Environmental parasitology: stressor effects on aquatic parasites

Unveiling new data on fish parasite diversity in reservoirs of the Brazilian semi-arid

Parasite biodiversity is underestimated or unknown in many regions, yet information on parasites is critical to understanding ecosystem structure and how this will change into the future. Understanding the diversity and role of parasites is especially important in regions exposed to anthropogenic pressures, such as aquatic ecosystems, as their interactions with other stressors can either exacerbate or mediate negative impacts. Water scarcity in the Brazilian semi-arid has led to a proliferation of reservoirs for human use. These artificial waterbodies host a diversity of taxa, including a large number of fish species; however, fish parasite diversity remains undocumented. This study investigated the parasitological diversity of fishes from reservoirs in the Paraíba and Mamanguape River basins in the Caatinga domain, Brazil - one of the most populated semi-arid regions worldwide. Eight reservoirs were studied, with fish sampled across the two phases of the hydrological cycle (dry and rainy seasons) using gillnets, cast nets, and trawl nets. Endo- and ecto-parasites were identified and enumerated, and parasitological indices (prevalence, intensity, and abundance) were calculated. In total, 1,170 individuals of 21 fish species were examined. Of these individuals, 42% were parasitized with at least one of 54 parasite taxa. We recorded 32 new geographical occurrences of parasites and 23 new fish-parasite interactions, expanding our understanding of ichthyoparasite diversity in the Brazilian semi-arid. Moving forward, it is important to develop knowledge around how anthropogenic changes (e.g., biological invasions, climate, and land use change) influence host-parasite structure and dynamics and ecosystem functioning in these ecosystems.

Evaluating fatty acid profiles in anisakid nematode parasites and adjacent tissue of European hake (Merluccius merluccius): a first insight into local host-parasite lipid dynamics

Parasitism in fish is a widespread and ecologically significant phenomenon, affecting fish in both wild and aquaculture environments. Comprehending parasitism is essential for managing fish populations, protecting fish health, and preventing human exposure to zoonotic parasites. Understanding lipid dynamics between parasitic organisms and their hosts is crucial for elucidating host-parasite interactions. Although the third larval (L3) stage of anisakid larvae is not a developing stage, and therefore not as dependent on the host for the acquisition of nutrients, there are hints of interplay between parasites and fish hosts, also in terms of lipid content. This study aimed to characterize for the first time the fatty acid profiles of anisakid nematode parasites and adjacent tissue in the European hake (Merluccius merluccius) in order to shed some light on these intricate relationships. Fatty acid analysis revealed significant differences in the percentages of individual fatty acids between anisakid nematodes and adjacent European hake tissue. Anisakids presented a higher content in stearic (18:0), vaccenic (18:1n-7), and linoleic (18:2n-6) acids, while in turn, the belly flap tissue of the fish presented significantly higher contents in palmitic (16:0) and especially docosahexaenoic acid (22:6n-3) than the parasite. These differences suggest unique lipid metabolic pathways between parasite and fish, and that parasitism and the possible acquisition of lipids from the host (hake) do not profoundly shape the fatty acid profile of the parasites. Furthermore, the distinct fatty acid signatures described for parasites and hosts may serve as baselines to follow possible changes in the ecological statuses of both species and even to appraise the nutritional features of European hake when affected by parasitism. This study provides valuable insights into the lipid dynamics within host-parasite systems and underscores the importance of further research to unravel the complexities of these interactions.

An interdisciplinary approach to improving conservation outcomes for parasites

Parasites represent a significant proportion of Earth's biodiversity and play important roles in the ecology and biology of ecosystems and hosts, making them an important target for conservation. Despite increasing calls to prioritize protection for parasites in the academic literature, they remain undervalued and underrepresented in global biodiversity conservation efforts, not least due to the perception that the interests of parasite and host conservation are opposing and the common misconception that parasites are a threat, rather than a benefit, to conservation. We considered whether taking an interdisciplinary approach to parasite conservation research will generate novel insights and solutions concerning why and how parasite conservation should be practiced for the benefit of parasites, their hosts, ecosystems, and people. We argue that 2 of the main barriers to more widespread parasite conservation are the knowledge gap concerning the role of sociocultural factors affecting the willingness to enact parasite conservation and the lack of a consistent and cohesive philosophical basis for parasite conservation. Possible sociocultural barriers to parasite conservation include misconceptions of the risks posed by parasites, taxonomic bias, differences in conservation values, economic constraints, and technical challenges. The use of social science can generate insights into levels of awareness and support for parasite conservation and improve understanding of how human values and attitudes mediate conservation practices concerning parasites. Such knowledge will have a critical role in addressing sociocultural barriers and improving support for parasite conservation. Issues with the current philosophical basis for parasite conservation include contradictory accounts of which parasites merit conservation, insufficient explanation of how different conservation values apply to parasite biodiversity, and the existence of a false antagonism between host and parasite conservation. Greater engagement with philosophical work on environmental ethics and biological unitization will strengthen existing arguments for parasite conservation and will support conservation decision-making processes.

Parasites in a Changing World: Troublesome or in Trouble?

There are plenty of reasons to believe that parasite populations will respond to biodiversity loss, warming, pollution, and other forms of global change. But will global change enhance transmission, increasing the incidence of troublesome parasites that put people, livestock, and wildlife at risk? Or will parasite species decline in abundance-or even become extinct-suggesting trouble on the horizon for parasite biodiversity? Here, I explain why answers have thus far eluded us and suggest new lines of research that would advance the field. Data collected to date suggest that parasites can respond to global change with increases or decreases in abundance, depending on the driver and the parasite. The future will certainly bring outbreaks of some parasites, and these should be addressed to protect human and ecosystem health. But troublesome parasites should not consume all of our research effort, because this changing world contains many parasite species that are in trouble.

Locomotor activity and physiological responses of parasite-infected Gammarus fossarum exposed to the herbicide metazachlor

Herbicides are among the most commonly found contaminants in freshwater ecosystems. Standard tests are frequently employed to assess their ecotoxicological impacts, but sublethal endpoints in non-target species are often not considered. In addition, ecotoxicological investigations rarely take into account that many species from field populations are naturally infected with parasites. To overcome these gaps, our study aimed to investigate how environmentally relevant concentrations of the herbicide metazachlor affect the locomotor activity and selected physiological responses of Gammarus fossarum infected with the acanthocephalan Polymorphus minutus and microsporidians. Prior to the study of sublethal effects, acute immobility, and lethality (EC50 and LC50) tests were conducted. Polymorphusminutus, but not microsporidians, slightly enhanced chemical stress tolerance in infected G. fossarum in the acute immobility and lethality test. Infections with P. minutus significantly increased the host's locomotory activity in comparison to uninfected individuals when exposed to environmentally relevant concentrations of metazachlor, while metazachlor exposure alone had no apparent impact on locomotion. In contrast, the effects of metazachlor on physiological responses (glutathione S-transferase, glycogen, and phenoloxidase) of G. fossarum were significant, while parasite infection alone did not exhibit any significant impact on these biomarkers. The findings of our study indicate that the locomotor activity of G. fossarum in the conducted exposure tests was mostly influenced by P. minutus infections. Conversely, physiological responses were predominantly associated with exposure to metazachlor at environmentally relevant concentrations. We recommend future ecotoxicological studies involving non-target, field-collected species to consider the potential bias introduced by parasitic infections to ensure accurate evaluations of the effects of environmental contaminants.

Evolution of parasites in the Anthropocene: new pressures, new adaptive directions

The Anthropocene is seeing the human footprint rapidly spreading to all of Earth's ecosystems. The fast-changing biotic and abiotic conditions experienced by all organisms are exerting new and strong selective pressures, and there is a growing list of examples of human-induced evolution in response to anthropogenic impacts. No organism is exempt from these novel selective pressures. Here, we synthesise current knowledge on human-induced evolution in eukaryotic parasites of animals, and present a multidisciplinary framework for its study and monitoring. Parasites generally have short generation times and huge fecundity, features that predispose them for rapid evolution. We begin by reviewing evidence that parasites often have substantial standing genetic variation, and examples of their rapid evolution both under conditions of livestock production and in serial passage experiments. We then present a two-step conceptual overview of the causal chain linking anthropogenic impacts to parasite evolution. First, we review the major anthropogenic factors impacting parasites, and identify the selective pressures they exert on parasites through increased mortality of either infective stages or adult parasites, or through changes in host density, quality or immunity. Second, we discuss what new phenotypic traits are likely to be favoured by the new selective pressures resulting from altered parasite mortality or host changes; we focus mostly on parasite virulence and basic life-history traits, as these most directly influence the transmission success of parasites and the pathology they induce. To illustrate the kinds of evolutionary changes in parasites anticipated in the Anthropocene, we present a few scenarios, either already documented or hypothetical but plausible, involving parasite taxa in livestock, aquaculture and natural systems. Finally, we offer several approaches for investigations and real-time monitoring of rapid, human-induced evolution in parasites, ranging from controlled experiments to the use of state-of-the-art genomic tools. The implications of fast-evolving parasites in the Anthropocene for disease emergence and the dynamics of infections in domestic animals and wildlife are concerning. Broader recognition that it is not only the conditions for parasite transmission that are changing, but the parasites themselves, is needed to meet better the challenges ahead.

Influence of salinity on the thermal tolerance of aquatic organisms

Aquatic organisms are challenged by changes in their external environment, such as temperature and salinity fluctuations. If these variables interacted with each other, the response of organisms to temperature changes would be modified by salinity and vice versa. We tested for potential interaction between temperature and salinity effects on freshwater, brackish, and marine organisms, including algae, macrophytes, heterotrophic protists, parasites, invertebrates, and fish. We performed a meta-analysis that compared the thermal tolerance (characterised by the temperature optimum, lower and upper temperature limits, and thermal breadth) at various salinities. The meta-analysis was based on 90 articles (algae: 15; heterotrophic protists: 1; invertebrates: 43; and fish: 31). Studies on macrophytes and parasites were lacking. We found that decreasing salinity significantly increased and decreased the lower and upper temperature limits, respectively, in all groups. Thus, a lowered salinity increased the thermal sensitivity of organisms. These findings mainly reflect the response of brackish and marine organisms to salinity changes, which dominated our database. The few studies on freshwater species showed that their lower thermal limits increased and the upper thermal limits decreased with increasing salinity, albeit statistically nonsignificant. Although non-significant, the response of thermal tolerance to salinity changes differed between various organism groups. It generally decreased in the order of: algae > invertebrates > fish. Overall, our findings indicate adverse effects of salinity changes on the temperature tolerance of aquatic organisms. For freshwater species, studies are comparatively scarce and further studies on their thermal performance at various salinity gradients are required to obtain more robust evidence for interactions between salinity and temperature tolerance. Considering test conditions such as acclimation temperature and potential infection with parasites in future studies may decrease the variability in the relationship between salinity and thermal tolerance.

Unveiling the potential of parasites as proxy bioindicators for water quality assessment in river Jhelum Kashmir, India

This study aimed to evaluate the effects of deteriorated physicochemical conditions in the river Jhelum on parasitic infestations and to investigate the potential of fish parasites as bioindicators of water quality. All the physicochemical parameters exhibited statistically significant differences based on both site and season (p < 0.01). The interaction term (Site × Season) was also kept in the model since it was statistically significant (p < 0.01). A parasitological survey of 360 schizothoracine fish revealed a 30.3% prevalence (109/360) of endohelminth infection. The study identified four predominant parasitic taxa across two distinct classes: Cestoda, including Adenoscolex oreini and Schyzocotyle acheilognathi, and Acanthocephala, comprising Pomphorhynchus kashmirensis and Neoechinorhynchus manasbalensis. For the assessment of parasitic load, we calculated the prevalence, mean intensity, mean abundance, and index of infection for each sampling period. Correspondence analysis identified associations between parasite occurrence and specific water quality parameters. Regression analysis, including R2 and p values, demonstrated a positive correlation between the number of parasites and both the proportion of infected fish and the ratio of infected to examined fish. Given that parasitic load is significantly influenced by a range of water quality parameters, fish parasites can serve as a robust indicator of declining water quality. Fish parasites are highly sensitive to water quality changes such as pollutants, toxins, and fluctuations in pH, temperature, and oxygen levels. Deteriorating water quality can stress fish, compromising their immune systems and increasing their susceptibility to parasitic infections. Additionally, complex life cycles of parasites can be disrupted by poor water conditions, making them indicators of water quality issues.

Association of Frailty With Risk of Incident Hospital-Treated Infections in Middle-Aged and Older Adults: A Large-Scale Prospective Cohort Study

BACKGROUND

Although frailty is associated with a range of adverse health outcomes, its association with the risk of hospital-treated infections is uncertain.

METHODS

A total of 416 220 participants from the UK Biobank were included in this prospective cohort study. Fried phenotype was adopted to evaluate frailty, which included 5 aspects (gait speed, physical activity, grip strength, exhaustion, and weight). More than 800 infectious diseases were identified based on electronic health records. Cox proportional models were used to estimate the associations.

RESULTS

During a median 12.3 years (interquartile range 11.4-13.2) of follow-up (4 747 345 person-years), there occurred 77 988 (18.7%) hospital-treated infections cases. In the fully adjusted model, compared with participants with nonfrail, the hazard ratios (HRs) (95% confidence intervals [CIs]) of those with prefrail and frail for overall hospital-treated infections were 1.22 (1.20, 1.24) and 1.78 (1.72-1.84), respectively. The attributable risk proportion of prefrail and frail were 18.03% and 43.82%. Similarly, compared to those without frailty, the HRs (95% CIs) of those with frailty for bacterial infections were 1.76 (1.70-1.83), for viral infections were 1.62 (1.44-1.82), and for fungal infections were 1.75 (1.47-2.08). No association was found between frailty and parasitic infections (HR: 1.17; 95% CI: 0.62-2.20).

CONCLUSIONS

Frailty was significantly associated with a higher risk of hospital-treated infections, except for parasitic infections. Studies evaluating the effectiveness of implementing frailty assessments are needed to confirm our results.

Assessing the response of an urban stream ecosystem to salinization under different flow regimes

Urban streams are exposed to a variety of anthropogenic stressors. Freshwater salinization is a key stressor in these ecosystems that is predicted to be further exacerbated by climate change, which causes simultaneous changes in flow parameters, potentially resulting in non-additive effects on aquatic ecosystems. However, the effects of salinization and flow velocity on urban streams are still poorly understood as multiple-stressor experiments are often conducted at pristine rather than urban sites. Therefore, we conducted a mesocosm experiment at the Boye River, a recently restored stream located in a highly urbanized area in Western Germany, and applied recurrent pulses of salinity along a gradient (NaCl, 9 h daily of +0 to +2.5 mS/cm) in combination with normal and reduced current velocities (20 cm/s vs. 10 cm/s). Using a comprehensive assessment across multiple organism groups (macroinvertebrates, eukaryotic algae, fungi, parasites) and ecosystem functions (primary production, organic-matter decomposition), we show that flow velocity reduction has a pervasive impact, causing community shifts for almost all assessed organism groups (except fungi) and inhibiting organic-matter decomposition. Salinization affected only dynamic components of community assembly by enhancing invertebrate emigration via drift and reducing fungal reproduction. We caution that the comparatively small impact of salt in our study can be due to legacy effects from past salt pollution by coal mining activities >30 years ago. Nevertheless, our results suggest that urban stream management should prioritize the continuity of a minimum discharge to maintain ecosystem integrity. Our study exemplifies a holistic approach for the assessment of multiple-stressor impacts on streams, which is needed to inform the establishment of a salinity threshold above which mitigation actions must be taken.

Gaps in parasitological research in the molecular era

We live in the age of molecular biology and '-omics', and molecular methods have opened up unimagined possibilities for biological research, including parasitology. However, too one-sided a focus on new approaches can lead to major gaps as less 'cool' topics are neglected. Selected areas of research are briefly discussed to highlight the gaps caused by the current excessive focus on molecular and '-omics' methods. It is crucial to combine both 'classical' and modern methods without neglecting the complexity of the interactions of parasites with their hosts and the environment (One Health concept), which is even more urgent in today's rapidly changing world. Parasitologists should be more involved in field studies and multidisciplinary assessment of parasites.

Halocercus lagenorhynchi infection in a stranded striped dolphin Stenella coeruleoalba (Meyen, 1833) on the Southwest coastline of India

Necropsy on a striped dolphin Stenella coeruleoalba (Meyen, 1833) entangled in ghost fishing net and dead while rescuing yielded some helminth parasites, later identified as Halocercus lagenorhynchi. DNA barcoding of the host and parasite and the phylogenetic analysis of the parasite was conducted. This study provides valuable information towards establishing basal data of marine mammal parasite diversity and distribution in the Indian waters. We believe this is the first report of the occurrence of Halocercus lagenorhynchi in marine mammals in India.

Light pollution may alter host-parasite interactions in aquatic ecosystems

With growing human populations living along freshwater shores and marine coastlines, aquatic ecosystems are experiencing rising levels of light pollution. Through its effects on hosts and parasites, anthropogenic light at night can disrupt host-parasite interactions evolved under a normal photoperiod. Yet its impact on aquatic parasites has been ignored to date. Here, I discuss the direct effects of light on the physiology and behaviour of parasite infective stages and their hosts. I argue that night-time lights can change the spatiotemporal dynamics of infection risk and drive the rapid evolution of parasites. I then highlight knowledge gaps and how impacts on parasitic diseases should be incorporated into the design of measures aimed at mitigating the impact of anthropogenic light on wildlife.

Novel insights into the genetics, morphology, distribution and hosts of the global fish parasitic digenean Proctoeces maculatus (Looss, 1901) (Digenea: Fellodistomidae)

Larval stages of the widely distributed digenean species Proctoeces maculatus (Looss, 1901) were reported 40 years ago from South Africa in the common octopus, Octopus vulgaris Cuvier (Octopodidae). However, the absence of adult specimens and molecular data from this region has hindered a comprehensive understanding of its distribution. In this study, we collected three species of intertidal and near-shore marine fishes [Clinus superciliosus (L.) (Clinidae), Diplodus capensis (Smith) (Sparidae) and Sparodon durbanensis (Castelnau) (Sparidae)] along the South African coast and discovered adult specimens of P. maculatus at five localities. By employing a combination of morphological and molecular techniques, including 28S rDNA, 18S rDNA and COI mtDNA analyses, the first report of adult P. maculatus from South Africa is presented. The findings encompass a comprehensive morphological description and molecular data, illuminating the true distribution of this species in the region.

An update and ecological perspective on certain sentinel helminth endoparasites within the Mediterranean Sea

The Mediterranean Sea is recognized as a marine biodiversity hotspot. This enclosed basin is facing several anthropogenic-driven threats, such as seawater warming, pollution, overfishing, bycatch, intense maritime transport and invasion by alien species. The present review focuses on the diversity and ecology of specific marine trophically transmitted helminth endoparasites (TTHs) of the Mediterranean ecosystems, aiming to elucidate their potential effectiveness as ‘sentinels’ of anthropogenic disturbances in the marine environment. The chosen TTHs comprise cestodes and nematodes sharing complex life cycles, involving organisms from coastal and marine mid/upper-trophic levels as definitive hosts. Anthropogenic disturbances directly impacting the free-living stages of the parasites and their host population demographies can significantly alter the distribution, infection levels and intraspecific genetic variability of these TTHs. Estimating these parameters in TTHs can provide valuable information to assess the stability of marine trophic food webs. Changes in the distribution of particular TTHs species can also serve as indicators of sea temperature variations in the Mediterranean Sea, as well as the bioaccumulation of pollutants. The contribution of the chosen TTHs to monitor anthropogenic-driven changes in the Mediterranean Sea, using their measurable attributes at both spatial and temporal scales, is proposed.

Rickettsia communities and their relationship with tick species within and around the national park of Iguaçu, Brazil

We report Rickettsia species from 2,334 ticks collected from environment (1,939 ticks) and animals (395 ticks) in the largest inland fragment of the Atlantic rainforest of southern Brazil and its fragments. Additionally, the DNA infection rates of Amblyomma ovale tick populations in the Neotropics with Rickettsia bellii and Rickettsia parkeri strain Atlantic rainforest were calculated using data from scientific publications, and their correlation was evaluated. From 11 tick species Rickettsia DNA was detected in seven (Amblyomma brasiliense, Amblyomma coelebs, Amblyomma incisum, Amblyomma longirostre, A. ovale, Haemaphysalis juxtakochi, Ixodes fuscipes) and was not detected in four species (Amblyomma dubitatum, Ixodes loricatus, Rhipicephalus microplus and Rhipicephalus sanguineus sensu lato). DNA of five Rickettsia species was detected (R. bellii, Rickettsia amblyommatis, Rickettsia rhipicephali, Rickettsia felis and Rickettsia sp. Aragaoi). To determine the prevalence of Rickettsia DNA positivity according to vector species, ticks were processed individually or in pools of 2-10 individuals (samples). The most prevalent Rickettsia species was R. bellii, found in 112 samples, followed by R. amblyommatis, R. rhipicephali, R. felis and Rickettsia sp. Aragaoi, found in 16, five, two and one sample, respectively. Rickettsia bellii DNA was found in five tick species with the highest infection rate in A. ovale and A. brasiliense. Absence of R. parkeri strain Atlantic rainforest in A. ovale ticks was an unexpected result. Furthermore, a negative correlation was identified between the infection rates (DNA) of R. bellii and/or R. parkeri strain Atlantic rainforest within A. ovale tick populations in the Neotropics. Putting together current knowledge, it can be proposed that, within natural settings, the diversity of rickettsiae and ticks creates a buffering effect on the overgrowth of rickettsiae and episodes of bacteremia in the hosts.

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.

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.

Conservation of parasites: A primer

Although parasites make up a substantial proportion of the biotic component of ecosystems, in terms of both biomass and number of species, they are rarely considered in conservation planning, except where they are thought to pose a threat to the conservation of their hosts. In this review, we address a number of unresolved questions concerning parasite conservation. Arguments for conserving parasite species refer to the intrinsic value conferred by their evolutionary heritage and potential, their functional role in the provision of ecosystem services, and their value as indicators of ecosystem quality. We propose that proper consideration of these arguments mean that it is not logically defensible to automatically exclude parasite species from conservation decisions; rather, endangered hosts and parasites should be considered together as a threatened ecological community. The extent to which parasites are threatened with extinction is difficult to estimate with any degree of confidence, because so many parasite species have yet to be identified and, even for those which have been formally described, we have limited information on the factors affecting their distribution and abundance. This lack of ecological information may partially explain the under-representation of parasites on threatened species lists. Effective conservation of parasites requires maintaining access to suitable hosts and the ecological conditions that permit successful transmission between hosts. When implementing recovery plans for threatened host species, this may be best achieved by attempting to restore the ecological conditions that maintain the host and its parasite fauna in dynamic equilibrium. Ecosystem-centred conservation may be a more effective strategy than species-centred (or host-parasite community-centred) approaches for preventing extinction of parasites, but the criteria which are typically used to identify protected areas do not provide information on the ecological conditions required for effective transmission. We propose a simple decision tree to aid the identification of appropriate conservation actions for threatened parasites.

Fish parasites as proxy bioindicators of degraded water quality of River Saraswati, India

The nature and intensity of water pollution determine the effects on aquatic biota and aquatic ecosystem health. The present study aimed at assessing the impact of the degraded physicochemical regime of river Saraswati, a polluted river having a historical legacy, on the parasitic infection and the role of fish parasite as a bioindicator of water quality. Two Water Quality Indices (WQIs) were adopted as useful tools for assessing the overall water quality status of polluted river based on 10 physicochemical parameters. Total 394 fish (Channa punctata) were examined. Ectoparasite Trichodina sp., Gyrodactylus sp., and endoparasites Eustrongylides sp. were collected from the host fish. Prevalence, mean intensity and abundance for each sampling period were calculated for the determination of parasitic load. The parasitic load of Trichodina sp. and Gyrodactylus sp. was significantly (p < 0.001) higher in winter, whereas the parasitic load of Eustrongylides sp. showed no significant (p > 0.05) seasonal fluctuation. The parasitic load of ectoparasites was negatively correlated with temperature, free carbon dioxide, biochemical oxygen demand, and WAWQI but positively correlated with electrical conductivity and CCMEWQI. Fish health was found to be adversely affected by degrading water qualities and parasitic infection. A 'vicious cycle' develops as a result of the interplay among deteriorating water quality, withering fish immunological defence, and amplifying parasitic infection. Since parasitic load was strongly conditioned by the combined influence of a suite of water quality parameters the fish parasites can be used as a powerful indicator of deteriorating water quality.