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Recent molecular studies from different geographical regions, especially Europe and North America, have disclosed a rich species diversity of Diplostomum parasites. However, our current knowledge regarding the true diversity and distribution of Diplostomum spp. in India is fairly limited and incomplete. Consequently, the diversity of this group of parasites is expected to be extremely rich, and the present study aims to fill this gap. Two freshwater fish species, Labeo bata (Cyprinidae) and Wallago attu (Siluridae), were sampled during helminth survey of freshwater fish from the Ganga River at Bairaj, Bijnor, in the state of Uttar Pradesh, India. Isolates of both Diplostomum spp. were characterized morphologically and molecularly. Sequences of the ribosomal ITS1-5.8 S-ITS2 cluster, 28 S rRNA gene region and mitochondrial cox1 gene were used for molecular identification of the isolates. Furthermore, genetic data revealed that the DNA sequences of our isolates from L. bata are linked with the lineage of the Diplostomum sp. 14 sensu Locke et al. (2015), while the isolates from W. attu form a separate clade as Diplostomum sp. WA. This is the first molecular exploration of the diversity of Diplostomum spp. in India. Regarding the complicated taxonomy of Diplostomum, we advocate using molecular approaches to study digenean systematics in addition to morphology. It is also expected that there are many unknown diplostomid species that await discovery and molecular characterization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eye flukes are suggested to change the defensive behavior of fish via vision impairment. • We tested whether changes in fish anti-predatory behavior depend on light conditions. • Trematodes Diplostomum pseudospathaceum manipulated Salvelinus malma behavior, making fish less vigilant. • The expression of behavioral changes did not differ under light or dark conditions. • A mechanism of manipulation other than vision impairment is likely to take place. Trematodes localizing in the lenses of fish change the behavior of their hosts. These behavioral changes are widely suggested to be parasitic manipulations of host behavior aimed at increasing the possibility of eye flukes completing their life cycle. It is often assumed that fish change their behavior due to the vision deterioration caused by trematode larvae. We checked this assumption by testing Salvelinus malma infected with eye flukes (Diplostomum pseudospathaceum) under different lighting conditions. We suggested that if the parasite alters the host's behavior through vision impairment, then in the dark (when fish do not rely on vision to navigate), the difference in the behavior of infected and uninfected fish would disappear. Eye flukes, indeed, changed fish behavior, making their hosts less vigilant. We believe this is the first evidence of possible parasitic manipulation in this study system. However, contrary to expectations, the difference in the behavior of infected and control fish was independent of the lighting conditions. Our results suggest that mechanisms of behavioral change other than vision impairment should be taken into account in this fish-eye fluke study system. [ABSTRACT FROM AUTHOR]

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[Display omitted] • Novel sequence data for Diplostomum , Tylodelphys and related genera are provided. • Molecular phylogenies of the group based on 28S and cox 1 sequences are presented. • Sequences of 10 previously unidentified larvae are matched with those from adults. • Paralaria alarioides transferred to Diplostomum. • Phylogenetic analysis reveals several host switching events in the history of the group. The Diplostomidae Poirier, 1886 is a large, globally distributed family of digeneans parasitic in intestines of their definitive hosts. Diplostomum and Tylodelphys spp. are broadly distributed, commonly reported, and the most often sequenced diplostomid genera. The majority of published DNA sequences from these genera originated from larval stages only, which typically cannot be identified to the species level based on morphology alone. We generated partial large ribosomal subunit (28S) rRNA and cytochrome c oxidase subunit 1 (cox 1) mtDNA gene sequences from 14 species/species-level lineages of Diplostomum , six species/species-level lineages of Tylodelphys , two species/species-level lineages of Austrodiplostomum , one species previously assigned to Paralaria, two species/species-level lineages of Dolichorchis and one unknown diplostomid. Our DNA sequences of 11 species/species-level lineages of Diplostomum (all identified to species), four species/species-level lineages of Tylodelphys (all identified to species), Austrodiplostomum compactum , Paralaria alarioides and Dolichorchis lacombeensis originated from adult specimens. 28S sequences were used for phylogenetic inference to demonstrate the position of Paralaria alarioides and Dolichorchis spp. within the Diplostomoidea and study the interrelationships of Diplostomum , Tylodelphys and Austrodiplostomum. Our results demonstrate that two diplostomids from the North American river otter (P. alarioides and a likely undescribed taxon) belong within Diplostomum. Further, our results demonstrate the non-monophyly of Tylodelphys due to the position of Austrodiplostomum spp., based on our phylogenetic analyses and morphology. Furthermore, the results of phylogenetic analysis of 28S confirmed the status of Dolichorchis as a separate genus. The phylogenies suggest multiple definitive host-switching events (birds to otters and among major avian groups) and a New World origin of Diplostomum and Tylodelphys spp. Our DNA sequences from adult digeneans revealed identities of 10 previously published lineages of Diplostomum and Tylodelphys , which were previously identified to genus only. The novel DNA data from this work provide opportunities for future comparisons of larval diplostomines collected in ecological studies. [ABSTRACT FROM AUTHOR]

Objective of research: A study of the fauna and ecology of cercariae and metacercariae of the genus Diplostomum in the main reservoirs in the northeast of Uzbekistan. Materials and methods. This paper is based on the results of the study of the fauna and ecology of cercariae and metacercariae of the genus Diplostomum in the Syrdarya river basin (within Uzbekistan). Cercariae and metacercariae were investigated by the most common methods of trematodology. Results and discussion. The results of this study revealed that cercariae of the genus Diplostomum were found only in mollusks Lymnaea inhabiting different types of water bodies of the investigated region. Infestation of mollusks with parthenia and cercariae D. helveticum was observed in L. stagnalis - 1,5 %, L. auricularia - 1,3 %. The infection rate of cercariae D. spathaceum was in L. stagnalis, L. auricularia, L. peregra - 0,7 %, L. corvus - 0,5 %. The last species was described as a new host for D. spathaceum. Original data on the morphology and biology of cercariae D. helveticum and D. spathaceum developing in mollusks of the genus Lymnaea fauna in Uzbekistan, are presented. In the surveyed water bodies numerous species of Cypriniformes were infected with metacercariae of D. helveticum and D. spathaceum.

The continuing decline of many natural plant and animal populations emphasizes the importance of conservation strategies. Hybridization as a management tool has proven successful in introducing gene flow to small, inbred populations, but can be also associated with health risks. For example, hybridization can change susceptibility to infection in either direction due to heterosis (hybrid vigor) and outbreeding depression, but such health effects have rarely been considered in the genetic management of populations. Here, we investigated the effects of experimental outcrossing between the critically endangered Saimaa landlocked salmon (Salmo salar m. sebago) and the genetically more diverse Atlantic salmon (S. salar) on infection susceptibility. We exposed the parent populations and their hybrids to two parasites that commonly infect these species, the bacterium Flavobacterium columnare and the macroparasitic fluke Diplostomum pseudospathaceum. We found that landlocked salmon had lower survival during the bacterial epidemic, but higher resistance against the fluke, compared with Atlantic salmon. Hybrids showed intermediate survival and resistance, suggesting that hybridization decreased susceptibility to one parasite, but concurrently increased it to another. Our results emphasize the importance of considering health effects of different types of infections when employing hybridization for conservation. [ABSTRACT FROM AUTHOR]

• Species-specific emergence patterns of three Diplostomum spp. were studied. • Daily periodicity-dependent patterns in cercarial emergence were observed. • There was seasonal intraspecific variation in the daily cercarial output. • Patterns synchronised with reproduction and activity of fish second intermediate hosts. • Diplostomum spp. cercariae evolutionarily adapted to fish behaviour. The cercarial emergence patterns of three species of Diplostomum (Diplostomum ' mergi ', Diplostomum spathaceum and Diplostomum parviventosum) parasitizing freshwater first intermediate host Radix lagotis sampled in Most Lake, Czech Republic, were studied under various experimental conditions, i.e. field, laboratory and incubator, and seasons, i.e. spring, summer and autumn. We discovered unexpected daily periodicity-dependent species-specific emergence patterns among the three Diplostomum spp. depending on experimental conditions. At the same time, the intraspecific variation of D. spathaceum cercarial release in response to seasonal conditions was observed. We found that a complex array of mechanisms can affect Diplostomum species-specific patterns in cercarial emergence, of which behavioural characteristics of fish related to reproduction and feeding processes are considered the most important factors. This might represent a specific adaptive evolutionary mechanism to maximise transmission success while avoiding competition for host resources. Our results contribute to a better understanding of ecological and epidemiological aspects with respect to specific adaptive strategies compartmentalised among species of Diplostomum and consequences for infection risk in fish hosts. [ABSTRACT FROM AUTHOR]

Parasite infectivity, virulence and host resistance have been in the centre of the scientific interest when it comes to host–parasite relationships. In addition to resistance, hosts may also vary in their tolerance against parasites. This is important to notice because resistance and tolerance have different consequences in host–parasite co‐evolution. Here, we show that families of farmed rainbow trout (Oncorhynchus mykiss) show both host defence strategies, resistance, and tolerance, against infectivity and virulence of Diplostomum sp. (Trematoda) parasites. Both strategies have moderate genetic variation and are genetically independent of each other. It is also shown that the families having the highest performance measured as higher weight, better condition factor and lower mortality in absence of the parasites suffer the most when parasitism increases. For practical breeding programmes, this means that both resistance and tolerance can be improved by selection without compromising one of the strategies. These results give new insight into defence strategies against parasites in fish and into processes of fish–parasite co‐evolution. [ABSTRACT FROM AUTHOR]

Many aquatic organisms can consume parasite larvae, thus hampering parasite transmission; however, information about feeding on them in the presence of an alternative prey remains scarce. When having a food choice, predators may decrease parasite consumption, therefore, it is important to assess the role of parasites in the diet of predators in natural communities with different types of prey available. Our study aims to test whether common freshwater cyclopoids feed on trematode free‐living stages (cercariae) when an alternative food source is present.We experimentally studied ingestion rates of cyclopoids Macrocyclops distinctus fed with cercariae of trematode Diplostomum pseudospathaceum, a common and harmful parasite of freshwater fishes, and ciliates Paramecium caudatum (an alternative prey, known as suitable food for copepods). First, the feeding response of cyclopoids to different densities of each prey was studied. Then, feeding selectivity in the mixtures of cercariae and ciliates was tested.Feeding rates of cyclopoids increased with prey densities (both ciliates and cercariae) but almost stopped growing at high prey densities, which indicated saturation (Holling type II functional response). In most cases, cyclopoids consumed cercariae at higher rates than ciliates. Maximum ingestion rates estimated from the obtained curves were 37 cercariae ind−1 hr−1 and 17 ciliate ind−1 hr−1.When exposed to prey mixtures, cyclopoids fed on cercariae selectively. When cercariae were offered to cyclopoids at concentrations exceeding the saturation level, the ingestion of ciliates remained constantly low at all ciliate densities. In contrast, the ingestion of cercariae increased with rising cercariae densities even when ciliates were presented ad libitum, decreasing only at very high prey densities. Possible reasons of such feeding preferences are discussed.Our study demonstrated that cyclopoids may prefer to feed on cercariae when there is an alternative food choice and can ingest cercariae at high rates. These experimental results could be extended to natural communities, suggesting that cyclopoids can reduce the transmission of parasites and contribute to the incorporation of parasite production in food webs of lentic ecosystems. [ABSTRACT FROM AUTHOR]

Abstract Background Metacercariae of Diplostomum are important fish pathogens, but reliable data on their diversity in natural fish populations are virtually lacking. This study was conducted to explore the species diversity and host-parasite association patterns of Diplostomum spp. in a large riverine system in Europe, using molecular and morphological data. Methods Twenty-eight species of fish of nine families were sampled in the River Danube at Nyergesújfalu in Hungary in 2012 and Štúrovo in Slovakia in 2015. Isolates of Diplostomum spp. were characterised morphologically and molecularly. Partial sequences of the ‘barcode’ region of the cytochrome c oxidase subunit 1 (cox1) and complete sequences of the nicotinamide adenine dinucleotide dehydrogenase subunit 3 (nad3) mitochondrial genes were amplified for 76 and 30 isolates, respectively. The partial cox1 sequences were used for molecular identification of the isolates and an assessment of haplotype diversity and possible host-associated structuring of the most prevalent parasite species. New primers were designed for amplification of the mitochondrial nad3 gene. Results Only lens-infecting Diplostomum spp. were recovered in 16 fish species of five families. Barcoding of representative isolates provided molecular identification for three species/species-level genetic lineages, D. spathaceum, D. pseudospathaceum and ‘D. mergi Lineage 2’, and three single isolates potentially representing distinct species. Molecular data helped to elucidate partially the life-cycle of ‘D. mergi Lineage 2’. Many of the haplotypes of D. spathaceum (16 in total), D. pseudospathaceum (15 in total) and ‘D. mergi Lineage 2’ (7 in total) were shared by a number of fish hosts and there was no indication of genetic structuring associated with the second intermediate host. The most frequent Diplostomum spp. exhibited a low host-specificity, predominantly infecting a wide range of cyprinid fishes, but also species of distant fish families such as the Acipenseridae, Lotidae, Percidae and Siluridae. The nad3 gene exhibited distinctly higher levels of interspecific divergence in comparison with the cox1 gene. Conclusions This first exploration of the species diversity and host ranges of Diplostomum spp., in natural fish populations in the River Danube, provided novel molecular, morphological and host-use data which will advance further ecological studies on the distribution and host ranges of these important fish parasites in Europe. Our results also indicate that the nad3 gene is a good candidate marker for multi-gene approaches to systematic estimates within the genus.

Parasitic infections may affect the reproductive success of the host either directly, through behavioural modification, or indirectly, by altering their reproductive investment in response to infection. We determined the effects of infection with the eye fluke Diplostomum pseudospathaceum (Trematoda) on the reproductive traits of European bitterling (Rhodeus amarus , Cyprinidae), an intermediate fish host with a resource-based mating system. Male bitterling infected by Diplostomum exhibited a larger but less pronounced red eye spot (sexually selected signal) than control males, suggesting that infected males were less preferred by females. The frequency of female ovulation and number of offspring were comparable between the infected and the control group, although there was a 1–2 week delay in the peak of ovulation and offspring production in infected fish, which is known to coincide with higher juvenile mortality. Chronic eye fluke infection had minimal metabolic costs (measured as oxygen consumption) and, consistent with these results, reproductive activity did not differ between infected and control fish in an experimental test of intersexual selection. Overall, the impact of eye fluke infection on the reproduction of European bitterling was limited. We consider the potential effect of favourable conditions during experiments (abundant food, access to spawning substrate and lack of predators and co-infections) on experimental outcomes and recognize that the effects of chronic eye fluke infection in natural conditions might be more pronounced. [ABSTRACT FROM AUTHOR]

The life cycles of many species of Diplostomum (Digenea) have been elucidated; however, few studies include the details of egg development and hatching success. Here the eggs of 2 molecularly delineated sympatric species of Diplostomum were observed for differences in developmental parameters. These parameters included prepatent period, time required for first visible eyespot formation, hatching time, and hatching success. There was no significant difference in the mean prepatent period, total number of miracidia that developed eyespots, or number of days to hatch between the 2 species. There was a significant difference in the average time for first visible eyespots to appear and hatching success. These data highlight the need for further studies investigating sympatric species of Diplostomum to document and understand differences in life history traits during the various phases of their life cycles and their role in transmission success. [ABSTRACT FROM AUTHOR]

The development of metacercariae of Diplostomum pseudospathaceum Niewiadomska, 1984 is accompanied by profound morphological transformations often characterized as metamorphosis, which makes these metacercariae an interesting case for studying the morphogenesis of the digenean nervous system. Although the nervous system of D. pseudospathaceum is one of the most extensively studied among digeneans, there are still gaps in our knowledge regarding the distribution patterns of some neuroactive substances, most notably neuropeptides. The present study addresses these gaps by studying pre-infective metacercariae of D. pseudospathaceum using immunochemical staining and confocal microscopy to characterize the distribution patterns of serotonin (5-HT) and two major groups of flatworm neuropeptides, FMRFamide-related (FaRPs) and substance P-related (SP) peptides. The general morphology of the nervous system was examined with antibodies to alpha-tubulin. The nervous system of the metacercariae was shown to conform to the most common morphology of the nervous system in the hermaphroditic generation, with three pairs of posterior nerve cords and four pairs of anterior nerves. The patterns of FaRP- and 5-HT immunoreactivity (IR) were similar to those revealed in earlier studies by cholinesterase activity, which is in accordance with the known role of these neurotransmitters in controlling muscle activity in flatworms. The SP-IR nervous system was significantly different and consisted of mostly bipolar cells presumably acting as mechanoreceptors. The architecture of the nervous system in D. pseudospathaceum metacercariae is discussed in comparison to that in cercariae of D. pseudospathaceum and metacercariae of related digenean species. [ABSTRACT FROM AUTHOR]

Removal of parasite free-living stages by predators has previously been suggested an important factor controlling parasite transmission in aquatic habitats. Experimental studies of zooplankton predation on macroparasite larvae are, however, scarce. We tested whether trematode cercariae, which are often numerous in shallow waters, are suitable prey for syntopic zooplankters. Feeding rates and survival of freshwater cyclopoids (Megacyclops viridis , Macrocyclops distinctus), calanoids (Arctodiaptomus paulseni), cladocerans (Sida crystallina) and rotifers Asplanchna spp., fed with cercariae of Diplostomum pseudospathaceum , a common fish trematode, were studied. In additional long-term experiments, we studied reproduction of cyclopoids fed with cercariae. All tested zooplankton species consumed cercariae. The highest feeding rates were observed for cyclopoids (33 ± 12 cercariae ind−1 h−1), which actively reproduced (up to one egg clutch day−1) when fed ad libitum with cercariae. Their reproductive characteristics did not change significantly with time, indicating that cercariae supported cyclopoids' dietary needs. Mortality of rotifers and cladocerans was high (25–28% individuals) when exposed to cercariae in contrast to cyclopoids and calanoids (<2%). Cercariae clogged the filtration apparatus of cladocerans and caused internal injuries in predatory rotifers, which ingested cercariae. Observed trophic links between common freshwater zooplankters and cercariae may significantly influence food webs and parasite transmission in lentic ecosystems. [ABSTRACT FROM AUTHOR]

Preinfection by one parasitic species may facilitate or by contrast hamper the subsequent penetration and/or establishment of other parasites in a host. The biology of interacting species, timing of preinfection, and dosage of subsequent parasite exposure are likely important variables in this multiparasite dynamic infection process. The increased vulnerability to subsequent infection can be an important and often overlooked factor influencing parasite virulence. We investigated how the preinfection by freshwater pearl mussel Margaritifera margaritifera glochidia could influence the success of subsequent infection by the common trematode Diplostomum pseudospathaceum in brown trout Salmo trutta and vice versa whether preinfection by the trematode made fish more susceptible to glochidia infection. The first experiment was repeated twice with different (low and high) exposure doses to initiate the subsequent trematode infection, while in the second experiment we varied the timing of the preinfection with trematodes. The preinfection with glochidia made fish more vulnerable to subsequent infection with trematodes. Since the trematodes penetrate through the gills, we suggest that increased host vulnerability was most likely the result of increased respiration caused by the freshwater pearl mussel glochidia encysted on gills. In turn, brown trout preinfected with trematodes were more vulnerable to the subsequent glochidial infection, but only if they were preinfected shortly before the subsequent infection (20 hr). Fish preinfected with trematodes earlier (2 weeks before the subsequent infection) did not differ in their vulnerability to glochidia. These effects were observed at moderate intensities of infections similar to those that occur in nature. Our study demonstrates how the timing and sequence of exposure to parasitic species can influence infection success in a host–multiparasite system. It indicates that the negative influence of glochidia on host fitness is likely to be underestimated and that this should be taken into consideration when organizing freshwater pearl mussel restoration procedures. Freshwater pearl mussels's parasitic stage (glochidia) is usually considered to be not very harmful to their host, brown trout. However, even a small damage to fish gills caused by this parasite can make its host more vulnerable to subsequent infections. We demonstrate that the glochidia infection predispose fish to the infection by common trematode. Interestingly, fish preinfected with trematode was also more vulnerable to infection with glochidia, but only, if preinfection happened shortly before the second infection. [ABSTRACT FROM AUTHOR]

Trematode genus Diplostomum comprises of parasitic species which cause diplostomiasis, the 'white eye' disease in fish and heavy infection can result in mortality. The increasing availability of DNA sequences of accurately identified Diplostomum species on public data base presently enables the rapid identification of species from novel sequences. We report the first molecular evidence of the occurrence of D. pseudospathaceum in the United Kingdom. Two gene regions, nuclear internal transcribed spacer cluster (ITS1-5.8S-ITS2) and mitochondrial cytochrome c oxidase subunit 1 (cox1) of cercariae from infected aquatic snails, Lymnaea stagnalis collected in several locations in Southern England were sequenced. Phylogenetic analysis based on both sequenced genes revealed that the novel sequences were D. pseudospathaceum. Molecular diversity analysis of published D. pseudospathaceum cox1 sequences from seven countries in Europe and the novel sequences from the present study revealed high diversity, but low nucleotide divergence and a lack of gene differentiation between the populations. Haplotype network analysis depicted a star-like pattern and revealed a lack of geographic structure in the population. Fixation indices confirmed gene flow between populations and we suspect high levels of dispersal facilitated by highly mobile second intermediate (fish) and definitive (piscivorous birds) host may be driving gene flow between populations. Neutrality tests and mismatch distribution indicated recent population growth/expansion for D. pseudospathaceum in Europe. [ABSTRACT FROM AUTHOR]

Histologic studies of fish from Douglas Lake, Cheboygan County, Michigan, USA show that Diplostomum spp. infect the lens of spottail shiners ( Notropis hudsonius ) and common shiners ( Luxilus cornutus ). In contrast, infection was confined to the choroidal vasculature of yellow perch ( Perca flavescens ), and the morphology of the pigment epithelium and retina in regions adjacent to the metacercariae was abnormal. The difference in location of metacercariae within the host suggested that different Diplostomum species may infect shiners and perch in Douglas Lake. Species diversity was investigated by sequencing the barcode region of the cytochrome oxidase I gene of metacercariae. Four species of Diplostomum were identified, all four of which were present in shiner lenses; however, only Diplostomum baeri was present in the perch choroid. To determine whether infection of perch eyes affects the response of the retina to a light stimulus, electroretinograms (ERG) were recorded. The amplitude of the b-wave of the ERG was reduced and the b-wave latency was increased in infected perch, as compared to uninfected eyes, and the flicker-fusion frequency was also reduced. Infection of the yellow perch choroid by Diplostomum baeri , which shows strong host and tissue specificity, has an adverse effect on retinal function, lending support to the hypothesis that parasite-induced impairment of host vision may afford Diplostomum baeri the evolutionary benefit of increasing the likelihood of transmission, via host fish predation, to its definitive avian host. [ABSTRACT FROM AUTHOR]

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

Abstract: Group‐living animals can gain protection against parasitic infections through social contacts with previously infected conspecifics (social immunization). Recent research suggests that such protective effects can be induced through visual or chemical cues released by infected individuals, resulting in anticipatory immune upregulation among group members. Here, we study cue‐induced social resistance in rainbow trout Oncorhynchus mykiss exposed to a trematode parasite, the eye‐fluke Diplostomum pseudospathaceum. We established groups of naïve individuals (receivers) that were paired with previously infected individuals (donors) at different ratios of donors to receivers and at different time points since donor exposure to capture varying concentrations of the anticipated cues. While the pre‐infection elevated resistance among the donors, there was no evidence of social transfer of resistance, regardless of the ratio of donors and receivers in a group or the time since the pre‐infection. The results suggest that resistance through social signalling may be system‐specific and requires further study into the generality of the phenomenon as well as the nature of the cues involved. [ABSTRACT FROM AUTHOR]

The ability to compete with conspecifics and to adequately respond to visual stimuli of group mates are important prerequisites for profiting from group benefits such as confusion of predators and greater efficiency in acquiring food. By impairing their host's physical abilities or making the host conspicuous, even non-contagious parasites that do not pose a direct risk of infection can interfere with group dynamics. Diplostomum pseudospathaceum, a widespread parasite of freshwater fishes, infects the eye lens and can impair the vision of its fish host. To test whether this eyefluke affects competitiveness and/or shoaling behaviour in three-spined stickleback (Gasterosteus aculeatus), experimentally infected fish were kept in mixed groups comprising infected and uninfected sticklebacks under limited food availability in semi-natural outdoor tanks. Change in body mass over time was measured and sticklebacks were given the choice to shoal with uninfected conspecifics or a mixed group in binary shoal choice experiments. Surprisingly, uninfected sticklebacks spent significantly more time with mixed shoals than with uninfected shoals while this preference was not found in infected sticklebacks. Infection did not significantly affect body condition or immune parameters indicative of stress level (relative spleen mass, granulocyte-to-lymphocyte ratio). The results suggest that sticklebacks can distinguish mixed from uninfected groups, but that they are also able to tolerate potential detrimental effects of infection. Whether uninfected fish can benefit from shoaling with infected but non-contagious conspecifics remains to be tested. Although the present data do not indicate a significant effect of infection on competitiveness, this should be examined further. [ABSTRACT FROM AUTHOR]

While it generally has been accepted that evolutionary pressures may drive parasitic worms to produce many small eggs to overcome the challenges of transmission, recent studies suggest wide variability in reproductive strategies among such worms. Although egg morphometrics and numbers have been reported from many species of Diplostomum, the presence of cryptic species has resulted in uncertainty in morphometric measurements for different life history stages. Here we examine differences between egg characteristics of 2 molecularly delineated species of Diplostomum (Digenea). We investigate whether interspecific differences exist in egg morphometrics or egg number and test if there are intraspecific relationships between size of the egg and the hindbody of adult worms or between size of the egg and fecundity. Egg measurements were obtained from both those collected in feces of experimentally infected ring-billed gulls ( Larus delawarensis) and those observed in stained adult specimens of Diplostomum spp. Regardless of the source of measurement, there was a significant difference in the length of the eggs and in egg number between the 2 species, while there was no difference in the widths. Larger worms did not produce significantly larger eggs in either species. Further, egg size was not correlated with the number of eggs present in the stained specimens of either species; smaller eggs were not present in greater numbers. Egg morphometrics can assist in differentiating between these 2 species of Diplostomum. Furthermore, differences in egg sizes and number may reflect other potential differences in life history traits between the 2 species, such as miracidial longevity and infectivity and cercarial output, among others, that still need to be investigated. [ABSTRACT FROM AUTHOR]

Background: Metacercariae of Diplostomum are important fish pathogens, but reliable data on their diversity in natural fish populations are virtually lacking. This study was conducted to explore the species diversity and hostparasite association patterns of Diplostomum spp. in a large riverine system in Europe, using molecular and morphological data. Methods: Twenty-eight species of fish of nine families were sampled in the River Danube at Nyergesújfalu in Hungary in 2012 and Štúrovo in Slovakia in 2015. Isolates of Diplostomum spp. were characterised morphologically and molecularly. Partial sequences of the 'barcode' region of the cytochrome c oxidase subunit 1 (cox1) and complete sequences of the nicotinamide adenine dinucleotide dehydrogenase subunit 3 (nad3) mitochondrial genes were amplified for 76 and 30 isolates, respectively. The partial cox1 sequences were used for molecular identification of the isolates and an assessment of haplotype diversity and possible host-associated structuring of the most prevalent parasite species. New primers were designed for amplification of the mitochondrial nad3 gene. Results: Only lens-infecting Diplostomum spp. were recovered in 16 fish species of five families. Barcoding of representative isolates provided molecular identification for three species/species-level genetic lineages, D. spathaceum, D. pseudospathaceum and 'D. mergi Lineage 2' and three single isolates potentially representing distinct species. Molecular data helped to elucidate partially the life-cycle of 'D. mergi Lineage 2'. Many of the haplotypes of D. spathaceum (16 in total), D. pseudospathaceum (15 in total) and 'D. mergi Lineage 2 (7 in total) were shared by a number of fish hosts and there was no indication of genetic structuring associated with the second intermediate host. The most frequent Diplostomum spp. exhibited a low host-specificity, predominantly infecting a wide range of cyprinid fishes, but also species of distant fish families such as the Acipenseridae, Lotidae, Percidae and Siluridae. The nad3 gene exhibited distinctly higher levels of interspecific divergence in comparison with the cox1 gene. Conclusions: This first exploration of the species diversity and host ranges of Diplostomum spp., in natural fish populations in the River Danube, provided novel molecular, morphological and host-use data which will advance further ecological studies on the distribution and host ranges of these important fish parasites in Europe. Our results also indicate that the nad3 gene is a good candidate marker for multi-gene approaches to systematic estimates within the genus. [ABSTRACT FROM AUTHOR]

Members of the Diplostomoidea mature in amniotes and employ vertebrates, annelids and molluscs as second intermediate hosts. Diplostomoid life cycles generally follow a three-host pattern typical of digeneans, but novelties have arisen in some species, including obligate four-host life cycles, vertical transmission, and intracellular parasitism. In this review, we summarize the basic biology of diplostomoids with reference to molecular studies, and present challenges, gaps and areas where molecular data could address long-standing questions. Our analysis of published studies revealed that most molecular surveys find more diplostomoid species than expected, but this tendency is influenced by how much effort goes into examining specimens morphologically and the number of sequenced worms. To date, molecular work has concentrated disproportionately on intraspecific or species-level diversity of larval stages in the Diplostomidae in temperate northern regions. Although the higher taxonomy of the superfamily is recognized to be in need of revision, little molecular work has been conducted at this level. Our phylogenetic analysis indicates several families and subfamilies require reconsideration, and that larval morphotypes are more reflective of evolutionary relationships than definitive hosts. The host associations of adult diplostomoids result from host-switching processes, whereas molecular surveys indicate that larval diplostomoid metacercariae have narrow ranges of second intermediate hosts, consistent with coevolution. Molecular data are often used to link diplostomoid developmental stages, and we provide data from adult Neodiplostomum and Mesoophorodiplostomum that correct earlier misidentifications of their larval stages and propose alternatives to collecting definitive hosts. [ABSTRACT FROM AUTHOR]

Daily energy expenditure (DEE) in animals is influenced by many factors although the impact of stressors remains largely unknown. The objective of this study was to determine how multiple physiological stressors (parasite infection and contaminant exposure) and natural challenges (energy-demanding activities and weather conditions) may affect DEE in nesting ring-billed gulls ( Larus delawarensis ) exposed to high concentrations of persistent organic contaminants (POPs). Physical activity, temperature, gastrointestinal parasitic worm abundance, relative spleen mass, plasma thyroid hormone levels and liver concentrations of POPs were determined; field metabolic rate (FMR) was used as a measure of DEE. For females, FMR was best explained by the percent of time spent in nest-site attendance and exposure to temperatures below their lower critical limit (65% of variation); 32% was also explained by relative spleen mass. In males, FMR was best explained by the number of hours spent in nest site attendance and either relative spleen mass or liver concentrations of tetra-brominated diphenyl ethers (tetra-BDEs) (55% of variation). Relative spleen mass, as an important factor relating to FMR, was best explained by models with a combination of parasite abundance ( Diplostomum for females and Eucoleus for males) in a negative relationship, and liver POP concentrations ( p , p ′-DDE for females and tetra-BDEs for males) in a positive relationship (34%, 55% of variation for females and males, respectively). This study demonstrates that immune activity may be an important factor affecting energy expenditure in ring-billed gulls, and that contaminants and parasite abundance may have both a direct and/or indirect influence on FMR. [ABSTRACT FROM AUTHOR]

Larvae of the eye fluke, Diplostomum, emerge from snails and infect fish by penetrating skin or gills, then move to the lens where they may impair the vision of the fish. For the fluke to reproduce, a bird must eat the infected fish, and it has been suggested that they therefore actively manipulate the fish's behaviour to increase the risk of predation. We found that round gobies Neogobius melanostomus, a species that was recently introduced to the Kalmar Sound of the Baltic Sea, had an eye fluke prevalence of 90-100%. We investigated how the infection related to behavioural variation in round gobies. Our results showed that the more intense the parasite-induced cataract, the weaker the host's response was to simulated avian attack. The eye flukes did not impair other potentially important anti-predator behaviours, such as shelter use, boldness and the preference for shade. Our results are in accordance with the suggestion that parasites induce changes in host behaviour that will facilitate transfer to their final host. [ABSTRACT FROM AUTHOR]

Strigea brayi n.sp. was obtained from the small intestine of cattle egret (Bubulcus ibis Linn.) from Sindh, Pakistan. The trematodes were present in four hosts. This new species is characterized by a small body which includes a forebody and a hindbody. The tegment is without spines or tubercles. Tribocytic oral bilobed, oral sucker small, pharynx slightly smaller than oral sucker, caeca reaching posterior end of body, ventral sucker in posterior half of forebody, ovary roughly oval, testes in middle of hindbody. Vitellaria confined to lateral fields of hindbody reaching up to caecal end, copulatory bursa large, eggs oval and large in size. Specific differences between S. brayi n.sp. and other species of the genus include body size, egg size, body shape and position of various structures. Species comparasions are included. [ABSTRACT FROM AUTHOR]

Parasitological indexes of Austrodiplostomum compactum (Digenea, Diplostomidae) in fishes from the Paraná River, Presidente Epitácio region, state of São Paulo, Brazil, and their relationship with climate and water quality are evaluated. Fifty-one specimens of Plagioscion squamosissimus, 39 Geophagus surinamensis, 27 Hoplias malabaricus and 23 Cichla sp. were collected between June 2007 and June 2008. Water quality and rainfall indexes were measured monthly. P. squamosissimus had the highest parasite rate, with 98% total prevalence, intensity of infection varying between 1 and 255 and parasite mean abundance totaling 40.5 ± 9.9. H. malabaricus had the next parasite rate, with 66.6% total prevalence, parasite intensity between 2 and 184 and mean abundance totaling 22.4  20.9. Cichla sp. had a total prevalence of 52.1%, intensity between 1 and 21, and mean abundance 4.3 ± 2.9. Finally, G. surinamensis had a total prevalence of 46.1%, intensity between 1 and 53 and mean abundance 7.1  8.8. A survey of diplostomid infection in Brazil and the role of piscivore fish as an important host have also been discussed.Este estudo avaliou os índices parasitológicos de Austrodiplostomum compactum (Digenea, Diplostomidae) em peixes do rio Paraná, região de Presidente Epitácio, Estado de São Paulo, Brasil e sua relação com o clima e qualidade da água. Cinquenta e um espécimes de Plagioscion squamosissimus, 39 Geophagus surinamensis, 27 Hoplias malabaricus e 23 Cichla sp. foram coletados de junho de 2007 a junho de 2008. Qualidade da água e pluviosidade foram medidas mensalmente. O peixe mais parasitado foi P. squamosissimus com 98% de prevalência total, intensidade de infecção variando de 1 a 255 e abundância média de 40,5 ± 9,9. O segundo peixe mais parasitado foi H. malabaricus com 66,6% de prevalência total, intensidade de 2 a 184 e abundância média de 22,4 ± 20,9. Cichla sp. apresentou 52,1% de prevalência, intensidade de 1 a 21 e abundância média de 4,3 ± 2,9. Finalmente, G. surinamensis apresentou 46,1% de prevalência, intensidade de 1 a 53 e abundância média de 7,1 ± 8,8. Um levantamento de infecções por diplostomídeos no Brasil e o papel de peixes piscívoros como importantes hospedeiros é também discutido.

Parasitological indexes of Austrodiplostomum compactum (Digenea, Diplostomidae) in fishes from the Paraná River, Presidente Epitácio region, state of São Paulo, Brazil, and their relationship with climate and water quality are evaluated. Fifty-one specimens of Plagioscion squamosissimus, 39 Geophagus surinamensis, 27 Hoplias malabaricus and 23 Cichla sp. were collected between June 2007 and June 2008. Water quality and rainfall indexes were measured monthly. P. squamosissimus had the highest parasite rate, with 98% total prevalence, intensity of infection varying between 1 and 255 and parasite mean abundance totaling 40.5 ± 9.9. H. malabaricus had the next parasite rate, with 66.6% total prevalence, parasite intensity between 2 and 184 and mean abundance totaling 22.4 ± 20.9. Cichla sp. had a total prevalence of 52.1%, intensity between 1 and 21, and mean abundance 4.3 ± 2.9. Finally, G. surinamensis had a total prevalence of 46.1%, intensity between 1 and 53 and mean abundance 7.1 ± 8.8. A survey of diplostomid infection in Brazil and the role of piscivore fish as an important host have also been discussed.

This study aimed to assess the health status of grey mullet Mugil cephalus by means of relative condition factor under the coexisting parasite groups within seasons. Fish were captured monthly in the Lower Kızılırmak Delta in Samsun, Turkey, from December 2011 to November 2012. A total of five taxonomic groups containing 13 parasite species were constituted: Trichodina ( Trichodina puytoraci, T. lepsii), Monogenea ( Ligophorus cephali, L. mediterraneus, Gyrodactylus sp ., Microcotyle mugilis), Digenea ( Ascocotyle (Phagicola) longa, Diplostomum spathaceum, Tylodelphys clavata, Posthodiplostomum sp., Haplosplanchnus pachysomus), Acanthocephala ( Neoechinorhynchus agilis) and Copepoda ( Ergasilus lizae). Only one mullet was not parasitized and 13.8%, 36.3%, 29.2%, 16.2% and 4.5% were infected by one, two, three, four and five parasite groups respectively. Health assessment of mullets was performed by means of relative condition factor based on weight-length relationship estimated by robust regression methods. General linear modelling was employed to investigate any effect of season and infection load on this condition measure. Potential impacts of multiple parasitism on the community, which have been largely overlooked in the literature, were first visually revealed by relating the levels of co-infections (in terms of prevalence and intensity) to the seasons. Then, a correlation analysis was carried out between condition estimates and the log-ratios of relative abundances of parasite groups. The results showed that mullets suffering from Monogenea-Digenea-Acanthocephala (M-D-A) and also along with Copepoda (M-D-A-C) co-infection had weights less than expected ( K n < 1) under winter conditions. However, Trichodina involved co-infections appeared to prefer large sized hosts ( K n > 1) particularly in autumn. [ABSTRACT FROM AUTHOR]

The genetic diversity and population structure of a parasite with a complex life cycle generally depends on the dispersal by its most motile host. Given that high gene flow is assumed to hinder local adaptation, this can impose significant constraints on a parasite's potential to adapt to local environmental conditions, intermediate host populations, and ultimately to host-parasite coevolution. Here, we aimed to examine the population genetic basis for local host-parasite interactions between the eye fluke Diplostomum lineage 6, a digenean trematode with a multi-host life cycle (including a snail, a fish, and a bird) and its second intermediate host, the three-spined stickleback Gasterosteus aculeatus L. We developed the first microsatellite primers for D. lineage 6 and used them together with published stickleback markers to analyse host and parasite population structures in 19 freshwater lakes, which differ in their local environmental characteristics regarding water chemistry and Diplostomum abundance. Our analyses suggest that one parasite population successfully infects a range of genetically differentiated stickleback populations. The lack of neutral genetic differentiation in D. lineage 6, which could be attributed to the motility of the parasite's definitive host as well as its life cycle characteristics, makes local host-parasite co-adaptations seem more likely on a larger geographical scale than among the lakes of our study site. Our study provides a suitable background for future studies in this system and the first microsatellite primers for a widespread fish parasite. [ABSTRACT FROM AUTHOR]

A multi-disciplinary approach was used to evaluate the health of yellow perch ( Perca flavescens) in the St. Lawrence River (Quebec, Canada), which is experiencing a severe population decline in the downstream portion of the river. Physiological parameters, liver alterations, trace metal concentrations, parasite prevalence and abundance, stable isotope composition, and the presence/absence of the viral hemorragic septicemia virus (VHSV) were evaluated in perch collected at six sites along the river: Lake St. François, Lake St. Louis (north and south), Beauregard Island, and Lake St. Pierre (north and south). Trace metal concentrations in surface water were higher in Lake St. Louis and downstream of a major urban wastewater treatment plant discharge, indicating that this effluent was a significant source of Cu, As, Ag, Zn, and Cd. Levels of Pb in surface water exceeded thresholds for the protection of aquatic life in Lake St. Louis and were negatively correlated with body condition index in this lake. In Lake St. Pierre, Cu, Ag, and Cd bioaccumulated significantly in perch liver and lower body condition index and greater liver damage were observed compared to upstream sites. Parasite analyses indicated a higher abundance of metacercariae of the trematodes Apophallus brevis and Diplostomum spp . in Lake St. Louis, and VHSV was not detected in the liver of yellow perch for all studied sites. Overall, results suggested that the global health of yellow perch from Lake St. Pierre is lower compared to upstream studied sites, which could contribute to the documented population collapse at this site. [ABSTRACT FROM AUTHOR]

Among the ecological factors acting on the evolution and expression of animal personalities and behavioral syndromes, parasitism has received comparatively little attention. However, infection and host behavior are often strongly intertwined, because host behavior can predict the risk of infection and can also be changed by an infection. We conducted a controlled experimental infection study to explore the effects of infection on host boldness, exploration and activity using rainbow trout Oncorhynchus mykiss and its trematode parasite Diplostomum pseudospathaceum, which infects a central sensory organ of the fish, the eye lens. Contrary to our expectation, infection did not change the within-individual consistency of the personality traits or the relationships between the traits, but infected individuals were less bold than uninfected control individuals. We also found no relationship between personality in uninfected fish and resistance against parasite infection, suggesting that behaviors which increase parasite encounter do not select for improved resistance. Thus, we found only weak support for parasite-mediated effects on animal personalities. [ABSTRACT FROM AUTHOR]

Analysing spatial differences among macroparasite communities is an important tool in the study of host–parasite interactions. Identifying patterns can shed light on the underlying causes of heterogeneity of parasite distribution and help to better understand ecological constraints and the relative importance of host and parasite adaptations. In the present study, we aimed to find correlational evidence that the macroparasite distribution patterns on the Scottish island of North Uist, which had been described by de Roij and MacColl (2012) , are indicative of local processes rather than an unspecific influence of habitat characteristics. We therefore reinvestigated parasite abundances and tested for associations with habitat characteristics and host traits. Distribution patterns of the most common parasites were largely consistent with the observations of de Roij and MacColl (2012) . In accordance with the published results, we found that the most obvious abiotic habitat characteristic varying among the lakes on the island, pH, did not statistically explain parasite abundances (except for eye fluke species inside the lens). Instead, we found that genetic differentiation between host populations, measured as pairwise F ST values based on available microsatellite data, was significantly correlated with dissimilarity in parasite community composition. Our results indicate that individual lake characteristics rather than physicochemical variables shape parasite distribution on this island, making it an ideal place to study host–parasite interactions. Furthermore, additionally to geographic distance measures taken from maps, we suggest taking into account connectivity among freshwater habitats, indirectly measured via fish population structure, to analyse spatial distribution patterns. [ABSTRACT FROM AUTHOR]

Metacercariae of the Diplostomum spp., the cause of Larval Eye Diplostomiasis (LED), are located in the lenses of the eyes of fresh water fish and cause degeneration, lens opacity and blindness as disease progresses. Feed uptake is hindered in fish with failing eyesight causing loss of apetite and mortality becomes inevitable with the onset of secondary diseases. Freshwater molluscs and waterfowl have an important role in the fast spread of the disease to nearby farms. In this work, a total of 534 trout samples obtained from 24 farms located in southeastern Turkey were examined for LED. Histopathological findings were evaluated in thirty fish with lens opacity in varying degrees. Also these fish were examined in terms of bacterial agents as well. As a result of this work, Diplostomum spp. metacercariae were found to be prevalent in the lenses offish. In fish with marked lens opacity, focal to extensive subcapsular cataract was observed. Cataract lesions included abnormal proliferation of the lens epithelium at the site of capsular rupture, often followed by degeneration, fragmentation and liquefaction of adjacent cortical lens fibers. Additionally, Lactococcus garvieae was also isolated in 10 of 24 farms. [ABSTRACT FROM AUTHOR]

Non-random species associations occur in naturally sampled parasite communities. The processes resulting in predictable community structure (e.g. particular host behaviours, cross-immunity, interspecific competition) could be affected by traits that vary within a parasite species, like growth or antigenicity., We experimentally infected three-spined sticklebacks with a large tapeworm ( Schistocephalus solidus) that impacts the energy needs, foraging behaviour and immune reactions of its host. The tapeworms came from two populations, characterized by high or low growth in sticklebacks. Our goal was to evaluate how this parasite, and variation in its growth, affects the acquisition of other parasites., Fish infected with S. solidus were placed into cages in a lake to expose them to the natural parasite community. We also performed a laboratory experiment in which infected fish were exposed to a fixed dose of a common trematode parasite., In the field experiment, infection with S. solidus affected the abundance of four parasite species, relative to controls. For two of the four species, changes occurred only in fish harbouring the high-growth S. solidus; one species increased in abundance and the other decreased. These changes did not appear to be directly linked to S. solidus growth though. The parasite exhibiting elevated abundance was the same trematode used in the laboratory infection. In that experiment, we found a similar infection pattern, suggesting that S. solidus affects the physiological susceptibility of fish to this trematode., Associations between S. solidus and other parasites occur and vary in direction. However, some of these associations were contingent on the S. solidus population, suggesting that intraspecific variability can affect the assembly of parasite communities. [ABSTRACT FROM AUTHOR]

Recent confocal microscopy studies have greatly expanded our knowledge of muscle systems in cercariae and adult digeneans, but the gross anatomy and development of metacercarial musculature remain relatively little known. To further our understanding of metacercarial development, this study used phalloidin staining and confocal microscopy to examine changes in muscle architecture over the course of development from cercariae to infective metacercariae in Diplostomum pseudospathaceum Niewiadomska, 1984. The paper describes muscle development in the body wall, anterior organ (oral sucker), acetabulum, pharynx and midgut and in the musculo-glandular organs that first appear in metacercariae (lappets and holdfast). The muscle architecture of the cercarial tail is also described. The results of the study support previously reported observations that diplostomid musculature undergoes substantial transformation during metacercarial development. The most profound changes, involving extensive remodelling and replacement of cercarial muscles, were seen in the body-wall musculature and in the anterior organ as it developed into the oral sucker. Muscle systems of other cercarial organs showed more gradual changes. The adaptive importance of developmental changes in musculature is discussed. [ABSTRACT FROM PUBLISHER]

Co-infections by multiple parasite genotypes are common and have important implications for host-parasite ecology and evolution through within-host interactions. Typically, these infections take place sequentially, and therefore, the outcome of co-infection may be shaped by host immune responses triggered by previous infections. For example, in vertebrates, specific immune responses play a central role in protection against disease over the course of life, but co-infection research has mostly focused on previously uninfected individuals., Here, we investigated whether sequential exposure and activation of host resistance in rainbow trout Oncorhynchus mykiss affects infection success and interactions between co-infecting parasite genotypes of the trematode eye-fluke Diplostomum pseudospathaceum., In accordance with earlier results, we show that a simultaneous attack of two parasite genotypes facilitates parasite establishment in previously uninfected hosts. However, we find for the first time that this facilitation in co-infection is lost in hosts with prior infection., We conclude that vertebrate host infection history can affect the direction of within-host-parasite interactions. Our results may have significant implications for the evolution of co-infections and parasite transmission strategies. [ABSTRACT FROM AUTHOR]

The manipulation of host behaviour by the not-fully-developed, immature larvae of trophically transmitted parasites is attracting growing interest. A theoretical model predicts that while facilitation of host predation risk is advantageous for fully developed parasite larvae, the immature ones should make hosts less vulnerable to the predators (predation suppression hypothesis). However, there is still little evidence of such manipulation by non-infective parasite stages. We tested whether immature trematode larvae of the eye fluke, Diplostomum pseudospathaceum, a common parasite of many freshwater fishes, enhance the anti-predatory responses of their host ( Oncorhynchus mykiss). To test the predation suppression hypothesis, we experimentally infected young-of-the-year (YOY) rainbow trout and studied the influence of pre-infective metacercariae of the eye fluke on the anti-predator behaviour of the fish. Fish activity, depth preference and the ability to avoid simulated predation were evaluated in the experiments. Infected fish-harbouring a moderate number of immature metacercariae-were significantly less vulnerable to simulated predation (dip-net catch) and less active (horizontal move), but their swimming depth (vertical position) was not changed when compared with the control fish harbouring no larvae. Our findings suggest that immature larvae of D. pseudospathaceum induce changes in host behaviour that can protect them from predation, thereby supporting the predation suppression hypothesis and indicating that manipulations caused by immature parasites may play an important role in modulating predator-prey interactions. [ABSTRACT FROM AUTHOR]

This study provides information on seasonal occurrence of developmental stages of endoparasites infecting three cyprinids in the Nwanedi-Luphephe dams, Limpopo River System. Labeobarbus marequensis (Smith, 1841), Barbus trimaculatus Peters, 1852 and Barbus radiatus Peters, 1853 were investigated seasonally from January 2008 to October 2008. The following larvae of metazoan parasites were collected: Diplostomum sp. from the eyes of L. marequensis and B. trimaculatus; Ornithodiplostomum sp. from the gills of B. trimaculatus; Posthodiplostomum sp. from muscle, skin and fins of B. trimaculatus and B. radiatus; third-stage Contracaecum larvae (L3) from the mesentery fats and on the liver lobes of L. marequensis and B. trimaculatus and gryporynchid cestode larvae from the outer intestinal wall of B. radiatus. All the flukes encountered were metacercariae. Diplostomum sp. and Contracaecum sp. dominated the parasite communities. Their prevalence exhibited seasonal fluctuations with maxima in summer. Factors likely to influence fish infection such as the body size of fish and their condition factors were also briefly considered in this study. [ABSTRACT FROM AUTHOR]

Eye flukes of the genus Diplostomum were recorded with a prevalence of 7.4% and a mean intensity of 11.9 (range 1-75) parasites per fish in eye lenses of a total of 188 Atlantic cod, Gadus morhua, sampled in the Southeastern Baltic Sea from March 2013 to February 2014. A slight decrease of infection level, among the fish with body length ranging from 30 to 89.5 cm, was found when data were compared to a corresponding survey in the 1980s. Due to imprecise species identification of eye flukes based on morphometric analyses we present, as a baseline for further studies, rDNA sequences from a subsample of 19 eye flukes based on sequencing of a part of 18S, ITS-1, 5.8S, ITS-2 and part of 28S. We discuss the use of eye fluke recordings in Baltic cod as an environmental indicator due to the dependence of the parasite´s life cycle on biotic (occurrence of snail and bird hosts) and abiotic (temperature and salinity) parameters. [ABSTRACT FROM AUTHOR]

Background: The genus Diplostomum (Platyhelminthes: Trematoda: Diplostomidae) is a diverse group of freshwater parasites with complex life-cycles and global distribution. The larval stages are important pathogens causing eye fluke disease implicated in substantial impacts on natural fish populations and losses in aquaculture. However, the problematic species delimitation and difficulties in the identification of larval stages hamper the assessment of the distributional and host ranges of Diplostomum spp. and their transmission ecology. Methods: Total genomic DNA was isolated from adult worms and shotgun sequenced using Illumina MiSeq technology. Mitochondrial (mt) genomes and nuclear ribosomal RNA (rRNA) operons were assembled using established bioinformatic tools and fully annotated. Mt protein-coding genes and nuclear rRNA genes were subjected to phylogenetic analysis by maximum likelihood and the resulting topologies compared. Results: We characterised novel complete mt genomes and nuclear rRNA operons of two closely related species, Diplostomum spathaceum and D. pseudospathaceum. Comparative mt genome assessment revealed that the cox1 gene and its 'barcode' region used for molecular identification are the most conserved regions; instead, nad4 and nad5 genes were identified as most promising molecular diagnostic markers. Using the novel data, we provide the first genome wide estimation of the phylogenetic relationships of the order Diplostomida, one of the two fundamental lineages of the Digenea. Analyses of the mitogenomic data invariably recovered the Diplostomidae as a sister lineage of the order Plagiorchiida rather than as a basal lineage of the Diplostomida as inferred in rDNA phylogenies; this was concordant with the mt gene order of Diplostomum spp. exhibiting closer match to the conserved gene order of the Plagiorchiida. Conclusions: Complete sequences of the mt genome and rRNA operon of two species of Diplostomum provide a valuable resource for novel genetic markers for species delineation and large-scale molecular epidemiology and disease ecology studies based on the most accessible life-cycle stages of eye flukes. [ABSTRACT FROM AUTHOR]

Background: Recent molecular studies have discovered substantial unrecognised diversity within the genus Diplostomum in fish populations in Europe and North America including three species complexes. However, data from the first intermediate host populations are virtually lacking. This study addresses the application of an integrative taxonomic approach to the cryptic species diversity of Diplostomum spp. in natural lymnaeid snail populations in Europe with a focus on the 'D. mergi' species complex. Methods: Totals of 1,909 Radix auricularia, 349 Radix peregra, 668 Stagnicola palustris and 245 Lymnaea stagnalis were sampled at five reservoirs of the Ruhr river system in Germany and screened for infections with Diplostomum spp. Cercariae were examined and identified alive, fixed and under scanning electron microscopy. Sequences from the barcode region of the cytochrome c oxidase subunit 1 (cox1) mitochondrial gene and from the internal transcribed spacer cluster (ITS1-5.8S-ITS2) of the rRNA gene were amplified for 51 and 13 isolates, respectively. Results: Detailed morphological and molecular analyses provided evidence for three named species (Diplostomum spathaceum, D. pseudospathaceum and D. parviventosum), and a further four species-level lineages ('D. mergi Lineages 2-4' and 'Diplostomum sp. Clade Q' in the lymnaeid snail populations from the Ruhr river basin. The paper provides the first descriptions of molecularly identified cercariae of D. spathaceum and of the cercariae of D. parviventosum, three lineages of the 'D. mergi' species complex and of 'Diplostomum sp. Clade Q'. Conclusion: The integration of molecular and morphological evidence for Diplostomum spp. achieved in this study will serve as a baseline for species identification of these important parasites of snail and fish populations and thus advance further studies on the distribution of Diplostomum spp. in Europe. [ABSTRACT FROM AUTHOR]

Fish rely upon vision as a dominant sensory system for foraging, predator avoidance, and mate selection. Damage to the visual system, in particular to the neural retina of the eye, has been demonstrated to result in a regenerative response in captive fish that serve as model organisms (e.g. zebrafish), and this response restores some visual function. The purpose of the present study is to determine whether damage to the visual system that occurs in wild populations of fish also results in a regenerative response, offering a potentially ecologically relevant model of retinal regeneration. Adult threespine stickleback were collected from several water bodies of Iceland, and cryosectioned eye tissues were processed for hematoxylin and eosin staining or for indirect immunofluorescence using cell-specific markers. In many of the samples, eye flukes (metacercariae of Diplostomum spp) were present, frequently between the neural retina and retinal pigmented epithelium (RPE). Damage to the retina and to the RPE was evident in eyes containing flukes, and RPE fragments were observed within fluke bodies, suggesting they had consumed this eye tissue. Expression of a cell proliferation marker was also observed in both retina and RPE, consistent with a proliferative response to the damage. Interestingly, some regions of infected retina displayed "laminar fusions," in which neuronal cell bodies were misplaced within the major synaptic layer of the retina. These laminar fusions are also frequently found in regenerated zebrafish retina following non-parasitic (experimental) forms of retinal damage. The stickleback retina may therefore respond to fluke-mediated damage by engaging in retinal regeneration. • Eye fluke larvae infect eyes of wild threespine stickleback fish. • Eye flukes invade the subretinal space, causing retinal detachments. • Eye flukes damage retina/RPE, possibly in part by consuming them. • Infected stickleback retinas respond by local increases in cell proliferation. • Infected stickleback retinas show histological features of regenerated retinas. [ABSTRACT FROM AUTHOR]

Metacercariae of Diplostomum petromyzifluviatilis (Digenea, Diplostomidae) from the brain of European river lamprey Lampetra fluviatilis from the Baltic Sea basin and Arctic lamprey Lethenteron camtschaticum from the White Sea basin were studied with the use of genetic and morphological methods. Phylogenetic analysis based on cox 1 marker showed that the parasites of both lamprey species were conspecific with Diplostomum sp. Lineage 4 of Blasco-Costa et al. (2014). The name Diplostomum petromyzifluviatilis Müller (Diesing, 1850) has historical precedence as a species described from the brain of lampreys and should be used in genus nomenclature. There were no morphological qualitative differences between the metacercariae from the two lamprey species but those from L. fluviatilis were larger than those from L. camtschaticum. We expanded the data on the second intermediate hosts and the localization of D. petromyzifluviatilis , showing that its metacercariae occur not only in the brain of lampreys but also in the brain and the retina of three-spined stickleback Gasterosteus aculeatus and the vitreous humour of the perch Perca fluviatilis across the European part of the Palearctic. [Display omitted] • Diplostomum petromyzifluviatilis molecularly corresponds to Diplostomum sp. Lineage 4 of Blasco-Costa et al. (2014). • D. petromyzifluviatilis metacercariae parasitize freshwater lampreys, Gasterosteus aculeatus and Perca fluviatilis. • D. petromyzifluviatilis metacercariae occur not only in the brain but also in retina and vitreous humour of fish hosts. [ABSTRACT FROM AUTHOR]

Host–parasite systems at high latitudes are promising model systems for detecting and predicting the impact of accelerated environmental change. A major challenge is the lack of baselines for the diversity and distribution of parasites in Arctic wildlife, especially in the freshwater environment. Here we present the first known estimates of the species diversity and host associations of Diplostomum spp. in sub-Arctic freshwater ecosystems of the Palaearctic. Our analyses integrating different analytical approaches, phylogenies based on mitochondrial and nuclear DNA, estimates of genetic divergence, character-based barcoding, morphological examination, precise detection of microhabitat specialisation and host use, led to the discovery of one described and five putative new species that complete their life-cycles within a fairly narrow geographic area in Iceland. This increases the species richness of Diplostomum in Iceland by 200% and raises the number of molecularly characterised species from the Palaearctic to 17 species. Our results suggest that the diversity of Diplostomum spp. is underestimated globally in the high latitude ecosystems and call for a cautionary approach to pathogen identification in developing the much needed baselines of pathogen diversity that may help detect effects of climate change in the freshwater environment of the sub-Arctic. [ABSTRACT FROM AUTHOR]

The study aimed to describe morphological and morphometric characteristics of species representing the genera Diplostomum Nordmann, 1832 and Ornithodiplostomum Dubois, 1936, originating from naturally infected birds in the Czech Republic and in Poland, and to compare their species richness and the intensity of infection in their avian hosts. Diplostomum mergi Dubois, 1932, D. parviventosum Dubois, 1932, D. phoxini (Faust, 1918), D. pusillum (Dubois, 1928), and Ornithodiplostomum scardinii (Schulman, 1952) were found in the gossander ( Mergus merganser). D. parviventosum was found in the velvet scoter ( Melanitta fusca). D. pungitii Shigin, 1965 was found in the tufted duck ( Aythya fuligula), common eider ( Somateria mollissima), common goldeneye ( Bucephala clangula), and in the long-tailed duck ( Clangula hyemalis). D. spathaceum (Rudolphi, 1819) was found in the mallard ( Anas platyrhynchos). Morphology and morphometry of those Diplostomum species from the Czech Republic and from Poland were not analyzed before. The morphological and morphometric description of the adult form of O. scardinii presented in this study has been the first such description of a specimen obtained from a naturally infected bird. The highest intensity of infection was observed in the gossander ( D. pusillum and D. mergi). Study results provided new data on the occurrence of the Diplostomum and O. scardinii trematodes in the Czech Republic and in Poland. [ABSTRACT FROM AUTHOR]