Academic literature on the topic 'Freshwater fish parasites'

We used nestedness analysis to seek non-random patterns in the structure of component communities of metazoan parasites collected from 31 sympatric fish species from the northeastern Bothnian Bay, the most oligohaline area of the Baltic Sea. Only 8 marine parasite species were found among the 63 species recorded, although some marine fish species reproduce in the bay and others occasionally visit the area. Marine parasite species can utilize both freshwater and marine fish species as intermediate or final hosts, and marine fish can harbour freshwater parasite species. This exchange of parasite species between marine and freshwater fish has probably resulted from ecological factors acting over short time scales rather than from evolutionary processes acting over longer time; the key factor probably being the immediate presence of suitable intermediate and definitive hosts. Marine fish were expected to harbour species-poor parasite communities consisting mainly of generalists acquired from the sympatric freshwater fish species, which would result in a nested pattern among the different component communities. However, an anti-nested pattern was found in the component communities of metazoan parasites of fishes from the Bothnian Bay. A likely explanation for the observed pattern is that there are specialist parasite species, the majority of which are cestodes, in some of the freshwater fish species which otherwise have depauperate parasite communities.

The current work has been proposed to accumulate baseline information regarding prevalence, diversity and distribution of the protozoan parasites found in the freshwater fishes of Bangladesh from its inception to 2019. This is an attempt to compile a baseline data on protozoan parasites of freshwater fishes in Bangladesh. A total of thirty four articles were reviewed whereas sixteen articles reported systematic, taxonomic and morphometric analysis of protozoan parasites, five articles described seasonal parasitic infestation in carp fishes including protozoan parasites, seven articles reported overall parasitic infestation along with protozoan infection, three articles described protozoan infection in consort with the histo-pathological analysis, one article revealed the occurrence of one protozoan parasite named Trypanosoma sp. and one study described monthly fluctuation of overall parasitic infection together with protozoan infestation. A number of thirty four freshwater fish species under nine orders in Bangladesh were retrieved on the mentioned articles and found 48 species of protozoan parasites under 19 genera. Noticeably, parasites under genus Trichodina was frequently found in the freshwater fish species. Most of the parasites were found from the gills (micro-habited) of the host fish. To sum up, from this compilation a primary database of protozoan parasites of freshwater fish species might be expected to establish that will be supportive for further extensive study. Bangladesh J. Zool. 48(1): 21-35, 2020

Provided is a list of the protozoan parasites of freshwater and marine fishes from Brazil. This report includes informationabout the site of infection, host habitat, localities and references of 100 parasite species (1 amoeba, 70 flagellates, 13 api-complexa and 16 ciliates) distributed among 112 different host species, mainly from freshwater. It is concluded that thediversity of protozoan parasites from Brazilian fish is understudied, and it is suggested that appropriate measures be taken in the research efforts to increase studies on the diversity of Protozoans parasites of fish from Brazil.

A checklist of the metazoon parasites of freshwater fish in Turkey has been compiled from parasitological studies done in Turkey between 1964 and 2003. The parasite species list is arranged by phylum and class, providing parasite species name and author, host fish, location of host fish capture and author and date of published record. The host list consists of all parasite species listed by host species. One hundred and thirteen parasite species are listed from 41 host species belonging to 26 genera.

A total of 33 species of metazoan parasites were identified (31 helminth and 2 crustaceans) from 10 species of fish (n = 1,030) collected from Coyuca Lagoon, Guerrero, Mexico, between May 2001 and February 2003. Digeneans (7 adults and 11 larvae) dominated the parasite fauna. The most widespread species of parasite were: Digenea- Pseudoacanthostomum panamense, Diplostomum (Austrodiplostomum) compactum, Clinostomum complanatum; Nematoda- Contracaecum sp.; Branchiura- Argulus sp.; and Copepoda- Ergasilus sp. Species composition of the parasite fauna exhibited a clear freshwater influence; 57.5% (19/33) of the identified species have a freshwater distribution. This is the first survey of parasites of fish from this location and all reported species are new geographical host records for Coyuca Lagoon, Guerrero, Mexico.

Abstract An extensive literature review is made of the parasites in marine and freshwater fish in mainland Portugal, the Portuguese archipelagos of the Azores and Madeira, as well as in farmed fish. The host(s) of each parasite species, its location in the host, site of capture of the host, whenever possible, and all the available bibliographic references are described. The economic importance of some parasites and the zoonotic relevance of some parasitic forms are discussed. A general overview of the data is provided, and some research lines are suggested in order to increase and complement the current body of knowledge about the parasites of fish from Portugal.

Neobenedenia girellae is one of the most pathogenic parasites affecting marine fish in captivity conditions. The use of chemicals for parasite prevention and treatment have several benefits; however, they can cause various negative side-effects. In an effort to discover cost-effective and sustainable practices, our current study was aimed at investigating the efficiency of freshwater treatments on N. girellae. A challenge test was conducted to produce infected fish which became materials for the freshwater immersion experiments. The duration and reaction of the parasites at different development stages from eggs to adult parasites were examined. Our findings revealed that 100% of the adults and oncomiracidia of N. girellae were killed quickly in freshwater. The eggs of N. girellae, however, were highly resistant to freshwater with a hatching success rate of more than 95% in all the freshwater immersion treatments (2, 5, 10 and 30min). The eggs hatched mainly on day 7 and finished hatching on day 8. Thus, the freshwater immersion method can be applied to treat N. girellae at most stages excepted for the egg stage. The best practical treatment for this parasite is to perform a replicated immersion recommended 8 days following the first treatment.

Neobenedenia girellae is one of the most pathogenic parasites affecting marine fish in captivity conditions. The use of chemicals for parasite prevention and treatment have several benefits; however, they can cause various negative side-effects. In an effort to discover cost-effective and sustainable practices, our current study was aimed at investigating the efficiency of freshwater treatments on N. girellae. A challenge test was conducted to produce infected fish which became materials for the freshwater immersion experiments. The duration and reaction of the parasites at different development stages from eggs to adult parasites were examined. Our findings revealed that 100% of the adults and oncomiracidia of N. girellae were killed quickly in freshwater. The eggs of N. girellae, however, were highly resistant to freshwater with a hatching success rate of more than 95% in all the freshwater immersion treatments (2, 5, 10 and 30min). The eggs hatched mainly on day 7 and finished hatching on day 8. Thus, the freshwater immersion method can be applied to treat N. girellae at most stages excepted for the egg stage. The best practical treatment for this parasite is to perform a replicated immersion recommended 8 days following the first treatment.

SUMMARYVariations in levels of parasitism among individuals in a population of hosts underpin the importance of parasites as an evolutionary or ecological force. Factors influencing parasite richness (number of parasite species) and load (abundance and biomass) at the individual host level ultimately form the basis of parasite infection patterns. In fish, diet range (number of prey taxa consumed) and prey selectivity (proportion of a particular prey taxon in the diet) have been shown to influence parasite infection levels. However, fish diet is most often characterized at the species or fish population level, thus ignoring variation among conspecific individuals and its potential effects on infection patterns among individuals. Here, we examined parasite infections and stomach contents of New Zealand freshwater fish at the individual level. We tested for potential links between the richness, abundance and biomass of helminth parasites and the diet range and prey selectivity of individual fish hosts. There was no obvious link between individual fish host diet and helminth infection levels. Our results were consistent across multiple fish host and parasite species and contrast with those of earlier studies in which fish diet and parasite infection were linked, hinting at a true disconnect between host diet and measures of parasite infections in our study systems. This absence of relationship between host diet and infection levels may be due to the relatively low richness of freshwater helminth parasites in New Zealand and high host–parasite specificity.

This study is concerned with two strigeid genera which utilise fish as their second intermediate host and piscivorous birds as a definitive host, i.e. Apatemon (Apatemon) Sudarikov, 1959 and Ichthyocotylurus Odening, 1969. Although the lifecycle has been ascertained for most Ichthyocotylurus spp., confusion and disagreement still exist as to the constituent species, while all of the life-stages have been described for only a single member of the subgenus Apatemon (Apatemon). In order to clarify species membership to these taxa and indeed the taxonomic position of the subgenus Apatemon (Apatemon) further information was required on the life-cycles and life-stages of these strigeids. Although, metacercariae from this family have been recorded from a variety of British fishes, confirmed records, i.e. those supported with life-cycle data, are limited to a single species. It was this lack of confidence in identifying metacercariae recovered from fishes and the lack of known good criteria for distinguishing the adults that prompted the present study. Collections of metacercariae from a variety of hosts and locations were made, from which all subsequent life-cycle stages were obtained. The project aims were to establish the identity of the forms occurring in British fishes, by applying discriminatory techniques to the experimentally reared life-stages. In addition to traditional methods, techniques with little previous application to these genera were used and included, scanning electron microscopy (SEM), chaetotaxy, principal components analysis (PCA), and karyology. Furthermore, behavioural aspects such as the release patterns of cercariae from their molluscan hosts were studied to investigate whether they would prove to be of diagnostic value. Metacercariae obtained from the sampling survey were tentatively identified, using all currently employed methods for their determination, i.e. morphology, nature of cyst, host and site specificities, as Ichthyocotylurus erraticus (Rudolphi, 1809), I. variegatus (Creplin, 1825), Apatemon gracilis (Rudolphi, 1819) and A. annuligerum (Nordmann, 1832). Material collected from Finland was considered to contain both Ichthyocotylurus spp. recovered in the U.K., as well as I. platycephalus (Creplin, 1825) and I. pileatus (Rudolphi, 1802). The Ichthyocotylurus spp. were found to be more host specific than A. gracilis, although A. annuligerum was considered oioxenic to perch Perea fluiatilis L. Records of I. erraticus from gwyniad Coregonus lavaretus (L.) and grayling Thymallus thymallus (L.), and A. gracilis from arctic charr Salvelinus alpinus (L.) constitute first listings from Britain. The large number of sensilla present on the body surface of these metacercariae, observed by SEM and chaetotaxy, precluded their diagnostic use. PCA was, however, found to be of value for distinguishing between species and determining morphological variation within a species. I. erraticus, I. variegatus and A. gracilis adults were successfully reared in experimental hosts using metacercariae from a variety of fish hosts, sites within a single fish host and geographical sites. The adults obtained enabled clarification of the identities assigned to the metacercariae. Those metacercariae believed to represent I. pileatus and A. annuligerum failed to establish in experimental hosts. Herring gulls and lesser black-backed gulls proved to be extremely good experimental hosts for both Ichthyocotylurus spp., with the vast majority of infections establishing and providing high yields of eggs and adults. These infections yielded information on the establishment, development, fecundity, site specificity, longevity and morphological variability of the adults. Aspects of the morphology and biology of I. variegatus adults recorded were found to support its validity as a species discrete from I. platycephalus which was in some doubt. The experimental hosts used for A. gracilis infections, domestic and mallard ducklings, were found to be less satisfactory. Challenges were performed with A. gracilis metacercariae from three sources, rainbow trout, salmon parr and stone loach. The latter source was the only one to result in egg producing adults, with specimens exhibiting normal morphology and demonstrating an increased longevity over adults raised from salmonid metacercariae. These findings suggest that the metacercarial host may affect the successful completion of the life-cycle. Eggs of known origin were collected for all three cultured strigeid species, enabling further life-cycle studies, these were incubated and miracidia successfully raised. Developmental periods were found to be temperature dependent and differed for the three species at 20°C: A. gracilis < I. erraticus < I. variegatus. Light microscopy revealed the morphology of all three species to be identical, as were the epidermal plate formulae and chaetotaxy, indicated by silver-staining. The nomenclature for the distribution of miracidial sensilla derived by Dimitrov et al. (1989) was amended to enable a full description of these species. Osmotic shock resulted in an improved deciliation of the miracidia compared to sonication and subsequent SEM observation confirmed the arrangement of body surface structures, while revealing sensilla forms. Behavioural aspects of I. variegatus miracidia were examined, with a maximum longevity (< 11 hours) recorded at the lowest temperature studied (l0 degrees C), and host finding demonstrated to occur by an increased turning response in the presence of substances emitted from the susceptible snail host, following an initial unresponsive dispersal phase. Ichthyocotylurus cercariae were found in naturally infected Valvata piscinalis which constitutes the first record in Britain of cercariae of this genus. Cercariae of I. erraticus and I. variegatus were successfully raised experimentally from miracidia of known identity and origin within naive, experimentally raised V. piscinalis hosts, while A. gracilis cercariae were obtained from laboratory reared Lymnaea peregra. Cercarial developmental periods within the molluscan host were found to be temperature dependent and markedly different for the strigeid genera investigated, as were their behaviour and morphology. The Ichthyocotylurus spp. exhibit a distinct diurnal emergence rhythm from their molluscan host, being shed during the hours of daylight, while A. gracilis cercariae demonstrate a reciprocal pattern, emerging during the hours of darkness. Behavioural contrasts were also observed in longevities, emergence strategies (route of exit) and swimming behaviour. The two Ichthyocotylurus spp. were extremely similar, the only cercarial features found to be of diagnostic use were: the presence or absence of eye-spots; their differing developmental periods from miracidium to cercaria; the number and distribution of sensilla when compared by PCA; and their differing longevities at 20 degrees C. Characters considered to be of value in differentiating between strigeid cercariae at the species level, including the armature, chaetotaxy pattern and resting posture, did not differ between these two species. SEM observations enabled descriptions of the variety and structure of sensilla present on different life-stages, while transmission electron microscopy revealed the internal structure of cercarial sensory structures. Experimentally raised cercariae were found to be infective and the life-cycle was completed for the three strigeid species. Host specificities were observed for I. erraticus and A. gracilis, being particularly stringent for the latter species, while site specificities recorded were as observed in natural infections. Metacercarial maturation periods (for encystment) were highly temperature dependent, being comparable for the two Ichthyocotylurus spp. and more rapid than for A. gracilis specimens.

A study of myxozoan parasites has been investigated in hosts from freshwater environments in the UK. Over 17,000 oligochaetes, almost 5,000 juvenile cyprinids representing 7 species and over 60 invertebrate species have been examined for the presence of myxozoan parasites. In addition, studies on the lifecycle of Tetracapsuloides bryosalmonae (the causative agent of salmonid proliferative kidney disease, PKD) and of selected cyprinid myxozoans were conducted. A total of 21 actinospore types in seven collective groups were isolated and described from oligochaetes collected from seven different river systems in England and Wales. Twelve of the actinospores isolated appear to be new to science. Differences were noted in types of actinospores released at different sites and between seasons. Most actinospores were released from oligochaetes in spring and summer with prevalence of release ranging from 0.11% up to 5.83%. The most common actinospores were members of the collective group Echinactinomyxon with seven types identified, followed by the collective group Triactinomyxon, of which 6 types were identified. Five actinospores types were each encountered only once during the study. In juvenile cyprinid fish, 14 identifiable species of myxozoans in the genera Myxidium, Myxobolus and Sphaerospora plus three developmental stages were detected by histological examination. The most common myxozoans in cyprinids were Myxobolus pseudodispar and Myxobolus pfeifferi. Roach contained the most number of myxozoan species. Only seven myxozoan species were found in chub, but pathological responses and intensity of infections, particularly with M. pseudodispar, M. pfeifferi and Myxobolus buckei were greater when compared to other cyprinids examined. Juvenile cyprinids only appear to mount a pathological response to myxozoans once sporogony is initiated and some of those responses were considered severe enough to be detrimental to host survival. Mathematical models were produced using parasite data and incorporating a variety of data, including fish length, year class strength and environmental data to attempt to demonstrate a population level effect of disease. Many of the models developed clearly show that parasitism by Myxobolus spp. and Bucephalus polymorphus in juvenile fish is strongly correlated with population success in selected UK rivers. Laboratory experiments to transmit Myxobolus spp., Myxidium spp. and Sphaerospora spp. from selected cyprinid hosts to oligochaetes were unsuccessful. The most likely explanation is that the genetic strain of Tubifex tubifex used in the trials was not susceptible to infections by the myxospores selected. Specific DNA primers for Tetracapsuloides bryosalmonae were used on samples of over 60 invertebrate species collected from sites enzootic for PKD and on all 21 actinospore types isolated during the current study. All PCR reactions were negative for the presence of T. bryosalmonae DNA. Naive rainbow trout exposed to T. bryosalmonae spores from naturally infected bryozoans by bath challenge for 10 minutes developed PKD. Intraperitoneal injection of spores failed to induce the disease. The favoured route of entry by the parasite appears to be through mucous cells in the skin epithelium.

Parasites can have considerable consequences for their freshwater fish hosts, irrespective of whether they are intermediate or final hosts. The ecological consequences of infection arise from processes including parasite manipulation, where the parasite manipulates the host to increase their chance of transmission to the next host in the lifecycle, and parasite-mediated competition, where a consequence of infection is an alteration in the symmetry of competition between hosts and their uninfected conspecifics, or with other species. Whilst there is a great deal of existing knowledge on some of these consequences, there also remain some considerable knowledge gaps. This research covered the role of parasite exposure and water temperature on infection consequences, the foraging responses of fishes to intermediate hosts of the fish parasite Pomphorhynchus laevis that has an indigenous and non-indigenous range in Great Britain, the ecological consequences of this parasite for some freshwater fishes across these ranges, the issue of ‘enemy release’ and ‘parasite acquisition’ in introduced freshwater fishes, and the ecological consequences of infection by some native parasites for native freshwater fish. When the freshwater fish chub (Squalius cephalus) was exposed to different levels of intermediate hosts (Gammarus pulex) of P. laevis under two water temperature treatments, ambient and warmed, it revealed this interaction had considerable consequences for both parasite prevalence and the infection parameters. Whilst parasite prevalence was substantially higher at the elevated temperature, where infections did develop at lower temperatures, they were associated with fewer but larger parasites resulting in significantly higher parasite burdens, indicating complex consequences for host-parasite relationships under conditions of warming. Studies into parasite manipulation have frequently used the P. laevis: G. pulex parasite-intermediate host system for investigating how infections can result in behavioural modifications to the host that then results in their elevated risk of being predated by a fish. Here, comparative behavioural functional response experiments were used to test differences in the consumption rates of three fishes exposed to either uninfected or infected G. pulex, testing the hypothesis that the consumption rate of infected G. pulex would be significantly higher. The Type II functional response curves indicated that the results of the experiments were contrary to this hypothesis, with subsequent behavioural and foraging experiments also supporting these results. These counter-intuitive outcomes were also contrary to most other studies that suggested a parasite would manipulate its intermediate host in a way that promotes its transmission to a final host and facilitating the continuation of its life cycle. The reasons for these outputs were discussed as likely to relate to different selection pressures in this host-parasite system, given this is a generalist parasite with a wide range of potential fish final hosts. This was revealed by studies on this parasite from four fish species from five rivers that demonstrated high parasite prevalence in all species studied and suggested that small-bodied fishes, such as bullhead Cottus gobio, might play important roles in the P. laevis lifecycle. These prevalences, and the pathological consequences of the P. laevis infections, were also consistent across their indigenous and non-indigenous range, suggesting parasite origin had minimal consequences on their virulence and on the susceptibility of hosts to infection. That parasite origin often has minimal ecological consequences for their ecological impacts was reinforced by work on the ‘enemy release hypothesis’ in non-native fish in England and Wales. This revealed very few non-native parasites had been introduced with their non-native fish hosts. Those that had been introduced tended to be specialist parasites with direct lifecycles that had little opportunity to be transmitted to native fishes. Instead, the acquisition of native parasites by the non-native fishes was frequently observed, leading to potential concerns these fish would act as reservoir hosts and spill-back the parasites to the native fishes. Given the low probability of parasite introduction, the ecological consequences of three native parasites with complex lifecycles were then tested on three native fishes, and revealed consistent patterns of trophic niche divergence between infected and uninfected population sub-groups. Whilst the actual mechanism underpinning this, such as parasite-mediated competition, could not be tested, these results did reveal that the consequences of infection can be far-reaching for hosts and can be measured through a variety of methodologies. In summary, the research provided some comprehensive insights into many aspects of the pathological and ecological consequences of infection for some freshwater fishes from native/ non-native and indigenous/ non-indigenous parasites. In doing so, it has raised a series of new questions and hypotheses for further investigation, with the host-parasite systems used here capable of answering these.

A checklist of parasites of freshwater fish in the UK is an important source of information concerning hosts and their distribution for all aspects of scientific research. An interactive, electronic, web-based databse, Aquatic Parasite Information has been designed, incorporating all freshwater and brackish species of fish, parasites, taxonomy, synonyms, authors and associated hosts, together with records for their distribution. One of the key features of Aquatic Parasite Information is this checklist can be updated. Interrogation of Aquatic Parastie Information has revealed that some parasites of freshwater and brackish species of fish, such as the unicellular groups or those metzoans that are difficult to identify using morphological characters, are under reported. Aquatic Parasite Information identified the monogenean family Dactylogyridae and the cestodes infecting UK freshwater fish as under-represented groups, owing to the difficulties identifying them morphologically. Both the Dactylogyridae and cestodes have implications for pathology, outbreaks of disease and morbidity in freshwater fish in the UK, therefore accurate identification is critical. Studies were undertaken using both standard morphological techniques of histology and molecular techniques to identify dactylogyrid species and tapeworms commonly found parasitizing fish in the UK. Morphological studies demonstrated that histological processes could lead to distortion of the specimins and permanent mounting may affect the orientation which may obscure vital characteristics. Moleculr techniques were successfully employed using ITS1 for the Dactylogyridae and cox1 and r28s for the cestodes, to demonstrate genetic variability for the interspecific identification of species. Histology, scanning electron microscopy and molecular techniques have also identified an Atractolytocestus sp. tapeworm, parasitizing carp in the UK, as a potentially new species. Analysis of parasite records extracted from Aquatic Parasite Information has implicated freshwater fishery management policies as impacting on the dissemination and distribution of parasites, resulting in the spread of some species and decline of others.

Fewer than 200 fish species are found in freshwater habitats in Australia, of which 144 are confined exclusively to freshwater. At least 22 species of exotic freshwater fish have been introduced into Australia, and 19 of these have established self-sustaining populations. However, the parasite fauna of both native and exotic freshwater fishes in Australia is poorly known. This is particularly the case in the south-west of Western Australia, where there have been no previous comprehensive studies of the parasites of 14 native species and nine or more exotic species of fish found in freshwater habitats. This study represents a survey of the parasites of freshwater fishes in the South West Coast Drainage Division and reports 44 putative species of parasites in 1429 individual fishes of 18 different species (12 native and six exotic) from 29 locations. Parasites were found in 327 (22.88%) fishes, and of the infected fishes, 200 (61.16%) were infected with only one species of parasite and 127 (38.84%) were infected with two or more species of parasites. For helminth and arthropod parasites, which were more comprehensively surveyed than protozoan and myxozoans, I found 37 species compared to 77 species found in a recent study of fishes from the East Coast Drainage Division. The present study demonstrated that parasitic infection was significantly more common in native fish species (mean prevalence of infection with any species of parasite = 0.36 ± 0.09) than in exotic fish species (0.01 ± 0.12). Parasites were found in all native fish species, but in only two exotic fish species that were examined. Parasite regional and component community diversity were estimated by species richness (the number of species, S) and by an index of taxonomic diversity (HT). Both parasite species richness and parasite taxonomic diversity were significantly greater in native fish species (mean S = 10.5 ± 2.3; mean HT = 1.19 ± 0.14) than in exotic fish species (mean S = 1.6 ± 3.3; mean HT = 0.27 ± 0.20). These relationships were consistent over all geographic locations that were sampled. The reduced parasite load of exotic species compared to native species has been previous reported across a wide range of taxa. It is thought to arise partly because founding populations of hosts have a low probability of harbouring the species’ total parasite fauna, and partly because parasites that infect introduced exotic species may not be able to maintain their life cycle in the new environment. It has been suggested that a reduced parasite load increases the competitive ability of exotic species compared to native species (the parasite release hypothesis) and this may partly explain the abundance and apparent competitive success of exotic over native species of freshwater fish in the South West Coast Drainage Division. For native species of fish, there were major differences among species in both prevalence of parasitic infection and parasite community diversity, but this variation was not related to fish size, whether the fish were primarily freshwater or primarily estuarine, or whether they were primarily demersal or pelagic. In this study, I report two new parasites in south western Australian waters. Both are copepod parasites; Lernaea cyprinacea and a new species of Dermoergasilus. The Dermoergasilus appears to be native to the south-west of Western Australia and has been described as Dermoergasilus westernensis. It differs from previously described species in the genus principally by the armature of the legs. This new species was found on the gills of freshwater cobbler, Tandanus bostocki and western minnow, Galaxias occidentalis in two different river systems. Lernaea cyprinacea is an introduced parasitic copepod found on the skin and gills of freshwater fishes in many areas of the world. The parasite has not previously been reported in Western Australia. We found infestations of L. cyprinacea on four native fish species (G. occidentalis; Edelia vittata; Bostockia porosa; T. bostocki) and three introduced fish species (Carassius auratus; Gambusia holbrooki; Phalloceros caudimaculatus) at two localities in the Canning River, in the south-west of Western Australia. The parasite has the potential to have serious pathogenic effects on native fish species, although it appears to be currently localised to a small section of the Canning River. Over all localities from which fishes were sampled in the present study, the proportion of native freshwater fishes with parasitic infections and the component community diversity of the parasite fauna of native fishes were both negatively related to habitat disturbance, in particular to a suite of factors (river regulation, loss of riparian vegetation, eutrophication and presence of exotic fish species) that indicate increased human usage of the river and surrounding environment. The reduced parasite load and diversity in native fishes from south-west rivers with greater human usage was due principally to the loss of a number of species of trematode, cestode and nematode endoparasites which use fishes as intermediate hosts. Other studies have also found that endoparasites with complex life cycles are most likely to be adversely affected by environmental changes, presumably because any environmental changes which impact on either free-living parasite stages or on any of the hosts in the complex train of parasite transmission will reduce parasite population size and may cause local extinction of the parasite species. The most heavily infected species of native freshwater fish in the South West Coast Drainage Division was T. bostocki with 96% of all individuals containing at least one species of parasite. As with most freshwater fishes of south-west Australia, T. bostocki is limited in its distribution to waterways with relatively low salinity. The degree of parasitism and histopathology of internal and external organs in T. bostocki from the Blackwood River was examined over a period of rapid, seasonal changes in water salinity. As salinity increased, the infracommunity richness and prevalence of ectoparasites on the skin of fishes decreased, while the infracommunity richness and prevalence of endoparasites increased. This was associated with a decrease in histopathological lesion scores in the skin and an increase in histopathological lesion scores in internal organs, particularly the intestine. I hypothesise that the seasonal spike in salinity had two contrasting effects on parasitic infections of T. bostocki. Firstly, it increased the mortality rate of parasites directly exposed to water, leading to a decrease in ectoparasitic infection and associated pathology. Secondly, it suppressed immune function in fish, leading to a decreased mortality rate of parasites not directly exposed to water and a more severe pathological response to endoparasitism.

L'exposition à des mélanges complexes de substances chimiques dans l'environnement peut avoir de graves conséquences pour les animaux sauvages. En milieux naturels, ces organismes sont également affectés par de nombreux autres facteurs de stress, y compris le parasitisme. L'exposition chimique et l'infection parasitaire ont toutes deux été bien étudiées et documentées, mais dans de nombreux cas, elles ont été étudiées indépendamment l'une de l'autre. Cependant, il est crucial d'évaluer simultanément leur effet combiné étant donné que certains parasites peuvent interférer sur le devenir des polluants chez leur hôte grâce à leur capacité de bioaccumulation. Sur la base d'une étude de terrain, complétée par une approche expérimentale, j'ai étudié le devenir et les conséquences de six familles de contaminants organiques, et certains de leurs métabolites, dans un système hôte-parasite composé d'un poisson d'eau douce et de son parasite intestinal, Pomphorhynchussp. issus de la Marne, en France. Plus précisément, j'ai cherché à savoir si ces vers intestinaux étaient capables d'accumuler des substances toxiques et comment leur présence affectait la réponse au stress de leur hôte exposé aux contaminants environnementaux, à différents échelles biologiques à l'aide de biomarqueurs généraux (télomère, lysozyme, peroxydase, antioxydants, dommages oxydatifs, microbiote intestinal, indices de Fulton et hépatosomatique). Nous avons démontré que ces vers intestinaux étaient capables d'accumuler des contaminants organiques, de détoxifier leurs hôtes et que leurs effets sur l’hôte basculaient de négatifs à positifs à mesure que l'exposition aux contaminants organiques augmentait
Exposure to complex mixtures of environmental contaminants may have severe consequences in free-living. Under natural conditions, organisms are also exposed to other stressors, including parasites. Both chemical exposure and parasite infection have been well studied and documented, but have in many cases been investigated independently from one another. However, it is crucial to simultaneously assess their combined effect on wild organisms given that parasites may interfere with the fate of environmental contaminants within their host through their bioaccumulation capacity. Based on a field study, completed by an experimental approach, I investigated the fate and consequences of six families of organic contaminants, and some of their metabolites, in a host-parasite system composed of a freshwater fish, the European chub, Squalius cephalus, and its intestinal parasite, Pomphorhynchus sp. from the Marne River, France. Specifically, I investigated whether intestinal parasites were able to accumulate toxicants and how their presence affected the stress response of their definitive host exposed to environmental contaminants, at different biological levels with the use of general biomarkers (telomere, lysozyme, peroxidase, antioxidants, oxidative damage, gut microbiota, Fulton’s index and hepatosomatic index). Importantly, we demonstrated that intestinal worms were able to accumulate organic contaminants, detoxify their hosts and that their effects on the host shifted from negative to positive as chemical exposure increased

Capillaria species are members of the superfamily Trichinelloidae. These worms have a filamentous thin anterior end and a slightly thicker oesophagus which is surrounded by glandular cells or stichocytes. This oesophageal pattern is called stichosomal oesophagus. Capillaria species are parasites which are found in many vertebrate animals. More than two hundred species have been reported in several vertebrate species, including fish, amphibians, reptiles, birds, and mammals (Cross 1992; Chitwood et al. 1968), but only three species infect humans. These are Capillaria hepatica , C. aerophila and C. philippinensis (McCarthy and Moore 2000). Of these intestinal capillariosis, a fish-borne parasitic zoonosis caused by C. philippinensis , is the most important. Humans acquire the parasite, C. philippinensis, by eating uncooked or raw freshwater fish (Cross and Basaca-Sevilla 1991). The disease is endemic mainly in Philippines and Thailand where there are many reported fatalities.Although C . hepatica is found in rodents worldwide, only a few cases of hepatic capillariosis have been reported in humans from Europe, Asia, Africa, North and South America. The infection is acquired by the ingestion of embryonated eggs from the soil. Female worms deposit eggs in the liver tissue and granulomas develop around the egg. The eggs are released after the rodent is eaten and the liver digested. Eggs pass in the faeces and are deposited in the soil where they embryonate. Avoidance of contaminated soil would prevent human infection and destruction of rodents would control animal infections.Only 12 cases of human infection caused by Capillaria aerophila have been reported, the majority from Russia. The parasite is found within tissue of the respiratory passages of canines and felines worldwide.Anatrichosoma cutaneum (Nematoda, Trichosomoididae), also included in this chapter, is primarily a subcutaneous parasite of monkeys, but there are two reports of cutaneous infections in humans resulting in serpiginous lesions in the skin of the soles, palms, and nasal passages. In addition there is a further suspected case isolated from a breast nodule and a possible case of mucosal lesions in the mouth reported. Whole monkey colonies can be infected with this parasite and control is difficult.

<em>Abstract.</em>—A new checklist of 36 metazoan parasites recorded in European eels <em>Anguilla anguilla </em>in Ireland is presented and reviewed. Some of these parasite taxa are eel specialists but most utilize a range of fish hosts. Many were accidentally brought to Ireland during fish introductions. Changing distributions of preferred intermediate hosts have affected some parasite species. Commercial transport of eels has been implicated in the introduction and spread of several potentially pathogenic parasites, including the Asian nematode <em>Anguillicola crassus</em>. The current status of this and two <em>Pseudodactylogyrus </em>species, similarly introduced to Ireland, is discussed. Analysis of parasite assemblages of Irish eel populations indicates that individual host characteristics, such as size and diet, are important at the infra-community level. Likewise, variation in biotic and abiotic features of ecosystems is reflected in composition and structure of eel parasite component communities. Environmental changes, such as eutrophication and species introductions, were found to affect eel parasite assemblages. Better regulation of fish introductions and translocations is needed to protect the ecological integrity of Ireland’s freshwater systems and to avoid economic damage by nonindigenous parasites. Restrictions on live eel transport and on eel stocking programs may be necessary to protect recreational fisheries and the Irish aquaculture industry.

The unusual behavior of cleaner fish has attracted both popular and scientific curiosity since its discovery early in the 20th century. These fish apparently make their living by removing external parasites from “host” fishes of other species (some also remove bacteria or diseased and injured tissue). When they approach cleaners, hosts assume an unusual motionless posture that allows cleaners to feed from their scales, from their gill cavities, or even inside their mouths. For their trouble, cleaner fish get a meal, and hosts get a good cleaning. The interaction between cleaner fish and their hosts is generally classified as a mutualism, or mutually beneficial interaction between species. Stories about this and other mutualisms have become staples of nature documentaries and the popular literature and have helped lure many students into a lifetime of studying biology. From the perspective of evolutionary ecology, however, the cleaner-host relationship is anything but straightforward (Poulin and Grutter 1996). First, it is not at all clear that this interaction confers reciprocal fitness benefits. Despite several decades of effort, only one study has shown that cleaners significantly reduce hosts’ parasite loads (Grutter 1999), and none has yet demonstrated that reducing parasite loads increases host success. Since cleaners often gouge the host’s flesh, particularly when parasites are few, the interaction is often more costly than beneficial. Second, if cleaning does not confer an advantage, it is not evident why hosts should tolerate and even actively solicit cleaners’ attention. In fact, sometimes hosts lure cleaners only to eat them, but the conditions under which it might be beneficial for a host to doublecross its cleaners like this remain unexplored. Third, we don’t really understand how cleaning behaviors arose in the first place, considering that the first individuals that approached hosts to feed on parasites were very likely eaten. Despite this constraint, cleaning has apparently evolved multiple times; it is found in at least five families, in both marine and freshwater species, and in both the temperate zone and the tropics.

Gnathostomiasis is an extraintestinal infection with larval or immature nematodes of the genus Gnathostoma (order Spirurida), the most common mode of human infection being consumption of undercooked freshwater fish. Clinical manifestations include recurrent cutaneous migratory swellings (common), creeping eruption (rare), and neurological deficits (occasional). Definitive diagnosis is by identification of the worm in surgical specimens; serological testing for antibody against gnathostoma antigen can confirm a presumptive diagnosis. Treatment of choice is albendazole or if possible, surgical removal of the worm in accessible areas and when the parasite can be located. Prevention is by avoiding all dishes that contain raw or poorly cooked flesh of animals or fish in or imported from endemic areas....