Search

This study was conducted to examine the pathogenesis of gill degeneration in the Korean rockfish Sebastes schlegelii, infested with the monogenean ectoparasite, Microcotyle sebastis. We collected 30 Korean rockfish from a fish farm in Tongyeong-si, Gyeongsangnam-do, and examined them with light microscopy, scanning electron microscopy (SEM), and histopathology, in March 2018. The monogenean trematode, M. sebastis, was detected in 27 Korean rockfish (90%), with the intensity of infection being 31.7 per fish. The characteristic surface ultrastructures such as tegument with transverse striations, genital atrium, genital pore, and opisthaptor with numerous clamps were observed. The worms were firmly attached to the gill lamellae using clamps from the opisthaptor, causing gill damage and degeneration. The distal part of the lamellae was ruptured by the sclerites of the clamps. The histopathological examination revealed epithelial hypertrophy, hyperplasia, and occasionally fusion of the lamellae. These ultrastructural and histopathological findings provide some understanding of the pathogenesis of gill degeneration in the Korean rockfish infested with M. sebastis.

The mechanisms of action of silver nanoparticles (AgNPs) in monogenean parasites of the genus Cichlidogyrus were investigated through a microarray hybridization approach using genomic information from the nematode Caenorhabditis elegans . The effects of two concentrations of AgNPs were explored, low (6 µg/L Ag) and high (36 µg/L Ag). Microarray analysis revealed that both concentrations of AgNPs activated similar biological processes, although by different mechanisms. Expression profiles included genes involved in detoxification, neurotoxicity, modulation of cell signaling, reproduction, embryonic development, and tegument organization as the main biological processes dysregulated by AgNPs. Two important processes (DNA damage and cell death) were mostly activated in parasites exposed to the lower concentration of AgNPs. To our knowledge, this is the first study providing information on the sub-cellular and molecular effects of exposure to AgNPs in metazoan parasites of fish.

Heterobothrium okamotoi, a monogenean gill parasite, exhibits high host specificity for the tiger puffer, Takifugu rubripes, and it has been experimentally verified that the parasite cannot colonize either closely related species such as the grass puffer Takifugu niphobles or distantly related fish such as the red seabream Pagrus major. Previously, we demonstrated in T. rubripes that immunoglobulin M (IgM) with d-mannose affinity induced deciliation of the oncomiracidia, the first step of parasitism, indicating that the parasite utilizes the molecule as a receptor for infection. In the present study, we purified mannose-specific IgM from 2 nonhost species, T. niphobles and P. major, by affinity and gel-filtration chromatography techniques and compared their deciliation-inducing activity against H. okamotoi oncomiracidia. The IgM of the former showed activity, whereas the latter had no effect, suggesting that in addition to d-mannose-binding ability, the crystallizable fragment domain of IgM, which is not part of the antigen-binding domain, plays an important role in host recognition by the oncomiracidia, such as direct binding to the parasites. It also suggests that the host specificity of H. okamotoi is relatively low upon initial recognition, and the specificity is established by exclusion in nonhosts during a later stage., (© American Society of Parasitologists 2020.)

Background: Monogenean flatworms are the main fish ectoparasites inflicting serious economic losses in aquaculture. The polyopisthocotylean Sparicotyle chrysophrii parasitizes the gills of gilthead sea bream (GSB, Sparus aurata) causing anaemia, lamellae fusion and sloughing of epithelial cells, with the consequent hypoxia, emaciation, lethargy and mortality. Currently no preventive or curative measures against this disease exist and therefore information on the host-parasite interaction is crucial to find mitigation solutions for sparicotylosis. The knowledge about gene regulation in monogenean-host models mostly comes from freshwater monopysthocotyleans and almost nothing is known about polyopisthocotyleans. The current study aims to decipher the host response at local (gills) and systemic (spleen, liver) levels in farmed GSB with a mild natural S. chrysophrii infection by transcriptomic analysis., Results: Using Illumina RNA sequencing and transcriptomic analysis, a total of 2581 differentially expressed transcripts were identified in infected fish when compared to uninfected controls. Gill tissues in contact with the parasite (P gills) displayed regulation of fewer genes (700) than gill portions not in contact with the parasite (NP gills) (1235), most likely due to a local silencing effect of the parasite. The systemic reaction in the spleen was much higher than that at the parasite attachment site (local) (1240), and higher than in liver (334). NP gills displayed a strong enrichment of genes mainly related to immune response and apoptosis. Processes such as apoptosis, inflammation and cell proliferation dominated gills, whereas inhibition of apoptosis, autophagy, platelet activation, signalling and aggregation, and inflammasome were observed in spleen. Proteasome markers were increased in all tissues, whereas hypoxia-related genes were down-regulated in gills and spleen., Conclusions: Contrasting forces seem to be acting at local and systemic levels. The splenic down-regulation could be part of a hypometabolic response, to counteract the hypoxia induced by the parasite damage to the gills and to concentrate the energy on defence and repair responses. Alternatively, it can be also interpreted as the often observed action of helminths to modify host immunity in its own interest. These results provide the first toolkit for future studies towards understanding and management of this parasitosis.

Planarian flatworms possess pluripotent stem cells (neoblasts) that are able to differentiate into all cell types that constitute the adult body plan. Consequently, planarians possess remarkable regenerative capabilities. Transcriptomic studies have revealed that gene expression is coordinated to maintain neoblast pluripotency, and ensure correct lineage specification during differentiation. But as yet they have not revealed how this regulation of expression is controlled. In this review, we propose that planarians represent a unique and effective system to study the epigenetic regulation of these processes in an in vivo context. We consolidate evidence suggesting that although DNA methylation is likely present in some flatworm lineages, it does not regulate neoblast function in Schmidtea mediterranea. A number of phenotypic studies have documented the role of histone modification and chromatin remodelling complexes in regulating distinct neoblast processes, and we focus on four important examples of planarian epigenetic regulators: Nucleosome Remodeling Deacetylase (NuRD) complex, Polycomb Repressive Complex (PRC), the SET1/MLL methyltransferases, and the nuclear PIWI/piRNA complex. Given the recent advent of ChIP-seq in planarians, we propose future avenues of research that will identify the genomic targets of these complexes allowing for a clearer picture of how neoblast processes are coordinated at the epigenetic level. These insights into neoblast biology may be directly relevant to mammalian stem cells and disease. The unique biology of planarians will also allow us to investigate how extracellular signals feed into epigenetic regulatory networks to govern concerted neoblast responses during regenerative polarity, tissue patterning, and remodelling., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Diplozoidae (Monogenea) are blood-feeding freshwater fish gill ectoparasites with extraordinary body architecture and a unique sexual behaviour in which two larval worms fuse and transform into one functioning individual. In this study, we describe the body organisation of Paradiplozoon homoion adult stage using a combined approach of confocal laser scanning and electron microscopy, with emphasis on the forebody and hindbody. Special attention is given to structures involved in functional adaptation to ectoparasitism, i.e. host searching, attachment and feeding/metabolism. Our observations indicate clear adaptations for blood sucking, with a well-innervated mouth opening surrounded by sensory structures, prominent muscular buccal suckers and a pharynx. The buccal cavity surface is covered with numerous tegumentary digitations that increase the area in contact with host tissue and, subsequently, with its blood. The buccal suckers and the well-innervated haptor (with sclerotised clamps controlled by noticeable musculature) cooperate in attaching to and moving over the host. Putative gland cells accumulate in the region of apical circular structures, pharynx area and in the haptor middle region. Paired club-shaped sacs lying laterally to the pharynx might serve as secretory reservoirs. Furthermore, we were able to visualise the body wall musculature, including peripheral innervation, the distribution of uniciliated sensory structures essential for reception of external environmental information, and flame cells involved in excretion. Our results confirm in detail that P. homoion displays a range of sophisticated adaptations to an ectoparasitic life style, characteristic for diplozoid monogeneans.

Monogenoidea pathogenic activity can elicit various histological responses in fish. Species of Ligophorus are specific parasites of mullets, and its relationship with host fish may result in a moderate pathogenic action. In order to ascertain this relationship, estuarine mullets (Mugil liza) were collected in an estuary, reared in laboratory, for three weeks, and forwarded for histological and parasitological analyses. Ligophorus uruguayense (Monogenoidea) infestation in the gills of the mullets was identified. The severe infestation by only one species of Monogenoidea may result from the specificity of these parasites to mullets. Mullets submitted to histological analysis exhibited respiratory epithelium detachment; mild, moderate and severe hyperplasia of the respiratory epithelium; atrophy; and telangiectasia of the gills. This is the first study reporting that mullets highly infested by Monogenoidea can show mild (100%) to severe (20%) gill changes with a distinct frequency of occurrence. Because of the high prevalence of mild alterations observed, it is possible to accept that L. uruguayense is moderately pathogenic to M. liza, even during high prevalence and intensity of infestation, as a result of its specificity.

The Atlantic salmon, Salmo salar L., in the Tornio River in the Northern Baltic Sea basin accommodates a monogenean ectoparasite, Gyrodactylus salaris. The aim of the study was to understand the population structure of apparently co-adapted host-parasite system: no parasite-associated mortality has been reported. The parasite burden among salmon juveniles (parr) was monitored along 460km of the river in 2000-2009. Among the parr, 33.0% were infected (n fish =1913). The genetic structure of the parasite population was studied by sequencing an anonymous nuclear DNA marker (ADNAM1, three main genotypes) and mitochondrial CO1 (three clades, six haplotypes). During the ten years, the parasite population was strongly and stably genetically differentiated among up- and downstream nurseries (n ADNAM1 =411, F ST =0.579; n CO1 =443, F ST =0.534). Infection prevalence among the smolts migrating to sea was higher than in the sedentary parr populations (82.2%, n fish =129). The spatial differentiation observed among the sedentary juveniles was reflected temporally in the smolt run: parasite genotypes dominating the upper part of the river arrived later than downstream dwellers (medians June 4 and June 2) to the trap 7km from the river mouth. The nuclear and mitochondrial markers were in stable disequilibrium which was not relaxed in the contact zone or among the smolts where the parasite clones often met on individual fish. Only five parasite specimens on smolts (n worms =217) were putative recent sexual recombinants. The contribution of extant salmon hatcheries into the infection was negligible. The host salmon population in Tornio River is known to show significant spatial differentiation (F ST =0.022). The stable spatial genetic structure of the parasite against the high physical mobility suggested a possibility of local co-adaptation of the host-parasite subpopulations., (Copyright © 2016. Published by Elsevier B.V.)

We examined the global mitochondrial phylogeography of Gyrodactylus arcuatus, a flatworm ectoparasite of three-spined stickleback Gasterosteus aculeatus. In accordance with the suggested high divergence rate of 13%/million years, the genetic variation of the parasite was high: haplotype diversity h=0.985 and nucleotide diversity π=0.0161. The differentiation among the parasite populations was substantial (Φst=0.759), with two main allopatric clades (here termed Euro and North) accounting for 54% of the total genetic variation. The diversity center of the Euro clade was in the Baltic Sea, while the North clade was spread across the Barents and White Seas. A single haplotype within the North clade was found in the western and eastern Pacific Ocean. Divergence of main clades was estimated to be circa 200 thousand years ago. Each main clade was further divided into six distinct subclades, estimated to have diverged in isolation since 135 thousand years ago. This second division corresponds approximately to the Eemian interglacial predating the last glacial maximum. A demographic expansion of the subclades is associated with colonisation of northern Europe since the last glacial maximum, circa 15-40 thousand years ago. The parasite phylogeny is most likely explained by sequential isolated bottlenecks and expansions in numerous allopatric refugia. The postglacial intermingling and high variation in the marine parasite populations, separately in the Baltic and Barents Seas, suggest low competition of divergent parasite matrilines, coupled with a large population size and high rate of dispersal of hosts. The genetic contribution of the assumed refugial fish populations maintaining the parasite during the last glacial maximum was not detected among the marine sticklebacks, which perhaps were infected after range expansion., (Copyright © 2016 Australian Society for Parasitology. All rights reserved.)

Inbreeding can threaten population persistence by reducing disease resistance through the accelerated loss of gene diversity (i.e. heterozygosity). Such inbreeding depression can affect many different fitness-related traits, including survival, reproductive success, and parasite susceptibility. Empirically quantifying the effects of inbreeding on parasite resistance is therefore important for ex-situ conservation of vertebrates. The present study evaluates the disease susceptibility of individuals bred under three different breeding regimes (inbred, crossed with full siblings; control, randomly crossed mating; and fully outbred). Specifically, we examined the relationship between inbreeding coefficient (F-coefficient) and susceptibility to Gyrodactylus turnbulli infection in a live bearing vertebrate, the guppy Poecilia reticulata. Host-breeding regime significantly affected the trajectories of parasite population growth on individual fish. Inbred fish showed significantly higher mean parasite intensity than fish from the control and outbred breeding regimes, and in addition, inbred fish were slower in purging their gyrodactylid infections. We discuss the role of inbreeding on the various arms of the immune system, and argue that the increased disease susceptibility of inbred individuals could contribute to the extinction vortex. This is one of the first studies to quantify the effects of inbreeding and breeding regime on disease susceptibility in a captive bred vertebrate of wild origin, and it highlights the risks faced by small (captive-bred) populations when exposed to their native parasites., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)

Mitochondrial genomes (mitogenomes) are useful and relatively accessible sources of molecular data to explore and understand the evolutionary history and relationships of eukaryotic organisms across diverse taxonomic levels. The availability of complete mitogenomes from Platyhelminthes is limited; of the 40 or so published most are from parasitic flatworms (Neodermata). Here, we present the mitogenomes of two free-living flatworms (Tricladida): the complete genome of the freshwater species Crenobia alpina (Planariidae) and a nearly complete genome of the land planarian Obama sp. (Geoplanidae). Moreover, we have reanotated the published mitogenome of the species Dugesia japonica (Dugesiidae). This contribution almost doubles the total number of mtDNAs published for Tricladida, a species-rich group including model organisms and economically important invasive species. We took the opportunity to conduct comparative mitogenomic analyses between available free-living and selected parasitic flatworms in order to gain insights into the putative effect of life cycle on nucleotide composition through mutation and natural selection. Unexpectedly, we did not find any molecular hallmark of a selective relaxation in mitogenomes of parasitic flatworms; on the contrary, three out of the four studied free-living triclad mitogenomes exhibit higher A+T content and selective relaxation levels. Additionally, we provide new and valuable molecular data to develop markers for future phylogenetic studies on planariids and geoplanids.

Aquaculture is the fastest-growing segment of food production and is expected to supply a growing portion of animal protein for consumption by humans. Because industrial aquaculture developed only recently compared to industrial agriculture, its development occurred within the context of a growing environmental awareness and acknowledgment of environmental issues associated with industrial farming. As such, parasites and diseases have become central criticisms of commercial aquaculture. This focus on parasites and diseases, however, has created a nexus of opportunities for research that has facilitated considerable scientific advances in the fields of parasitology and aquaculture. This paper reviews Myxobolus cerebralis , Lepeophtheirus salmonis , white spot syndrome virus, and assorted flatworms as select marquee aquaculture pathogens, summarizes the status of the diseases caused by each and their impacts on aquaculture, and highlights some of the significant contributions these pathogens have made to the science of parasitology and aquaculture.

Riverine fish are subjected to heterogeneous flow velocities and turbulence and may use this to their advantage by selecting regions that balance energy expenditure for station holding while maximizing energy gain through feeding opportunities. This study investigated microhabitat selection by guppies Poecilia reticulata in terms of flow characteristics generated by hemisphere boulders in an open channel flume. Velocity and turbulence influenced the variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the areas of high-velocity and low-turbulence regions beside the boulders, whereas smaller guppies frequented the low-velocity and high-turbulence regions directly behind the boulders. Male guppies selected the regions of low velocity, indicating possible reduced swimming ability owing to hydrodynamic drag imposed by their fins. With increasing Gyrodactylus turnbulli burden, fish spent more time in regions with moderate velocity and lowest turbulent kinetic energy which were the most spatially and temporally homogeneous in terms of velocity and turbulence. These findings highlight the importance of heterogeneous flow conditions in river channel design owing to the behavioural variability within a species in response to velocity and turbulence.

As part of a biological inventory of the Rio Lacantún basin in the Biosphere Reserve of Montes Azules from Chiapas State (southeastern, Mexico), the following monogenoid ectoparasites infecting the external surface of the anal opening and the gill lamellae of the freshwater fish Astyanax aeneus (Characidae) in ten streams were found: Cacatuocotyle chajuli sp. nov. (anus), Cacatuocotyle exiguum sp. nov., and Cacatuocotyle sp. (gill lamellae). C. chajuli is differentiated from its single congener, Cacatuocotyle paranaensis (Boeger et al. Syst Parasitol 36:75-78, 1997), from the gills of Characidium lanei (Characidae) from Paraná Brazil, in having a noticeably V-shaped haptoral bar and larger hooks and anchors. C. exiguum differs from these two latter species in the size of its anchors. Illustrations and data on morphological and biometric variability of individual specimens of C. chajuli and C. exiguum from different streams are provided. The present data support the statement about three species of Astyanax, which harbor the richest monogenoidean diversity in the Neotropics with a total of 18 species reported up to now. Occurrences of species of Cacatuocotyle on different sites of infection on three distant host species [including a Neotropical cichlid (Cichlidae) species] suggest that these monogenoideans switching to new hosts can result in the availability of potential hosts within the same habitat instead of showing signs of preferential switching between closely related hosts or on their respective microhabitats.

Theory predicts that sexual reproduction promotes disease invasion by increasing the evolutionary potential of the parasite, whereas asexual reproduction tends to enhance establishment success and population growth rate. Gyrodactylid monogeneans are ubiquitous ectoparasites of teleost fish, and the evolutionary success of the specious Gyrodactylus genus is thought to be partly due to their use of various modes of reproduction. Gyrodactylus turnbulli is a natural parasite of the guppy (Poecilia reticulata), a small, tropical fish used as a model for behavioural, ecological and evolutionary studies. Using experimental infections and a recently developed microsatellite marker, we conclusively show that monogenean parasites reproduce sexually. Conservatively, we estimate that sexual recombination occurs and that between 3.7-10.9% of the parasites in our experimental crosses are hybrid genotypes with ancestors from different laboratory strains of G. turnbulli. We also provide evidence of hybrid vigour and/or inter-strain competition, which appeared to lead to a higher maximum parasite load in mixed infections. Finally, we demonstrate inbreeding avoidance for the first time in platyhelminths which may influence the distribution of parasites within a host and their subsequent exposure to the host's localized immune response. Combined reproductive modes and inbreeding avoidance may explain the extreme evolutionary diversification success of parasites such as Gyrodactylus, where host-parasite coevolution is punctuated by relatively frequent host switching.

One of the major threats to biodiversity involves biological invasions with direct consequences on the stability of ecosystems. In this context, the role of parasites is not negligible as it may enhance the success of invaders. The red-eared slider, Trachemys scripta elegans, has been globally considered among the worst invasive species. Since its introduction through the pet trade, T. s. elegans is now widespread and represents a threat for indigenous species. Because T. s. elegans coexists with Emys orbicularis and Mauremys leprosa in Europe, it has been suggested it may compete with the native turtle species and transmit pathogens. We examined parasite transfer from American captive to the two native species that co-exist in artificial pools of a Turtle Farm in France. As model parasite species we used platyhelminth worms of the family Polystomatidae (Monogenea) because polystomes have been described from American turtles in their native range. Phylogenetic relationships among polystomes parasitizing chelonian host species that are geographically widespread show patterns of diversification more complex than expected. Using DNA barcoding to identify species from adult and/or polystome eggs, several cases of host switching from exotic to indigenous individuals were illustrated, corroborating that parasite transmission is important when considering the pet trade and in reintroduction programmes to reinforce wild populations of indigenous species.

Parasites with high host specificity maximally depend on their hosts, which should increase the likelihood of coevolution. However, coevolution requires reciprocal selection exerted by the host and the parasite, and thus a considerable level of parasite virulence. In species of the monogenean ectoparasite genus Gyrodactylus consecutive generations are confronted with a single host, which may constrain the evolution of virulence. Transmission, which is often important in the ecology of Gyrodactylus species, may have the opposite effect, but may also lead to the avoidance of coevolutionary arms races. We investigated the potential outcome of coevolution between Gyrodactylus gasterostei Gläser, 1974 and its host, the three-spined stickleback (Gasterosteus aculeatus L.) by determining the strength of genotype by genotype (GxG) interactions on two levels: within and between sympatric and allopatric host populations. To do so, we compared the parasite's infection dynamics on laboratory-reared sympatric (Belgian) and allopatric (German) hosts. We found that a parasite line successfully infected a range of sympatric host genotypes (represented by families), while it failed to establish on allopatric hosts. Phylogeographic studies suggest that neutral genetic divergence between the host populations cannot explain this dramatic difference. Provided that this result can be generalised towards other parasite lines, we conclude that coevolution in this host-parasite system is more likely to lead to local adaptation on the population level than to GxG interactions within populations.

Background: Infection incidence increases with the average number of contacts between susceptible and infected individuals. Contact rates are normally assumed to increase linearly with host density. However, social species seek out each other at low density and saturate their contact rates at high densities. Although predicting epidemic behaviour requires knowing how contact rates scale with host density, few empirical studies have investigated the effect of host density. Also, most theory assumes each host has an equal probability of transmitting parasites, even though individual parasite load and infection duration can vary. To our knowledge, the relative importance of characteristics of the primary infected host vs. the susceptible population has never been tested experimentally., Methodology/principal Findings: Here, we examine epidemics using a common ectoparasite, Gyrodactylus turnbulli infecting its guppy host (Poecilia reticulata). Hosts were maintained at different densities (3, 6, 12 and 24 fish in 40 L aquaria), and we monitored gyrodactylids both at a population and individual host level. Although parasite population size increased with host density, the probability of an epidemic did not. Epidemics were more likely when the primary infected fish had a high mean intensity and duration of infection. Epidemics only occurred if the primary infected host experienced more than 23 worm days. Female guppies contracted infections sooner than males, probably because females have a higher propensity for shoaling., Conclusions/significance: These findings suggest that in social hosts like guppies, the frequency of social contact largely governs disease epidemics independent of host density.

Platydemus manokwari is a broadly distributed invasive terrestrial flatworm that preys heavily on land snails and has been credited with the demise of numerous threatened island faunas. We examined whether P. manokwari tracks the mucus trails of land snail prey, investigated its ability to determine trail direction, and evaluated prey preference among various land snail species. A plastic treatment plate with the mucus trail of a single species and a control plate without the trail were placed side by side at the exit of cages housing P. manokwari. All trials were then videotaped overnight. The flatworms moved along plates with mucus trails, but did not respond to plates without trails, blank control (distilled water), or with conspecific flatworm trails. When presented at the midpoint of a snail mucus trail, the flatworms followed the trail in a random direction. The flatworms showed a preference when choosing between two plates, each with a mucus trail of different land snail species. Our results suggest that P. manokwari follows snail mucus trails based on chemical cues to increase the chance of encountering prey; however, trail-tracking behavior showed no directionality.

Summary: Macroparasites are generally aggregated within their hosts with infection and aggregation levels resulting from a continuous arms race between maintaining high mating probability and host mortality low for which host and environmentally related factors contribute to some extent. Here, infection and aggregation patterns of the macroendoparasites infecting the flatfish Citharus linguatula, Arnoglossus laterna, Lepidorhombus boscii, Scophthalmus rhombus and Platichthys flesus in 3 areas along the Portuguese coast were analysed. Of the 21 macroendoparasite species found only 1 infected all hosts and most were host or area exclusive. For each host-parasite system, values of the indices varied between areas and macroendoparasites were not always aggregated; in fact, some macroendoparasites were generally uniformly distributed, which can be related to specific density-dependent regulation mechanisms. No general pattern was found for infection or aggregation levels of the 3 species infecting more than 2 hosts along the Portuguese coast, i.e. Lecithochirium rufoviride, Nybelinia lingualis and Anisakis simplex s.l., suggesting that regulation mechanisms are not species specific but are locally determined, with host ecology playing a significant role.

Various strains of Atlantic salmon exhibit different levels of susceptibility to infections with the ectoparasitic monogenean Gyrodactylus salaris. The basic mechanisms involved in this differential ability to respond to this monogenean were elucidated using controlled and duplicated challenge experiments. Highly susceptible East Atlantic salmon allowed parasite populations to reach up to 3000 parasites per host within 6 weeks, whereas less susceptible Baltic salmon never reached larger parasite burdens than 122 parasites per host during the same period. The present study, comprising immunohistochemistry and gene expression analyses, showed that highly susceptible salmon erected a response mainly associated with an increased expression of interleukin-1beta (IL-1beta), interferon-gamma (IFN-gamma), IL-10 and infiltration of CD3-positive cells in the epidermis of infected fins. Less susceptible salmon showed no initial response in fins but 3-6 weeks post-infection a number of other genes (encoding the immune-regulating cytokine IL-10, cell marker MHC II and the pathogen-binding protein serum amyloid A) were found to be up-regulated. No proliferation of epithelial cells was seen in the skin of less susceptible salmon, and IL-10 may play a role in this regard. It can be hypothesized that resistant salmon regulate the parasite population by restricting nutrients (sloughed epithelial cells and associated material) and thereby starve the parasites. In association with this 'scorched-earth strategy', the production of pathogen-binding effector molecules such as serum amyloid A (SAA) (or others still not detected) may contribute to the resistance status of the fish during the later infection phases.

This study was carried out to investigate the reasons for scale loss, hemorrhage and local lesions on the skin of cultured meagre (Argyrosomus regius Asso, 1801), that are an alternative to the sea bass and sea bream. All of the 40 fish examined (5.63 +/- 0.89 kg in weight, 91.3 +/- 3.6 cm in length) had parasites on the area with lesions and the parasite was identified as Benedenia sciaenae van Beneden, 1856 (Monogenea: Capsalidae) after examination. The dimensions of the parasite were measured and drawn. This is the first report of B. sciaenae in Turkey.

Gyrodactylus salaris Malmberg, 1957 is a freshwater monogenean ectoparasite of salmonids, first recorded in Norway in 1975 and responsible for extensive epizootics in wild Atlantic salmon Salmo salar L. The susceptibility of different populations of Atlantic salmon to G. salaris infection differs markedly, with fish from the Baltic being characterised as relatively resistant whereas those from Norway or Scotland are known to be (extremely) susceptible. Resistance to Gyrodactylus infection in salmonids has been found to be heritable and a polygenic mechanism of control has been hypothesised. The current study utilises a 'Quantitative trait loci' (QTL) screening approach in order to identify molecular markers linked to QTL influencing G. salaris resistance in B1 backcrosses of Baltic and Scottish salmon. Infection patterns in these fish exhibited 3 distinct types; susceptible (exponential parasite growth), responding (parasite load builds before dropping) and resistant (parasite load never increases). B1 backcross fish were screened at 39 microsatellite markers and single marker-trait associations were examined using general linear modelling. We identified 10 genomic regions associated with heterogeneity in both innate and acquired resistance, explaining up to 27.3% of the total variation in parasite loads. We found that both innate and acquired parasite resistance in Atlantic salmon are under polygenic control, and that salmon would be well suited to a selection programme designed to quickly increase resistance to G. salaris in wild or farmed stocks.

A parasitological study of rays captured on the Atlantic continental shelf off the estuary Muros-Noia in NW Spain (42 degrees 35' to 42 degrees 41' N, 9 degrees 2' to 9 degrees 10' W; mean capture depth 11.6 +/- 4.1 m) was performed. A total of 128 rays were examined: 52 specimens of Raja microocellata, 60 of R. brachyura, 6 of R. montagui, 3 of R. undulata and 7 of an unidentified Raja species, known locally as 'fancheca'. A total of 23 macroparasite species were detected: 5 monogeneans (Acanthocotyle sp., Calicotyle kroyeri, Empruthotrema raiae, Merizocotyle undulata, Rajonchocotyle emarginata), 11 cestodes (Acanthobothrium sp., Crossobothrium sp., Echeneibothrium sp., Echinobothrium brachysoma, Grillotia erinaceus, Grillotia sp., Lecanicephalum sp., Nybelinia lingualis, Onchobothrium uncinatum, Phyllobothrium lactuca, Tritaphros retzii), 6 nematodes (Anisakis simplex, Hysterothylacium sp., Histodytes microocellatus, Piscicapillaria freemani, Proleptus sp., Pseudanisakis baylisi) and a copepod (Holobomolochus sp.). All parasite species were present in several ray species, except for Acanthocotyle sp. and G. erinaceus (detected only in R. brachyura), H. microocellatus (detected only in R. microocellata) and T. retzii (detected only in R. montagui). Three species (C. kroyeri, M. undulata, E. brachysoma) have not been reported previously from Spain. The host with the highest parasite species richness was R. brachyura (18 species), followed by R. microocellata (17) and the unidentified Raja species (14). The parasite with the highest prevalence in R. microocellata was M. undulata, followed by R. emarginata, Acanthobothrium sp. and Echeneibothrium sp. The species with the highest prevalence in R. brachyura was R. emarginata, followed by C. kroyeri and P. baylisi. Some differences in parasite prevalence were detected between sexes and among size classes in both R. brachyura and R. microocellata.

A recent epidemic of the invasive monogenean Neoheterobothrium hirame is suspected to have caused the significant decline of the commercial catch of olive flounder, Paralichthys olivaceus, in Japan. To clarify the causal link between parasite invasion and host depletion, we monitored the infections of N. hirame on juvenile flounder for 2 years at two widely separate bays, Obama Bay, experiencing a devastating reduction in flounder catches, and Miyako Bay with a stable catch. Prevalence, mean intensity and abundance of developmental stages of N. hirame were compared between the bays and between fish year classes. Fishes captured at Obama Bay harboured three times more worms than those at Miyako Bay and had a significantly higher overall prevalence of infection. In addition, there was a negative correlation between parasite intensity and host condition factor at Obama Bay, suggesting a causal link between the N. hirame epidemic and the reduction of local flounder populations.

Patterns and likely processes connected with evolution of host specificity in congeneric monogeneans parasitizing fish species of the Cyprinidae were investigated. A total of 51 Dactylogyrus species was included. We investigated (1) the link between host specificity and parasite phylogeny; (2) the morphometric correlates of host specificity, parasite body size, and variables of attachment organs important for host specificity; (3) the evolution of morphological adaptation, that is, attachment organ; (4) the determinants of host specificity following the hypothesis of specialization on more predictable resources considering maximal body size, maximal longevity, and abundance as measures of host predictability; and (5) the potential link between host specificity and parasite diversification. Host specificity, expressed as an index of host specificity including phylogenetic and taxonomic relatedness of hosts, was partially associated with parasite phylogeny, but no significant contribution of host phylogeny was found. The mapping of host specificity into the phylogenetic tree suggests that being specialist is not a derived condition for Dactylogyrus species. The different morphometric traits of the attachment apparatus seem to be selected in connection with specialization of specialist parasites and other traits favored as adaptations in generalist parasites. Parasites widespread on several host species reach higher abundance within hosts, which supports the hypothesis of ecological specialization. When separating specialists and generalists, we confirmed the hypothesis of specialization on a predictable resource; that is, specialists with larger anchors tend to live on fish species with larger body size and greater longevity, which could be also interpreted as a mechanism for optimizing morphological adaptation. We demonstrated that ecology of host species could also be recognized as an important determinant of host specificity. The mapping of morphological characters of the attachment organ onto the parasite phylogenetic tree reveals that morphological evolution of the attachment organ is connected with host specificity in the context of fish relatedness, especially at the level of host subfamilies. Finally, we did not find that host specificity leads to parasite diversification in congeneric monogeneans.

Phalloidin fluorescence technique, enzyme cytochemistry and immunocytochemistry in conjunction with confocal scanning laser microscopy have been used for the first time to describe the nervous and muscle systems of the viviparous monogenean gill parasite, Macrogyrodactylus clarii. The gross spatial arrangement of muscle and associated cholinergic, peptidergic and aminergic innervations has been examined. The central nervous system (CNS) consists of paired cerebral ganglia from which emanate three pairs of longitudinal ventral, lateral and dorsal nerve cords, connected at intervals by transverse connectives. The CNS is better developed ventrally than dorsally or laterally, and has the strongest reactivity for all neuroactive substances examined. Structural and functional correlates of the neuromusculature of the pharynx, haptor and reproductive tracts have been examined. Results implicate acetylcholine, FMRFamide-related peptides (FaRPs) and serotonin in sensory and motor function in this monogenean, although confirmatory physiological data are obviously required.

The susceptibility of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) to the monogenean Discocotyle sagittata in the United Kingdom was assessed by experimental infection of naive fish. One month postinfection with 100 oncomiracidia/host, brown trout harbored significantly lower burdens (27.7 worms/host +/- 4.13 SE) than rainbow trout (47.8 worms/host +/- 3.90; P = 0.002). This indicates that the consistently lower prevalence and intensity of D. sagittata recorded in naturally infected farmed fishes reflects differences in susceptibility to the parasite. The outcome may be related to the comparatively short-term association of this parasite with rainbow trout (introduced to Britain in the 1880s) compared with the established native host-parasite association.

The relationship between Discocotyle sagittata intensities and host length, weight and specific anti-parasite antibody titres was studied in 3 year-classes of farmed rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta at the end of the annual transmission cycle. Antibody titres were significantly higher in infected farmed fish than in naive controls, indicating that infection elicits immunoglobulin production. No correlation was found between host size and parasite burdens, nor between infection intensities and antibody titres.

Tilapia cabrae Boulenger, 1899, a cichlid fish from coastal lowlands of the Republic of Congo (Africa), was examined for gill parasites. Four new species of the Monogenea were found, all belonging to Cichlidogyrus (Ancyrocephalidae): C. berradae sp. n., C. revesati sp. n., C. legendrei sp. n., and C. lemoallei sp. n. A possible relationship between the relative size of haptoral sclerites (i.e., uncinuli compared to gripi) and microhabitat selection in the studied host-parasite model is discussed.

Immune responses in ectothermic vertebrates and the life-processes of their parasites are profoundly linked to ambient temperature, but the functional effect of thermal environment on infectivity and host-specificity in helminths from ectotherms is poorly known. Primary infection establishment of Protopolystoma xenopodis (Monogenea) in compatible hosts ( Xenopus laevis: Anura) is strongly modulated by ambient temperature. Significantly fewer worms survived to the urinary bladder stage at 25 degrees C than at 15 degrees C (relatively high and low temperatures for this system in nature). Pre-infection exposure of X. laevis to cold (10 degrees C) did not significantly affect parasite establishment in the urinary bladder (at 15 or 25 degrees C p.i.), nor shorter-term postlarval survival in the kidneys (at 20 degrees C p.i.), suggesting that residual immunosuppressive effects on host susceptibility are not important. Low temperatures had no permissive effect on the establishment of P. xenopodis in incompatible hosts (Xenopus wittei). The link between thermal conditions and parasitic infection of ectotherms is discussed.

This review is the first to draw together knowledge about bioadhesives secreted by a group of parasites. Mechanisms of mechanical attachment are well known among parasites, but some can also attach to host surfaces by chemical means using a thin layer of adhesive material secreted at the parasite-host interface. Attachment by adhesives to living surfaces has not been studied in detail previously. A significant volume of research has determined much about the chemistry and nature of bioadhesives secreted by various marine macroinvertebrates from different phyla for attachment to inert substrates. Mussels and barnacles are sessile and adhere permanently, whereas starfish display temporary but firm adhesion during locomotion, feeding and burrowing. We focus on the Platyhelminthes that comprises the largely free-living Turbellaria and the wholly parasitic Monogenea, Cestoda, Digenea and Aspidogastrea. The term tissue adhesion is introduced to describe attachment by adhesives to epithelial surfaces such as fish epidermis and the lining of the vertebrate gut. These living layers regenerate rapidly, secrete mucus, are a site for immune activity and are therefore especially hostile environments for organisms that inhabit them, presenting a significant challenge for adhesion. Not all platyhelminths adhere to living surfaces and types of adhesion to inert substrates by the free-living turbellarians are also reviewed. Tissue adhesion is particularly well exemplified by monopisthocotylean monogeneans, parasites that are especially mobile as larvae, juveniles and adults on the epidermis of the body and gill surfaces of fish. These monogeneans secrete adhesives from the anterior end when they move from site to site, but some have secondarily developed adhesives at the posterior end to supplement or replace mechanical attachment by hooks and/or by suction. The temporary but tenacious anterior adhesives of monogeneans display remarkable properties of instant attachment to and detachment from their host fish surfaces. In contrast to the mobility of turbellarians and monopisthocotylean monogeneans and the simplicity of their direct life cycles, the largely endoparasitic Cestoda and Digenea are considered to be less mobile as adults. The complex cestode and digenean life cycles, involving intermediate hosts, place different demands on their various stages. Diverse, mostly anterior, gland cells in larvae, metacestodes and adults of the true tapeworms (Eucestoda), and in larval and adult Gyrocotylidea and Amphilinidea are reviewed. Conspicuous gland cells, mostly but not exclusively at the anterior end, in miracidia, cercariae and adults of digeneans and in cotylocidia and adults of aspidogastreans are also reviewed. Unlike turbellarians and monogeneans, accounts of unequivocal adhesive secretions in the Cestoda, but especially in the Digenea and Aspidogastrea, are relatively rare. The primary purpose of many conspicuous glands in the different stages of these mostly endoparasitic flatworms is for penetration into, or escape from, different hosts in their life cycle. We provide a detailed review of current knowledge about adhesion (in the sense of a thin layer of chemical material) in the Platyhelminthes including uses among eggs, larval, juvenile and adult stages. Information on structure, morphology and ultrastructure of the various adhesive systems that have been described is reviewed. Application of the 'duo gland' model is discussed. Comparisons are made between the little that is known about the chemistry of flatworm adhesives and the significant knowledge of the chemical nature of other invertebrate bioadhesives, especially those from marine macroinvertebrates. The potential importance of adhesives in parasitism is discussed. (ABSTRACT TRUNCATED)

Skin lesions caused by the ectoparasite Dermophthirius penneri Benz, 1987 (Monogenea: Microbothriidae) on 2 wild-caught blacktip sharks (Carcharhinus limbatus) from the northern Gulf of Mexico were studied using light and scanning electron microscopy. Grossly, lesions appeared as multifocal, well-demarcated, ovoid or irregularly shaped, light gray patches of skin. Scanning electron microscopy of lesions revealed gaps between placoid scales apparently created by detachment and loss of placoid scales, rotated and tilted placoid scales with blunt distal tips and shallow ridges, and a frayed epithelium that covered some placoid scales and filled some spaces between placoid scales. Light microscopy of lesions revealed epithelial hyperplasia accompanied by dermal infiltrates of moderate numbers of loosely arranged lymphocytes interposed between collagen bundles in the superficial layers of the stratum compactum. This report provides the first details of microbothriid skin lesions on wild sharks. Our results indicate that D. penneri caused chronic skin lesions not associated with bacterial infection or severe, debilitating, skin disease in the studied sharks.