver> Ni Muscles > Ni Skin) and uninfected (Ni Liver> Ni Skin> Ni Muscles) specimens of bleak. The obtained values for nickel content in liver, muscles and skin of A. alburnus infected with P.laevis were found to be lower than the obtained values for nickel content in liver, muscles and skin of uninfected specimens of bleak. The acanthocephalan Pomphorhynchus laevis showed significantly higher content of nickel than its host tissues and organs. Significant correlation (p

DNA (meta)barcoding is used to study biodiversity and is available for standardised assessments. However, it suffers from PCR bias, which can lead to the loss of specific taxa. PCR-free techniques such as shotgun metagenomics are therefore thought to be more suited for biodiversity assessments, but are currently limited by incomplete reference libraries.The technique of ‘mitogenome-skimming’ or ‘mitogenomics’, in which complete mitochondrial genomes are sequenced, is ideal to bridge the techniques of (meta)barcoding and metagenomics. However, without the enrichment of mitochondria, roughly 99 % of all sequencing reads are of non-mitochondrial origin and mostly useless for common applications, e.g. species identification.Here, we present a simple centrifugation protocol that leads to an average 140-fold enrichment of mitochondrial DNA. By sequencing six ‘mock’- communities – comprising the freshwater taxa Corbicula fluminea, Gammarus roeselii and Hydropsyche exocellata each – we recovered whole mitochondrial genomes of these species and the acanthocephalan endoparasite Pomphorhynchus laevis.The presented protocol will greatly speed up building reference libraries for whole mitochondrial genomes, as dozens of species could be sequenced on a single MiSeq run. Subsequently, it will also allow biodiversity assessments using mitogenomics at greatly reduced costs in comparison to mitogenomic approaches without prior enrichment for mitochondria.

During the ecological study of 45 specimens of bleak (Alburnus alburnus (Linnaeus, 1758)) by applying standard techniques for parasites in ten specimens of fish an infestation was found with the acantocephalan Pomphorhynchus laevis. Aim of the present study is to establish the content of arsenic in water, sediments, tissues and organs of A. alburnus and its parasite Pomphorhynchus laevis, and the impact that the acanthocephalan has on the content of arsenic in his host tissues and organs. From the tissues and organs of the studied specimens of Alburnus alburnus, the content of arsenic in samples of liver were higher than in the samples of muscles and skin, and ranged as followed: CAs/Liver>CAs/Muscles>CAs/Skin (in both infected and uninfected specimens). The obtained values for the content of arsenic in skin of uninfected specimens of A. alburnus were found to be more than 3 times higher than the obtained values for content of arsenic in skin of A. alburnus infected with P. laevis. In general the content of arsenic in tissues and organs of uninfected A. alburnus was higher than the content of arsenic in tissues and organs of infected with P. laevis specimens of bleak. The acanthocephalan Pomphorhynchus laevis showed 115-3042 times higher content of arsenic than its host tissues and organs. Significant negative correlation (p

SUMMARYPredicting how elevated temperatures from climate change alter host–parasite interactions requires understandings of how warming affects host susceptibility and parasite virulence. Here, the effect of elevated water temperature and parasite exposure level was tested on parasite prevalence, abundance and burden, and on fish growth, using Pomphorhynchus laevis and its fish host Squalius cephalus. At 60 days post-exposure, prevalence was higher at the elevated temperature (22 °C) than ambient temperature (18 °C), with infections achieved at considerably lower levels of exposure. Whilst parasite number was significantly higher in infected fish at 22 °C, both mean parasite weight and parasite burden was significantly higher at 18 °C. There were, however, no significant relationships between fish growth rate and temperature, parasite exposure, and the infection parameters. Thus, whilst elevated temperature significantly influenced parasite infection rates, it also impacted parasite development rates, suggesting warming could have complex implications for parasite dynamics and host resistance.

a b s t r a c t Recent findings suggest that grouping with conspecifics is part of the behavioural defences developed by amphipod crustaceans to face predation risk by fish. Amphipods commonly serve as intermediate hosts for trophically transmitted parasites. These parasites are known for their ability to alter intermediate host phenotype in a way that promotes predation by definitive hosts, where they reproduce. If aggregation in amphipods dilutes the risk to be preyed on by fish, then it may dilute the probability of transmission for the parasite using fish as definitive hosts. Using experimental infections, we tested whether infection with the fish acanthocephalan Pomphorhynchus laevis alters attraction to conspecifics in the amphipod intermediate host Gammarus pulex. We also measured G. pulex’s activity and reaction to light to detect potential links between changes in aggregation and changes in other behaviours. The attraction to conspecifics in the presence of predator cue, a behaviour found in uninfected gammarids, was cancelled by the infection, while phototaxis was reversed and activity unchanged. We found no correlation between the three behaviours in infected amphipods, while activity and aggregation were negatively correlated in uninfected individuals after the detection of predation cue. The physiological causes and the adaptive value of aggregation suppression are discussed in the context of a multidimensional manipulation.

Pomphorhynchus tereticollis (Rudolphi, 1809) is here redescribed on the basis of Rudolphi’s material, deposited in the Museum für Naturkunde Berlin, and on acanthocephalans recently collected from the type host Platichthys flessus (L.) and the region embodying the type locality. Out of the paratypes of P. tereticollis, the lectotype and paralectotypes have been designated. Their morphology fits well with that of newly collected material of P. tereticollis dissected from the type fish host from the Baltic coast near Stralsund. The resurrection of P. tereticollis, previously considered a synonym of Pomphorhynchus laevis (Zoega in Müller, 1779), is supported by several morphological features distinguishing the two Pomphorhynchus species: 1. The basal parts of the proboscis hooks located on the posterior proboscis half possess proximal projections in P. tereticollis but not in P. laevis. This shape of the hook bases is clearly visible only in unfixed fresh worms; 2. The last hooks are situated at the anterior part of the bulbus or rarely at the posterior-most end of the proboscis in P. tereticollis, while they lie anterior to the end of the proboscis in P. laevis; 3. The proboscis hooks No. 5 or 6 are markedly stout (robust) and clearly distinct in comparison with the surrounding hooks in P. tereticollis, while less robust and more similar to the hooks in P. laevis. In addition, genetic divergence between P. tereticollis and P. laevis based on ITS1, ITS2 and COI sequencing supports the existence of two distinct species and reveals that some isolates previously identified as P. laevis were actually P. tereticollis. Previous and present morphological and genetic data show that both Pomphorhynchus species occur in freshwaters throughout Europe and may infect the same fish hosts, such as chub and barbel, and also several species of isopods (Gammaridae). This study also provides morphological evidence that Pomphorhynchus intermedius Engelbrecht, 1957 is a synonym of P. tereticollis, because the only discrimination character of the former species, the “existing but small proximal projections of basal parts of the proboscis hooks located on the posterior proboscis half” are present also in P. tereticollis.

Although trophically transmitted parasites are recognized to strongly influence food-web dynamics through their ability to manipulate host phenotype, our knowledge of their host spectrum is often imperfect. This is particularly true for the facultative paratenic hosts, which receive little interest. We investigated the occurrence and significance both in terms of ecology and evolution of paratenic hosts in the life cycle of the fish acanthocephalan Pomphorhynchus laevis. This freshwater parasite uses amphipods as intermediate hosts and cyprinids and salmonids as definitive hosts. Within a cohort of parasite larvae, usually reported in amphipod intermediate hosts, more than 90% were actually hosted by small-sized fish. We demonstrated experimentally, using one of these fish, that they get infected through the consumption of parasitized amphipods and contribute to the parasite's transmission to a definitive host, hence confirming their paratenic host status. A better knowledge of paratenic host spectrums could help us to understand the fine tuning of transmission strategies, to better estimate parasite biomass, and could improve our perception of parasite subwebs in terms of host-parasite and predator-parasite links.

Many trophically transmitted parasites with complex life cycles manipulate their intermediate host behavior in ways facilitating their transmission to final host by predation. This facilitation generally results from lowering host's antipredatory defenses when the parasite is infective to the final host. However, a recent theoretical model predicts that an optimal parasitic strategy would be to protect the intermediate host from predation when noninfective, before switching to facilitation when the infective stage is reached. We tested this hypothesis in the fish acanthocephalan parasite Pomphorhynchus laevis using the amphipod Gammarus pulex as intermediate host. Gammarids parasitized by noninfective stage of P. laevis (acanthella) hid significantly more under refuges than uninfected ones. In addition, acanthella-infected gammarids were less predated upon by trout than uninfected ones. As predicted, a switch toward decreased antipredatory behavior of G. pulex and enhanced vulnerability to predation was found when P. laevis reached the stage infective to its final host. The parasites appear to be able to exploit plasticity in host antipredatory responses, and shift the host optimal response toward their own optimal balance.

SUMMARY Immunopathological and ultrastructural studies were conducted on the intestine of barbel Barbus barbus and sheatfish Silurus glanis that were naturally infected with the acanthocephalan Pomphorhynchus laevis. Enteric helminths often cause inflammation of the digestive tract, inducing the recruitment of different types of immune cells at the site of infection. The results of our study clearly demonstrated that mast cells (MC) were the dominant immune cells which occur at the site of inflammation in both hosts. MC were associated with fibroblasts and were found in close proximity to, and inside, the capillaries of the intestine, thus, migration of mast cells via the bloodstream was suggested. Significant degranulation of MC was present. Immunohistochemical staining revealed met-enkephalin and serotonin (5-HT) in intestinal MC of both uninfected and infected barbel and the absence of the antimicrobial peptides piscidin 3 and piscidin 4 in both species. Data are discussed with respect to host immune response to an intestinal helminth and compared with other host-parasite systems.

Competitive interactions between coinfecting parasites are expected to be strong when they affect transmission success. When transmission is enhanced by altering host behaviour, intraspecific conflict can lead to ‘coinfection exclusion’ by the first-in parasite or to a ‘sabotage’ of behavioural manipulation by the youngest noninfective parasite. We tested these hypotheses in the acanthocephalan parasite Pomphorhynchus laevis, reversing phototaxis in its intermediate host Gammarus pulex. No evidence was found for coinfection exclusion in gammarids sequentially exposed to infection. Behavioural manipulation was slightly weakened but not cancelled in gammarids infected with mixed larval stages. Therefore, coinfecting infective and noninfective larvae both suffered competition, potentially resulting in delayed transmission and increased risk of mortality, respectively. Consequently, noninfective larva is not just a ‘passive passenger’ in the manipulated host, which raises interesting questions about the selective pressures at play and the mechanisms underlying manipulation.

Urquhart, K., Pert, C. C., Fryer, R. J., Cook, P., Weir, S., Kilburn, R., McCarthy, U., Simons, J., McBeath, S. J., Matejusova, I., and Bricknell, I. R. 2010. A survey of pathogens and metazoan parasites on wild sea trout (Salmo trutta) in Scottish waters. – ICES Journal of Marine Science, 67: 444–453. In all, 300 wild sea trout were sampled from three east coast and two west coast sites around Scotland over a 3-year period to establish the prevalence and the abundance of bacteria, viruses, and ecto- and endoparasites. No bacterial pathogens were isolated from any fish. One fish tested positive for viral pathogens (infectious pancreatic necrosis virus). The viral agent syncytium, resulting from aquareovirus infection, was found in four fish from the east coast. The parasitic fauna consisted of three classes of ectoparasite, Monogenea, Isopoda, and Copepoda, and four classes of endoparasite, Cestoda, Digenea, Nematoda, and Acanthocephala. Sea trout from the east coast sites were larger than those from the west coast. The abundance of Lepeophtheirus salmonis, Hysterothylacium aduncum, and Anisakis sp. was significantly greater at the east coast sites. The only parasite found in significantly greater numbers at a west coast site was Pomphorhynchus laevis.

The lumpsucker (Cyclopterus lumpus Linnaeus, 1758) is a marine fish inhabiting shallow coastal areas of North Atlantic. In 1996-2006, 224 lumpsucker individuals caught in the Gulf of Gdańsk and Vistula Lagoon (Poland) were examined for metazoan parasites. The fish were found to support the cestode Eubothrium crassum (Bloch, 1779), the nematodes Contracaecum osculatum (Rudolphi, 1802) L3, Dichelyne minutus (Rudolphi, 1819), and Hysterothylacium aduncum (Rudolphi, 1802) L3, L4, ad. as well as the acanthocephalans Corynosoma strumosum (Rudolphi, 1802) cyst., Echinorhynchus gadi Zoega in Müller, 1776, and Pomphorhynchus laevis (Müller, 1776). The total (both areas) prevalence of parasites was 63.4% at a mean intensity of 2.1 inds. In the Gulf of Gdańsk, 66.3% of all the lumpsucker examined were infected (intensity 2 inds), the level of infection in the Vistula Lagoon being 46.5% of the fish (intensity 2.3 inds). The Gulf of Gdańsk lumpsucker supported all the parasitic species listed, while 4 species only (E. crassum, H. aduncum, E. gadi, and P. laevis) were recorded in the Vistula Lagoon. The dominant parasites were H. aduncum (43.3%, 2.1 inds) and E. gadi (21.0%, 1.2 inds). All the parasitic species, except C. strumosum, are being reported from the southern Baltic lumpsucker for the first time.

This study assessed the diets and parasites of larval and 0+ juvenile twaite shad Alosa fallax fallax in the lower reaches and estuaries of the rivers Wye, Usk and Towy, UK. There were significant differences between the diets of larvae and co-habiting 0+ juveniles, and of larvae and 0+ juveniles among sites, both within and among rivers. In the Wye and Usk, the diets of twaite shad larvae were dominated by chironomid larvae, whereas those in the Towy specialised upon cyclopoid copepods. The diets of 0+ juvenile twaite shad from freshwater (River Wye) were characterised by chironomid larvae, while estuarine (Towy Estuary) individuals specialised upon calanoid copepods. Parasites infecting 0+ twaite shad were Apiosoma sp. (Protozoa), Gyrodactylus sp. (Monogenea), Proleptinae (Nematoda) larvae, Pomphorhynchus laevis (Acanthocephala), Spinitectus sp. (Nematoda) larvae and Trichodina sp. (Protozoa). Over 60% of estuarine 0+ juvenile twaite shad were infected with Apiosoma sp., with maximal estimated loadings in excess of 3,000 parasites per fish. Other parasite taxa were generally present in only small numbers. There were no significant differences in the intensity of parasite infections among sites, or the condition of parasitised and non-parasitised 0+ twaite shad.

A specimen of common sole (Solea solea) was caught in the southeastern part of the Baltic Sea (ICES fishing subdivision 26) on 6 October 2007. It is the first documented report on this fish species from the southeastern part of the Baltic Sea. The fish had presumably strayed there from waters of higher salinity. It was caught during the hydrological autumn before the disappearance of the seasonal thermocline. The total body length of the specimen was 29 cm, and weight 290 g. It was a 2.5–3 year-old female with its gonads in the second stage of maturity. Parasitic helminths detected in its intestine were typical of brackish-water fish of the southeastern Baltic Sea: three immature specimens of acanthocephalans (Pomphorhynchus laevis Zoega (Muller, 1776)) and larvae L3 of roundworms (Hysterothylacium Aduncum Rudolphi, 1809). No remains of nutritive organisms were found in the stomach and intestine. From a biological viewpoint, it was a specimen that strayed into waters of low salinity beyond the species rep...

7 pages; International audience; Fish acanthocephalans can modify the antipredator behaviour of their intermediate hosts in response to cues from fish predators. However, it is still unclear whether such behavioural changes are adaptive, or are just the consequence of infection. We addressed this question through studying two acanthocephalans, Pomphorhynchus laevis and Polymorphus minutus, and their intermediate host, the amphipod Gammarus pulex. Pomphorhynchus laevis completes its cycle in a freshwater fish, whereas P. minutus exploits waterbirds as final hosts.We first assessed vulnerability of infected and uninfected gammarids to predation by bullheads, Cottus gobio. Pomphorhynchus laevis-infected gammarids were more susceptible to predation than uninfected ones when a refuge was available, whereas no selective predation on P. minutus-infected individuals was recorded, independently of refuge availability. We then quantified refuge use when a bullhead was present in an enclosure or when the enclosure was empty. Individuals of each group significantly increased refuge use in the presence of a bullhead. However, a larger proportion of P. laevis-infected gammarids remained out of the refuge in the presence of a predator, compared with uninfected controls, whereas no such effect was observed in P. minutus-infected ones. Finally, we assessed reaction to bullhead olfactory cues, using a Y-maze apparatus. Pomphorhynchus laevis-infected gammarids spent significantly more time in the predator-scented arm, whereas the reverse was observed in uninfected ones. Polymorphus minutus-infected individuals, however, did not differ from uninfected controls. We discuss our results in relation with the adaptiveness of host manipulation by parasites.

8 pages; International audience; Manipulative endoparasites with complex life cycles can alter their intermediate host immunity and behaviour in ways that increase survival probability within the host body cavity and enhance successful transmission to the definitive host. These parasitic manipulations are variable among and within parasite species and may result from co-evolutionary processes, in which the parasite is constrained for adaptation to the local intermediate host. Hence, arrival of a new host species in a local host population may promote local parasite maladaptation. This study tested the occurrence of local adaptation in two distantly located populations of the acanthocephalan parasite Pomphorhynchus laevis and its effect on the immunity and behaviour of its gammarid intermediate host Gammarus roeseli. This was done in France (an area for which G. roeseli is a recent invader) and Hungary (an area from which G. roeseli was believed to be native). As expected, we found no alteration in G. roeseli's immune defence and behaviour associated with infection by P. laevis in localities, where the gammarid is invasive. Unexpectedly, we found similar results in Hungarian populations, where the parasite was even more exposed to the host immune response. Whilst these results suggest maladaptation of the parasite to the gammarid in both countries, they also suggest that the gammarid host might be locally adapted to the parasite. Genetic analyses were performed on both the parasite and the host and the results suggest that the two subsets of populations we studied harbour rather isolated host-parasite systems, both probably deriving from a common ancestral population. We propose that G. roeseli is also of recent acquisition in Hungary, and that a recent co-evolutionary history between P. laevis and G. roeseli in association with a long generation time in the parasite has constrained parasite adaptations in Europe or even favoured host adaptation to the parasite.

The known metazoa parasite fauna of the invasive round goby Apollonia melanostoma (formerly Neogobius melanostomus) consists of 12 species. The core of the parasite fauna comprises two species: Cryptocotyle concavum and Diplostomum spathaceum; secondary species are absent; satellite species include Cercariae gen. sp. and Ergasilus sieboldi; rare species are Acanthocephalus lucii, Anguillicola crassus, Bothriocephalus sp., Dichelyne minutus, Hysterothylacium aduncum, Pomphorhynchus laevis, Piscicola geometra, and Tylodelphys clavata. Fifty percent of metazoa parasites that occurred in the invasive round goby in the Gulf of Gdańsk (an invasion that was first detected in 1990) are also typically found in the native Gulf of Gdańsk gobiids. The round goby hosts common fish parasite species: C. concavum and D. minutus, but none that are unique to the species and no Ponto-Caspian parasites. Notably, the parasite species of the invasive round goby in the Gulf of Gdańsk includes species that are atypical for this species in its native habitat. In its new habitat, the round goby variously serves the roles of definitive, second intermediate, and paratenic host for different parasite species. The fish species is involved in a parasitic system that includes fish-eating birds, fishes of different ecological groups (predatory, planktivorous, and benthivorous), and invertebrates.

Summary During a survey of the parasite fauna Neogobius spp., which only recently invaded Hungarian reaches of the Danube River upstream from Budapest, it was found that Neogobius melanostomus and N. fluviatilis had become common species. Neogobius kessleri was less frequent and the previously widespread Proterorhinus marmoratus was drastically reduced. The parasite fauna of the newcomer fish species was characterized by ubiquitous parasites of a wide host range, such as the trematode Nicolla skrjabini, the metacercariae of Metagonimus yokogawai and Apatemon cobitidis, the larval stages of the acanthocephalan Pomphorhynchus laevis and the nematode Rhaphidascaris acus, the glochidia of an Anodonta sp. (Mollusca) and the ciliophoran Ichthyophthirius multifiliis. The specific parasites of Neogobius spp. were represented by three intestinal coccidia: Eimeria daviesae, Goussia kessleri, and a new species described here as Goussia szekelyi sp. n. This survey showed that the rapid invasion of Ponto-Caspian gobies in the northern Danube caused important changes in the fish fauna composition of the Danube River and enriched the parasite fauna of Hungarian fishes.

Manipulative parasites can alter the phenotype of intermediate hosts in various ways. However, it is unclear whether such changes are just by-products of infection or adaptive and enhance transmission to the final host. Here, we show that the alteration of serotonergic activity is functionally linked to the alteration of specific behaviour in the amphipodGammarus pulexinfected with acanthocephalan parasites.Pomphorhynchus laevisand, to a lesser extent,Pomphorhynchus tereticollisaltered phototactism, but not geotactism, inG. pulex, whereas the reverse was true forPolymorphus minutus. Serotonin (5-hydroxytryptamine, 5-HT) injected to uninfectedG. pulexmimicked the altered phototactism, but had no effect on geotactism. PhotophilicG. pulexinfected withP. laevisorP. tereticollisshowed a 40% increase in brain 5-HT immunoreactivity compared to photophobic, uninfected individuals. In contrast, brain 5-HT immunoreactivity did not differ betweenP. minutus-infected and uninfectedG. pulex. Finally, brain 5-HT immunoreactivity differed significantly amongP. tereticollis-infected individuals in accordance with their degree of manipulation. Our results demonstrate that altered 5-HT activity is not the mere consequence of infection by acanthocephalans but is specifically linked to the disruption of host photophobic behaviour, whereas the alteration of other behaviours such as geotactism may rely on distinct physiological routes.

Summary Metazoan parasites were investigated in three non-native fishes (monkey goby Neogobius fluviatilis, bighead goby Neogobius kessleri and round goby Neogobius melanostomus) collected from the former and current main channel of the River Danube and from the River Hron, Slovakia, in November 2003. Thirteen parasite species were identified: Triaenophorus crassus, Diplostomum sp., Tylodelphys clavata, Metorchis xanthosomus, Nicolla skrjabini, Gyrodactylus proterorhini, Pomphorhynchus laevis, Contracoecum sp., Raphidascaris acus, Anguillicola crassus, Unio tumidus, Anodonta anatina and Pseudoanodonta complanata. The maximum parasite diversity was found in N. fluviatilis. Total parasite abundance was significantly higher in N. kessleri, but no significant differences among sampling sites were observed. Pomphorhynchus laevis and glochidia of Anodonta anatina reached 100% prevalence in N. kessleri in the new channel of the Danube and, in general, these species were also the most prevalent parasites in all three goby species. For endoparasites, gobies served mostly as intermediate (digenean, cestodes and nematodes) or paratenic (acantocephalan and nematodes) hosts. All parasite species found are common parasites in the Middle Danube basin. No parasites specific to Neogobius, known from their native populations, were observed.

The composition and diversity of the total and intestinal component endohelminth communities were determined in the cyprinid barbel from three study areas in two large river systems in Austria. Two sample sites in the Danube and one site in the River Drau are the only free flowing stretches of these rivers in Austria. Nine helminth species were identified, with the acanthocephalan Pomphorhynchus laevis being dominant in the Danube, with up to 100% prevalence. In the Drau, where the dominant species was the cestode Bathybothrium rectangulum, species diversity was higher than in the Danube.

Concentrations of the platinum group elements Pt, Pd, and Rh were analyzed by adsorptive cathodic stripping voltammetry (Pt, Rh) and total-reflection X-ray fluorescence (Pd) in the intestinal helminth Pomphorhynchus laevis and its host Barbus barbus. The fish were caught in the Danube river south of the city of Budapest (Hungary) and were exposed to ground catalytic material for 28 days. Following exposure all three precious metals were taken up and accumulated in host organs and the parasites. Interestingly, in all tissues of the unexposed controls Pt was found, whereas Pd was not present in the muscle of the controls and Rh was not detectable in muscle and intestine of unexposed barbel. All metals were found at significantly higher concentrations in the acanthocephalan than in the tissues of barbel. These results are discussed with respect to the application of P. laevis as an accumulation indicator for metals.

Background. The hitherto published records of the parasite fauna of Baltic cod, Gadus morhua callarias cover commercially-caught adult fish. The aim of this study was to determine the composition of the parasite fauna of young Baltic cod, the relevant infection parameters and to relate those data to published records on the diet of cod. Materials and methods. This survey was carried out on 154 young cod, caught in May and June 2002 in the Gulf of Puck, the Baltic Sea, Poland. The fish were examined using standard methods applied in parasitology. Results. No external parasites were found. In the digestive tracts of 58 cod, 3 species of parasites belonging to 2 higher taxa (Nematoda and Acanthocephala) were found. The dominant parasite was Echinorhynchus gadi Zoega in Müller, 1776. The mean abundance ranged from 0.15 to 2.75. The prevalence ranged from 14.6%, in the smallest fish, to 66.7% in the larger ones. Only two acanthocephalan specimens of Pomphorhynchus laevis (Zoega in Müller, 1776) and five nematode larvae of Hysterothylacium aduncum (Rudolphi, 1802) were found. Conclusion. The parasite fauna of young Baltic cod is significantly sparser than in larger fish examined by other authors. It is suggested that the occurrence of the species found, can be related to the composition of diet available.

An analysis was undertaken of intestinal helminth communities in flounderPlatichthys flesusfrom two sites on the River Thames. A comparison was made between helminth community richness and diversity from these sites at the component and infracommunity levels. At the component community level, a richer and more diverse parasite community was found in flounder from the Tilbury location (marine influence) than that from the Lots Road location (freshwater influence). At the infracommunity level, more parasite species and parasite individuals per host were found at Lots Road and the percentage of similarity values were low at both locations. Helminth species with high prevalence values in the parasite communities of the flounder are the dominant species in any individual fish, harbouring multi-specific infections. The presence of more invertebrate species, which are intermediate hosts in the helminth life cycle in the Thames, fish vagility and the high prevalence and abundance values ofPomphorhynchus laevisin the flounder, may explain the differences between the two locations.

Pomphorhynchus laevis is believed on ecological evidence to exist as three strains in the British Isles. However, the strains have never been shown to be capable of being distinguished using morphological characters. A morphological comparison was made between a sample of P. laevis from Salmo trutta in L. Feeagh in the west of Ireland and a sample from Leuciscus cephalus in R. Culm in the south of England. The length and width of the trunk, neck, bulb, proboscis and hooks were measured. The number of hooks per row, the number of rows and the positions of the stoutest and longest hooks were also recorded. A Principal Components Analysis based on the morphological measurements confirmed the separation of the two populations and showed that two characters successfully identified the populations: the position of the stoutest hook and the ratio of numbers of anterior to posterior hooks.

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.

Studies on parasite species with a wide geographic and ecological range may be confounded by still equivocal taxonomic identification. Here, we investigated genetic polymorphism and behavioural changes induced in a common intermediate host, in two different forms of Pomphorhynchus laevis based on the morphology of the larval infective stage (cystacanth). A 'smooth type' (S) and a 'wrinkled type' (W) of cystacanth were distinguished based on their surface and shape. We analysed sequence divergence at both nuclear (ribosomal gene 18S rDNA, and ribosomal internal transcribed spacers, ITS1/ITS2) and mitochondrial (cytochrome c oxidase subunit 1) genes of P. laevis cystacanths and adults at various geographical scales. A high level of sequence divergence at ITS1, ITS2 and cytochrome c oxidase subunit 1 (11, 8 and 20%, respectively) was found between these two forms. The divergence pattern consistently discriminated two groups independently of geographic origin or host, and was congruent with larval morphology. The two forms also strongly differed in the intensity of behavioural change induced in their common intermediate host, Gammarus pulex, with the S-type parasite inducing a positive phototactism, whereas W-type infected gammarids were as photophylic as uninfected ones. Overall, our data strongly support the specific status of these two forms. We suggest that smooth cystacanths correspond to P. laevis, whereas wrinkled cystacanths might correspond to the previously described and poorly documented, Pomphorhynchus tereticollis, considered a synonym of P. laevis. This study also confirms the value of a joint analysis of internal transcribed spacers and cytochrome c oxidase subunit 1 genes to biogeographic studies on these species. Finally, we emphasize the importance of linking morphological and biological characteristics of acanthocephalan cystacanths to molecular data, in the study of the evolutionary ecology and systematics of this group.

The aim of this paper was to test the hypothesis that when the 2 species of AcanthocephalanPomphorhynchus laevisandAcanthocephalus clavulaare found concurrently within the intestine of brown trout under field conditions, they have the potential to interact negatively. Evidence has shown that Acanthocephala are more likely to exhibit negative interactions with their own and other species, under both field and experimental conditions. Furthermore, the likelihood of these interactions is increased in Ireland because of the absence of certain definitive hosts and the fact that concurrent infections by two or more species of Acanthocephala are more commonly observed in fish. Data collected from wild and stocked brown trout and from 2 lakes provided an opportunity to compare the 2 potentially interacting helminth species in their fundamental and realized niche and several pieces of convincing evidence are provided here to support the hypothesis. A significant negative association between the numbers of each species found in individual fish was reported and this was consistent for both wild and stocked trout. Furthermore, an analysis of the proportions of low, moderate and high intensity infections in single and concurrent infections revealed a significant reduction in increasing intensities in concurrent infections compared to single infections. Finally, strikingly different patterns of niche inhabitation were observed, particularly forP. laevisin the presence ofA. clavulain wild trout. Results from the niche width analysis also support the observations on average position in single and concurrent infections. The niche width ofP. laeviswhen it co-occurred withA. clavuladecreased markedly in high intensity infections compared to low intensity infections.

The acanthocephalan parasite Pomphorhynchus laevis is transmitted by a suitable intermediate host such as the amphipod Gammarus pulex to its definitive fish host. Parasite-induced alterations in both appearance and behaviour concur to render infected gammarids more vulnerable to predation, thus promoting parasite transmission. Experimental infection of laboratory bred full- and half-sib groups of three-spined sticklebacks (Gasterosteus aculeatus) provided evidence that the parasite imposes a survival cost proportional to the severity of infection on its final host. Variation among sibships in the susceptibility to infection was consistent. When given a choice, fish consumed significantly more infected than uninfected prey. Overall, more resistant fish did not prey upon infected gammarids more often than did relatively susceptible fish. Only fish with a relatively high physical condition properly adjusted prey selection to the extent of their parasite susceptibility, thus exploiting the enhanced profitability of infected prey.

The histopathology, immunohistochemistry and ultrastructure of the alimentary canal of chub, Leuciscus cephalus (L.), from the River Brenta, naturally infected with the acanthocephalan Pomphorhynchus laevis Muller, 1776, was studied and described. Of 62 chub examined, 54 (87%) were infected with P. laevis, the intensity of infection ranged from five to 130 parasites per host, and a density of 8 P. laevis per cm 2 was common. Examination of histological material of infected chub revealed that both male and female acanthocephalans deeply penetrated all layers of the gut wall by means of their slender neck, bulb and proboscis. As a result, a capsule was formed around the bulb and proboscis on the external surface of the host intestine. In parasitized chub, four main types of reaction against the body of the acanthocephalan were recognized. Pomphorhynchus laevis caused local damage to the intestinal wall, eliciting catarrhal-erosive enteritis in the lumen and a fibroblastic-collagenous and fibro-epithelioid encapsulation in its thickness with tissue zonation according to the depth of parasite penetration. Furthermore, eosinophilic granular cells (EGC) within the inflammatory tissue were identified by immunohistochemical methods and transmission electron microscopy.

Here we report the genetic variability and presence of mtDNA-like sequences of Pomphorhynchus laevis from the chub, Squalius cephalus, caught at the sampling sites along the Sava River and its tributary the Sutla River in Croatia. Sequences of the cytochrome c oxidase subunit 1 (COI) gene of the recovered P. laevis specimens were used for haplotype network construction and phylogenetic analysis. These analyses showed that some specimens contained mitochondrial-like sequences, and they uncovered the existence of a Sava River basin strain different from known strains of P. laevis. This is the first time that P. laevis has been shown to contain mtDNA-like sequences, suggesting the need to exercise caution during COI analyses of P. laevis using universal primers. Highly conserved sequences of two nuclear markers, the ITS region and 18S rRNA, were not helpful for understanding genetic variability or differentiating strains. Furthermore, analysis of the dynamics of P. laevis infections in S. cephalus from the Sava and Sutla Rivers showed decreased prevalence and abundance at sites with inferior water quality, positive association of parasite abundance with fish size, and no clear association of parasite abundance with fish condition index or sex.

This experimental study assessed the role of the microhabitat in the uptake of metals by adult acanthocephalans. We examined the accumulation of lead by adult Pomphorhynchus laevis in the intestine of chub (Leuciscus cephalus) and compared it with that in goldfish, Carassius auratus auratus, in which the parasites penetrate the intestinal wall and enter the body cavity. Chub and goldfish experimentally infected with adult Pomphorhynchus laevis were exposed to 0.01 mg l(-1) Pb(2+) over 3 weeks. Lead was rapidly accumulated in the intestinal acanthocephalans reaching a mean concentration of 7.3 microg g(-1). This concentration was significantly greater than in the host muscle, liver and intestine and more than 730 times higher than the exposure concentration. Intraperitoneal P. laevis in goldfish exposed to lead did not accumulate the metal. Thus, it was conclusively shown that metal accumulation in acanthocephalans is associated with the intestinal location and does not occur in the body cavity.

Besides conspicuous changes in behaviour, manipulative parasites may also induce subtle physiological effects in the host that may also be favourable to the parasite. In particular, parasites may be able to influence the re-allocation of resources in their own favour. We studied the association between the presence of the acanthocephalan parasite, Pomphorhynchus laevis, and inter-individual variation in the lipid and glycogen content of its crustacean host, Gammarus pulex (Amphipoda). Infected gravid females had significantly lower lipid contents than uninfected females, but there was no difference in the lipid contents of non-gravid females and males that were infected with P. laevis. In contrast, we found that all individuals that were parasitised by P. laevis had significantly increased glycogen contents, independent of their sex and reproductive status. We discuss our results in relation to sex-related reproductive strategies of hosts, and the influence they may have on the level of conflict over energy allocation between the host and the parasite.

To investigate the relationship between fish parasite communities and water quality level, metazoan parasites were examined in 157 specimens of chub (Leuciscus cephalus L.), sampled in four lowland water courses (northern Italy): Ticino river (unpolluted), Naviglio Pavese Canal (slightly polluted), Lambro river near the Merone village (polluted) and near Monza (severely polluted). Dactylogyrus vistulae, Paradiplozoon ergensi, Bucephalus polymorphus, Acanthocephalus anguillae and larval stages of Tylodelphys clavata were found in all the sampled sites. The distribution of Lamproglena pulchella and Pomphorhynchus laevis was limited to the unpolluted and slightly polluted river sectors, while Asymphylodora tincae, glochidia, along with larval stages of Diplostomum spathaceum, were absent in the severely polluted site. The variability of the calculated infection indices (prevalence, mean abundance and mean intensity), the degree of interactivity among parasites, as well as parameters of species richness and diversity suggest that the structure of parasite communities are affected by the water contamination level.

When two parasite species are manipulators and have different definitive hosts, there is a potential for conflict between them. Selection may then exist for either avoiding hosts infected with conflicting parasites, or for hijacking, i.e. competitive processes to gain control of the intermediate host. The evidence for both phenomena depends largely on the study of the relative competitive abilities of parasites within their common intermediate host. We studied the effects of simultaneous infection by a fish acanthocephalan parasite, Pomphorhynchus laevis, and a bird acanthocephalan parasite, Polymorphus minutus, on the behaviour of their common intermediate host, the amphipod Gammarus pulex. We compared the reaction to light and vertical distribution of individuals infected with both parasites to those of individuals harbouring a single parasite species and uninfected ones under controlled conditions. Compared to uninfected gammarids that were photophobic and tended to remain at the bottom of the water column, P. laevis-infected gammarids were attracted to light, whereas P. minutus-infected individuals showed a modified vertical distribution and were swimming closer to the water surface. The effects of both P. laevis and P. minutus appeared to be dependent only on their presence, not on their intensity. Depending on the behavioural trait under study, however, the outcome of the antagonism between P. laevis and P. minutus differed. The vertical distribution of gammarids harbouring both parasites was half-way between those of P. laevis- and P. minutus-infected individuals, whereas P. laevis was able to induce altered reaction to light even in the presence of P. minutus. We discuss our results in relation to the occurrence of active avoidance or hijacking between conflicting manipulative parasites and provide some recommendations for future research.

A total of 112 flounder, Platichthys flesus, was surveyed for the presence of Pomphorhynchus laevis (Acanthocephala). No acanthocephalans were found in 35 fish, 40 fish were infected with 1–5 thorny-headed worms, and in 37 fish the intensity of infection exceeded 6. The fish surveyed were also studied for the composition of the resident microflora of the terminal portion of the intestine—the characteristic site for P. laevis. It turned out the number of worms was positively correlated with the bacterial count. The bacteria cultured from the material sampled from intestines of infected- and non-infected fish exhibited similar specific composition and the differences were only in the intensity of individual species. The most frequently isolated bacteria, represented the genera: Aeromonas, Pseudomonas and Shewanella. The least frequent were species of Chromobacterium, Escherichia, Providencia and Serratia. The presently reported study results, suggest that bacteria species, constituting physiological bacterial flora, may become, under certain conditions, potentially pathogenic, through substantial increase in their abundance. The factor responsible for disturbing the natural balance in the intestine may be the thorny-headed worm, Pomphorhynchus laevis.

Sures, B., and Siddall, R. 1999. Pomphorhynchus laevis: The intestinal acanthocephalan as a lead sink for its fish host, chub (Leuciscus cephalus). Experimental Parasitology93, 66–72. Aqueous lead exposure of chub (Leuciscus cephalus) experimentally infected with the parasite Pomphorhynchus laevis resulted in a rapid accumulation of this metal in the intestinal acanthocephalans, reaching concentrations which were significantly greater than in the host muscle, liver, and intestine and approximately 1000 times higher than the exposure con centration. Parasitized chub accumulated significantly less lead in their intestinal wall than their uninfected conspecifics (Mann-Whitney U test, P ≤ 0.05). From in vitro studies it was shown that lead uptake of P. laevis cystacanths clearly increases by adding 1% eel bile to a commercial RMPI-1640 medium containing 0.1 μg ml−1 Pb2+ compared to the controls, which were maintained in RMPI-1640 medium containing lead at the same concentration but without bile. It is therefore most likely that P. laevis in chub absorb bile-bound lead from the host intestine and thus reduce its reabsorption by the intestinal wall, thereby interrupting the hepatic–intestinal cycling of the metal. This is the first example of a beneficial impact of a parasite on its host.

In connection with the BMB/ICES Sea-going Workshop “Fish Diseases and Parasites in the Baltic Sea”, 200 specimens of flounder Platichthys flesus from eight stations (25 from each) distributed from the southwestern (Mecklenburg Bight) to the northeastern Baltic Sea (Gulf of Finland) were examined for metazoan parasites. A few species (e.g. Hysterothylacium aduncum, Cucullanus heterochrous, Cucullanellus minutus, and Pomphorhynchus laevis) were found at virtually all stations. Typical “marine” species (Podocotyle atomon, Brachyphallus crenatus, Anisakis simplex, Holobomolochus confusus, and Lernaeocera branchialis) were found at the western stations only, whereas the metacercariae of Diplostomum spathaceum, and Cotylurus sp., immature Corynosoma sp., the larvae of Raphidascaris acus and Contracaecum osculatum were most common towards the east and north. Echinorhynchus gadi only occurred at the western and southern stations. The small encapsulated larvae of the bird nematodes Contracaecum sp., Paracuaria sp., and Cosmocephalus sp. were found at most stations. The effects of salinity on the patterns observed in relation to the distribution of intermediate and final hosts are discussed.