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In recent years there has been an increasing number of papers showing how parasitism and pollution can interact with each other in aquatic organisms. Among the variety of investigated aspects especially the combined effects of pollution and simultaneous infection on the health of aquatic hosts (molluscs, crustaceans, fish, mammals) is of considerable interest. Effects of pollution on the occurrence and distribution of parasites is another interesting field of “Environmental Parasitology” attracting increasing attention. This mini-review presents some promising examples of interdisciplinary studies paying attention to the fact that under natural conditions no organism will only be affected by either parasites or pollution.

Invasive parasites may severely affect their new hosts. Two invasive parasites occurring in the European eel (Anguilla anguilla) are the Asian swim bladder nematode Anguillicola crassus and the Ponto-caspian acanthocephalan Pomphorhynchus sp., which were introduced to the river Rhine in the early 1980/90s. The Japanese eel (Anguilla japonica), as the native host of A. crassus , developed mutual adaptations to the swim bladder parasite, which are lacking in the European eel. Therefore, after its spread to Europe, infestations of European eels with A. crassus were found to be more severe and caused massive swim bladder wall damages mainly due to the feeding activity of the adult nematodes. A suppression of the immune system also appears to be likely, which allows secondary infections e.g. by bacteria or other parasites in European eels. Acanthocephalans of the genus Pomphorhynchus have not been described so far in Japanese eels, in contrast to European eels, which regularly show infestations with Pomphorhynchus sp. By using these differentially adapted host-parasite associations for experimental studies, host stress responses were examined in the present study in relation to the degree of mutual adaptations between eel hosts and parasites. Under laboratory conditions, Japanese and European eels were each inoculated with A. crassus and Pomphorhynchus sp., respectively, to investigate their stress responses against differently adapted parasites. The stress response was determined by analyzing plasma levels of cortisol, which is the main corticosteroid hormone during stress response of fish. The results show a strong cortisol release in European eels after infestation with A. crassus whereas Japanese eels only react against Pomphorhynchus sp. infestations. These results are consistent with the initial hypothesis that a low degree of host-parasite adaptations lead to stronger host stress responses against the parasite. [Display omitted] • We measured cortisol as the main corticosteroid hormone in fish. • Japanese and European eels were inoculated with A. crassus and Pomphorhynchus sp. • Lower mutual adaptations lead to a higher stress response in host-parasite-systems. [ABSTRACT FROM AUTHOR]

Acanthocephalans belonging to the species Neoechinorhynchus agilis were collected from two mullets, Mugil cephalus and Chelon ramada from Ichkeul Lagoon in northern Tunisia. Collected parasites, as well as tissues of their hosts (muscle, liver and intestine), were analysed for trace elements (silver, arsenic, cadmium, cobalt, copper, iron, manganese, nickel (Ni), lead (Pb), selenium, vanadium (V), zinc) using inductively coupled plasma mass spectrometry. Our results showed different accumulation patterns of trace elements in fish tissues and parasites. Among the host tissues, liver accumulated the highest metal amounts. Acanthocephalans showed Ni, Pb and V in significantly higher concentrations compared to their host's tissues. Further, the calculated bioconcentration factors demonstrated a 390-fold higher Pb accumulation in the parasite compared to fish muscle. This study is the first field survey in Tunisia dealing with elements' uptake in parasites and their hosts. Our results corroborate the usefulness of the acanthocephalans for biomonitoring of metal pollution in aquatic ecosystems and promote more research in order to understand host–parasite systems in brackish waters of the Mediterranean area. [ABSTRACT FROM AUTHOR]

Southern Africa has one of the highest densities of temporary pools and some of the most understudied temporary wetlands in the world. Additionally, the eastern African annual killifishes (Nothobranchius spp.) are rare in southern Africa and found exclusively in temporary habitats. There is a notable lack of literature regarding the diet of these fish, as well as the foodweb structures of temporary ecosystems. The current study aimed to address this paucity in literature by assessing the foodweb of a temporary pool located in the Ndumo Game Reserve (NGR) in northern Kwa-Zulu Natal using stable isotopes analysis. In addition, Bayesian mixing models were used to assess the diet of the spotted killifish Nothobranchius orthonotus over two seasons (dry and wet seasons). The foodweb consisted of only three trophic levels and comprised different foodweb items between the two seasons. Stable isotope analysis indicated significant increases in δ15N from the dry to wet season. It further revealed the diet of N. orthonotus to be more varied and omnivorous with primary producers contributing a much greater percentage toward their diet than previous studies have reported. This study contributes valuable information to the paucity of knowledge regarding foodweb structure and food-chain length of temporary pools in South Africa, as well as new insights into the extended diet of N. orthonotus. The analytical techniques used in this study could also be utilised as part of future research in ecological assessments of temporary pools and other aquatic ecosystems in Africa and globally. [ABSTRACT FROM AUTHOR]

Bithynids snails are a widespread group of molluscs in European freshwater systems. However, not much information is available on trematode communities from molluscs of this family. Here, we investigate the trematode diversity of Bithynia tentaculata, based on molecular and morphological data. A total of 682 snails from the rivers Lippe and Rhine in North Rhine-Westphalia, Germany, and 121 B. tentaculata from Curonian Lagoon, Lithuania were screened for infections with digeneans. In total, B. tentaculata showed a trematode prevalence of 12.9% and 14%, respectively. The phylogenetic analyses based on 55 novel sequences for 36 isolates demonstrated a high diversity of digeneans. Analyses of the molecular and morphological data revealed a species-rich trematode fauna, comprising 20 species, belonging to ten families. Interestingly, the larval trematode community of B. tentaculata shows little overlap with the well-studied trematode fauna of lymnaeids and planorbids, and some of the detected species (Echinochasmus beleocephalus and E. coaxatus) constitute first records for B. tentaculata in Central Europe. Our study revealed an abundant, diverse and distinct trematode fauna in B. tentaculata, which highlights the need for further research on this so far understudied host–parasite system. Therefore, we might currently be underestimating the ecological roles of several parasite communities of non-pulmonate snail host families in European fresh waters. [ABSTRACT FROM AUTHOR]

South Africa is one of six global fish invasion hotspots and as a result, non-native fishes are common components of the fish assemblages in all of the major river systems. The rate of establishment for introduced fish into South African rivers is high (79%) and the vector responsible for the highest establishment rate is interbasin transfer schemes with 80%. Introductions of non-native fish into river systems can negatively affect native fish species through hybridisation, competition for food sources and predation, and the introduction of associated parasites and diseases. The aims of the current study were to provide evidence of the introduction of Labeo capensis into the Crocodile River (West) system, using morphological and molecular techniques, and to record the fish health and gonadosomatic index to determine the invasive status of L. capensis. From the fish health assessment index and gonadosomatic index of L. capensis collected from Olifantsnek Dam, it can be concluded that L. capensis is a healthy reproducing population. Because this fish species can survive and reproduce in newly colonised river systems, it has the potential to compete with the native fish species for food and habitat, but can also hybridise with native Labeo species. [ABSTRACT FROM AUTHOR]

Abstract Hydrological alteration of rivers is recognised as a major threat to lotic biodiversity acting at broad spatial scales, however, the effect size and pathways of hydrology are rarely quantified in comparison with other stressors such as land use and physico-chemistry. Here we present a multiple stressor study that aims to disentangle the effect sizes and pathways of hydrological alteration on benthic invertebrate community structure and functional metrics. Therefore, we analyse the following four multiple stressor groups: land use, hydrology, physical habitat structure, and physico-chemistry at 51 sites including 72 surveys in the German mountain range. Stressor data were contrasted to benthic invertebrate data using partial canonical correspondence analysis to quantify the community-level response and path analysis to investigate the cause-effect pathway structure of single stressors affecting benthic invertebrate metrics either directly or indirectly (i.e. mediated by other stressors). Hydrological stressors showed a strong impact on community structure, with its unique effects being more dominant than those of any other stressor group. Path analysis confirmed strong direct effects of hydrological stressors on biological metrics but revealed land use to be the most influential stressor group in terms of the sum of direct and indirect effects on biology. Notably, indirect land use effects are mediated by hydrology. Our findings suggest a key role of hydrological stressors in lotic ecosystem assessment, which, however, are rarely addressed in operational river monitoring and management. In light of the wide-spread availability of hydrological data from gauging stations throughout Europe, we plea for a better involvement of hydrological data in river basin management. Graphical abstract Unlabelled Image Highlights • Stressor groups comprised land use, hydrology, morphology, and physico-chemistry. • Effects and pathways of stressor groups on benthic invertebrates were quantified. • Hydrology showed the highest direct effects at community and metric level. • Anthropogenic land uses were major causes of hydrological alteration. [ABSTRACT FROM AUTHOR]

The analysis of stable isotopes of carbon and nitrogen has been used as a fingerprint for understanding the trophic interactions of organisms. Most of these studies have been applied to free-living organisms, while parasites have largely been neglected. Studies dealing with parasites so far have assessed the carbon and nitrogen signatures in endoparasites or ectoparasites of different hosts, without showing general trends concerning the nutritional relationships within host–parasite associations. Moreover, in most cases such systems involved a single host and parasite species. The present study is therefore the first to detail the trophic interactions of a freshwater monogenean–host model using δ13C and δ15N, where a single monogenean species infects two distinctly different hosts. Host fishes, Labeobarbus aeneus and Labeobarbus kimberleyensis from the Vaal Dam, South Africa, were assessed for the monogenean parasite Paradiplozoon ichthyoxanthon , individuals of which were removed from the gills of the hosts. The parasites and host muscle samples were analysed for signatures of δ13C and δ15N using an elemental analyser connected to an isotope ratio mass spectrometer. Host fish appear to use partly different food sources, with L. aeneus having slightly elevated δ13C signatures compared to L. kimberleyensis , and showed only small differences with regard to their nitrogen signatures, suggesting that both species range on the same trophic level. Carbon and nitrogen signatures in P. ichthyoxanthon showed that the parasites mirrored the small differences in dietary carbon sources of the host but, according to δ15N signatures, the parasite ranged on a higher trophic level than the hosts. This relationship resembles predator–prey relationships and therefore suggests that P. ichthyoxanthon might act as a micropredator, similar to blood-sucking arthropods such as mites and fleas. [ABSTRACT FROM AUTHOR]

In contrast to the well-studied trematode fauna of lymnaeid snails, only little is known about the role of small planorbid snails as first intermediate hosts for trematodes in temperate freshwater systems. This study aims at closing this gap by assessing the diversity and composition of larval trematode communities in Gyraulus albus and Segmentina nitida in a Central European reservoir system, and by providing an updated comprehensive review of the published trematode records of these snail hosts. A total of 3691 planorbid snails (3270 G. albus; 421 S. nitida) was collected in three consecutive years from four reservoirs of the River Ruhr catchment area in Germany. Gyraulus albus showed a higher overall trematode prevalence (11.7%) and more diverse trematode fauna (12 species) compared to S. nitida, which harboured three species and showed a lower trematode prevalence (1.7%). Altogether, 13 trematode species belonging to four families were identified in both hosts. Seven trematode species encountered in this study represent novel records for these hosts, and/or constitute first records of these larval stages from Germany. Trematode component communities in G. albus were stable across seasons and years, indicating excellent conditions for trematodes in this snail host and the continuous presence of the final hosts of the most dominant trematode species. Overall, this study reveals the importance of small planorbid snails, in particular G. albus, as first intermediate hosts for a species-rich trematode fauna in European freshwater systems, and highlights the parasites' contribution to the ecosystem's biodiversity. [ABSTRACT FROM AUTHOR]

Despite the advances in our understanding of the ecological importance of parasites that we have made in recent years, we are still far away from having a complete picture of the ecological implications connected to parasitism. In the present paper we highlight key issues that illustrate (1) important contributions of parasites to biodiversity, (2) their integral role in ecosystems, (3) as well as their ecological effects as keystone species (4) and in biological invasion processes. By using selected examples from aquatic ecosystems we want to provide an insight and generate interest into the topic, and want to show directions for future research in the field of ecological parasitology. This may help to convince more parasitologists and ecologists contributing and advancing our understanding of the complex and fascinating interplay of parasites, hosts and ecosystems. [ABSTRACT FROM AUTHOR]

In recent years, there has been an increasing number of papers showing how parasitism and pollution can interact with each other in aquatic organisms. In addition to synergistic negative effects of both stressors, there are also indications of antagonistic interactions. The latter are related to the reduction of pollutant levels in infected hosts compared with uninfected conspecifics. As reduced pollutant concentrations are usually correlated with less adverse effects, it might be advantageous to be infected if hosts are confronted with environmental pollution. On the other hand, possible pathological effects might reduce a potentially beneficial effect of parasites. There are also examples, however, which show that parasites may enhance toxic effects of pollutants by interfering with host-protection mechanisms. In these cases, a parasitosis would have exclusively negative effects on the physiological homeostasis of their hosts. This presentation summarizes the current knowledge on interactions between parasites and pollutants with respect to their effects on the host’s health. [ABSTRACT FROM AUTHOR]

In this paper, we report on an investigation of affecting guppy fishes (Poecilia reticulata) by silver ions (0, 0.3, 0.6, 1.2, 2.5, and 5 muM) for seven days under well-controlled experimental conditions. To observe the physiological changes, we attempted to determine metallothionein (MT) as a biomarker of heavy metal stress. For this purpose, we proposed a sensor utilizing a carbon electrode coupled with flow injection analysis. The experimental conditions, which have been optimized, were as follows-applied potential: 750 mV, mobile phase: Britton-Robinson buffer (pH 1.9) with flow rate of 0.6 ml/min, time filter: 2.5 s, "current R": 1 muA. Under these conditions, the detection limit of MT was estimated as 100 pM. After the optimizing step, the fish tissues were measured. Based on the results obtained, MT content increased with increasing dose of silver ions and time of the treatment. The results obtained were in good correlation with those obtained by adsorptive transfer stripping technique coupled with differential pulse voltammetry Brdicka reaction, which was used as the reference technique. [ABSTRACT FROM PUBLISHER]

The impact of an infection with a parasite and a simultaneous cadmium exposure on the stress hormone levels of rats was studied. To this end, we introduce a nonlinear heteroscedastic model, which is able to describe the temporal evolution of cortisol concentrations in groups of rats treated by cadmium or parasite infection. A thorough analysis gives strong evidence that parasitic infection and cadmium exposure affect the stress hormone level of rats in an additive manner. Therefore, the host''s response to environmental pollution should be studied in relation to parasite infections. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]