Parasite communities of the Salzhaff (Northwest Mecklenburg, Baltic Sea) II. Guild communities, with special regard to snails, benthic crustaceans, and small-sized fish

Metazoan parasites of guilds of benthic snails and crustaceans and of four fish families – Gobiidae, Gasterosteidae, Syngnathidae, and Zoarcidae – were investigated off the brackish Salzhaff area (Southwest Baltic) in the semienclosed Salzhaff and the near Rerik Riff in the free Baltic. Comparisons revealed greater similarities in parasite populations and communities within the fish guilds than between them. According to an evaluation of the core-/satellite-species concept using abundance values, the most important parasites of fish were some generalists, such as Cryptocotyle spp., Podocotyle atomon, and Diplostomum spathaceum, as well as some specialists, such as Acanthostomum balthicum, Thersitina gasterostei, and Aphalloides timmi. These specialists revealed high degrees of prevalence in their main hosts and lower degrees in one or two by-hosts. Additional importance is assigned to parasites that cause harm to their hosts due to their large size, e.g., Schistocephalus spp., or via massive infestation, e.g., several digenean metacercariae. Because specialists were more prominent in snails and fish from the Rerik Riff, the correlation of host numbers with prevalence resulted in only a slight increase instead of a more rapid rise in regression among crustaceans and fish from the entire Salzhaff, where the generalists were more prevalent. The selected host guilds demonstrated the entire life cycles of three digeneans (P. atomon, A. balthicum, A. timmi), one acanthocephalan (Echinorhynchus gadi), and one nematode (Hysterothylacium sp.). The prevalence increased in these cycles from host level to host level and attained relatively high values in all guilds. The parasite fauna of the Salzhaff area is influenced by eutrophication stress, which leads to a high level of productivity and, consequently, to great densities in primary consumers such as snails and crustaceans. These are attractive for several secondary consumers such as fish and birds, which is the reason for the existence of at least 24 autogenic and 20 allogenic parasite species at this locality. The slight surplus of the first category indicates a yet-balanced environment in the investigation area. Received: 5 September 1999 / Accepted: 21 October 1999     

Four-year monitoring of parasite communities in gobiid fishes of the south-western Baltic

The parasite communities of goby species (Teleostei, Percomorphi) from the south-western Baltic Sea were investigated from 1997 to 2000 in three different seasons. In total, 30 parasite species were found in the guild of four goby spp. from Dahmeshöved (Lübeck Bight). The component community of Pomatoschistus minutus comprised 22, Pomatoschistus pictus 20, Gobiusculus flavescens 18 and Gobius niger 14 parasite species, whereas Pomatoschistus microps from the Salzhaff (Mecklenburg Bight) harboured 24 species. The digenean Podocotyle atomon (ingested with prey) and Cryptocotyle concavum (active penetration) were the most common parasites. Cryptocotyle lingua and the nematode Hysterothylacium sp. in Gobius niger as well as the specialists Aphalloides timmi and Apatemon gracilis (Digenea) in Pomatoschistus microps were also very abundant. There were large changes in the parasite communities within the years as well as between the seasons of a year; only Gobius niger presented rather homogeneous communities. The ratio of core parasite species in the hosts was at most 28% (Gobiusculus flavescens) and at least 9% (Gobius niger). The core species can attain their maximum values at different seasons, which is not only influenced by the parasite but also by the host species. It is concluded that the composition of parasite communities was predominantly determined by the ways of life of the host as well as of the parasite species. Another important factor is the population density of intermediate hosts.     

Four-year monitoring of parasite communities in gobiid fishes of the south-western Baltic

The parasite infracommunity of five goby species (Pomatoschistus minutus, P. pictus, P.microps, Gobiusculus flavescens, Gobius niger) from the south-western Baltic was investigated during spring, summer and autumn of the years 1997–2000. The mean parasite species number in single hosts was high, ranging between 1.1 (P. minutus), 2.1 (P. pictus) to even 3.3 (P. microps). Gobius niger is the only host which lives longer than a year and is infested by almost identical parasites for longer times, i.e. the parasite species composition has greater homogeneity. Most intensity of infestation values peaked in summer and were lowest in autumn; only a few exceptions were found in spring or autumn. Only the Digenea Podocotyle atomon and Cryptocotyle concavum were abundant enough to show a clear seasonal fluctuation in Pomatoschistus minutus, P. pictus and Gobiusculus flavescens. Aphalloides timmi and Apatemon gracilis (Digenea) also attained high intensities in P. microps. These four parasite species and, additionally, Cryptocotyle lingua (Digenea), and Hysterothylacium sp. (Nematoda) can be strongly accumulated from either prey or free-swimming larvae and, thus, decisively influence the structure of the infracommunities. Due to selection by filter mechanisms, rare parasites settle rather by chance after competition with other species. The number of parasite species usually increased significantly with host growth. As many as four parasite species were found at the same time in the intestinal tract microhabitat of Gobius niger and P. minutus; at most three parasite species were present on the skin and fins or in the body cavity. The level of infection is due to the respective life history patterns and the kinds of prey, which harbour different parasites as intermediate hosts. Additionally, it depends on the time of appearance of goby offspring in the course of the year.     

Four-year monitoring of parasite communities in gobiid fishes of the southwest Baltic

The parasite infrapopulations of five goby species (Pomatoschistus minutus, P. pictus, P.microps, Gobiusculus flavescens and Gobius niger) were investigated during spring, summer and autumn of the years 1997–2000. In total, 34 parasite species were found: 17 Digenea, 6 Nematoda, 5 Cestoda, 3 Acanthocephala, 2 Protozoa, and 1 Monogenea. The dominant parasites were the digeneans Podocotyle atomon and Cryptocotyle concavum, which represent different ecological groups in terms of their modes of transmission, either indirectly by prey or directly by larvae. The relationship between the parasite Cryptocotyle concavum and the host P. microps is a special one which results in a mean intensity of several hundred cysts (max. 1,329) which settle in the kidney. The diversity of the parasite component community was highest in autumn, but low in spring and summer, with the exception of P. microps for which high values were already found in spring when direct parasites were disregarded. These results depend on the respective seasonal variation in species, some of which occur in huge numbers in some hosts. The diversity of the prey parasite assemblage is higher in Pomatoschistus microps and Gobius niger than in the whole parasite spectrum; the other hosts present the opposite trend. A combination of the island theory of biogeography as modified for parasite infection with the theory of screens and filters leads to a model which considers three handicaps or distances for parasite colonisation: genetic, phylogenetic and ecological. Long-term investigations, as performed here over a time-span of 4 years, can detect more than 80% of parasite species in single hosts after 3 years, and in the whole goby guild after 2 years. Long-term investigations can be useful for finding rare parasites, in analysing parasite diversity, and for determining the seasonality of parasites.     

Comparative studies on goby (Teleostei) parasite communities from the North and Baltic Sea

The parasite communities of three goby species from the marine North and the brackish Baltic Sea were compared. The samples of summer 1992/93 from Helgoland, Lübeck and Kiel Bight comprised a parasite spectrum of 4–5 in Pomatoschistus microps, 2–3 in P. pictus or 3–8 parasite species in Gobiusculus flavescens. The highest numbers were found in Kiel Bight whereas those of Helgoland and Lübeck Bight differed between 3 and 7, respectively. In comparing the species identity of the studied localities the value was intermediate in P. microps, low in P. pictus and zero in G. flavescens. Values of prevalence and abundance were clearly lower in Helgoland than in Baltic localities. The prey of Helgoland goby populations comprised meio- and macrobenthos in P. microps, predominantly macrobenthos but also meiobenthos and some plankton in P. pictus, and predominantly plankton and some benthos in G. flavescens. Former studies (Zander in J Zool Syst Evol Res 32:220 1994) revealed a greater variability of prey choice in the Baltic. The greater parasite richness in the Baltic compared with that of Helgoland, may lie on better adaptations of genuine brackish components, lower defence mechanisms of hosts as a consequence of lower salinity, and greater variability in habitat choice. The effect of several filters on the colonisation of parasites in hosts is submitted here in a model.     

Colonization and seasonality of goby (Gobiidae, Teleostei) parasites from the southwestern Baltic Sea

A comparative parasitology study of gobiid fishes from two sites on the western Baltic Sea was done to get information on the quality of the respective environments. The parameters used were the infracommunity, the species numbers and abundance with respect to the size classes of the hosts, and the abundance with respect to the seasons. The hosts, Gobius niger, Gobiusculus flavescens, Pomatoschistus minutus, and P.?pictus, were caught at Blank Eck (Kiel Bight) and Dahmeshöved (Lübeck Bight) during 1992 and 1993. The infracommunities of Dahmeshöved attained higher rates of prevalence of helminth parasites than did those of Blank Eck, as was valid in all host specimens harboring one or two parasite species. The group bearing three parasite species was present in Dahmeshöved but absent in Blank Eck. Parasite species numbers, which were similar in the two sites, increased from the smallest to the largest hosts but changed with growth. With one exception, this result is also valid for the abundance, which clearly differed between the hosts and between the sites. Whereas species numbers as well as abundance rates were low in spring, they increased in summer. The results reveal that the composition of infracommunities depends on the local parasite fauna and on the strength of general host defense mechanisms, whereas that of the component community is dependent on the susceptibility of hosts to single parasite species and on the density of intermediate parasite stages. This is also the reason for the stronger infestation of hosts from Dahmeshöved as opposed to those from Blank Eck, where the degree of eutrophication is lower and, therefore, fewer herbivorous intermediate hosts can exist.     

Analysis of a parasite supra community from the Flensburg fjord

Parasites from Flensburg fjord, northern German Baltic coast, were investigated under regard of the component, guild, and supra community level. At least, 28 host species of the guilds snails, planktonic and benthic crustaceans, and fish (exclusively small-sized species) were infected by 53 parasite species (28 autogenic and 19 allogenic ones, six of uncertain status). The sampling location was a shallow water with muddy sand bottom and rich vegetation, which is influenced by brackish conditions and strong eutrophication. The density of hosts was high but corresponds to values from other locations in the western Baltic. Prevalence and parasite density was low in snails and planktonic copepods but moderate in benthic crustaceans and often high in the fish guild due to the peculiarities of the single parasite species. Diversity of parasites was high in snails and most crustaceans on the component level, but mostly low in fish. In contrast, only snails attained high diversity on the guild level. Species identity of parasites in mud snail hosts (three Hydrobia spp.) was high, and therefore, they can substitute each other, whereas fish hosts present predominantly their own parasite fauna. At least, 17 developmental cycles of helminths were pursued in the guilds. The supra community is decisively influenced by the host species richness which render possible the diversity of guild communities. The characteristics of the parasite supra community from Flensburg fjord are marked by a random agglomeration of helminth species and their larval stages and some species of other parasite groups.     

Effects of the digenean parasites Labratrema minimus and Cryptocotyle concavum on the growth parameters of Pomatoschistus microps and P. minutus from Southwest Wales

During the present study, about 800 specimens of gobies (Pomatoschistus microps and P. minutus) from two sites at Gower Peninsula, Southwest Wales, were studied. Both species were infected with the digenean parasites Labratrema minimus and Cryptocotyle concavum. The effects of these parasites on host-growth parameters such as the condition factor, the gutted condition factor, the hepatosomatic index, and the gonadosomatic index were considered. The results of multiple regression and hierarchical analysis of variance (ANOVA) show that in P. microps, increasing numbers of C. concavum in the peritoneum appear to reduce the hepatosomatic index, whereas rising numbers of L. minimus increase it. In P. minutus, increasing numbers of L. minimus in the liver and muscle decrease the hepatosomatic index and the gonadosomatic index. The opposite effects of L. minimus on the hepatosomatic index of these host species are discussed. Received: 21 March 2000 / Accepted: 6 June 2000     

Metazoa parasites of the invasive round goby <Emphasis Type="Italic">Apollonia melanostoma</Emphasis> (<Emphasis Type="Italic">Neogobius melanostomus</Emphasis>) (Pallas) (Gobiidae: Osteichthyes) in the Gulf of Gdańsk,Baltic Sea,Poland: a comparison with the Black Sea

The known metazoa parasite fauna of the invasive round goby Apollonia melanostoma (formerly Neogobius melanostomus) consists of 12 species. The core of the parasite fauna comprises two species: Cryptocotyle concavum and Diplostomum spathaceum; secondary species are absent; satellite species include Cercariae gen. sp. and Ergasilus sieboldi; rare species are Acanthocephalus lucii, Anguillicola crassus, Bothriocephalus sp., Dichelyne minutus, Hysterothylacium aduncum, Pomphorhynchus laevis, Piscicola geometra, and Tylodelphys clavata. Fifty percent of metazoa parasites that occurred in the invasive round goby in the Gulf of Gdańsk (an invasion that was first detected in 1990) are also typically found in the native Gulf of Gdańsk gobiids. The round goby hosts common fish parasite species: C. concavum and D. minutus, but none that are unique to the species and no Ponto–Caspian parasites. Notably, the parasite species of the invasive round goby in the Gulf of Gdańsk includes species that are atypical for this species in its native habitat. In its new habitat, the round goby variously serves the roles of definitive, second intermediate, and paratenic host for different parasite species. The fish species is involved in a parasitic system that includes fish-eating birds, fishes of different ecological groups (predatory, planktivorous, and benthivorous), and invertebrates.     

Parasitization of invasive gobiids in the eastern part of the Central trans-European corridor of invasion of Ponto-Caspian hydrobionts

Four gobiid species, Babka gymnotrachelus, Neogobius melanostomus, Neogobius fluviatilis, and Proterorhinus semilunaris, were parasitologically studied in different localities of the Dnieper and Vistula river basins. The highest number of parasitic species was found in N. fluviatilis (35 taxa). The parasite fauna of N. melanostomus, B. gymnotrachelus, and P. semilunaris consists of 23, 22, and 15 taxa, respectively. The species accumulation curves show stable accumulation of parasite species by all four fish hosts along the studied part of the corridor, from the Dnieper Estuary to the Vistula River delta. The plot reveals also that the studied gobies lose the parasites common in the host native range and accept new parasites from the colonized area. In the case of N. melanostomus, it complies with the enemy release hypothesis, as the parasite load was low in the invaded area if compared to the native range. The three other alien gobies are vector for Gyrodactylus proterorhini in the Baltic basin. Moreover, populations of this alien monogenean tend to be more abundant in their new range in comparison with the Black Sea basin. In general, the number of parasite species in the colonized area was of the same rank as in the native one for N. fluviatilis, and even higher for B. gymnotrachelus. This results from accumulating new parasite species along the gobiid invasion route. In particular, the N. fluviatilis, B. gymnotrachelus, and P. semilunaris lost some of their native parasites and gained the local ones after entering the post-dam part of the Vistula River; it can be interpreted as a partial escape from parasites.     

Ectoparasitic insects and mites on Yunnan red-backed voles (Eothenomys miletus) from a localized area in southwest China

Ectoparasitic insects and mites on Yunnan red-backed voles (Eothenomys miletus) in Dali prefecture, Yunnan Province, southwest China, were studied between 2003 and 2004. In total, 34,389 individuals of 86 species of ectoparasitic insects (seven species of fleas and five species of sucking lice) and mites (23 species of gamasid mites and 51 species of chigger mites) were collected from 916 individual hosts. The diversity of ectoparasites on this single rodent species in such a small area was much higher than in previous reports, which concerned more host species and greater geographical areas. The majority of the ectoparasites were chigger mites, which accounted for 59.3 % of the parasite species and 87.4 % of the individual parasites. Most voles harbored parasites with an overall prevalence (P) of 82.5 % and mean abundance (MA) of 37.5 parasites per host. The dispersion coefficient (C) and patchiness index (m*/m) were used to study the spatial patterns of the seven dominant parasite species, and all seven had aggregated distributions. The species abundance distribution of the ectoparasites on the vole was fitted by Preston’s lognormal distribution (R ²?=?0.82), and the total expected parasite species was estimated from this plot as 167 species. Yunnan red-backed voles harbor many ectoparasites as revealed by examination of a large host population. Future field investigations should sample large numbers of host individuals to assess ectoparasite populations.     

Contrasting patterns of structural host specificity of two species of Heligmosomoides nematodes in sympatric rodents

Host specificity is a fundamental property of parasites. Whereas most studies focus on measures of specificity on host range, only few studies have considered quantitative aspects such as infection intensity or prevalence. The relative importance of these quantitative aspects is still unclear, mainly because of methodological constraints, yet central to a precise assessment of host specificity. Here, we assessed simultaneously two quantitative measures of host specificity of Heligmosomoides glareoli and Heligmosomoides polygyrus polygyrus infections in sympatric rodent hosts. We used standard morphological techniques as well as real-time quantitative PCR and sequencing of the rDNA ITS2 fragment to analyse parasite infection via faecal sample remains. Although both parasite species are thought to be strictly species-specific, we found morphologically and molecularly validated co- and cross-infections. We also detected contrasting patterns within and between host species with regard to specificity for prevalence and intensity of infection. H. glareoli intensities were twofold higher in bank voles than in yellow-necked mice, but prevalence did not differ significantly between species (33 vs. 18 %). We found the opposite pattern in H. polygyrus infections with similar intensity levels between host species but significantly higher prevalence in mouse hosts (56 vs. 10 %). Detection rates were higher with molecular tools than morphological methods. Our results emphasize the necessity to consider quantitative aspects of specificity for a full view of a parasites’ capacity to replicate and transmit in hosts and present a worked example of how modern molecular tools help to advance our understanding of selective forces in host-parasite ecology and evolution.     

Host-parasite interactions in sympatric and allopatric populations of European bitterling

Susceptibility to parasite infection was examined in a field experiment for four populations of 0+ juvenile European bitterling (Rhodeus amarus): one sympatric to local parasite fauna, one allopatric, and two hybrid populations. Significantly higher parasite abundance was recorded in the allopatric bitterling population, suggesting a maladaptation of parasites to their sympatric host. Type of parasite life cycle played an important role in host–parasite interactions. While the abundance of allogenic species between populations was comparable, a significant difference was found in abundance of autogenic parasite species between fish populations, with the allopatric population more infected. These results correspond with a prediction of higher dispersion probability and higher gene flow among geographically distant populations of allogenic species as compared to autogenic species. Increased susceptibility to parasites that do not occur within the natural host's geographical distribution was found in the allopatric host, but only for autogenic species. A difference in infection susceptibility was detected among populations of early-hatched bitterling exposed to infection during a period of high parasite abundance and richness in the environment. Differences in parasite abundance and species diversity among populations diminished, however, with increasing time of exposure. No difference was found within late-hatched populations, probably due to a lower probability of infection in late-hatched cohorts.     

Parasite communities and feeding ecology of the European sprat (<Emphasis Type="Italic">Sprattus sprattus</Emphasis> L.) over its range of distribution

The metazoan parasite fauna and feeding ecology of 165 Sprattus sprattus (L., 1758) was studied from different geographic regions (Baltic Sea, North Sea, English Channel, Bay of Biscay, Mediterranean Sea). A total of 13 metazoan parasite species were identified including six Digenea, one Monogenea, two Cestoda, two Nematoda and two Crustacea. Didymozoidae indet., Lecithocladium excisum and Bomolochidae indet. represent new host records. The parasite species richness differed according to regions and ranged between 3 and 10. The most species-rich parasite fauna was recorded for sprats from the Bay of Biscay (North Atlantic), and the fishes from the Baltic Sea contained the lowest number of parasite species. More closely connected geographical regions, the North Sea, English Channel and Bay of Biscay, showed more similar parasite component communities compared with more distant regions. From the examined stomachs of S. sprattus, a total of 11 different prey items were identified, including Mollusca, Annelida, Crustacea and Tunicata. The highest number of prey organisms belonged to the crustaceans. The variety of prey items in the stomach was reflected by the parasite community differences and parasite species richness from the different regions. The feeding ecology of the fish at the sampled localities was responsible for the observed parasite composition and, secondarily, the zoogeographical distribution of the parasites, questioning the use of the recorded sprat parasites as biological indicators for environmental conditions and change.     

Parasite diversity of sticklebacks from the Baltic Sea

In the brackish Baltic Sea, the species richness and diversity of parasite communities of three- (Gasterosteus aculeatus) and nine-spined sticklebacks (Pungitius pungitius) were investigated. The studies regarded four localities at the Schleswig-Holstein and Mecklenburg coasts, northern Germany, where salinities were between 10 and 18‰. Species richness was relatively high, attaining 15 parasite species in G. aculeatus and 16 in P. pungitius, which are only surpassed by former investigations that lasted a year or more. An analysis of parasite species identity revealed clear differences in diverse localities referring to different supracommunities. The infracommunity comprised maximally of eight species in G. aculeatus and seven in P. pungitius, which corresponds to former investigations. The mean value of infracommunity with 5.3 parasites is the highest value ever found in small-sized fish. An infracommunity index revealed that the digenean Podocotyle atomon and Magnibursatus caudofilamentosa and the copepod Thersitina gasterostei were the most abundant parasites. The relationship of component community to mean infracommunity can judge about the threshold level, which allows parasite to settle successfully. An important factor to form parasite communities is the season of their appearance, which depends also on their reproduction and on the presence of intermediate hosts. In addition, the choice of prey (for passive infection) and quality of habitats (for active infection) influences the constitution of the parasite communities. The diversity values of parasites were low in all hosts, which is due to the brackish milieu and by different levels of eutrophication, which both create extreme environments. These do not mirror in every case the biodiversity of the respective habitats. The parasite community was in a level of early heterotrophic succession where low diversity is combined with high population density, which is characteristic for extreme environments. Therefore, intraspecific competition dominates and niches are wide. Under this aspect and regard of the actually valid definition that niches are dynamic systems between organisms and environment, the theory of vacant niches of some authors can be rejected.Contribution to the International Biodiversity Observation Year (IBOY) 2001, project: Survey of Stickleback Parasites.     

The first report of liver coccidian Goussia cruciata in jack mackerel,Trachurus murphyi,from the South Pacific and its relationship with host variables

The liver coccidian Goussia cruciata is considered as a specific parasite of the genus Trachurus, but to date, this parasite has only been reported for Atlantic species (Trachurus picturatus, Trachurus lathami, Trachurus trachurus and Trachurus mediterraneus). Therefore, this is the first report of this parasite in a species of Trachurus from the South Pacific. The prevalence and abundance of this coccidian in jack mackerel, T. murphyi, was determined, and its relationships with host variables such as total body length, condition factor and hepatosomatic index were evaluated. A total of 49 individuals were sampled from a commercial vessel of the central Chilean coast (36° 41′ S, 73° 06′ W) in November 2013 and February and May 2014. The parasite was identified by means of liver smears using light microscopy. The relationship between the abundance of the parasites and the host total length, condition factor and hepatosomatic index was analysed with Spearman’s correlations. The sporogonic stages exhibited sporocysts that were morphologically concordant with coccidian G. cruciata. All hosts were parasitised with this coccidian, and the abundance varied between 2 and 224 oocytes per host. The parasite abundance was negatively correlated with the host total length. Infection levels of G. cruciata in T. murphyi apparently do not produce negative effects on fish condition.     

Host specificity of the badger’s flea (Paraceras melis) and first detection on a bat host

Defining the whole spectrum of potential hosts of a parasite has large epidemiological and evolutionary implications in biology. Specialized parasites might be able to occasionally exploit a range of different host species, increasing the individual survival and the chances of successful dispersal. For long time Paraceras melis has been considered a specific flea of European badger Meles meles. Anyway, it has occasionally been reported on different hosts. In this work, we summarize the host spectrum of P. melis from literature and we report its first detection on a bat host. Ten species were identified as occasional hosts, man included, and the plasticity of this flea in host exploitation is noteworthy because of possible increase of pathogens transmission to humans and domestic species.     

The interaction between an introduced fish host and local parasite fauna: Neogobius kessleri in the middle Danube River

Parasite communities of introduced fish Neogobius kessleri Günther (Gobiidae) were studied at five localities in the Slovak section of the Danube River during 2002–2005. Thirty-three metazoan parasite species were identified. All fish were infected with at least two parasite species; most of the parasite species were generalists. At all sampling sites, high susceptibility to local parasites was observed. The parasite community was dominated by three parasite species: glochidia of Anodonta anatina, larval or subadult acanthocephalan Pomphorhynchus laevis, and larval nematode Raphidascaris acus. The infection of both A. anatina and P. laevis was affected by season and habitat type, with higher abundance in spring and more frequent occurrence of A. anatina in side channels and P. laevis in main river channels. At both the component and infracommunity levels, a more diverse parasite community was found in side channels. This habitat was dominated by actively transmitted parasites, whilst endoparasites were more abundant in fish from the main river channel. Larval stages of parasites dominated the endoparasite community at all sampling sites. The introduced N. kessleri was used as intermediate host for most of the recorded parasites, in some cases also as a paratenic host. Finally, the importance of gobies as suitable hosts for local non-native parasite species (Anguillicoloides crassus, Anodonta woodina, Hydrozetes lacustris) is discussed.     

Helminth parasites in freshwater fish from the Papaloapan river basin, Mexico

A checklist based on previously published records and original data is presented for the helminth parasites reported in 35 fish species from nine families from the Río Papaloapan basin, east Mexico. The checklist contains 85 taxa from 39 helminth families. Trematodes and nematodes were the most abundant taxonomic groups. The helminth fauna in the fish of the Papaloapan River basin predominantly consists of Neotropical species that are largely autogenic. The introduced species Centrocestus formosanus was the most widely distributed helminth, infecting 16 host species. Ten of the recorded helminth species have only been found in fish from the Papaloapan. This inventory contributes 157 new host records, and reports the presence of 30 helminth species in the Papaloapan for the first time . This inventory shows the richness of helminth parasite species in the fish of the Papaloapan River basin in comparison with the other hydrological basins in Mexico. It also demonstrates that this fauna is typically Neotropical and quite similar to that from the neighboring basins of the Grijalva–Usumacinta system and the Yucatan Peninsula. The data also suggest highly effective transmission between environments within the same basin and that the regional parasite fauna is strongly influenced by fish community composition.