Parasite Recruitment Research Articles

Recruitment and Seasonal Occurrence of Parasites in Juvenile Invasive Round Gobies (Neogobius melanostomus) in the St. Lawrence River, Quebec, Canada

The round goby (Neogobius melanostomus) is an invasive species that has become one of the most abundant fish in the St. Lawrence River, Quebec, Canada over the past 15 yr. Since its introduction, the round goby has acquired a number of native parasites, yet little is known about the dynamics of parasite recruitment. To examine this question, young-of-the-year and juvenile round gobies were collected monthly from 2 localities in the river (Îles de la Paix, Île Dorval) from June through November 2012. At Îles de la Paix, round gobies (n = 180) were infected with 3 species of parasites, all larval stages (Diplostomum spp., Tylodelphys scheuringi, Neoechinorhynchus tenellus). Prevalence of the digenean Diplostomum spp. varied from 3.3 to 13.3%, and mean abundance from 0.03 to 0.53 from June through September, with a maximum in August. The digenean T. scheuringi was seen only in August, at a prevalence of 10.0% and a mean abundance of 0.53. The acanthocephalan N. tenellus was observed in June, August, and September, prevalence ranging from 3.3 to 10.0% and mean abundance from 0.03 to 0.27. Maximum infection for all 3 species occurred in August. All infected fish were ≥44 mm in total length (TL). Fish infected with more than 1 parasite species were >60 mm TL. No round goby (n = 178) was infected at Île Dorval. This study demonstrated that the invasive round goby starts to acquire parasite infections in the St. Lawrence River in the first year of life and may contribute to the transmission of some parasites within this ecosystem.

PARASITISM IN HYBRID SUNFISH (LEPOMIS SPP.): PATTERNS OF INFECTION AT THE INDIVIDUAL AND COMMUNITY LEVEL.

Sunfish (Lepomis spp.) are among the most common piscine inhabitants of freshwater lakes and ponds in North America. Lepomis spp. breed at the same time creating hybrid zones, where genetically distinct populations mate and produce mixed offspring that are sexually viable hybrids. One aspect of hybridization that may have important consequences is parasitism and its patterns of recruitment in the hybrid sunfish. This study investigated these patterns both at the level of the individual parasite species as well as in the parasite communities infecting the fish. Two sample sites possessing hybrid sunfish populations were investigated: 1 system had bluegill sunfish (Lepomis macrochirus), redear sunfish (Lepomis microlophus), and their hybrids, while the other system had bluegill sunfish (L. macrochirus), green sunfish (Lepomis cyanellus), and their hybrids. The hybrids were infected by mostly generalist parasites that commonly infect all Lepomis spp. Most of the individual parasite species followed a dominance pattern (59.1%) of infection, where parasite abundance in hybrids resembled at least one of the parental species, with the remainder exhibiting intermediate levels of parasitism, supporting an additive pattern of parasite recruitment (40.1%). At the community level, the patterns of parasite recruitment differed in L. macrochirus × L. microlophus hybrids, which showed a dominance pattern, and L. macrochirus × L. cyanellus hybrids, which showed an additive pattern of parasite recruitment. These differences in parasite recruitment between hybrid groups may be attributed to varying degrees of dietary and niche overlap between the parental species in the 2 study systems.

Parasitism of Brook Trout (Salvelinus fontinalis) during the first month post-emergence in streams in southwest Nova Scotia

Parasite recruitment of recently emerged fry of brook trout (Salvelinus fontinalis) in three streams in southwestern Nova Scotia was documented. In early April, fry appeared to leave the protective gravel redds parasite free but began acquiring parasites within the next 2-4 weeks, with prevalence of infections of any given species reaching 21 to 46% by mid-May. The initial infections involved 1) directly transmitted ectoparasites Gyrodactylus colemanensis and Salmincola edwardsii and 2) food-borne endoparasites (Echinorhynchus lateralis and Crepidostomum sp.). Colonizing parasites found in the first month post-emergence varied by locality: at Bangor Creek, it involved G. colemanensis, E. lateralis, and Crepidostomum sp., while at Germaine East, it involved only G. colemanensis and at Germaine North, only S. edwardsii. In each case, the initial colonizers reflected what was abundant locally and within a regional pool of 10 parasite species. Localized skin thickening and sometimes tissue erosion were evident at sites of attachment of S. edwardsii. Minor disruption of fin margins was seen with G. colemanensis. No pathology was associated with E. lateralis nor Crepidostomum sp. The predictable timing of emergence and ease of sampling fry of S. fontinalis near redds represents a convenient system with which to assess impact of initial parasitism on fish recruitment at the local level. Keywords: Echinorhynchus, Gyrodactylus, initial parasite colonization, regional parasite pool, Salmincola

Helminth Infracommunities of the Montezuma's Frog Lithobates montezumae (Anura: Ranidae) in the Nearctic-Neotropical Transition Zone of Mexico.

Thirty specimens of the Montezuma's frog Lithobates montezumae were collected in San Pedro Tlaltizapán, in the Nearctic-Neotropical transition zone of Mexico, in April 2013, in order to establish the helminth infracommunity structure harbored by this amphibian host. A total of 5,493 individual helminths were obtained, representing 6 species (3 trematodes and 3 nematodes). The depauperate structure of the helminth infracommunities established for the studied frogs herein (richness = 2.4; mean abundance = 183.1; Brillouin's diversity = 0.42) fits with those described for the 6 Ranidae species studied in the Nearctic. Three of the 6 species of helminths recovered are generalists, 2 of them with the highest values for prevalence ( Falcaustra mexicana) and mean abundance ( Renifer sp.). The parasite recruitment process (ingestion) determining mean richness in the helminth infracommunities studied here (ingestion) is shared with those reported for the 9 Mexican frog species for which helminthological records exist; however, in this case, mean abundance was determined by directly penetrating species. The use of aquatic habits by this anuran species likely explains why the composition of their helminth infracommunities was mainly constituted of helminths acquired in this environment (5 of 6 species). Finally, the heterogeneity of their taxonomic composition and abundance of helminth species indicate the unpredictable nature of these host-parasite associations.

The NE Atlantic European hake: A neglected high exposure risk for zoonotic parasites in European fish markets

A sampling programme to understand the factors affecting zoonotic parasite presence and infection intensity of Atlantic European hake populations was conducted from 2013 to 2015. Commercial fish samples comprising 430 hake specimens from northern (Grand Sole) and southern (Atlantic Iberian Peninsula) fishing grounds were sampled, recorded and inspected. We also analysed 75 additional samples collected around Scotland. Parasites were microscopically identified to genus level. Fish biometric measurements were statistically evaluated as categorical predictors of parasite recruitment into fish stocks. Stable isotope composition was determined in another sample batch of 501 hakes from the NE Atlantic (Grand Sole and Galician grounds) to explore trophic indicators as potential predictors of parasite burden. Partial sequences from mitochondrial and nuclear marker genes (mtDNA cox2 and EF1 α-1 nDNA) from a set of 915 Anisakis larvae confirmed the northern stock to be parasitized by A. simplex (s.s.) while off the Iberian Peninsula hake there was a mixed infection pattern with larvae of A. simplex s.s. (67.4% of identified larvae), A. pegreffii (31.9%) and the F1hybrid (0.7%). The observed burden of Anisakis spp. larvae differed markedly between fishing areas. The presence of very high Anisakis spp. burdens in a comparatively small proportion of individual fish was well-illustrated with characteristic tensegrity grid architecture for parasite aggregation derived from a plaque-forming cell response observed in the abdominal cavity of larger fish specimens. Demographic infection values were remarkably high in Grand Sole and off the Iberian Peninsula, with 100% prevalence and mean abundances in the fillets ranging from 247 (A. simplex) in hake from Grand Sole to 60 A. simplex and 20 A. pegreffii in southern European populations. Infections were less prevalent and less intense in the hake sample from Scottish waters. Fish size was the most important factor affecting Anisakis spp. prevalence and abundance, with larger fish containing more Anisakis larvae. Anisakis abundance within individual fish was also positively correlated with the condition index although this does not rule out negative effects on the host, and with trophic level, even after fish size was accounted for. These results suggest that higher Anisakis burden is associated with a higher food intake and with eating larger prey. The risk profile for zoonotic parasites herein described for European hake populations underlines the urgent need for adopting a contingency plan that minimizes the risk exposure.

Approach to reduce the zoonotic parasite load in fish stocks: When science meets technology

The increasing public awareness on the presence of anisakids in the viscera and mostly the flesh of commercially important fish species provoked the search of technical solutions to reduce the abundance of infective viable larvae at sea. During the last decade, a technological device was tested and improved to check its viability to reduce the presence of parasites in a hot spot epidemiological area with high prevalence on anisakids. The device was monitored under laboratory conditions and at sea in Grand Sole fishing ground. The Technological Device for Avoiding Parasite Discarding at Sea (hereafter TEDEPAD®) is industrial equipment designed to process the viscera are generated on board commercial fishing vessels. This equipment inactivates the zoonotic parasites present in the viscera, especially those of the genus Anisakis (and congeners) affecting humans (anisakidosis and related allergies) and markets, before the offals are returned to the sea. This process would contribute to a substantial reduction of viable infective larvae returning to the water mass, which otherwise would reinfestate the food system if remained untreated. As a consequence, and bearing in mind than a single female of Anisakis spawn about 1.5 million eggs, a minimization of the incidence of infective parasite larvae (firstly in the water mass of the fishing grounds and later on major fish stocks of commercial interest) is expected. The cost-benefit analysis indicates important benefits from different perspectives: the minimization of the dispersion of viable larvae parasites, the reduction of the recruitment of parasites into fish species of commercial interest, the decrease of rejected fishing products, reduction in sanitary expenses to attend parasite-induced pathologies, and increase of the consumer confidence that derives in highest fish purchases. Overall, all these issues will improve the environmental health of the fishing grounds and, in parallel, will provide an important economic positive impact for the fishing sector.

Host density increases parasite recruitment but decreases host risk in a snail-trematode system.

Most species aggregate in local patches. High host density in patches increases contact rate between hosts and parasites, increasing parasite transmission success. At the same time, for environmentally transmitted parasites, high host density can decrease infection risk to individual hosts, because infective stages are divided among all hosts in a patch, leading to safety in numbers. We tested these predictions using the California horn snail, Cerithideopsis californica (=Cerithidea californica), which is the first intermediate host for at least 19 digenean trematode species in California estuaries. Snails become infected by ingesting trematode eggs or through penetration by free-swimming miracidia that hatch from trematode eggs deposited with final-host (bird or mammal) feces. This complex life cycle decouples infective-stage production from transmission, raising the possibility of an inverse relationship between host density and infection risk at local scales. In a field survey, higher snail density was associated with increased trematode (infected snail) density, but decreased trematode prevalence, consistent with either safety in numbers, parasitic castration, or both. To determine the extent to which safety in numbers drove the negative snail-density-trematode-prevalence association, we manipulated uninfected snail density in 83 cages at eight sites within Carpinteria Salt Marsh (California, USA). At each site, we quantified snail density and used data on final-host (bird and raccoon) distributions to control for between-site variation in infective-stage supply. After three months, overall trematode infections per cage increased with snail biomass density. For egg-transmitted trematodes, per-snail infection risk decreased with snail biomass density in the cage and surrounding area, whereas per-snail infection risk did not decrease for miracidium-transmitted trematodes. Furthermore, both trematode recruitment and infection risk increased with infective-stage input, but this was significant only for miracidium-transmitted species. A model parameterized with our experimental results and snail densities from 524 field transects estimated that safety in numbers, when combined with patchy host density, halved per capita infection risk in this snail population. We conclude that, depending on transmission mode, host density can enhance parasite recruitment and reduce per capita infection risk.

Enigmatic decline of a common fish parasite (Diplostomum spp.) in the St. Lawrence River: Evidence for a dilution effect induced by the invasive round goby.

As they integrate into recipient food webs, invasive exotic species may influence the population dynamics of native parasites. Here we assess the potential impact of the Eurasian round goby (Neogobius melanostomus) on the abundance of eyeflukes of the genus Diplostomum, which are common parasites in fishes of the St. Lawrence River (Canada). Analyses of data collected over nearly two decades revealed that the infection levels in three native fish [spottail shiner (Notropis hudsonius), golden shiner (Notemigonus crysoleucas) yellow perch (Perca flavescens)] declined sharply throughout the St. Lawrence River after the introduction of the goby. At two sites where data were collected at regular time intervals, declines of Diplostomum spp. in spottail shiners occurred within two years of the goby's first recorded appearance, with prevalence dropping as much as 77–80% between pre-invasion and post-invasion periods. Furthermore, in localities where gobies remained scarce, infection in native species did not change significantly over time. Altogether, these observations suggest that gobies play a role in the eyefluke collapse. The decline in populations of the main definitive host (ring-billed gulls, Larus delawarensis) and changes in hydrology during periods of parasite recruitment were not strongly supported as alternate explanations for this phenomenon. Since other snail-transmitted trematodes with similar life cycles to Diplostomum spp. did not show the same decreasing pattern, we conclude that eyeflukes did not decline as a result of snail depletion due to goby predation. Rather, we suggest that gobies acted as decoys, diluting the infection. As Diplostomum spp. occurred at lower abundance in gobies than in native fish hosts, the replacement of native fish with exotic gobies in the diet of gulls might have played a part in reducing parasite transmission. In contrast to the typically negative impact of invasions, the goby-induced decline of this pathogen may have beneficial effects for native fishes.

Temporal occurrence and community structure of helminth parasites in southern leopard frogs, Rana sphenocephala, from north central Oklahoma.

Currently, little information is available about the temporal recruitment of helminth communities in amphibian hosts. We examined the helminth community structure and temporal recruitment of helminth parasites in southern leopard frogs, Rana sphenocephala. Specifically, we were interested in how host life history such as habitat, age and/or size, diet, sex, and temporal variation in abiotic factors (precipitation and temperature) were important in determining monthly infection patterns of helminth populations and communities in southern leopard frogs. From May to September 2011, 74 southern leopard frogs were collected from Teal Ridge in Stillwater Payne County, OK, USA. Sixty-nine (93 %) of 74 frogs were infected with 1 or more helminth species. During our collecting period, the average monthly temperature was lowest in May and highest in July, and monthly precipitation was highest in May and lowest during the first week of September. The component community consisted of 11 species of helminth, including 1 larval and 1 adult cestode, 2 larval and 3 adult trematodes, and 1 juvenile and 3 adult nematodes. Of the 1790 helminths recovered, 51 % (911) were nematodes, 47 % (842) were cestodes, and 2 % (37) were trematodes. There were significant differences in the total abundance and mean species richness of helminths acquired by skin contact or through frog diet in monthly component communities of southern leopard frogs. A positive correlation existed for percentage of all helminths acquired by skin contact and monthly precipitation (r = 0.94, P < 0.01). Conversely, a negative correlation existed for monthly precipitation and percentage of helminths acquired by diet (r = -0.94, P < 0.01). Our results indicate that abiotic conditions such as precipitation have a major influence on the avenues for and constraints on the transmission of helminths with life cycles associated with water/moisture or terrestrial intermediate/paratenic hosts and are important in structuring helminth communities of amphibian hosts.

Trypanosoma cruzi-Host Cell Interaction.

Chagas disease was discovered by Carlos Chagas in Brazil in 1909 (1). It is caused by the pathogenic protozoan Trypanosoma cruzi, member of Trypanosomatidae family, Kinetoplastida order. Chagas disease is recognized by the World Health Organization as one of the main neglected tropical diseases, affecting about 8–15 million individuals in 18 countries in Central and South America, where it is endemic, as well as countries in North America and Europe (2). At least 30 million people are at risk. Public health programs have significantly reduced transmission of Chagas disease, however, blood and organ transplant transmission in non-endemic countries and a growing number of food borne (especially fruit juices) infections still require special attention. In addition, an increase in the rate of infection in the Amazon region has become a challenge for the control of Chagas disease (3). Trypanosoma cruzi presents a complex life cycle both in the vertebrate and invertebrate hosts, involving dramatic changes in cell shape (4). Its life cycle involves several developmental stages that are known as amastigotes, epimastigotes, and trypomastigotes. The first two stages are able to divide inside and outside host cells, respectively. The trypomastigote and amastigote stages are also able to infect host cells where they multiply, amplifying the number of parasites, and releasing millions of the infective trypomastigote forms in the intercellular spaces. This thematic issue deals with the ability of T. cruzi to penetrate into host cells. In the first article, de Souza and de Carvalho (5) make a review of the concept of active penetration and suggest that T. cruzi always penetrates the host cell through an endocytic process with the formation of a transient parasitophorous vacuole. The second article by Barrias et al. (6) reviews the various mechanisms of endocytosis, which are used by the protozoan to gain access to the intracellular portion of the host cells. These include processes such as classical phagocytosis, participation of membrane rafts, macropinocytosis, and clathrin-mediated endocytosis. In the third article, Calvet et al. (7) analyze in detail the process of interaction of T. cruzi with cardiomyocytes, an important host cell, because in vivo many of the parasite strains have a tropism for the heart. In the fourth article, Tonelli et al. (8) call the attention to the fact that most probably a large number of molecules are involved in the process of protozoan–host cell interaction and discuss the use of more powerful technologies, such as peptide-based phage display and oligonucleotide-based aptamer techniques. Using these approaches, the results obtained by the group highlight the importance of members of the 85-kDa family on the process of interaction. In the fifth article, Freire-de-Lima et al. (9) point out the relevance of a unique system of sialoglycoproteins and sialyl-binding proteins, which in the case of T. cruzi are represented by trans-sialidases. These proteins are involved in parasite–host cell recognition, infectivity, and survival. The sixth and seventh articles by Nde et al. (10) and Ferreira et al. (11) respectively, analyze the role played by components of the extracellular matrix during the interaction of the trypomastigote and amastigote forms of T. cruzi with the host cells. Infective trypomastigotes up-regulate the expression of laminin-gamma−1 and thrombospondin to facilitate recruitment of parasites to enhance cell infection. The extracellular matrix interactome network seems to be regulated by T. cruzi and its gp 83 ligand. The eighth article by Maeda et al. (12) reviews the cell signaling process that takes place during the interaction of metacyclic trypomastigotes, infective forms found in the invertebrate host, with host cells. Special emphasis is given to intracellular calcium mobilization and the triggering the exocytosis of host cell lysosomes during the interaction process mediated by a surface-expressed parasite glycoprotein of 82 kDa. This process leads to the activation of mammalian target of rapamycin (mTor), phosphatidylinositol 3-kinase, and protein kinase C. The last article, by Scharfstein et al. (13) initially analyses the process by which T. cruzi trypomastigotes elicit an inflammatory edema that stimulates protective type-1 effector cells through the activation of the kallikrein–kinin system, providing a framework to investigate the intertwined proteolytic circuits that couple the anti-parasite immunity to inflammation and fibrosis.

Host and parasite recruitment correlated at a regional scale

Drivers of large-scale variability in parasite prevalence are not well understood. For logistical reasons, explorations of spatial patterns in parasites are often performed as observational studies. However, to understand the mechanisms that underlie these spatial patterns, standardized and controlled comparisons are needed. Here, we examined spatial variability in infection of an important fishery species and ecosystem engineer, the oyster (Crassostrea virginica) by its pea crab parasite (Zaops ostreus) across 700 km of the southeastern USA coastline. To minimize the influence of host genetics on infection patterns, we obtained juvenile oysters from a homogeneous source stock and raised them in situ for 3 months at multiple sites with similar environmental characteristics. We found that prevalence of pea crab infection varied between 24 and 73% across sites, but not systematically across latitude. Of all measured environmental variables, oyster recruitment correlated most strongly (and positively) with pea crab infection, explaining 92% of the variability in infection across sites. Our data ostensibly suggest that regional processes driving variation in oyster recruitment similarly affect the recruitment of one of its common parasites.

Nyctiphanes couchii as intermediate host for Rhadinorhynchus sp. (Acanthocephala, Echinorhynchidae) from NW Iberian Peninsula waters

In the mesozooplanktonic community of the coastal upwelling system of the Ría de Vigo (NW Spain), the euphausiid Nyctiphanes couchii has been identified for the first time in temperate waters of the NE Atlantic as the intermediate host for cystacanths of Rhadinorhynchus sp. Parasites were identified using morphological characters described in 20 cystacanths. The hooks of the proboscis were arranged in 14 rows of 26 hooks each, while the hooks of the basal circle were only slightly erected and were longer than remaining spines. A maximum-likelihood estimation (ML) tree inferred from the 18S rRNA data set of Palaeacantocephala revealed that our specimens belong to a highly supported clade with Rhadinorhynchus sp., Pararhadinorhynchus sp. and Transvena annulospinosa. Nonetheless, our morphological and phylogenetic analyses suggested that the status of Rhadinorhynchus pristis should be re-examined. The prevalences of parasites were 0.0019% and 0.0001% for frontal and coastal summer communities, and 0.0068% and 0.0008% for coastal and oceanic autumn communities, respectively. The presence of these cystacanths in different mesozooplankton communities throughout the study suggests that the recruitment of parasites may be affected by the oceanography.

Baylisascaris procyonisInfection in White-Footed Mice: Predicting Patterns of Infection from Landscape Habitat Attributes

There is a growing body of evidence that habitat fragmentation resulting from anthropogenic land use can alter the transmission dynamics of infectious disease. Baylisascaris procyonis , a parasitic roundworm with the ability to cause fatal central nervous system disease in many mammals, including humans, is a zoonotic threat, and research suggests that parasite recruitment rates by intermediate hosts are highly variable among forest patches in fragmented landscapes. During 2008, we sampled 353 white-footed mice ( Peromyscus leucopus ) from 22 forest patches distributed throughout a fragmented agricultural ecosystem to determine the influence of landscape-level habitat attributes on infection rates of B. procyonis in mice. We characterized each mouse in terms of infection status and intensity of infection, and calculated (on a patch-wide basis) prevalence, mean abundance of B. procyonis , and mean intensity of infection. We used an information-theoretic approach to develop a suite of candidate models characterizing the influence of landscape attributes on each of our measured characteristics of B. procyonis infection in white-footed mice, based on previous knowledge of raccoon ( Procyon lotor ) ecology and B. procyonis distribution in agricultural ecosystems. We observed evidence of B. procyonis infection in mice across all 22 habitat patches sampled. However, parasite recruitment rates and intensity were highly variable among patches, and the results of our analyses suggest that spatial variability in B. procyonis infections was primarily driven by emergent properties of fragmented ecosystems. In particular, prevalence, abundance, and intensity of B. procyonis infections in mice were negatively associated with the size and connectivity of forest patches. These results support previous studies indicating that habitat fragmentation can alter the transmission dynamics of infectious disease, and suggest that factors below the scale of landscape, i.e., fine-scale habitat structure or demographic and behavioral attributes of intermediate and/or definitive hosts, also may be important for predicting patterns of B. procyonis infection in intermediate hosts.

Prevalence and reproduction of Bopyrina abbreviata (Isopoda, Bopyridae) in Laguna de Términos, SW Gulf of Mexico

Bopyrina abbreviata Richardson, 1904 parasitizes caridean Hippolytidae, important consumers of submerged aquatic vegetation. This study evaluates the prevalence and reproductive aspects of the parasite at two-month intervals during an annual cycle in the Gulf of Mexico. The average prevalence of B. abbreviata was 0.37% (range 0.01-1.47%). Sex ratio of infested host was skewed to females ( X 2 = 138 . 90 , df = 1; P 0 . 01 ). The parasite pattern distribution on its host was aggregated (ID = 1.83; d = 19 . 25 ). Host shrimps were infested principally by a couple of parasites, male and female, (74.7%). The intensity of infestation did not vary with host sex ( t = 1 . 69 ; P > 0 . 05 ) but varied with shrimp size classes ( t = 2 . 19 ; P < 0 . 05 ). The relationship between the host cephalothorax length and parasite total length was positive ( r 2 = 0 . 91 ), as was that between fecundity and size of B. abbreviata ( r 2 = 0 . 58 ). The main parasite recruitment took place during February and April, and its reproductive peak from April to June; this seems to reflect the mating period of the parasite larvae in the young hosts and the simultaneous growth of both species. The size at maturity of B. abbreviata was 1.64 mm TL and females produced an average of 637.3 ± 336 embryos, which increased their volume from 0.0005 mm3 to 0.0008 mm3 in stages I to III, respectively. Loss of eggs in B. abbreviata was estimated at 7.21%.

Intestinal Helminth Fauna of Bottlenose DolphinTursiops truncatusand Common DolphinDelphinus delphisfrom the Western Mediterranean

We report on the intestinal helminth fauna of 15 bottlenose dolphins Tursiops truncatus and 6 short-beaked common dolphins Delphinus delphis from the western Mediterranean. Eight helminth species were found in bottlenose dolphin, i.e., the digeneans Synthesium tursionis, Brachycladium atlanticum, and Pholeter gastrophilus, the nematode Anisakis sp., and the cestodes Tetrabothrius forsteri, Diphyllobothrium sp., Strobilocephalus triangularis, and tetraphyllidean plerocercoids. Brachycladium atlanticum, S. triangularis , and tetraphyllidean plerocercoids are new host records. No T. forsteri had previously been reported in Mediterranean bottlenose dolphins. Three species of helminths were recorded in the common dolphin, i.e., the digenean Synthesium delamurei (which was a new host record), and the cestodes T. forsteri and tetraphyllidean plerocercoids. The intestinal helminth communities of bottlenose and common dolphins are depauperate, similar to that of other cetacean species, but those from bottlenose dolphins harbored a higher number of helminth species. This study supports the notion that oceanic cetaceans, such as common dolphins, have a comparatively poorer helminth fauna than that of neritic species, such as bottlenose dolphins, because the likelihood of parasite recruitment is decreased.

More than meets the eye: detecting cryptic microgeographic population structure in a parasite with a complex life cycle

Nonrandom recruitment of parasites among hosts can lead to genetic differentiation among hosts and mating dynamics that promote inbreeding. It has been hypothesized that strictly aquatic parasites with intermediate hosts will behave as panmictic populations among hosts because ample opportunity exists for random mixing of unrelated individuals during transmission to the definitive host. A previous allozyme study on the marine trematode Lecithochirium fusiforme did not support this hypothesis; in that, there was genetic differentiation among, and significant heterozygote deficiencies within, definitive hosts. We revisit this system and use microsatellites to obtain multilocus genotypes. Our goal was to determine whether cryptic subgroups and/or the presence of clones could account for the apparent deviation from 'panmixia'. We find strong evidence for cryptic subdivision (three genetic clusters) that causes the Wahlund effect and differentiation among definitive hosts. After accounting for these cryptic groups, we see panmictic genetic structure among definitive hosts that is consistent with the 'high mixing in aquatic habitats' hypothesis. We see evidence for cotransmission of clones in all three clusters, but this level of clonal structure did not have a major impact in causing deviations from Hardy-Weinberg equilibrium, and only affected genetic differentiation among hosts in one cluster. A cursory examination of the data may have led to incorrect conclusions about nonrandom transmission. However, it is obvious in this system that there is more than meets the eye in relation to the actual make-up of parasite populations. In general, the methods we employ will be useful for elucidating hidden patterns in other organisms where cryptic structure may be common (e.g. those with limited morphology or complex life histories).

First record of Nippotaenia mogurndae Yamaguti and Miyata, 1940 (Cestoda, Nippotaeniidae), a parasite introduced with Chinese sleeper to Poland

A parasitological survey of an Asian fish, Chinese sleeper Perccottus glenii, inhabiting the Włocławek Reservoir on the lower Vistula River (central Poland) revealed the occurrence of an exotic cestode Nippotaenia mogurndae Yamaguti and Miyata, 1940, which spreads spontaneously with a host to European waters. This paper documented the first record of the parasite in Poland. Specimens were described, and the effect of fish size and season on the infection level was analyzed. Within the 3 years, 112 fish were examined. Samples were collected by electrofishing in the upper part of the Włocławek Reservoir three times (seasonally) in 2006 and 2007 and once in autumn 2008. Parasitological indices (prevalence, intensity of infection, and abundance) in particular samples as well as in two size groups of fish were calculated. Statistical tests were applied to analyze the results (Spearman's correlation coefficient and Mann-Whitney's U test). The infection level of Chinese sleeper with N. mogurndae in the Włocławek Reservoir (prevalence 54.7%, mean intensity of infection 7.2, maximum 29) was comparable to infection noted in the area of the natural range of the host. The infection of smaller fish (less than 80 mm, TL) increased gradually with increasing body size. The infection of bigger specimens was in general higher, but the parasite recruitment was of a more incidental character. The spreading of N. mogurndae with Chinese sleeper is still in progress. The Włocławek Reservoir provides suitable conditions for parasite development.

Parasite recruitment and oceanographic regime: evidence suggesting a relationship on a global scale

We here investigate the relationship between oceanographic processes and variability in parasite recruitment to host populations using existing data from host-parasite systems encountering differing hydrographic conditions. Combined epidemiological data obtained from both exploited fish and cephalopod populations indicate that variability in recruitment of parasite infracommunities tends to be associated with major current systems of the World's oceans. It appears that instability in water masses caused by physical perturbations (e.g. water mass convergence and turbulent mixing in upwelling systems) is associated with instability of trophic interactions over time, which in turn leads to a paucity of parasite communities in that area. The likely relationship between parasite recruitment and oceanographic regime should be extremely useful to the fishing industry and also as an indicator of ecosystem health.

Risk factors associated with Enteromyxum scophthalmi (Myxozoa) infection in cultured turbot, Scophthalmus maximus (L.)

An epidemiological cohort study of Enteromyxum scophthalmi in cultured turbot was performed on a farm in North Western Spain. Four different ongrowing stocks (A, B, C, D) were monitored monthly until market size. Fish from stocks C and D were divided into 2 subgroups, receiving filtered (CF and DF) or unfiltered (CUF and DUF) water. The lack of water filtration was positively associated with infection prevalence, as all fish kept in filtered water remained uninfected. Parasite abundance varied seasonally (P<0.05) in stock B and subgroup CUF. Infection was also associated (P<0.05) with host weight, and the highest prevalences and intensities were detected in 101-200 g and 201-300 g fish. Distribution pattern of E. scophthalmi in subgroups CUF and DUF had a variance higher than the mean, indicating overdispersion. The minimum period necessary for the first detection of the parasite and for the appearance of disease symptoms and mortality, varied depending on the stock and introduction date, although a long pre-patent period was always observed. Several factors, such as host density, parasite recruitment and parasite-induced fish mortality can contribute to the observed distribution pattern. Risk factors found to be associated with E. scophthalmi infection, including water quality and accumulation of infective stages in the culture tanks, should be considered when designing control strategies to prevent the introduction and spread of infective stages in the facilities.

Morphological, developmental and ecological evidence for a progenetic life cycle in Neochasmus (Digenea)

Seven species of fishes, Catostomus commersonii (Lacépède), Etheostoma nigrum Rafinesque, Micropterus dolomieu Lacépède, Notemigonus crysoleucas (Mitchill), Notropis hudsonius (Clinton), Perca flavescens (Mitchill), and Percina caprodes (Rafinesque) from the St. Lawrence River, Quebec, Canada, were found infected with progenetic specimens of Neochasmus spp. in the orbits and/or the body musculature. Worms displayed varying degrees of maturation. Eggs occupied the entirety of the worm in late stages of development and persisted as distinct clusters in situ after worm death. Populations of parasites were studied monthly in E. nigrum from one site between May and October in order to follow parasite recruitment, development and maturation. Recruitment of parasites was observed in young-of-the-year fish primarily in July and continued through October. Worms matured rapidly, displaying egg production within a month. Later developmental stages, in which eggs occupied most of the worm, and clusters of eggs became abundant by September. Infections in overwintered fish collected in May consisted mainly of worms in early stages of egg production and of clusters of eggs. When hatched artificially, eggs from the clusters released viable miracidia, indicating that they survive beyond the lifespan of the adult worm. It is suggested that progenesis is a fixed characteristic of the life cycle of these species, that egg dispersal requires the death of the host and that it is facilitated by predation. All prior records of Neochasmus spp. are examined, leading us to conclude that the role of the putative definitive host (primarily basses) has been reduced to that of a dispersal agent. Current hypotheses concerning the evolution and maintenance of progenesis are considered, but it is concluded that they do not apply to this host-parasite system.