Toxic pollution and parasitism in freshwater fish

Protozoan and helminths infestation of Nile tilapia Oreochromis niloticus and its correlation with certain water quality variables along river Nile in the area of Greater Cairo

Pollutants and parasites represent stressors for fish at the individual, population, or community levels. The current study outlines the seasonal infestation pattern of Oreochromis niloticus by protozoan and helminths parasites linked to some physicochemical parameters (pH, dissolved oxygen, total dissolved solids, and electrical conductivity), and metals (Cd, Pb, Fe, Zn, and Ca), at nine selected sites in River Nile (Greater Cairo area) from summer 2019 till spring 2020. Most of the studied criteria in Nile water samples showed normal levels during all seasons compared to the recommended limits of EPA. The parasitological examinations recorded three protozoan categories: Myxobolus (8 species), hemoflagellates (Trypanosoma mukasi) and Ciliates (Trichodina compacta), and three helminths; Clinostomum sp., Acanthocephala sp. and Euclinostomum ardeola. The highest incidence of infection was determined for Clinostomum sp., followed in descending order by Myxobolus sp., Acanthocephala sp., T. mukasi, E. ardeolathen, and T. compacta. Notably, this study introduces the novel identification of new species of Myxobolus in the blood of Oreochromis niloticus. The histopathological examination of gills, muscles, and kidneys reveals serious changes and the presence of encysted trematodes, metacercariae, and cysts of protozoan parasites. Additionally, the study employs cluster analysis based on site similarity in water variables and canonical correspondence analysis, explaining 98.7 % of the variables and indicating correlations between parasite infestation and environmental factors. These analytical approaches reveal the impact of land use activities on water variables and the influence of adjacent activities on fish parasite infestation patterns. In conclusion, this study provides a comprehensive perspective by considering various factors to enhance our understanding of pollutants and parasites affecting fish in the River Nile.

Parasites and Pollutants: Effects of Multiple Stressors on Aquatic Organisms

Parasites can affect their hosts in various ways, and this implies that parasites may act as additional biotic stressors in a multiple-stressor scenario, resembling conditions often found in the field if, for example, pollutants and parasites occur simultaneously. Therefore, parasites represent important modulators of host reactions in ecotoxicological studies when measuring the response of organisms to stressors such as pollutants. In the present study, we introduce the most important groups of parasites occurring in organisms commonly used in ecotoxicological studies ranging from laboratory to field investigations. After briefly explaining their life cycles, we focus on parasite stages affecting selected ecotoxicologically relevant target species belonging to crustaceans, molluscs, and fish. We included ecotoxicological studies that consider the combination of effects of parasites and pollutants on the respective model organism with respect to aquatic host-parasite systems. We show that parasites from different taxonomic groups (e.g., Microsporidia, Monogenea, Trematoda, Cestoda, Acanthocephala, and Nematoda) clearly modulate the response to stressors in their hosts. The combined effects of environmental stressors and parasites can range from additive, antagonistic to synergistic. Our study points to potential drawbacks of ecotoxicological tests if parasite infections of test organisms, especially from the field, remain undetected and unaddressed. If these parasites are not detected and quantified, their physiological effects on the host cannot be separated from the ecotoxicological effects. This may render this type of ecotoxicological test erroneous. In laboratory tests, for example to determine effect or lethal concentrations, the presence of a parasite can also have a direct effect on the concentrations to be determined and thus on the subsequently determined security levels, such as predicted no-effect concentrations. Environ Toxicol Chem 2023;42:1946-1959. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Preliminary data on the occurrence of PAH and Anisakis spp. in Moroccan anchovies: Environmental parasitology and human health risk

This survey focuses on an environmental parasitology study by investigating Polycyclic Aromatic Hydrocarbons (PAH) bioaccumulation and the occurrence of Anisakis spp. on common anchovies collected from Moroccan coasts over 9 months through chemical (PAH) and Biological (Biometrics and parasitic) analysis. Obtained results were statistically analyzed and human health risks from anchovies consumption were assessed. The results obtained highlighted the good biological and chemical status of this fish in all stations of Morocco's coasts. Anisakis spp. was present in only four stations in the Atlantic fringe (maximum prevalence 22.22 %). Results have shown non-significant differences for tissue nature (Muscle, viscera) or spatial variation and were within a low range of concentrations well below the European Commission standards. Results have shown no serious harmful risk for humans from this fish consumption (ILCR and HI), and statistical analysis had shown positive correlations between prevalence and Chr, prevalence and sex-ratio, and prevalence and weight.

Land use, season, and parasitism predict metal concentrations in Australian flying fox fur

Urban-living wildlife can be exposed to metal contaminants dispersed into the environment through industrial, residential, and agricultural applications. Metal exposure carries lethal and sublethal consequences for animals; in particular, heavy metals (e.g. arsenic, lead, mercury) can damage organs and act as carcinogens. Many bat species reside and forage in human-modified habitats and could be exposed to contaminants in air, water, and food. We quantified metal concentrations in fur samples from three flying fox species (Pteropus fruit bats) captured at eight sites in eastern Australia. For subsets of bats, we assessed ectoparasite burden, haemoparasite infection, and viral infection, and performed white blood cell differential counts. We examined relationships among metal concentrations, environmental predictors (season, land use surrounding capture site), and individual predictors (species, sex, age, body condition, parasitism, neutrophil:lymphocyte ratio). As expected, bats captured at sites with greater human impact had higher metal loads. At one site with seasonal sampling, bats had higher metal concentrations in winter than in summer, possibly owing to changes in food availability and foraging. Relationships between ectoparasites and metal concentrations were mixed, suggesting multiple causal mechanisms. There was no association between overall metal load and neutrophil:lymphocyte ratio, but mercury concentrations were positively correlated with this ratio, which is associated with stress in other vertebrate taxa. Comparison of our findings to those of previous flying fox studies revealed potentially harmful levels of several metals; in particular, endangered spectacled flying foxes (P. conspicillatus) exhibited high concentrations of cadmium and lead. Because some bats harbor pathogens transmissible to humans and animals, future research should explore interactions between metal exposure, immunity, and infection to assess consequences for bat and human health.

Streptococcus, Centrocestus formosanus and Myxobolus tilapiae concurrent infections in farmed Nile tilapia (Oreochromis niloticus)

Stress triggered concurrent microbial/parasitic infections are prevalent in earthen pond based farmed Nile tilapia Oreochromis niloticus. In the current study, a total of thirty five O. niloticus were collected from a commercial fish farm with a history of severe mortalities at Port Said, Egypt. Nile tilapia samples were subjected to bacteriological, parasitological and pathological examinations. Twenty one Enterococcus fecalis and 15 Streptococcus agalactiae isolates were presumptively identified utilizing the semi-automated API 20 Strept test kit. The identities of the retrieved bacteria were confirmed by the sequencing of 16 S rRNA gene. Moribund O. niloticus were found to be heavily infected by one or both of Centrocestus formosanus encysted metacercariae (EMC) and/or Myxobolus tilapiae spores presenting a unique form of synergistic and/or symbiotic relationship. The identities of both parasites were confirmed through morphological and molecular characterization. Variable circulatory, degenerative, necrotic and proliferative changes were also noticed in hematopoietic organs. Interestingly, multiple myxobolus spores and EMC were noticed in some histological sections. It was obvious that the current concurrent bacterial and parasitic infections are triggered by the deleterious effects of some stressing environmental conditions. The unfavorable climatic conditions (high temperature and high relative humidity) recorded at the surge of mortalities are probable predisposing stress factors.

Parasitic monogenoideans of Sciades herzbergii as bioindicators of environmental quality in amazonian estuarines ecosystems

This study evaluated the use of gill parasitic monogenoideans from Sciades herzbergii (Siluriformes: Ariidae) as bioindicators of environmental quality in Amazonian estuarine ecosystems. Fish were caught in the tidal channels in an impacted area - IA, near the port of São Luís and a reference area - RA, in the Caeté estuary, Bragança. The influence of the capture site and seasonality on parasite abundance, environmental variables and biometric data of hosts were verified. A total of 416 S. herzbergii specimens were analyzed. The weight and total length of fish from the RA were greater than those of the IA. The relative condition factor was influenced by seasonality. A total of 4,265 monogenoidean specimens from the following species were identified: Chauhanellus boegeri, C. susamlimae, C. velum, Calceostomella herzbergii and Dactylogyridae gen. sp. The seasonal mean parasitic abundance of C. susamlimae was significantly different, with the highest values recorded during the dry season. The mean abundance of C. herzbergii was influenced by seasonality and by the capture site. During the rainy period, the parasite indices in the RA were higher than those of IA. C. herzbergii is a bioindicator sensitive to low water quality, especially in relation to water turbidity in Amazon estuaries.

Evaluation of an in vitro assay to screen for the immunotoxic potential of chemicals to fish

A wide variety of environmental contaminants has been shown to disrupt immune functions of fish and may compromise their defense capability against pathogens. Immunotoxic effects, however, are rarely considered in ecotoxicological testing strategies. The aim of this study was to systematically evaluate the suitability of an in vitro immuno-assay using selected fish immune parameters to screen for chemicals with known immunotoxic potential and to differentiate them from non-immunotoxicants. Non-stimulated and lipopolysaccharide-stimulated head kidney leukocytes of rainbow trout (Oncorhynchus mykiss) were exposed for 3 h or 19 h to chemicals with different modes of action. As immune parameters, phagocytosis activity, oxidative burst activity and cytokine transcription (IL-1β, TNFα, IL-10) were examined, accompanied by in silico modelling. The immunotoxicants dexamethasone, benzo(a)pyrene, ethinylestradiol and bisphenol A significantly altered the immune parameters at non-cytotoxic concentrations whereas diclofenac had only weak effects. However, the two baseline chemicals with no known immunotoxic potential, butanol and ethylene glycol, caused significant effects, too. From our results it appears that the in vitro fish leukocyte assay as performed in the present study has only a limited capacity for discriminating between immunotoxicants and non-immunotoxicants.

Metabarcoding profiling of microbial diversity associated with trout fish farming

Earthy and musty off-flavors are routinely observed in farmed trout worldwide. The microbial association to the production of those off-flavors was previously reported. The current manuscript aimed to catalog the microbial enrichment (eukaryotes and prokaryotes) in semi-intensive aquaculture freshwater sources that might influence the trout aquaculture quality production. The 16S rRNA and ITS metabarcoding analyses were applied on the inflow- and pond-water samples from trout farms previously recorded a malodor fish products and located alongside Moosach and Sempt Rivers in Bavaria province, Germany. The results showed that more than 99% of the detected prokaryotic OTUs (Operational Taxonomic Unit identification) were bacteria as of ~ 75.57% were Proteobacteria, and ~ 14.4% were Bacteroidetes. Meanwhile, 118 out of 233 of the eukaryotic OTUs were known species. Of these, ~ 45% were plant pathogens, and ~ 28% were mushroom/yeasts. Based on the comparative analysis between inflow- and pond-water samples, several pro- and eukaryotic microorganisms that affect the trout aquaculture water quality and industry have been detected, including the malodor-producing microorganisms, e.g., Cyanobacteria and Actinobacteria, along with fish infectious microorganisms, e.g., Chilodonella cyprinid, Metschnikowia bicuspidate. Additionally, the effect of the human- and industrial-related activities around the sampling area on the microbiota of the investigated farms were highlighted.

Direct and indirect effects of multiple environmental stressors on fish health in human-altered rivers

Freshwater fish face multiple challenges in human-altered rivers such as trace metal contamination, temperature increase and parasitism. These multiple stressors could have unexpected interactive effects on fish health due to shared physiological pathways, but few studies investigated this question in wild fish populations. In this study, we compared 16 populations of gudgeon (Gobio occitaniae) distributed along perturbation gradients in human-altered rivers in the South of France. We tested the effects of single and combined stressors (i.e., metal contamination, temperature, parasitism) on key traits linked to fish health across different biological levels using a Structural Equation Modelling approach. Parasitism and temperature alone had limited deleterious effects on fish health. In contrast, fish living in metal-contaminated sites had higher metal bioaccumulation and higher levels of cellular damage in the liver through the induction of an inflammatory response. In addition, temperature and contamination had interactive negative effects on growth. These results suggest that trace metal contamination has deleterious effects on fish health at environmentally realistic concentrations and that temperature can modulate the effects of trace metals on fish growth. With this study, we hope to encourage integrative approaches in realistic field conditions to better predict the effects of natural and anthropogenic stressors on aquatic organisms.

The Ecological Importance of Amphipod–Parasite Associations for Aquatic Ecosystems

Amphipods are a key component of aquatic ecosystems due to their distribution, abundance and ecological role. They also serve as hosts for many micro- and macro-parasites. The importance of parasites and the necessity to include them in ecological studies has been increasingly recognized in the last two decades by ecologists and conservation biologists. Parasites are able to alter survival, growth, feeding, mobility, mating, fecundity and stressors’ response of their amphipod hosts. In addition to their modulating effects on host population size and dynamics, parasites affect community structure and food webs in different ways: by increasing the susceptibility of amphipods to predation, by quantitatively and qualitatively changing the host diet, and by modifying competitive interactions. Human-induced stressors such as climate change, pollution and species introduction that affect host–parasite equilibrium, may enhance or reduce the infection effects on hosts and ecosystems. The present review illustrates the importance of parasites for ecosystem processes using examples from aquatic environments and amphipods as a host group. As seen from the literature, amphipod–parasite systems are likely a key component of ecological processes, but more quantitative data from natural populations and field evidence are necessary to support the results obtained by experimental research.

Distribution of parasites of slimy sculpin Cottus cognatus Richardson, 1836 (Scorpaeniformes: Cottidae) in the Athabasca drainage, Alberta, Canada, and their relation to water quality

The composition and diversity of parasite communities are useful tools to characterise ecosystem health and integrity. Environmental disturbances may affect parasite infection in fish directly, by their effects on the free-living stages, or indirectly, on the intermediate hosts. Slimy sculpins, Cottus cognatus, a small fish inhabiting cold waters of North America, have been considered as sentinels due to their limited mobility, often occupying relatively small areas throughout their lives and thus reflecting the local environment. Ninety-six specimens of C. cognatus were sampled from four tributaries of the Athabasca River to assess patterns of helminth parasite community structure in this fish and to study the composition and diversity of its parasite communities in relation to water quality. The localities included single samples from High Hills, Horse and Dunkirk rivers, and two from the Steepbank River. Twelve metazoan parasite species were found, most of them being larval forms. Significant differences occurred in the structure and composition of parasite assemblages of sculpins from the tributaries, although similarities were observed in connected and nearby sites. Parasite communities were influenced mainly by a combination of local environmental conditions, distance and connectivity, and were separated based on the distribution and abundance of autogenic and allogenic parasites. Water quality appeared to influence the distribution of trematode species that use gastropods as intermediate hosts, while proximity and connectivity of sites led to sharing allogenic parasite species in slimy sculpin.

Anisakid nematode larvae in the liver of Atlantic cod Gadus morhua L. from West Greenland

Anisakid nematode larvae occur frequently in the liver of Atlantic cod, but merely few infection data from cod in waters around Greenland exist. The present study reports the occurrence of third-stage anisakid larvae in the livers of 200 Atlantic cod caught on fishing grounds along the West coast of Greenland (fjord systems of Maniitsoq) in May, June, August and September 2017. Classical and molecular helminthological techniques were used to identify the nematodes. A total of 200 cod livers were examined, and 194 were infected with third-stage nematode larvae (overall prevalence of infection 97%) with a mean intensity of 10.3 (range between 1 and 44 parasites per fish). Prevalences recorded were 96% for Anisakis simplex (s.l.), 55% for Pseudoterranova decipiens (s.l.) and 8% for Contracaecum osculatum (s.l.). Sequencing the mtDNA cox2 from 8 out of 23 these latter larvae conferred these to C. osculatum sp. B. A clear seasonal variation was observed, with a rise in A. simplex (s.l.) and P. decipiens (s.l.) occurrence in June and August and a decline in September. The study may serve as a baseline for future investigations using the three anisakids as biological indicators in Greenland waters.

Potential Benefits of Acanthocephalan Parasites for Chub Hosts in Polluted Environments

Some parasites are expected to have beneficial impacts on wild populations in polluted environments because of their bioaccumulation potential of pollutants from their hosts. The fate of organic micropollutants in host-parasite systems and the combined effect of parasitism and pollution were investigated in chub Squalius cephalus, a freshwater fish, infected (n = 73) or uninfected (n = 45) by acanthocephalan parasites Pomphorhynchus sp. from differently contaminated riverine sites. Several ubiquitous pollutants (polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl-ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), phthalates, insecticides, pyrethroids, and N,N-diethyl-meta-toluamide (DEET)) and some of their metabolites were characterized for the first time in parasites and various fish matrices (muscle, liver, and stomach content). Most organic pollutants reached higher levels in parasites than in chub matrices. In contrast, metabolite levels were lower in parasite tissues compared to fish matrices. Infected and uninfected chub exhibited no significant differences in their pollutant load. Body condition, organo-somatic indices, and immunity were not affected by parasitism, and few correlations were found with chemical pollution. Interestingly, infected chub exhibited lower oxidative damage compared to uninfected fish, irrespective of their pollutant load. In light of these results, this correlative study supports the hypothesis that acanthocephalan parasites could bring benefits to their hosts to cope with organic pollution.

Effects of River Hydrology and Physicochemistry on Anchovy Abundance and Cymothoid Isopod Parasitism

The flow regime of a river is an important driver of many ecosystem components. However, few studies explore how differences in flow rates and water chemistry can influence communities of parasites and their hosts. Here, we investigate the impact of dissolved oxygen, pH, salinity, water temperature, and river flow on the abundance and prevalence of cymothoid isopod parasitism (Lironeca ovalis) of the Bay Anchovy (Anchoa mitchilli) in the Alafia and Hillsborough rivers of Tampa Bay (Florida). We also explore seasonality by comparing monthly samples preserved throughout 2005-2007. Although both the Alafia and Hillsborough rivers had similar average water temperatures and salinity, and similar wet and dry season cycles, the upstream damming of the Hillsborough River had numerous negative effects on water flow rate, dissolved oxygen content, and acidity. This disruption in water quality corresponded with a lower abundance of anchovy hosts, fewer free-swimming cymothoids, and low prevalence of anchovy parasitism. Anchovies were much more abundant in the Alafia River, but flow negatively affected abundance-a negative effect that could be mitigated by positive changes in water temperature, salinity, and pH. Flow rates also negatively affected free-swimming cymothoid abundance; however, water flow was less important in predicting their parasitism of anchovies. In Alafia, fewer anchovies were parasitized when dissolved oxygen was high and water acidity was low, but more were parasitized during the wet season. These findings corroborate predictions that flow can moderate habitat stability and complexity which, in turn, can impact opportunities for parasitism of host communities.

Ecotoxicoparasitology of mercury and trace elements in semi-aquatic mammals and their endoparasite communities

Many contaminants persist in the environment for decades or more, influencing ecosystem health. Environmental contamination with mercury (Hg) is a particular concern due to its ability to biomagnify in food webs and its lethal and sub-lethal effects in exposed organisms. Despite the known impacts of anthropogenic contamination, there remains a need for data on wildlife exposure to Hg and other contaminants, and the effects of exposure on wildlife health. The objectives of this study were to: 1) quantify differences in concentrations of mercury and other trace elements among three sympatric semiaquatic mammals of different assumed trophic position: North American river otter (Lontra canadensis), raccoon (Procyon lotor), and North American beaver (Castor canadensis), 2) compare trace element concentrations between animals captured on the Savannah River Site (SRS) in South Carolina, USA, where known inputs of Hg and other trace elements have occurred, and reference sites in South Carolina (SC) and Georgia (GA), USA, and 3) investigate the relationship between host trace element concentrations and endoparasite communities. River otters, beavers, and raccoons were sampled from the SRS, SC, and GA to quantify trace element concentrations in liver tissue and quantify endoparasite communities. Both species and sampling location were important factors determining hepatic trace element concentration, however, there was no consistent trend of elevated trace element concentrations among animals sampled on the SRS. Only Hg demonstrated biomagnification based on assumed trophic position, with river otters having the highest Hg concentrations among the sampled species. Additionally, the results suggest a possible relationship between host hepatic mercury concentration and endoparasite abundance, while hepatic selenium concentration may be related to endoparasite diversity. These findings further demonstrate how wildlife can accumulate anthropogenic contamination, although future research is needed to determine the mechanisms contributing to patterns observed between endoparasite communities and the contaminant concentrations of their mammalian hosts.

Water boatman survival and fecundity are related to ectoparasitism and salinity stress

Salinity is increasing in aquatic ecosystems in the Mediterranean region due to global change, and this is likely to have an important impact on host-parasite interactions. Here we studied the relationships between infection by ectoparasitic water mites and salinity variation, on survival and fecundity of water boatmen Corixidae in the laboratory. Larvae of Sigara lateralis parasitised by larval mites (Hydrachna skorikowi) had lower survivorship, and failed to moult to the adult stage. In adult corixids (S. lateralis and Corixa affinis) fitness was reduced at high salinities and in individuals infected by H. skorikowi, both in terms of survival and fecundity. We also found evidence for parasitism-salinity interactions. Our results suggest that ongoing increases in salinity in Mediterranean ponds due to climate change and water abstraction for agriculture or urban use have a strong impact on water bugs, and that their interactions with ectoparasites may modify salinity effects.

Occurrence of Clinostomum Metacercariae in Oreochromis mossambicus from Mashoko Dam, Masvingo Province, Zimbabwe

Mashoko Dam is in Ago-ecological Region 4 in Zimbabwe. Five sampling sites were randomly selected and each site was sampled twice per month, for six months. A total of 180 Oreochromis mossambicus fish (101 females and 79 males) were caught. The fish were examined for Clinostomum metacercariae by cutting the ventral side from the anal opening to the lower jaw. The gill chambers were examined and inspected visually to detect macroscopic parasites. Of the 180 fish collected during the study, 113 (62.8%) were infected by 284 Clinostomum larvae in the cranial cavity while 67 fish were not infected. Among the infected fish, 46 were males and 67 were females. Greater parasite burden and mean intensity were observed in female fish (2.7 MI) than males (2.2 MI). There was no statistically significant difference in mean intensity of infection between male and female fish (n=180; t=0.521; p < 0.05). Uninfected fish were in a poorer condition than infected fish in July and October only. The lowest monthly condition factor for both infected (1.8) and uninfected (1.7) fish occurred in October. The monthly condition factors for both infected (1.94-3.51) and noninfected fish (1.81-5.28) were greater than 1. For prevalence by total length groups, highest prevalence (66.3%) was recorded in the medium length group (10-12 cm) and lowest (25.0%) in the (16-18 cm) length group. Highest mean intensity (2.8) and parasite density (146 parasites) was observed in the length group (13-15 cm) and lowest mean intensity (1.0) in larger length groups (16-18 cm and above 19 cm). Highest abundance (1.74) was recorded in the length group 13-15 cm and lowest abundance (0.25) in the length group 16-18 cm. Parasite burden was positively correlated to fish size (total length). It was concluded that Clinostomum metacercariae are a common parasite in Oreochromis mossambicus in Mashoko dam.

Do fish get wasted? Assessing the influence of effluents on parasitic infection of wild fish

Many ecosystems are influenced simultaneously by multiple stressors. One important environmental stressor is aquatic pollution via wastewater treatment plant (WWTP) effluents. WWTP effluents may contribute to eutrophication or contain anthropogenic contaminants that directly and/or indirectly influence aquatic wildlife. Both eutrophication and exposure to anthropogenic contaminants may affect the dynamics of fish-parasite systems. With this in mind, we studied the impact of WWTP effluents on infection of brown trout by the parasite Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD). PKD is associated with the long-term decline of wild brown trout (Salmo trutta) populations in Switzerland. We investigated PKD infection of brown trout at two adjacent sites (≈400 m apart) of a Swiss river. The sites are similar in terms of ecology except that one site receives WWTP effluents. We evaluated the hypothesis that fish inhabiting the effluent site will show greater susceptibility to PKD in terms of prevalence and disease outcome. We assessed susceptibility by (i) infection prevalence, (ii) parasite intensity, (iii) host health in terms of pathology, and (iv) estimated apparent survival rate. At different time points during the study, significant differences between sites concerning all measured parameters were found, thus providing evidence of the influence of effluents on parasitic infection of fish in our study system. However, from these findings we cannot determine if the effluent has a direct influence on the fish host via altering its ability to manage the parasite, or indirectly on the parasite or the invertebrate host via increasing bryozoa (the invertebrate host) reproduction. On a final note, the WWTP adhered to all national guidelines and the effluent only resulted in a minor water quality reduction assessed via standardized methods in this study. Thus, we provide evidence that even a subtle decrease in water quality, resulting in small-scale pollution can have consequences for wildlife.

The Diversity of Teleost Fish Trematodes in the Bay of Bizerte, Tunisia (Western Mediterranean)

A total of 39 digeneans species allocated to 28 genera in 12 families were recovered from 534 fishes belonging to 14 species in three families (Carangidae, Mullidae and Sparidae) collected in the Bay of Bizerte off the coast of Tunisia. We provide a host-parasite list of records from this locality, including 63 host-parasite combinations. The Opecoelidae Ozaki, 1925 is the most diverse group with 12 species. The species richness of individual digenean genera in the Bay of Bizerte ranges from 1 - 6 species. The mean number of 2.58 species per host indicates a relatively high digenean diversity in the Bay of Bizerte, which is related to its geographical location, its connection with the neighbouring Bizerte Lagoon and the nature of the bottoms of the littoral marine areas off the northern Tunisian coasts. This diversity is significantly higher than that reported off the southern coast of Tunisia and distinctly lower than that observed for teleost hosts in the Scandola Nature Reserve off Corsica. Generally, the levels of infection in teleosts fishes from the Bay of Bizerte are lower than those from the other two localities.

Fish parasites as indicators of organic pollution in southern Brazil

Increasing urbanization along riverbanks is a constant source of stressors to the aquatic community, and the use of bioindicators is suitable to detect and monitor the effect of each stressor. We investigated the parasites of the 'cará' fish (Geophagus brasiliensis) as potential bioindicators in a river whose banks are subject to increasing anthropogenic pressure. Samples were taken at four points of the Sangradouro River, in Florianópolis, southern Brazil, bimonthly for 12 months. Water temperature, pH, dissolved oxygen, conductivity and salinity were measured at each point and water samples were taken for nutrient analysis (total nitrogen, nitrite, total ammonia nitrogen, total phosphorus, phosphate), and total and faecal coliforms. A generalized linear model (GLM) was constructed using the abundance of each parasite species as the response variable and biometric characteristic of the fish and water variables as possible predictors. Among the 137 fish examined, 114 (83.2%) were parasitized by at least one parasite species. Two species of ectoparasites (Sciadicleithrum guanduensis and Neascus-type metacercariae) and two species of endoparasites (Pandosentis aff. iracundus and Homalometron pseudopallidum) were observed. This is the first record of the genus Pandosentis in Brazilian waters and the first record of the species G. brasiliensis as a host for this parasite. Among the analysed groups of parasites, monogeneans and acanthocephalans proved to be the most sensitive to the concentrations of dissolved oxygen, faecal coliforms and total ammonia nitrogen in the water. Our study suggests that the abundance of both monoxenic and heteroxenous parasites can be negatively affected by organic pollution in the aquatic environment, reinforcing the potential of fish parasites as indicators of water quality.

Experimental and modelling investigations of Opisthorchis viverrini miracidia transmission over time and across temperatures: implications for control

Transmissibility is a significant factor in parasite fitness. The rate and magnitude of parasite transmission affect prevalence and infection intensity in individual hosts and are influenced by environmental factors. In this context, the objectives of this study were: (i) to experimentally assess Opisthorchis viverrini miracidia survival and infectivity over time and across temperatures; and (ii) to combine these experimental results with environmental data to build a key component of a transmission model, identifying seasonal windows of transmission risk in hyper-endemic northeastern Thailand. Five replicates of 50 O. viverrini eggs were randomly distributed and maintained under four temperature conditions (25°C, 30°C, 35°C, 40°C). Microscopic observations were performed on all experimental units over a period of 3months to record miracidia motility and mortality trends. Six infection trials were also conducted to assess infectivity of miracidia over time and across temperatures, using observations of egg hatching success and infection rates. Upon completion of experiments, data were integrated into a transmission model to create a transmission risk index and to simulate seasonal transmission risk. Miracidia survival rate and motility decreased steadily with 50% mortality observed after 2weeks. Hatching and infection success also decreased significantly after 3weeks. Temperatures over 30°C were associated with increased mortality and decreased infectivity. When incorporating local environmental parameters into our model, we observed low transmission risk during the dry season and increasing transmission risk at the onset of the rainy season, culminating with the highest risk in September. We believe that our results provide the first estimates of O. viverrini miracidia survival and transmission potential under variable temperature conditions and suggest that high temperature treatment (>40°C) of fecal waste could be an efficient control strategy.

Parasite responses to pollution: what we know and where we go in 'Environmental Parasitology'

Environmental parasitology deals with the interactions between parasites and pollutants in the environment. Their sensitivity to pollutants and environmental disturbances makes many parasite taxa useful indicators of environmental health and anthropogenic impact. Over the last 20 years, three main research directions have been shown to be highly promising and relevant, namely parasites as accumulation indicators for selected pollutants, parasites as effect indicators, and the role of parasites interacting with established bioindicators. The current paper focuses on the potential use of parasites as indicators of environmental pollution and the interactions with their hosts. By reviewing some of the most recent findings in the field of environmental parasitology, we summarize the current state of the art and try to identify promising ideas for future research directions. In detail, we address the suitability of parasites as accumulation indicators and their possible application to demonstrate biological availability of pollutants; the role of parasites as pollutant sinks; the interaction between parasites and biomarkers focusing on combined effects of parasitism and pollution on the health of their hosts; and the use of parasites as indicators of contaminants and ecosystem health. Therefore, this review highlights the application of parasites as indicators at different biological scales, from the organismal to the ecosystem.

Raccoons (Procyon lotor) as Sentinels of Trace Element Contamination and Physiological Effects of Exposure to Coal Fly Ash

Anthropogenic pollutants disrupt global biodiversity, and terrestrial sentinels of pollution can provide a warning system for ecosystem-wide contamination. This study sought to assess whether raccoons (Procyon lotor) are sentinels of local exposure to trace element contaminants at a coal fly ash site and whether exposure resulted in health impairment or changes in the intestinal helminth communities. We compared trace element accumulation and the impact on health responses and intestinal helminth communities of raccoons inhabiting contaminated and reference sites of the U.S. Department of Energy's Savannah River Site (South Carolina, USA). Data on morphometry, hematology, histopathology, helminth community and abundance, and liver trace element burdens were collected from 15 raccoons captured adjacent to a coal fly ash basin and 11 raccoons from a comparable uncontaminated site nearby. Of eight trace elements analyzed, Cu, As, Se, and Pb were elevated in raccoons from the contaminated site. Raccoons from the contaminated site harbored higher helminth abundance than animals from the reference site and that abundance was positively associated with increased Cu concentrations. While we found changes in hematology associated with increased Se exposure, we did not find physiological or histological changes associated with higher levels of contaminants. Our results suggest that raccoons and their intestinal helminths act as sentinels of trace elements in the environment associated with coal fly ash contamination.

Larval digenean preferences in two sympatric snail species at differing tidal levels off the Atlantic coast of Patagonia

Larval stages of the trematodesMaritrema madrynenseand Hemiuroidea fam. gen. et sp. differentially parasitizedSiphonaria lessoniiandS. lateralis, two sympatric pulmonate snail species on the rocky intertidal shore at Puerto Deseado, south-western Atlantic coast of Patagonia, Argentina. Snail specimens were collected at two sampling sites with contrasting physical–chemical characteristics. One site, in the upper intertidal, was exposed to sewage from fish-processing plants, greater hydrodynamic forcing and desiccation, a wider temperature range, longer exposure to ultraviolet radiation and higher abundance of birds. The second site, in the lower intertidal, was generally characterized by less stressful environmental conditions. At both sites,S. lateralisshowed a markedly higher density thanS. lessonii(55.13 vs. 5.87 snails/m2, respectively). Despite this, the prevalence of both digeneans was higher inS. lessonii(17.37% and 3.52% forM. madrynenseand Hemiuroidea, respectively) than inS. lateralis(0.09% and 0% forM. madrynenseand Hemiuroidea, respectively). This study demonstrates high parasite specificity for the host. Low densities ofS. lessoniiare attributed to castration of parasitized hosts and reduction of their physiological condition. The prevalence and intensity of infection of both digenean parasites were higher at the more stressful, upper intertidal site, thus suggesting that a higher abundance of birds and exposure to sewage pollution may promote the transmission of trematodes.

Distribution of Helminth Parasites in Intestines and Their Seasonal Rate of Infestation in Three Freshwater Fishes of Kashmir

The present study was undertaken to determine the incidence of helminth parasites in fishes with special reference to water quality parameters in Dal Lake and River Jhelum and correlate the observations. Water, fish, and parasite samples were collected during different seasons from various sites and processed. Three fish species, namely, Schizothorax niger Heckel 1838, Schizothorax esocinus Heckel 1838, and Schizothorax curvifrons Heckel 1838, were recovered from these water bodies. The physicochemical parameters temperature, dissolved oxygen, pH, and free carbon dioxide showed variation vis-à-vis the season and location of the stations in water bodies. Acanthocephalan parasite Pomphorhynchus kashmirensis Kaw 1941 (27.47%) and two intestinal cestodes Bothriocephalus acheilognathi Yamaguti 1934 (30.63%) and Adenoscolex oreini Fotedar 1958 (32.43%) were recovered from all the three species of Schizothorax. All the three parasites showed higher prevalence during summer and the least prevalence during winter. Parasitic infections were prevalent more in male fishes compared to females. The presence of the parasites had reduced the condition coefficient of the infected fishes in both water bodies. The study also showed that some of the physicochemical features showed a significant positive correlation with the prevalence.

Endoparasites of some economically important food fishes of River Jhelum, Kashmir (India)

During the present study endo-parasitic fauna of fish at different sites of River Jhelum were analysed. Four different species of endoparasites were recovered from Schizothorax species which include Adenoscolex kashmirensis Mehra, 1930, Bothriocephalus acheilognathi Yamaguti, 1934, Echinorhynchus sp., Pomphorhynchus kashmirensis Kaw, 1941, belong to Phylum Platyhelminths and Phylum Acanthocephala. Prevalence and generation time were inversely proportional to each other. Prevalence and mean abundance were highest at Qamarwari. Diversity was more at Tengpora. Cestodes including Adenoscolex kashmirensis and Bothriocephalus acheilognathi were more dominant than Pomphorhynchus kashmirensis and Echinorhynchus sp.

Parasite community similarity in Athabasca River trout-perch (Percopsis omiscomaycus) varies with local-scale land use and sediment hydrocarbons, but not distance or linear gradients

Parasite communities have been shown to be structured by processes at scales ranging from continental to microhabitat, but few studies have simultaneously considered spatial and environmental variables, measured at different scales, to assess their relative influences on parasite abundance, species richness, and community similarity. Parasite abundance, diversity, and community similarity in Athabasca River trout-perch (Percopsis omiscomaycus) were examined in relation to water quality, substrate profile, metal and organic compound levels in water and sediment, and landscape use patterns at different scales, as well as distance among sites and upstream-downstream position along the river. Although species richness did not differ among sites, there were significant differences in abundance of individual taxa and community structure. We observed a shift from communities dominated by larval trematodes Diplostomum spp. to domination by gill monogeneans Urocleidus baldwini, followed by a reversion further downstream. Variations in the abundance of these taxa and of overall community similarity were strongly correlated with sediment hydrocarbons (alkanes and polycyclic aromatic hydrocarbons (PAHs)) as well as landscape use within 5 km of study sites. No correlations were noted with any other predictors, indicating that parasite populations and communities in this system were likely primarily influenced by habitat level and landscape-scale filters, rather than larger-scale processes such as distance decay or river continuum effects.

Oestrogenic pollutants promote the growth of a parasite in male sticklebacks

Aquatic environments are especially susceptible to anthropogenic chemical pollution. Yet although knowledge on the biological effects of pollutants on aquatic organisms is increasing, far less is known about how ecologically-important interspecific interactions are affected by chemicals. In particular, the consequences of anthropogenic pollution for the interaction of hosts and parasites are poorly understood. Here, we examine how exposure to 17β-oestradiol (E2)-a natural oestrogen and a model endocrine disrupting chemical (EDC) -affects infection susceptibility and emergent infection phenotypes in an experimental host-parasite system; three spined sticklebacks (Gasterosteus aculeatus) infected with the common, debilitating cestode Schistocephalus solidus. We exposed individual sticklebacks to a 0ngl(-1) (control), 10ngl(-1) or 100ngl(-1) E2 treatment before feeding them infective stages of S. solidus. E2 exposure significantly elevated vitellogenin (VTG) levels-a biomarker of exposure to xenoestrogens-in both female and male fish, and reduced their body condition. Susceptibility to parasite infection was unaffected by EDC exposure; however, E2 treatment and fish sex interacted significantly to determine the growth rate of parasites, which grew quickest in male hosts held under the higher (100ngl(-1)) E2 treatment. Tissue VTG levels and parasite mass correlated positively across the whole sample of experimentally infected fish, but separate regressions run on the male and female datasets demonstrated a significant relationship only among male fish. Hence, among males-but not females-elevated VTG levels elicited by E2 exposure led to more rapid parasite growth. We outline plausible physiological mechanisms that could explain these results. Our results demonstrate that oestrogenic pollutants can alter host-parasite interactions by promoting parasite growth, and that male hosts may be disproportionately affected. Because ecologically-relevant effects of infection on host antipredator responses, growth, energetics and reproductive development all depend on parasite mass in this host-parasite system, our results indicate that EDCs can mediate the ecological consequences of infections. We therefore consider the implications of our results for the ecology of hosts and parasites in polluted environments.

Shark parasites as bio-indicators of metals in two South African embayments

Concentrations of metals in the tissues of the sharks Callorhinchus capensis, Rhinobatos annulatus and Rhinobatos blochii collected in False Bay and Saldanha Bay, South Africa, in 2013 were investigated. Metal concentrations in the tissue of the parasites Gyrocotyle plana infecting the spiral intestine of C. capensis and Proleptus obtusus infecting the stomach of R. annulatus and R. blochii were also analysed. G. plana showed accumulation of arsenic (4073.52±5561.54 μg/g), manganese (522.16±578.21 μg/g), lead (64.87±101.7 μg/g), titanium (1821.42±1348.16 μg/g) and zinc (12439.57±9743.60 μg/g). These results when compared to baseline values, showed that accumulation of the metals in G. plana are orders of magnitude higher than those in the surrounding environment and 2 to 6 times the concentration of the surrounding host's tissues. These results show the usefulness of marine endoparasites as early warning indicators of heavy metal pollution.

Variation in Parasite Communities in Spottail Shiners (Notropis hudsonius) Linked with Precipitation

The Richelieu River, Quebec, is a highly-regulated waterway subject to numerous anthropogenic influences from municipal effluents and agricultural activities. Parasite communities in 234 spottail shiners (Notropis hudsonius) were examined from 4 localities in late spring 2003 and 2004. Component species richness varied between 15 and 18 species in 2003 but declined to 9 to 13 in 2004, while total parasite abundance was consistently lower in 2003. Parasite component community similarity among localities could not be directly linked to available upstream water quality measurements or anthropogenic activity and was best explained by precipitation. Total precipitation in May 2003 was approximately 40% more than in May 2004, presumably altering patterns of runoff, river flow rates, and water quality. This study suggests that fish parasite species composition and richness in the Richelieu River are influenced by environmental parameters which in turn ultimately are driven by a combination of climatic conditions and anthropogenic activities in the watershed.

Prevalence and seasonal variation of ectoparasites in cultured Nile tilapia Oreochromis niloticus in Saudi Arabia

The prevalence, mean intensity and abundance of ectoparasites (monogeneans and trichodinids) from Nile tilapia Oreochromis niloticus were investigated during different seasons of two consecutive years, from January 2011 to December 2012. A total of 360 O. niloticus was collected from three fish farms located in the central region of Saudi Arabia. Prevalence, mean intensity and mean abundance of monogeneans on fish gills were found to be significantly (p < 0.01) higher in farm(C) (81.67, 495.23, 405.84 %) than farm (A) (7.5, 81.25, 8.34 %) and farm (B) (4.17, 62.5, 5 %) respectively. Similarly, the same parameters for trichodinids on gills were found to be significantly (p < 0.01) higher in farm (C) (97.5, 97.5, 97.5 %), followed by farm (A) (39.17, 234.37, 35.00 %) and farm (B) (6.67, 347.92, 30.00 %) respectively. The results of monogenean parameter on fish skin were found to be significantly (p < 0.01) higher in farm (C) (66.67, 443.68, 294.16) followed by farm (A) (16.67, 124.58, 21.67 %) then farm (B) (0.83, 25, 0.83 %) respectively. Similar results for trichodinid parameters on the skin were found to be higher (p < 0.01) in farm (C) (97.5, 875, 857.5 %), then farm (A) (26.67, 399.70, 215.01 %) and farm (B) (4.17, 154.17, 12.5 %) respectively. These results indicated that water quality and nutritional qualities were the major factors that affecting parasite occurrence, while the effect of temperature, seasonality and stocking density might have a secondary role on ectoparasite occurrence. Further studies should investigate that how the nutritional and water qualities affect the immunity of the fish to resist parasite infection.

Bioaccumulation and speciation of selenium in fish and insects collected from a mountaintop removal coal mining-impacted stream in West Virginia

A major contaminant of concern for mountaintop removal/valley fill (MTR/VF) coal mining is selenium (Se), an essential micronutrient that can be toxic to fish. Creek chubs (Semotilus atromaculatus), green sunfish (Lepomis cyanellus), and composite insect samples were collected in March-July, 2011-2013 at two sites within the Mud River, West Virginia. One site (MR7) receives MTR/VF coal mining effluent, while the reference site (LFMR) does not. MR7 water had significantly higher concentrations of soluble Se (p < 0.01) and conductivity (p < 0.005) compared to LFMR. MR7 whole insects contained significantly higher concentrations of Se compared to LFMR insects (p < 0.001). MR7 creek chubs had significantly higher Se in fillets, liver, and ovary tissues compared to LFMR samples (p < 0.0001, p < 0.0001, and p < 0.02, respectively). MR7 green sunfish fillets contained significantly higher Se (p < 0.0001). Histological examination showed LFMR creek chub gills contained a typical amount of parasitic infestations; however MR7 gills contained minimal to no visible parasites. X-ray absorption spectroscopic analyses revealed that MR7 whole insects and creek chub tissues primarily contained organic Se and selenite. These two species of Mud River fish were shown to specifically accumulate Se differently in tissues compartments. Tissue-specific concentrations of Se may be useful in determining potential reproductive consequences of Se exposure in wild fish populations.

Parasites as biological tags to assess host population structure: Guidelines, recent genetic advances and comments on a holistic approach

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Parasites as biological tags to assess host population structure.

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Recent molecular advances support incorporation of parasite genetic data.

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Guidelines for selection of a parasite species as a tag candidate updated.

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Holistic approach allows for robustness and support of observed result.

We review the use of parasites as biological tags of marine fishes and cephalopods in host population structure studies. The majority of the work published has focused on marine fish and either single parasite species or more recently, whole parasite assemblages, as biological tags. There is representation of host organisms and parasites from a diverse range of taxonomic groups, although focus has primarily been on host species of commercial importance. In contrast, few studies have used parasites as tags to assess cephalopod population structure, even though records of parasites infecting cephalopods are well-documented. Squid species are the only cephalopod hosts for which parasites as biological tags have been applied, with anisakid nematode larvae and metacestodes being the parasite taxa most frequently used. Following a brief insight into the importance of accurate parasite identification, the population studies that have used parasites as biological tags for marine fishes and cephalopods are reviewed, including comments on the dicyemid mesozoans. The advancement of molecular genetic techniques is discussed in regards to the new ways parasite genetic data can be incorporated into population structure studies, alongside host population genetic analyses, followed by an update on the guidelines for selecting a parasite species as a reliable tag candidate. As multiple techniques and methods can be used to assess the population structure of marine organisms (e.g. artificial tags, phenotypic characters, biometrics, life history, genetics, otolith microchemistry and parasitological data), we conclude by commenting on a holistic approach to allow for a deeper insight into population structuring.

Exposure of the snail Potamopyrgus antipodarum to herbicide boosts output and survival of parasite infective stages

Anthropogenic stressors such as pollutants can modulate levels of parasitic infections in aquatic animals by suppressing host immunity or through some other mechanisms. One such mechanism could involve increases in either the quantity or quality of infective stages produced by parasites. We investigated the effect of exposure of infected snails, Potamopyrgus antipodarum, to different concentrations of the widely-used herbicide glyphosate, on (i) the production of infective cercariae by three trematode species, Coitocaecum parvum, Apatemon sp. and an undescribed renicolid, and (ii) the survival of cercariae of the latter species. For all three trematode species, infected snails exposed over a month to low (0.36 mg a.i. L(-1)) or medium (3.6 mg a.i. L(-1)) formulated glyphosate concentrations released between 1.5 and 3 times more cercariae per day than snails under control conditions. The similar pattern seen in all trematodes suggests a general weakening of the host benefiting any of its parasites rather than some parasite species-specific mechanism. In addition, the survival of renicolid cercariae improved with increasing glyphosate concentrations, with cercariae living about 50% longer in the medium concentration (3.6 mg a.i. L(-1)) than in control conditions. Our results demonstrate a clear interaction between glyphosate pollution and parasitism by trematodes in freshwater systems, occurring at glyphosate concentrations recorded in aquatic habitats, and within the environmental exposure limit allowed in New Zealand freshwaters. Future risk assessments and toxicity tests need to consider indirect impacts resulting from infections to invertebrate and vertebrate species penetrated by cercariae and serving as second intermediate hosts of trematodes.

Infection level of monogenean gill parasite, Diplozoon kashmirensis (Monogenea, Polyopisthocotylea) in the Crucian Carp, Carassius carassius from lake ecosystems of an altered water quality: What factors do have an impact on the Diplozoon infection?

Monogeneans are of great interest to the ecologists because of their simple life cycle and are considered as one of the important and sensitive parasites to any changes in water quality. The monogenean gill parasite, Diplozoon kashmirensis of the Carassius carassius was examined with the aim to evaluate the infection level and the factors influencing the infection. Our results showed that highest prevalence (34.22%) of D. kashmirensis was in the lake having high trophic status and least prevalence (10.90%) in the lake having least trophic status. Infection levels were significantly higher at the basins/sites having deteriorated water quality in comparison to the basins/sites having better water quality. The combined effect of pollutants and eutrophication showed decrease in intensity of D. kashmirensis in one of the polluted/hypertrophied site in the hypertrophic lake (Anchar Lake), while as synergistic effect (i.e. increase) on prevalence and intensity was observed in one of the polluted/hypertrophied site in the eutrophic lake (Dal Lake). Sex was not an important factor influencing the D. kashmirensis in three lakes. The study showed that condition factor was significantly higher in the hypertrophic lake and in an uninfected fish. In addition microhabitat influenced the Diplozoon infection. Most preferable site for the D. kashmirensis was middle sector of the gill. Furthermore, the gill parasite showed significantly positive correlation (r(p)=0.6, P<0.05) with water temperature in the hypertrophic lake, thus showing the impact of water temperature on this parasite. It was concluded that intra lake differences, season, condition factor, microhabitat and water temperature influenced the infection of D. kashmirensis. It seems from the data that eutrophic and hypertrophic habitats were favourable for the D. kashmirensis. The D. kashmirensis showed both antagonistic and synergistic response to the combined effect of pollution and eutrophication.

Parasite communities in the red mullet, Mullus barbatus L., respond to small-scale variation in the levels of polychlorinated biphenyls in the Western Mediterranean

We examined parasite populations and communities in the Mediterranean sentinel fish species, Mullus barbatus, sampled at a small-scale PCB gradient at the shelf sediments off Catalonian coasts of the Western Mediterranean. A recurrent feature at both the population and community level was the differentiation of the samples along the increasing PCB levels simultaneously registered in the sediments. Both directly transmitted ectoparasites and endoparasites with complex life-cycles transmitted via food chains exhibited a decrease in abundance with the increase in PCB levels. Parasite numerical responses translated into significant differences in infracommunity structure with decreasing predictability associated with increasing PCB levels. The abundance of two species, the specialist Opecoeloides furcatus and the generalist nematode Hysterothylacium fabri, contributed substantially to the observed dissimilarity between infracommunity samples along the gradient. The observed parasite responses to moderate levels of pollution were simultaneously validated by both chemical monitoring and effect biomarkers.

Chemical contaminants and parasites: assessment of human health risks associated with consumption of whitefish (Coregonus clupeaformis) from two boreal lakes in northern Saskatchewan, Canada

In Canada there is increasing concern about potential effects of industrial activities on wildlife and human health. In an interdisciplinary study concentrations of inorganic (metals, metalloids) and organic (PCBs, organochlorine pesticides) contaminants, and parasitic infections of lake whitefish (Coregonus clupeaformis) from Montreal and Reindeer lakes, Saskatchewan, were investigated to assess human health risk related to fish consumption. In both lakes contamination of fish with chemical substances and compounds, respectively, were very low and often close to detection limits. Lake whitefish parasite communities consisted of 15 (Montreal Lake) and 12 (Reindeer Lake) species most of which were found in the intestinal tract. Many parasite species showed seasonal differences in prevalence and/or mean intensity of infection. None of the identified parasites are known to be human-pathogenic and overall, whitefish from both locations can be considered safe and healthy food. Nevertheless, women of child-bearing age and young children should limit their consumption to 3 and 2 meals, respectively, of Reindeer Lake whitefish per week to minimize potentially harmful exposure to mercury. As well, intestines of Montreal Lake fish should be removed prior to fish consumption if large parasite cysts containing a yet unidentified cestode species are detected.

Assessment of environmental quality through analysis of frequency of the black spot disease in an assemblage of fish, Guaíba lake, RS, Brazil

The frequency of the black spot disease caused by digenetic trematodes in fish was tested as an indicator of the quality of water in the watershed of Lake Guaíba. Samples were standardised and quarterly made using a seine net at eleven sites in the basin. A total of 53,408 individuals of 66 specimens pertaining to 22 families and 8 orders were collected and analysed. The highest frequency of the disease was found in Astyanax fasciatus. The simple Chi-Squared test applied to the species showed statistically significant frequency of occurrence for three sampled sites. Two of these sites showed the highest frequencies for two consecutive sampling periods of one year and the best levels of water quality. Results of this study suggest that the association between high frequency of infestation by a parasite that causes the black spot disease in fish, and environments with less degradation in water quality, recorded from physical, chemicals and microbiological variables, could be used as an indicator of water quality in these environments.

A Comparative Study of the Common Protozoan Parasites of Clarias gariepinus from the Wild and Cultured Environments in Benue State, Nigeria

A total of one hundred and twenty Clarias gariepinus comprising 30 dead and 30 live fishes were examined for protozoan parasites infestation, sixty each from the wild and a pond (cultured environment) over a period of six months. Ichthyophthirius multifiliis was the most common protozoan parasites found in C. gariepinus from the wild (River Benue) and cultured (pond) environments. These protozoan parasites constitute 37.08% of the total parasites encountered for fishes in the pond and 42.51% of fishes in the wild. Among the body parts of the sampled fishes from the pond, the gills had the highest parasite load (38.86%). Also, the gills had the highest parasite load (40.54%) among the body parts of the fishes sampled from the wild. Fishes not infested with any protozoan parasites from the pond constituted 36.70% of the total fish sampled. On the other hand, fishes not infested with any protozoan parasites from the wild constituted 31.65% of the total fish sampled. Female fishes had more protozoan parasites than the male fishes. Bigger fishes of total length (25–48 cm) had more parasite load than the smaller ones (19–24 cm). Also, fishes between 150–750 g had more parasite load than the smaller ones of less than 150 g. Protozoan parasite load of fish from the cultured environment (pond) did not differ significantly (P < 0.05) from those from River Benue (wild).

Infection level of the Asian tapeworm (Bothriocephalus acheilognathi) in the cyprinid fish, Schizothorax niger, from Anchar Lake, relative to season, sex, length and condition factor

Various studies have shown that the Asian fish tapeworm, Bothriocephalus acheilognathi causes great economic loss in hatcheries, fish farms as well as in lakes. In order to understand the seasonal variation of infection in a nutrient-enriched lake, parasitological investigation was carried out in the indigenous cyprinid fish, Schizothorax niger Heckel 1838 from September, 2008 to August, 2009. Overall, this study revealed definite seasonality of infection (p < 0.05), with greater infection in summer (prevalence = 39.5%) and lesser in winter (prevalence = 8.1%). The prevalence among different seasons revealed significant differences (p < 0.05). Sex was not an important factor influencing the prevalence of the Asian tapeworm. A strong positive correlation (Pearson's correlation, r = 0.7; p = 0.02) between total length of S. niger and number of Asian fish tapeworms was observed. Similarly, a strong positive correlation existed between weight of fish and number of tapeworms (Pearson's correlation, r = 0.7; p = 0.005). Prevalence and mean abundance were positively and significantly correlated with water temperature (r = 0.8, p < 0.01 and r = 0.8, p < 0.01, respectively). Thus seasonal dynamics, total length and weight of the host significantly influenced the tapeworm infection. The above findings will be useful in devising the appropriate control strategies for the Asian tapeworm in wild fish in Kashmir valley as well as in similar climatic zones of other parts of the world. Also, information from this study will be used to assess the spread and extent of B. acheilognathi which is a potential threat to the indigenous fish fauna of Anchar Lake.

Effects of water quality and trophic status on helminth infections in the cyprinid fish, Schizothorax niger Heckel, 1838 from three lakes in the Kashmir Himalayas

Water quality greatly influences the population density of aquatic biota, including parasites. In order to evaluate the relationship between fish parasites and water quality in Kashmir Himalayas, we assessed helminth parasite densities in Schizothorax niger Heckel, 1838 (an endemic cyprinid fish of Kashmir) from three lakes, namely Anchar, Manasbal and Dal, which reflected the varied stages of eutrophication. The overall prevalence of helminth infections was higher in the hypertrophic Anchar Lake (prevalence = 18.6%) compared to Manasbal Lake, which was the least eutrophied (prevalence = 6.4%). Furthermore, mean prevalence of monoxenous and heteroxenous parasites was higher in lakes containing higher levels of water degradation (Anchar and Dal). The mean number of helminth species per fish host was the highest in the hypertrophic lake (1.3 ± 0.3) in comparison to the least eutrophic lake (0.2 ± 1.5). Variability of calculated infection indices (prevalence, mean intensity and mean abundance) revealed that helminth parasite composition in the fish was affected by the lakes' environmental stress (degraded water quality). Therefore, data on the density of helminth parasites in fish can provide supplementary information on the pollution status of a water body.

Sazonalidade da fauna de metazoários de Pygocentrus nattereri (Kner, 1858) no lago Piranha (Amazonas, Brasil) e a avaliação de seu potencial como indicadora da saúde do ambiente

Foi estudada a fauna de metazoários parasitos de Pygocentrus nattereri capturadas no lago Piranha, durante as fases do ciclo hidrológico do ano de 2007. Foi verificada a relação entre o fator de condição e a ocorrência de parasitos, e também a viabilidade da utilização da fauna parasitária de P. nattereri como bioindicadora da saúde do ambiente. Foram coletados monogenóideos das espécies Amphithecium microphalum, Amphitecium brachycirrum, Amphitecium calycinum, Amphithecium catalaoensis, Amphithecium junki, Pithanothecium amazonensis e Rhinoxenus piranhus, o nematóide Procamallanus inopinatus, copépodos da espécie Miracetyma sp. e o isópoda Anphira branchialis. Não houve correlação significativa entre a ocorrência dos parasitos com o fator de condição dos peixes. Houve variações significativas entre os índices parasitários nos diferentes períodos do ciclo hidrológico e P. nattereri satisfez os requisitos descritos na literatura para selecionar um peixe hospedeiro e sua parasitofauna como bioindicadora.

Accumulation of some heavy metals in Hysterothylacium aduncum (Nematoda) and its host sea bream, Sparus aurata (Sparidae) from North-Eastern Mediterranean Sea (Iskenderun Bay)

The sea bream's nematode and Sparus aurata, sampled from the Iskenderun Bay, Mediterranean, in March 2008 were analyzed by inductively coupled plasma-atomic emission spectrometry for their some heavy metal (Cd, Cr, Cu, Fe, Hg, Mn, Mg, Pb, and Zn) levels. The metal concentrations of the parasites were compared to different organs (liver, muscle, gill, intestine, and skin) of the fish hosts. There were significant differences in Cd, Cr, Cu, Fe, Mn, Zn, Hg, Mg, and Pb concentrations in tissues of fish and its parasite. The parasite Cd, Cu, and Pb concentration was higher than the other tissues. Furthermore, significant differences were detected in the heavy metal accumulations between the parasitized and unparasitized fish tissues in Cd, Cu, Hg, and Pb concentrations. The Cd, Hg, and Pb concentrations were found in fish muscle at mean concentrations over the permissible limits proposed by the Food and Agriculture Organization.

Zebra mussel (Dreissena polymorpha) parasites: potentially useful bioindicators of freshwater quality?

In environmental quality bioassessment studies, analysis of host-parasite interactions may well be a valuable alternative to classical macroinvertebrate sampling approaches. Herein, we investigated whether zebra mussel (Dreissena polymorpha) parasites could be useful biomonitoring tools. Mussel populations were sampled twice at two sites in northeastern France representing different levels of contamination and were characterized for parasite infection following standard histological methods. Our results indicated that sites of different environmental quality (i.e. chemical contamination) exhibited different parasite communities characterized by different trematode species and parasite associations. An additional significant finding was the positive correlation established between the prevalence of Rickettsiales-like organisms and metal contamination. Multivariate analyses were valuable in examining parasite communities.

Metazoan parasites of Mandi-amarelo Pimelodus maculatus and of Jundiá Rhamdia quelen (Osteichthyes: Siluriformes) of Paraíba do Sul River, Volta Redonda, Rio de Janeiro

Forty-one specimens of mandi-amarelo Pimelodus maculatus Lacépède, 1803 (Siluriformes: Pimelodidae) and 54 specimens of jundiá Rhamdia quelen (Quoy & Gaimard, 1824) (Siluriformes: Heptapteridae) were collected from the Paraíba do Sul River, Volta Redonda, State of Rio de Janeiro, Brazil between November 2007 and October 2008. These fish underwent necropsy so their infracommunities of metazoan parasites could be studied. The same three species of parasites were collected in the two fish species studied. These were one monogenean, one nematode, and one hirudinean. Cucullanus pinnai (Travassos, Artiga, and Pereira, 1928) (Nematoda: Cucullanidae) and Aphanoblastella sp. (Monogenea: Dactylogyridae) were the dominant species with the highest prevalence in P. maculatus and R. quelen. The parasite species of P. maculatus and R. quelen showed an atypical over-dispersed pattern of distribution. No parasite species showed significant correlation between the body total length of the siluriform hosts and their prevalence and abundance. The parasite species richness showed a mean value of 0.87 ± 0.67 (0 -2) and 0.57 ± 0.56 (0 -2) in P. maculatus and R. quelen, respectively, and no correlation with the body total length.

Exposure to a mixture of zinc and copper decreases survival and fecundity of Discocotyle sagittata (Leuckart) parasitizing juvenile Atlantic salmon, Salmo salar L

We assessed the effects of zinc and copper on freshwater monogenean ectoparasites (Discocotyle sagittata Leuckart) infecting juvenile Atlantic salmon (Salmo salar L.). Exposure to 47 microg/L zinc and 3 microg/L copper reduced survival and fecundity of adult D. sagittata, while egg hatching success was only reduced at high exposure concentrations (2704 microg/L zinc and 164 microg/L copper). Parasitized salmon had decreased plasma chloride, but this was negated in infected fish exposed to metals. No other effects on Atlantic salmon survival and physiology (plasma osmolality, hematocrit) were noted, suggesting that D. sagittata may be more susceptible to metal toxicity than its host fish.