Hybridization between Anguillicola crassus and A. novaezelandiae, and viability of the F1 generation.

For decades, it has remained unclear how the Asian swim bladder nematode Anguillicola crassus was able to supplant the previously stable population of its relative from New Zealand Anguillicola novaezelandiae in the Lake Bracciano, Italy. Previously, researchers have hypothesized that A. crassus possesses an ecological advantage due to a more efficient life cycle in combination with a pattern of unidirectional hybridization between A. novaezelandiae females and A. crassus males. The present study focuses on the viability of hybrid offspring and their allelic pattern, particularly in developed adult stages of the hybrid F1 generation. While the percentages of hybrid individuals from A. novaezelandiae mothers and A. crassus fathers increased from egg to adult stages, it was more distinct in egg stages of A. crassus females and A. novaezelandiae males, but did not occur in adult F1 individuals at all. Therefore, we corroborate the hypothesis of unidirectional hybridization by differentiating between egg and adult stages, and suggest this as another explanatory factor for the extinction of A. novaezelandiae in Lake Bracciano in Italy and the predominance of A. crassus.

Metal accumulation in ecto- and endoparasites from the anadromous fish, the Pontic shad (Alosa immaculata).

Among the parasitic taxa studied for their metal accumulation properties, especially Acanthocephala and Cestoda proved to be promising sentinels for metal pollution. However, studies on metal accumulation are still sparse for other parasite groups, mainly due to their small body size. In the present study, we collected the relatively large-sized monogenean Mazocraes alosae Hermann, 1782 from the gills of Pontic Shad (Alosa immaculata Bennet 1835) from its spawning region ­ the Danube River. The host tissues gills, muscle, intestine and liver, the monogeneans as well as the nematode Hysterothylacium aduncum (Rudolphi, 1802), in the cases of coinfected fish, were analysed for the elements As, Cd, Co, Cu, Fe, Mn, Pb, Se and Zn. All elements (except of As) were found in higher concentrations in monogeneans and nematodes compared to host muscle tissue. High bioconcentration factors were obtained for toxic elements such as Cd and Pb with concentrations being approximately 12 and 251 times higher in monogeneans and 773 and 33 in nematodes, respectively, as compared to host muscle tissue. In comparison to other host organs, however, some elements were found in similar or even lower concentrations in the parasites. Thus, monogeneans do not exhibit the high accumulation potential reported for other parasitic taxa. Physiological adaptations of the migratory host fish between freshwater and marine habitats with differences in uptake pathways and biological availability of elements can be discussed as a possible explanation for this divergent accumulation pattern.

Trace element assessment in Neoechinorhynchus agilis (Rudolphi, 1918) (Acanthocephala: Neoechinorhynchidae) and its fish hosts, Mugil cephalus (Linnaeus, 1758) and Chelon ramada (Risso, 1827) from Ichkeul Lagoon, Tunisia.

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.

High parasite diversity in a neglected host: larval trematodes of Bithynia tentaculata in Central Europe.

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.

How Ponto-Caspian invaders affect local parasite communities of native fish.

Invasive species are a major threat to ecosystems worldwide. Their effects are versatile and mostly well studied. However, not much is known about the impact of invasion on native parasite communities, although parasites are usually important response variables for ecosystem health. To improve the knowledge on how native fish parasite communities and their dynamics are affected by invasive species and how these processes change local host-parasite interactions over time, we studied different host-parasite systems in four German rivers. Three of these rivers (Rhine, Ems, and Elbe) are heavily invaded by different Ponto-Caspian species such as the amphipod Dikerogammarus villosus and various gobiids such as Neogobius melanostomus and Ponticola kessleri that serve as potential hosts for different local parasite species, while the fourth river (Schwentine) was free of any Ponto-Caspian invaders. Due to the lack of additional uninvaded river systems, literature data on parasite communities before invasion were compared with the post invasion status for the rivers Rhine and Elbe. The results showed differences among the parasite communities of different host species from the three invaded rivers when compared to the Schwentine River. Among the local internal parasite communities, especially the acanthocephalan Pomphorhynchus laevis and the nematode Raphidascaris acus have to be considered as key species associated with invasions from the Ponto-Caspian region. As the examined invasive Ponto-Caspian fish species serves as suitable host for both parasite species, the increases in their infection rates in native fish species are examples of parasite spill back (R. acus) and spill over (P. laevis, at least in the river Rhine). These results were further supported by the analysis of literature data on parasite communities of the past 20 years. Consequences for local parasite communities range from decreased prevalence of native parasites towards an extinction of entire parasite species.

The monogenean Paradiplozoon ichthyoxanthon behaves like a micropredator on two of its hosts, as indicated by stable isotopes.

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.

Riverine regime shifts through reservoir dams reveal options for ecological management.

Worldwide, dams are a main threat reducing river ecological functioning and biodiversity by severely altering water temperature, flow, and sediment regimes up- and downstream. Sustainable dam management therefore has a key role in achieving ecological targets. Here, we present an analysis of the effects of reservoir dams and resulting regime shifts on community structure and function of lotic macroinvertebrates. Our study derived management options to improve ecological integrity of affected streams. To do this, we contrasted time series data for water temperature (15-min intervals over one year), discharge (daily means over 10 yr), and records of deposited fine sediments against macroinvertebrate samples from pairs of river reaches downstream of dams and of comparable tributaries not affected by dams in the German low mountain range. We observed a decline in the density and diversity of disturbance-sensitive macroinvertebrates (Ephemeroptera, Plecoptera, and Trichoptera) and a correlation between hydrologic metrics and macroinvertebrate deterioration downstream of the dams. Typical "rhithral" (flow-adapted) species changed to "littoral" (flow-avoiding) species below dams, thus indicating a hydrologic regime shift. Increased fine sediment accumulations and deficits of pebbles and small cobbles below dams indicated a severe habitat loss below dams. Additional comparison with undisturbed reference streams allowed us to derive management options that could mitigate the negative impact of hydrologic alterations and accumulations of fine sediments downstream of dams. These options are conditional on the season and in particular address the frequency and duration of low and high flow events.

Small but diverse: larval trematode communities in the small freshwater planorbids Gyraulus albus and Segmentina nitida (Gastropoda: Pulmonata) from the Ruhr River, Germany.

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.

Parasites as drivers of key processes in aquatic ecosystems: Facts and future directions.

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.

The Hsp70 response of Anguillicola species to host-specific stressors.

The present study is based on infection experiments of two different swim bladder parasite species, Anguillicola crassus Kuwahara et al., 1974 and Anguillicola novaezelandiae Moravec and Taraschewski, 1988, which were experimentally transferred to the two eel species Anguilla anguilla Linnaeus, 1758 and Anguilla japonica Temmink and Schlegel, 1846, respectively. The host-parasite groups were selected due to their different grades of mutual adaptation. The main aim of this study was to analyze the stress responses within the parasites, which were confronted with different hosts, i.e. with different stressors related to the respective host. For this purpose, mean intensities, recovery rates, larvae output, and levels of synthesized heat shock proteins (Hsp70) were determined in nematodes of each infection group. Increased stress responses were detected in the endemic system of A. crassus parasitizing A. japonica and A. crassus in its recently acquired host A. anguilla, which seems to be associated with the immune response of the particular host species and the expenditure of energy on producing larvae. A. novaezelandiae showed overall weak activities in its unknown host species A. japonica, with the lowest recovery rate of all examined groups neither featuring elevated Hsp responses, nor a high mean intensity, nor any reproductive output. On the contrary, in A. anguilla, the parasite reached higher recovery rates, mean intensities, and reproductive output, but no increased Hsp70 levels could be detected. The four considered factors proved partially interdependent, whereas few results did not follow a clear pattern.

Size does matter-a closer look on Anguillicola morphology.

The present study deals with morphological differences between two closely related parasitic nematode species (Anguillicola crassus Kuwahara et al., 1974 and Anguillicola novaezelandiae Moravec & Taraschewski, 1988) in two different experimentally infected eel species (Anguilla anguilla Linnaeus, 1758 and Anguilla japonica Temminck & Schlegel, 1847). Furthermore, it considers the question whether size differences between those two species are ontogenetically determined or host species-dependent. In order to analyse these questions, experimental infections with the four possible host-parasite systems have been performed, followed by precise morphometric measurements related to body size and head structures of all resulting nematodes 120 days post infection. Body size measurements (length and width) of A. crassus generally exceeded those of A. novaezelandiae, while both Anguillicola species turned out to be smaller in Japanese eels than in European eels. Comparative measurements of neck width, maximum oesophagus width, and posterior head end width were found to be highly significant with regard to the different host-parasite systems. Shape and width of neck have been identified as reliable discriminating factors for species distinction. Generally, the relation of anterior head end width and neck width proved to be distinctly species-specific and can thus serve as a decisive and easily measureable distinguishing feature.

Effects of Anguillicola novaezelandiae on the levels of cortisol and hsp70 in the European eel.

The nematodes Anguillicola novaezelandiae and Anguillicola crassus are both alien parasites of the European eel with severe adverse effects on their new host. Both species differ in terms of their invasiveness and their severity of harmful effects on the European eel. The purpose of this study was to determine under laboratory conditions whether stages of A. novaezelandiae induce stress in European eels (Anguilla anguilla) and if these levels differ from stress levels induced by A. crassus. We analysed levels of plasma cortisol and hepatic hsp70 of eels experimentally infected with A. novaezelandiae and compared them to uninfected eels as well as to eels experimentally infected with A. crassus. Larval stages of A. novaezelandiae induced higher levels of plasma cortisol compared to uninfected controls, while adult parasites increased the levels of hepatic hsp70 above those of uninfected controls. The eels' cortisol response is induced by larval stages of A. novaezelandiae, while adult stages elevate levels of hepatic hsp70. Levels of stress induced by A. novaezelandiae are comparable to those induced by A. crassus.

Comparison of infection success, development and swim bladder pathogenicity of two congeneric Anguillicola species in experimentally infected Anguilla anguilla and A. japonica.

Two closely related parasites, Anguillicola crassus and Anguillicola novaezelandiae, originally parasitizing swim bladders of the Japanese eel (Anguilla japonica and the Short-finned eel (Anguilla australis), respectively, were used for analyzing the infection success of each parasite species on either long-known, recently acquired or new definitive host species and the associated effects on the eels' swim bladders. On that account, European eels (Anguilla anguilla) and Japanese eels were experimentally infected with both Anguillicola species in the laboratory. Susceptibility of the two eel species to both parasite species was determined by analyses of infection data. Subsequently, histopathological effects of the nematodes on the hosts' swim bladders were characterized according to already established indices.The present study revealed significant differences between the four different host-parasite systems regarding recovery rates, infrapopulations, and damage levels. Both nematode species achieved significantly lower recovery rates in Japanese eels than in European eels, since the examined swim bladders of Japanese eels contained a high amount of dead encapsulated larvae, whereas those of European eels contained only living nematodes. Encapsulation of larvae in Japanese eels was associated with a distinct thickening of the swim bladder walls. The swim bladders of uninfected Japanese eels turned out to be generally thicker than those of European eels. Infection with both Anguillicola species resulted in a further thickening process of the swim bladder walls in Japanese eels, whereas those of European eels showed only minor changes. The two established classification systems turned out to be inapplicable, since the measurements and the macroscopic evaluations of the swim bladders of the two infected eel species did not entirely correspond to the underlying criteria.

Can differences in life cycle explain differences in invasiveness? - A study on Anguillicola novaezelandiae in the European eel.

Anguillicola crassus is the most invasive species of its genus and it is a successful colonizer of different eel species worldwide. It is so far the only species of the genus Anguillicola whose life cycle has been studied completely. To analyse whether differences in life cycle may explain differences in invasiveness, we infected European eels with Anguillicola novaezelandiae under laboratory conditions. Anguillicola novaezelandiae shows a synchronized development in the European eel. Eggs with second-stage larvae appeared 120 days after infection. No density-dependent effect in parasite development could be found for A. novaezelandiae. The present study shows that the life cycle of A. novaezelandiae differs on final host level compared with A. crassus in ways which result in a less successful invasion of new host species.

Natural Anguillicola novaezelandiae infection--is there seasonality in New Zealand?

Knowledge of natural Anguillicola infections of Short-finned eels (Anguilla australis) in New Zealand is very limited. So far, no study contains data on all life cycle stages of Anguillicola novaezelandiae in naturally infected eels. In order to study the frequency of A. novaezelandiae in New Zealand Short-finned eels, we examined eels of the North and the South Island for the presence of the swim bladder parasite. The results show that A. novaezelandiae is a common parasite of the Short-finned eel. The parasite was present in both regions. Eels from both localities show differences in their infection status with respect to prevalence, abundance and intensity. While eels of the South Island were only infected with larval stages, adult and preadult stages could be detected in eels of the North Island. Nevertheless, infrapopulations at both sites were dominated by larval parasite stages. This unique composition of infrapopulations has never been described for any Anguillicola species before and suggests a seasonal occurrence as a possible reason. Export of live eels should be handled cautiously to prevent the spread of A. novaezelandiae throughout other eel populations.

The use of fish parasitic isopods as element accumulation indicators in marine pollution monitoring.

Marine ecosystems are continuously under threat due to pollutants, which endanger marine biodiversity. The present study determines the potential use of the parasitic isopod, Cinusa tetrodontis Schjödte et Meinert, 1884, together with its fish host, Amblyrhynchotes honckenii (Bloch) for marine bioaccumulation monitoring. The concentrations of As, Cd, Cu, Mn, Ni, Pb, Se, and Zn were determined in muscle and liver tissues of infested and uninfested fish, and male and female parasites on the South African temperate south coast. The concentrations of Cu and Ni in C. tetrodontis differed significantly between two sampling sites, a near-pristine (Breede River Estuary, Witsand) and a more polluted site (harbour area in Mossel Bay). Mossel Bay isopods had higher concentrations of Ni, while Witsand isopods had higher concentrations of Cu. In contrast to fish hosts, parasitic isopods accumulated significantly higher levels of all elements except Cd. Most significant relationships between elements accumulated by C. tetrodontis and an increase of elements in fish tissues were seen in liver, rather than muscle tissue samples. Specimens of C. tetrodontis can be defined as good bioindicators for elements such as As, Cu, Mn, Ni, Pb, Se, and Zn, as they possess high bioaccumulation capabilities. This study addresses one of several future directions needed within environmental parasitology and highlights the importance of studying and utilising this host-ectoparasite model system.

Bioaccumulation and trophic transfer of total mercury through the aquatic food webs of an African sub-tropical wetland system.

Anthropogenic activities, including combustion of fossil fuels, coal, and gold mining, are significant sources of mercury (Hg) emissions into aquatic ecosystems. South Africa is a major contributor to global Hg emissions (46.4 tons Hg in 2018), with coal-fired power stations as the main source. Atmospheric transport of Hg emissions is the dominant cause of contamination, especially on the east coast of southern Africa where the Phongolo River Floodplain (PRF) is located. The PRF is the largest floodplain system in South Africa, with unique wetlands and high biodiversity, and provides essential ecosystem services to local communities who rely on fish as a protein source. We assessed the bioaccumulation of Hg in various biota, the trophic positions and food webs, as well as the biomagnification of Hg through the food webs in the PRF. Elevated Hg concentrations were found in sediments, macroinvertebrates and fish from the main rivers and associated floodplains in the PRF. Mercury biomagnification was observed through the food webs, with the apex predator tigerfish, Hydrocynus vittatus, having the highest Hg concentration. Our study shows that Hg in the PRF is bioavailable, accumulates in biota and biomagnifies in food webs.

Nutritional status and gene expression along the somatotropic axis in roach (Rutilus rutilus) infected with the tapeworm Ligula intestinalis.

The tapeworm Ligula intestinalis inhibits gametogenesis of its fish host, the roach (Rutilus rutilus). We investigated whether L. intestinalis infection makes significant demands on nutritional resources and consequently manipulates the endocrine somatotropic axis of roach. Two groups of naturally infected and uninfected roach were studied: a field group (natural feeding) and a laboratory group (ad libitum food supply). In females, no significant impact of parasitization on storage substrates (glycogen, lipids, and protein) was detected, whereas in males, either lipid content of the liver (field group) or lipid of the muscle and glycogen of the liver (laboratory group) were slightly decreased. Except for the females of the field group, higher mRNA expression of growth hormone (gh) in the pituitary of infected fish was observed. Furthermore, the expression of hypophyseal somatolactin α and ß (slα, slß) was up-regulated in infected females of the field and laboratory group, respectively. In liver and muscle, mRNA expression of insulin-like growth factors (igf1, igf2) and igf receptor (igfr) remained either unchanged or were up-regulated with infection. Parasitization showed inconsistent effects on gh receptor 1 (ghr1) expression in liver and muscle, whereas ghr2 mRNA was mostly not influenced by infection. In general, the expression profile of genes involved in the somatotropic axis as well as the content of storage substances in infected roach did not resemble that of food-deprived fish either under natural or ad libitum feeding. In conclusion, the present study does not indicate starvation of L. intestinalis infected roach, and it is suggested that the inhibition of reproduction attenuated the nutritional demand of parasitization.

Microbial community shifts induced by plastic and zinc as substitutes of tire abrasion.

Aquatic environments serve as a sink for anthropogenic discharges. A significant part of the discharge is tire wear, which is increasingly being released into the environment, causing environmental disasters due to their longevity and the large number of pollutants they contain. Main components of tires are plastic and zinc, which therefore can be used as substitutes for tire abrasion to study the effect on microbial life. We investigate environmentally realistic concentrations of plastic and zinc on a freshwater microeukaryotic community using high-throughput sequencing of the 18S V9 region over a 14-day exposure period. Apart from a generally unchanged diversity upon exposure to zinc and nanoplastics, a change in community structure due to zinc is evident, but not due to nanoplastics. Evidently, nanoplastic particles hardly affect the community, but zinc exposure results in drastic functional abundance shifts concerning the trophic mode. Phototrophic microorganisms were almost completely diminished initially, but photosynthesis recovered. However, the dominant taxa performing photosynthesis changed from bacillariophytes to chlorophytes. While phototrophic organisms are decreasing in the presence of zinc, the mixotrophic fraction initially benefitted and the heterotrophic fraction were benefitting throughout the exposure period. In contrast to lasting changes in taxon composition, the functional community composition is initially strongly imbalanced after application of zinc but returns to the original state.

Human health risks associated with consumption of fish contaminated with trace elements from intensive mining activities in a peri-urban region.

Worldwide, numerous rural communities and low-income groups depend on fish harvested by subsistence fishers from local rivers and its impoundments as a source of protein. The aim of the present study was to determine the trace element bioaccumulation (As, Cd, Cr, Cu, Ni, Pb, Pt, Zn) in three edible fish species (Cyprinus carpio, Clarias gariepinus, Oreochromis mossambicus) from two impoundments in the Hex River system, South Africa, as well as the chronic health risk these trace elements pose to regular fish consumers. Trace element concentrations in the Hex River are naturally high (geogenic source), however, increased anthropogenic activities, such as intensive platinum mining activities, elevate the already high background concentrations. Concentrations of As, Cr, and Pt in C. carpio and C. gariepinus, as well as Ni and Zn in O. mossambicus were significantly higher in the impacted impoundment as compared to the reference impoundment. Concentrations of Cr and Cu were at both sampling sites the highest in O. mossambicus. From the human health risk assessment, As poses non-carcinogenic (HQ = 2-7) and carcinogenic risks (33-93 out of 10,000 people), while Cr (3-10 out of 10,000 people) and Ni (2-6 out of 10,000 people) pose only carcinogenic risks for the regular consumption of all three fish species from both impoundments, indicating a high probability of adverse human health effects. For As, Cr and Ni, also the sediment concentrations exceeded the levels of concern within the consensus based sediment quality guideline (CBSQG), while Cd, Cu, Ni and Zn exceeded the water quality guideline values. Thus, the CBSQG approach could be a promising tool for predicting human health risk associated with fish consumption. Since the present study only focused on the individual trace element risks, mixed toxicity of these trace elements and possible other pollutants within these fish species may pose an even greater risk to people who consume these fish regularly.