Community ecology of the parasites of adult spot, Leiostomus xanthurus, and Atlantic croaker, Micropogonias undulatus (Sciaenidae) in the Cape Hatteras region

Twenty-three species of metazoan parasites were recorded from adult spot and 26 from adult croaker. Of the 33 parasitic species found, 17 occurred in both spot and croaker. No significant differences in intensity of parasites occurred between sexes of either spot or croaker. All of the parasites had over-dispersed, or clumped, distributions among hosts. Adult spot and croaker collected offshore had much greater species-richness, diversity, and total number of individual parasites than juvenile fishes collected in adjoining estuaries during another study. The juvenile spot and croaker had less time to acquire parasites and inhabited less diverse and more confined habitats in inshore estuaries, which resulted in less diverse parasite communities than offshore fishes. The number of species and diversity of parasites in adult fish was greater in croaker than spot. However, when only gastrointestinal helminths were considered, spot had greater species-richness as well as greater numbers of individual helminths, suggesting that they had a more diverse diet and that they fed on more infected intermediate hosts than croaker. In both adult spot and croaker the mean number of parasitic species was greater than those of freshwater fishes and fewer than those for birds and mammals. The total number of individual parasites was similar to that of freshwater fishes. The opportunistic diet and the migratory habits of both spot and croaker contribute to their diverse parasite faunas. Comparison of adult spot and croaker parasite faunas collected offshore indicated that their respective parasite component communities were distinct and that similar parasite infracommunity variability existed in both hosts and that their communities were not ‘random’ samples, but restricted subsets of the compound community. Although the parasite dominance hierarchy in adults of both species varied slightly between areas and seasons sampled, there appeared to be a predictable dominant species that was accompanied by subordinate, less predictable species. However, the variability in both relative intensities and presence-absence of parasites within communities resulting from their diverse diets make them less predictable than those of other vertebrates with less diverse diets such as the lesser scaup duck and more like those of other marine fishes.     

Metazoan parasites of African annual killifish (Nothobranchiidae): abundance,diversity, and their environmental correlates

Estimates of biodiversity and its global patterns are affected by parasite richness and specificity. Despite this, parasite communities are largely neglected in biodiversity estimates, especially in the tropics. We studied the parasites of annual killifish of the genus Nothobranchius that inhabit annually desiccating pools across the African savannah and survive the dry period as developmentally arrested embryos. Their discontinuous, non‐overlapping generations make them a unique organism in which to study natural parasite fauna. We investigated the relationship between global (climate and altitude) and local (pool size, vegetation, host density and diversity, and diversity of potential intermediate hosts) environmental factors and the community structure of killifish parasites. We examined metazoan parasites from 21 populations of four host species (Nothobranchius orthonotus, N. furzeri, N. kadleci, and N. pienaari) across a gradient of aridity in Mozambique. Seventeen parasite taxa were recorded, with trematode larval stages (metacercariae) being the most abundant taxa. The parasites recorded were both allogenic (life cycle includes non‐aquatic host; predominantly trematodes) and autogenic (cycling only in aquatic hosts; nematodes). The parasite abundance was highest in climatic regions with intermediate aridity, while parasite diversity was associated with local environmental characteristics and positively correlated with fish species diversity and the amount of aquatic vegetation. Our results suggest that parasite communities of sympatric Nothobranchius species are similar and dominated by the larval stages of generalist parasites. Therefore, Nothobranchius serve as important intermediate or paratenic hosts of parasites, with piscivorous birds and predatory fish being their most likely definitive hosts.     

Structure of component parasite communities in the grayling, Thymallus thymallus L. (Salmoniformes, Thymallidae), and minnow, Phoxinus phoxinus L. (Cypriniformes, Cyprinidae), from the upper reaches of the Pechora River

A comparative analysis of parasite communities in the grayling and minnow has been performed. These communities differ in the number of constituent species and in the fact that the community of the minnow is dominated by one allogenic species, whereas that of the grayling usually has two dominants, both being autogenic species. The values of species diversity indices characterizing these communities are also different. Differences between the parasite communities of these fish species reflect the position of their hosts in the hydrobiocenosis. Species prevailing in both communities are classified as specialists, which is characteristic of parasite communities of the boreal-piedmont faunal complex. Both these communities consist of three species groups distinguished by their proportions in the total biomass, which indicates that parasitic communities are structured in a certain way and that the distribution of species in them is not random.     

Infection with acanthocephalans increases the vulnerability of Gammarus pulex (Crustacea, Amphipoda) to non-host invertebrate predators

Phenotypic alterations induced by parasites in their intermediate hosts often result in enhanced trophic transmission to appropriate final hosts. However, such alterations may also increase the vulnerability of intermediate hosts to predation by non-host species. We studied the influence of both infection with 3 different acanthocephalan parasites (Pomphorhynchus laevis, P. tereticollis, and Polymorphus minutus) and the availability of refuges on the susceptibility of the amphipod Gammarus pulex to predation by 2 non-host predators in microcosms. Only infection with P. laevis increased the vulnerability of amphipods to predation by crayfish, Orconectes limosus. In contrast, in the absence of refuges, the selectivity of water scorpions, Nepa cinerea, for infected prey was significant and did not differ according to parasite species. When a refuge was available for infected prey, however, water scorpion selectivity for infected prey differed between parasite species. Both P. tereticollis- and P. laevis-infected gammarids were more vulnerable than uninfected ones, whereas the reverse was true of P. minutus-infected gammarids. These results suggest that the true consequences of phenotypic changes associated with parasitic infection in terms of increased trophic transmission of parasites deserve further assessment.     

Trematode communities in snails can indicate impact and recovery from hurricanes in a tropical coastal lagoon

In September 2002, Hurricane Isidore devastated the Yucatán Peninsula, Mexico. To understand its effects on the parasites of aquatic organisms, we analyzed long-term monthly population data of the horn snail Cerithidea pliculosa and its trematode communities in Celestún, Yucatán, Mexico before and after the hurricane (February 2001 to December 2009). Five trematode species occurred in the snail population: Mesostephanus appendiculatoides, Euhaplorchis californiensis, two species of the genus Renicola and one Heterophyidae gen. sp. Because these parasites use snails as first intermediate hosts, fishes as second intermediate hosts and birds as final hosts, their presence in snails depends on food webs. No snails were present at the sampled sites for 6 months after the hurricane. After snails recolonised the site, no trematodes were found in snails until 14 months after the hurricane. It took several years for snail and trematode populations to recover. Our results suggest that the increase in the occurrence of hurricanes predicted due to climate change can impact upon parasites with complex life cycles. However, both the snail populations and their parasite communities eventually reached numbers of individuals and species similar to those before the hurricane. Thus, the trematode parasites of snails can be useful indicators of coastal lagoon ecosystem degradation and recovery.     

Component communities of parasites in the grayling Thymallus thymallus (L.) (Salmoniformes, Thymallidae) and the minnow Phoxinus phoxinus (L.) (Cypriniformes, Cyprinidae) from the Pechora River

Component communities of parasites of Thymallus thymallus and Phoxinus phoxinus are described. The communities differ in the number of species and in the number of dominate species, which is one in P. phoxinus and usually two in T. thymallus. In the first case the dominate species is allogenic, while in the second case dominate species are autogenic. Values of the species diversity indexes are also different for these communities. The differences between parasite communities of T. thymallus and P. phoxinus underline positions of these hosts in hydrobiocenose. Species specialists take first place in the parasite communities both of the hosts, that is characteristic for the parasite communities of the fishes from the boreal submountain faunistic complex. Parasite communities in both of the hosts consist of three groups of species discriminated by the ratio of their biomasses, that suggests forming of the groups by a coordination of the species biomasses.     

The combined influence of trematode parasites and predatory salamanders on wood frog (<Emphasis Type="Italic">Rana sylvatica</Emphasis>) tadpoles

Predators can have important impacts on host–parasite dynamics. For many directly transmitted parasites, predators can reduce transmission by removing the most heavily infected individuals from the population. Less is known about how predators might influence parasite dynamics in systems where the parasite relies on vectors or multiple host species to complete their life cycles. Digenetic trematodes are parasitic flatworms with complex life cycles typically involving three host species. They are common parasites in freshwater systems containing aquatic snails, which serve as obligate first intermediate hosts, and multiple trematode species use amphibians as second intermediate hosts. We experimentally examined the impact of predatory salamanders (Ambystoma jeffersonianum) and trematode parasites (Echinostoma trivolvis and Ribeiroia ondatrae) on short-term survival of wood frog tadpoles (Rana sylvatica) in 150-L outdoor pools. Two trematode species were used in experiments because field surveys indicated the presence of both species at our primary study site. Parasites and predators both significantly reduced tadpole survival in outdoor pools; after 6 days, tadpole survival was reduced from 100% in control pools to a mean of 46% in pools containing just parasites and a mean of 49% in pools containing just predators. In pools containing both infected snails and predators, tadpole survival was further reduced to a mean of 5%, a clear risk-enhancement or synergism. These dramatic results suggest that predators may alter transmission dynamics of trematodes in natural systems, and that a complete understanding of host–parasite interactions requires studying these interactions within the ecological framework of community interactions.     

Body size,trophic level,and the use of fish as transmission routes by parasites

Within food webs, trophically transmitted helminth parasites use predator–prey links for their own transfer from intermediate prey hosts, in which they occur as larval or juvenile stages, to predatory definitive hosts, in which they reach maturity. In large taxa that can be used as intermediate and/or definitive hosts, such as fish, a host species’ position within a trophic network should determine whether its parasite fauna consists mostly of adult or larval helminths, since vulnerability to predation determines an animal’s role in predator–prey links. Using a large database on the helminth parasites of 303 fish species, we tested whether the proportion of parasite species in a host that occur as larval or juvenile stages is best explained by their trophic level or by their body size. Independent of fish phylogeny or habitat, only fish body length emerged as a significant predictor of the proportion of parasites in a host that occur as larval stages from our multivariate analyses. On average, the proportion of larval helminth taxa in fish shorter than 20 cm was twice as high as that for fish over 100 cm in length. This is consistent with the prediction that small fishes, being more vulnerable to predation, make better hosts for larval parasites. However, trophic level and body length are strongly correlated among fish species, and they may have separate though confounded effects on the parasite fauna exploiting a given species. Helminths show varying levels of host specificity toward their intermediate host when the latter is the downstream host involved in trophic transmission toward an upstream definitive host. Given this broad physiological compatibility of many helminths with fish hosts, our results indicate that fish body length, as a proxy for vulnerability to predators, is a better predictor of their use by helminth larvae than their trophic level based on diet content.     

Nested assemblages resulting from host size variation: the case of endoparasite communities in fish hosts

Nested species subsets are a common pattern in many types of communities found in insular or fragmented habitats. Nestedness occurs in some communities of ectoparasites of fish, as does the exact opposite departure from random assembly, anti-nestedness. Here, we looked for nested and anti-nested patterns in the species composition of communities of internal parasites of 23 fish populations from two localities in Finland. We also compared various community parameters of nested and anti-nested assemblages of parasites, and determined whether nestedness may result simply from a size-related accumulation of parasite species by feeding fish hosts. Nested parasite communities were characterised by higher prevalence (proportion of infected fish) and intensities of infection (number of parasites per fish) than anti-nested communities; the two types of non-random communities did not differ with respect to parasite species richness, however. In addition, the correlation between fish size and the number of parasite species harboured by individual fish was much stronger in nested assemblages than in anti-nested ones, where it was often nil. These results were shown not to be artefacts of sampling effort or host phylogeny. They apply to both assemblages of adult and larval parasites, which were treated separately. Since species of larval parasites are extremely unlikely to interact with one another in fish hosts, the establishment of nestedness appears independent of the potential action of interspecific interactions. The species composition of these parasite communities is not determined from within the community, but rather by the extrinsic influence of host feeding rates and how they amplify differences among parasite species in probabilities of colonisation or extinction. Nested patterns occur in parasite communities whose fish hosts accumulate parasites in a predictable fashion proportional to their size, whereas anti-nested communities occur in parasite communities whose fish hosts do not, possibly because of dietary specialisation preventing them from sampling the entire pool of parasite species available locally. Thus, nestedness in parasite communities may result from processes somewhat different from those generating nested patterns in free-living communities.     

Predicting the similarity of parasite communities in freshwater fishes using the phylogeny,ecology and proximity of hosts

Parasite communities tend to be dissimilar in hosts that are geographically, phylogenetically, ecologically and developmentally distant from one another. The decay of community similarity is a powerful and increasingly common method of studying parasite beta diversity, but most studies have examined only a single type of distance. Here, we evaluate distances based on the phylogeny, ecology, spatial proximity and size of hosts, as predictors of the similarity of parasite communities in individual hosts, host populations and host species. We surveyed parasites in six species of fish collected simultaneously from six localities in the St. Lawrence River, Canada, and species in a common group of larval parasites were discriminated using DNA sequences from barcode region of cytochrome c oxidase I. Distances based on the habitat use patterns of host species were good predictors of short‐term, ecological similarity of parasite communities, such as that operating at the scale of the individual host. The genetic distance between host species was associated with almost all types of similarity at all scales, particularly qualitative and phylogenetic similarity of parasite communities at the level of populations and meta‐populations of hosts. The trophic level, diet, spatial proximity and size of hosts were poor predictors of parasite community similarity. The increased taxonomic resolution provided by molecular data increased the explanatory power of regression models, and different factors were implicated when parasite species were distinguished with DNA barcodes than when larval parasites were lumped into morphospecies, as is commonly practiced.     

Observations on the distribution, specificity and pathogenicity of the acanthocephalan Pomphorhynchus laevis (Müller)

The distribution, specificity and pathogenicity of the acanthocephalan Pomphorhynchus laevis (Müller) were studied in the River Avon, Hampshire. The parasite occurred in every fish species, but three categories of hosts could be distinguished. Using growth and maturation as criteria of specificity, only chub Leuciscus cephalus (L.) and barbel Barbus barbus (L.) were recognized as its preferred hosts. Parasites occasionally matured in trout Salmo trutta (L.) and dace Leuciscus leuciscus (L.), but none grew or matured in other host species. Changes in the abundance of P. laevis along the river were related to changes in the abundance of both the intermediate host, Gammarus pulex , and the preferred hosts, and its occurrence in fish to the importance of G. pulex in their diet. In the upper reaches of the River Avon and in other localities populations could be maintained at a low level by parasites maturing in trout, and presence and abundance at any site depended upon the presence and abundance of both intermediate and definitive hosts especially and upon the dietary preferences of the latter. The absence of P. laevis from many parts of Britain is nevertheless still inexplicable. The parasite caused local damage to the intestinal wall of fish, the extent of which varied from species to species, but did not affect host growth rate or cause direct mortality and P. laevis cannot be regarded as an important pathogen in the River Avon or any other British River.     

Distance decay of similarity among parasite communities of three marine invertebrate hosts

The similarity in species composition between two communities generally decays as a function of increasing distance between them. Parasite communities in vertebrate definitive hosts follow this pattern but the respective relationship in intermediate invertebrate hosts of parasites with complex life cycles is unknown. In intermediate hosts, parasite communities are affected not only by the varying vagility of their definitive hosts (dispersing infective propagules) but also by the necessary coincidence of all their hosts in environmentally suitable localities. As intermediate hosts often hardly move they do not contribute to parasite dispersal. Hence, their parasite assemblages may decrease faster in similarity with increasing distance than those in highly mobile vertebrate definitive hosts. We use published field survey data to investigate distance decay of similarity in trematode communities from three prominent coastal molluscs of the Eastern North-Atlantic: the gastropods Littorina littorea and Hydrobia ulvae, and the bivalve Cerastoderma edule. We found that the similarity of trematode communities in all three hosts decayed with distance, independently of local sampling effort, and whether or not the parasites used the mollusc as first or second intermediate host in their life cycle. In H. ulvae, the halving distance (i.e. the distance that halves the similarity from its initial similarity at 1 km distance) for the trematode species using birds as definitive hosts was approximately two to three times larger than for species using fish. The initial similarities (estimated at 1 km distance) among trematode communities were relatively higher, whereas mean halving distances were lower, compared to published values for parasite communities in vertebrate hosts. We conclude that the vagility of definitive hosts accounts for a high similarity at the local scale, while the strong decay of similarity across regions is a consequence of the low probability that all necessary hosts and suitable environmental conditions coincide on a large scale.     

The population biology of parasite-induced changes in host behavior

The ability of parasites to change the behavior of infected hosts has been documented and reviewed by a number of different authors (Holmes and Bethel, 1972; Moore, 1984a). This review attempts to quantify the population dynamic consequences of this behavior by developing simple mathematical models for the most frequently recorded of such parasite life cycles. Although changes in the behavior of infected hosts do occur for pathogens with direct life cycles, they are most commonly recorded in the intermediate hosts of parasites with complex life cycles. All the changes in host behavior serve to increase rates of transmission of the parasites between hosts. In the simplest case the changes in behavior increase rates of contact between infected and susceptible conspecific hosts, whereas in the more complex cases fairly sophisticated manipulations of the host's behavioral repertory are achieved. Three topics are dealt with in some detail: (1) the behavior of the insect vectors of such diseases as malaria and trypanosomiasis; (2) the intermediate hosts of helminths whose behavior is affected in such a way as to make them more susceptible to predation by the definitive host in the life cycle; and (3) the behavior and fecundity of molluscs infected with asexually reproducing parasitic flatworms. In each case an expression is derived for R0, the basic reproductive rate of the parasite when first introduced into the population. This is used to determine the threshold numbers of definitive and intermediate hosts needed to maintain a population of the pathogen. In all cases, parasite-induced changes in host behavior tend to increase R0 and reduce the threshold number of hosts required to sustain the infection. The population dynamics of the interaction between parasites and their hosts are then explored using phase plane analyses. This suggests that both the parasite and intermediate host populations may show oscillatory patterns of abundance. When the density of the latter is low, parasite-induced changes in host behavior increase this tendency to oscillate. When intermediate host population densities are high, parasite population density is determined principally by interactions between the parasites and their definitive hosts, and changes in the behavior of intermediate hosts are less important in determining parasite density. Analysis of these models also suggests that both asexual reproduction of the parasite within a host and parasite-induced reduction in host fecundity may be stabilizing mechanisms when they occur in the intermediate hosts of parasite species with indirect life cycles.(ABSTRACT TRUNCATED AT 400 WORDS)     

Patterns of intermediate host use and levels of association between two conflicting manipulative parasites.

For many parasites with complex life cycles, manipulation of intermediate host phenotypes is often regarded as an adaptation to increase the probability of successful transmission. This phenomenon creates opportunities for either synergistic or conflicting interests between different parasite species sharing the same intermediate host. When more than one manipulative parasite infect the same intermediate host, but differ in their definitive host, selection should favour the establishment of a negative association between these manipulators. Both Polymorphus minutus and Pomphorhynchus laevis exploit the amphipod Gammarus pulex as intermediate host but differ markedly in their final host, a fish for P. laevis and a bird for P. minutus. The pattern of host use by these two conflicting manipulative parasites was studied. Their incidence and intensity of infection and their distribution among G. pulex were first examined by analysing three large samples of gammarids collected from the river Tille, Eastern France. Both parasites had low prevalence in the host population. However, temporal fluctuation in the level of parasitic infection was observed. Overall, prevalence of both parasite species was higher in male than in female G. pulex. We then assessed the degree of association between the two parasites among their intermediate hosts, using two different methods: a host-centred measure and a parasite-centred measure. Both measures gave similar results; showing random association between the two acanthocephalan species in their intermediate hosts. We discuss our results in relation to the selective forces and ecological constraints that may determine the pattern of association between conflicting manipulative parasites.     

Parasites of Cynoscion guatucupa along South American Atlantic coasts: evidence for stock discrimination

Two stocks of striped weakfish Cynoscion guatucupa in the south‐west Atlantic Ocean, were identified using parasites as biological tags. A total of 297 fish caught in Brazil, Uruguay and Argentina, contained 29 species of metazoan parasites. Univariate analysis on parasite populations, as well as multivariate discriminant analysis, calculated for juvenile and adult fish separately, allowed the identification of the two stocks, one from Argentina and Uruguay and the other from Brazil, to be made. Southern samples were characterized by higher prevalences and abundance of larval endohelminths, whereas in the northern stock, gastrointestinal and ectoparasitic species were common. Discriminant analyses on parasite infracommunities of Brazilian fish showed notable differences between juvenile and adult hosts; no such trend was observed in fish from Argentina and Uruguay, despite differences between juveniles and adults at the population level. Different oceanographic conditions and their influence on the distribution of parasites as well as of other hosts involved in their life cycles could be key factors for the differences observed among stocks of C. guatucupa .     

Variations in the parasite fauna of the Patagonian toothfish (Dissostichus eleginoides Smitt, 1898), with length, season, and depth of habitat around the Falkland Islands

The parasite fauna of Dissostichus eleginoides was examined from locations around the Falkland Islands. In total, of 11,362 individual parasites of 27 taxa were recovered from 105 fish. Two species, Ceratomyxa dissostichi and Sphaerospora dissostichi, represent new host records. The nematode Ascarophis nototheniae and the larval acanothocephalan Corynosoma bullosum were found to be new locality records and add to the knowledge of the biogeography and host specificity of parasites on the Patagonian Shelf. There were no significant differences in the mean abundance and prevalence of parasites recovered between sexes. Therefore, sex was not considered in further analysis and the data were pooled. Cysts of unknown etiology (CUE), the monogenean Neopavlovskioides georgianus, the larval acanthocephalan Corynosoma bullosum, and the digenean Neolepidapedon magnatestis had significant positive correlations with increasing host length. The larval Trypanorhynch cestode Grillotia erinaceus and the digenean Elytrophalloides oatesi showed significant negative correlations with increasing host length. CUEs, N. georgianus, the digenean Gonocerca physidis and E. oatesi showed statistically significant prevalence between summer, winter, and spring. The effect of depth on parasite communities was also examined, initially using a linear discriminant function analysis. The prevalence of individual parasites was then compared between depth strata using the chi-square test. The parasite communities on the shelf and deep water (> 1,000 m) were found to be different, whereas those caught at intermediate depths on the shelf slope were found to have parasite communities that were intermediate, containing a mixture of shelf and deeper-water parasites. The causes of the variations in parasite faunas in association with these intrinsic and extrinsic factors are discussed.     

Are eels (Anguilla anguilla L.) planktonic feeders? Evidence from parasite communities

The metazoan parasite communities of eels Anguilla anguilla were investigated in three riverine localities and one lake in Devon. Altogether 21 species of parasite, the majority of the British eel parasite fauna, were recorded. Parasite communities in the three riverine localities were more similar to each other than to that of the lake. The four parasite component communities were typical and representative of those from eels in other parts of the U.K. They were characterized by low species diversity and domination by a single species: Pseudodacytlogyrus anguillae in the rivers and Diplostomum spathaceum in the lake. Both the dominant species and the majority of parasite species, and hence individuals, in any locality infected eels directly by free swimming planktonic larval stages or indirectly by the ingestion of infected planktonic copepod intermediate hosts. Examination of other species of fish in each locality showed that only Raphidascaris acus utilized a fish species as an intermediate or paratenic host to infect eels. Increases in prevalence and intensity of infection with size of eel by helminths such as Camallanus lacustris and Paraquimperia tenerrima were observed in localities in which transmission of these parasites could not have involved another fish species. Over 63% of the specialist, specific parasites of eels throughout Europe employ planktonic transmission to their hosts, as do several species of the commoner generalists. A study of eel parasite communities thus leads to the conclusion that eels are widely and closely associated in their habits with plankton and that eels of all sizes feed regularly upon planktonic copepods: the widely accepted view of eels as being more or less exclusively benthic in habit and feeding behaviour requires re-appraisal.     

Co‐evolutionary patterns in congeneric monogeneans: a review of Dactylogyrus species and their cyprinid hosts

Patterns associated with the evolution of parasite diversity, speciation and diversification were analysed using Dactylogyrus species (gill monogeneans) and their cyprinid hosts as a model. The aim of this study was to use this highly specific host–parasite systems to review: (1) the diversity and distribution of Dactylogyrus species, (2) the patterns of organization and structure of Dactylogyrus communities, (3) the evolution and determinants of host specificity and (4) the mode of Dactylogyrus speciation and co‐evolutionary patterns in this Dactylogyrus–cyprinid systems. Dactylogyrus are a highly diverse group of parasites, with their biogeography and distribution clearly linked to the evolutionary history of their cyprinid hosts. The coexistence of several Dactylogyrus species on one host is facilitated by increasing niche distances and the differing morphology of their reproductive organs. The positive interspecific and intraspecific interactions seem to be the most important factors determining the structure of Dactylogyrus communities. Host specificity is partially constrained by parasite phylogeny. Being a strict specialist is an ancestral character for Dactylogyrus, being the intermediate specialists or generalists are the derived characters. The evolution of attachment organ morphology is associated with both parasite phylogeny and host specificity. Considering larger and long‐lived hosts or hosts with several ecological characters as the measures of resource predictability, specialists with larger anchors occurred on larger or longer‐living fish species. Intra‐host speciation, a mode of speciation not often recorded in parasites, was observed in Dactylogyrus infecting sympatric cyprinids. Sister parasite species coexisting on the same host occupied niches that differed in at least one niche variable. Intra‐host speciation, however, was not observed in Dactylogyrus species of congeneric hosts from geographically isolated areas, which suggested association by descent and host‐switching events.     

Red List of macrofaunal benthic invertebrates of the Wadden Sea

Parasites were observed in medium- and small-sized fish taken from the discards of a commercial shrimper during seven different cruises in the tidal channels of the North Frisian Wadden Sea (Süderaue, North Sea) from April to September 1991. In total, 442 fish comprising four species (Sprattus sprattus, Hyperoplus lanceolatus, Ammodytes tobianus, Pomatoschistus minutus) were investigated. The parasite fauna consisted of 22 species. The parasite community structure of the 4 hosts was compared. The diet of the hosts seemed to be the main factor determining the structure of the parasite community. Other factors could not be assessed. Eight species of parasites occurred as larval stages. This indicated that fish were intermediate or paratenic hosts in their life cycle. The nematodeHysterothylacium sp. (Anisakidae) and the digeneanCryptocotyle lingua (Heterophyidea) were the dominant parasites, reaching their highest prevalence and density in sprat and sand eel. Sprat and sand eel play a very important role in parasite transmission to predacious fish and seabirds.     

Comparison of the parasitic fauna of Aplocheilus panchax and A. melastigma

The metazoan parasite fauna of two species of freshwater fishes Aplocheilus panchax and A. melastigma collected from a stream at Waltair is compared; 17 parasite species were found. Aplocheilus panchax served as a host to 13 parasite species and A. melastigma to 10 parasite species. Of the 17 parasites collected, 12 were larval helminths to which the fishes act as intermediate and paratenic hosts. This has been attributed to the interaction between terrestrial birds, mammals and fishes in determining the parasite fauna in the biocoenosis. The parasite fauna of these fishes is divided into typical and less typical according to their frequencies. Among less typical there are peripheral division parasites which are abundant in other fishes in the stream. Only six parasite species occurred in both A. panchax and A. melastigma and both fish shared most of their parasite fauna with other fishes. Differences in the parasite fauna of these fishes are attributed to the morphological, behavioural or ecological features of these fishes.