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Intraspecific variability of the cestode P. longicollis was studied in three host species: the Nelma ( Stenodus nelma ), the Lenok ( Brachymistax lenok ), and the Malma ( Salvelinus malma ) of the fish order Salmoniformes. Host forms of helminths were found to be similar in the intrapopulation diversity and in the proportion of rare forms evaluated by polymorphous features of the scolex shape and sexually mature segments. Host differences in morphophysiological traits such as the attachment, trophics, and reproduction have been revealed. The parasites from Nelma are shown to be the most diverse phenotypically. These forms show the maximum heterogeneity of diversity and distribution frequencies. The conclusion is drawn that the helminths respond to changes in the habitat conditions in the host predominantly by plastic traits.

Despite the importance of the electric catfish ( Malapterurus electricus ) and the African giant catfish ( Heterobranchus bidorsalis ) in the foodweb of Lake Nasser, Egypt, little is known about their diseases and parasitic fauna. This work describes, for the first time, cestodiasis in M. electricus and H. bidorsalis . Corallobothrium solidum and Proteocephalus sp. were identified morphologically and molecularly from M. electricus and H. bidorsalis , respectively. Using PCR, sequencing, and phylogenetic analysis, the two cestodes shared rRNA gene sequence similarities yet were unique and the two new sequences for the proteocephalid genera were submitted to the GenBank database. The prevalence of infection was 75% and 40% for the two fish species, respectively. Infections significantly increased in the summer and spring and were higher in female fish than in male fish. The intestine was the preferred site of the two adult cestodes. However, in the case of C. solidum some larval cestodes were found outside the intestine in between the skin and abdominal musculature, attached to the mesentery, and within intestinal tunica muscularis. Desquamation of the intestinal epithelium and inflammation at the site of infection in addition to congestion of the intestinal wall of the tapeworm infected fish were evident, indicating that C. solidum and Proteocephalus sp. impacted the infected fish. The larval stages of C. solidum attempted to penetrate the intestine and sometimes they were encircled within fibrous layers infiltrated with inflammatory cells. The infected fish’s musculature was free of cestode infections. Preventive measures should be implemented to prevent the spread of infections.

The European perch Perca fluviatilis L. serves as a host of different endohelminths of Trematoda, Cestoda, Nematoda, and Acanthocephala. Its natural range covers freshwater basins throughout much of Europe, including the Danube. Since information about endohelminths of European perch from this international river basin has been rather sporadic, the parasitological examinations of 700 perch from the central region of the Danube river basin in Slovakia were performed in October 2017 and April 2018. The larval stages of Triaenophorus nodulosus (Cestoda) were found in cysts located in the perch liver and adults of Proteocephalus percae (Cestoda) were isolated from the intestine. The larval stages of Eustrongylides sp. (Nematoda) and metacercariae of Clinostomum complanatum (Trematoda), both potential causative agents of fish-borne zoonoses, were found in the musculature. Spatial and seasonal differences in the occurrence of currently detected helminths were discussed with data on biological and environmental conditions of particular sampling site.

Twaite shad (Alosa fallax) includes two subspecies, the anadromous Alosa fallax nilotica, and the landlocked species Alosa fallax lacustris, representing the only Clupeidae inhabiting Lake Garda. Study of the parasitic fauna of this species in this area is still limited. For this reason, the aim of the present study was to evaluate the presence of tapeworms from A. fallax lacustris sampled in Lake Garda. Sixty-six A. fallax lacustris specimens were collected at the Milan fish market (Lombardy, Italy); specifically, an evaluation of the gastrointestinal contents was carried out for the presence of helminths. All parasites found were fixed in 70% ethanol and transferred to the laboratories of the University of Messina for morphological and molecular analysis. Parts of the parasites were stained with Semichon’s carmine red technique. Molecular analysis was carried out using LSU rRNA and ITS2 region genes. Eight specimens out of sixty-six (12.1%) were positive for adult cestodes within the pyloric caeca. Morphological and molecular analysis could to identify the parasites found to be Proteocephalus longicollis. This parasite species is not considered a zoonotic agent, representing a low risk of parasitic fish-borne zoonosis for consumers of this appreciated fish from Lake Garda.

Here we evaluate the potential of heavy metal accumulation of Proteocephalus macrophallus parasitizing the Butterfly Peacock Bass (Cichla ocellaris). A total of 19 fish specimens were collected. From the hosts, samples of intestine, liver, muscle, and parasites were taken. Heavy metal concentrations (Al, As, Ba, Cd, Cr, Fe, Hg, Mg, Mn, Ni, Pb, Ti, and Zn) were obtained using Atomic Absorption Spectrometry. All analyzed elements was found in higher concentrations in the parasites comparing to its host tissues. The bioconcentration factors were higher in the intestine, varying between 5.91 (Ti) to 8.00 (Ba), followed by the muscle, 1.88 (Mg) to 6.39 (Zn), and liver, 1.67 (Al) to 2.02 (Ba). These results show that at the infection site heavy metal concentrations are reduced, since the elements are absorbed directly from the intestinal wall by the parasites. In general, P. macrophallus presents a reasonable capacity of metal accumulation comparing to its hosts.

Non‐random species associations occur in naturally sampled parasite communities. The processes resulting in predictable community structure (e.g. particular host behaviours, cross‐immunity, interspecific competition) could be affected by traits that vary within a parasite species, like growth or antigenicity. We experimentally infected three‐spined sticklebacks with a large tapeworm (Schistocephalus solidus) that impacts the energy needs, foraging behaviour and immune reactions of its host. The tapeworms came from two populations, characterized by high or low growth in sticklebacks. Our goal was to evaluate how this parasite, and variation in its growth, affects the acquisition of other parasites. Fish infected with S. solidus were placed into cages in a lake to expose them to the natural parasite community. We also performed a laboratory experiment in which infected fish were exposed to a fixed dose of a common trematode parasite. In the field experiment, infection with S. solidus affected the abundance of four parasite species, relative to controls. For two of the four species, changes occurred only in fish harbouring the high‐growth S. solidus; one species increased in abundance and the other decreased. These changes did not appear to be directly linked to S. solidus growth though. The parasite exhibiting elevated abundance was the same trematode used in the laboratory infection. In that experiment, we found a similar infection pattern, suggesting that S. solidus affects the physiological susceptibility of fish to this trematode. Associations between S. solidus and other parasites occur and vary in direction. However, some of these associations were contingent on the S. solidus population, suggesting that intraspecific variability can affect the assembly of parasite communities.

Concurrent infections of helminths in vertebrates are widespread and may demonstrate synergistic, antagonistic or negligible levels of interactions between species that share a common site. However, indirect interactions between species that occur in different organs of a host are poorly documented, particularly in fish. Plerocercoids of Triaenophorus nodulosus are common liver infections of European perch (Perca fluviatilis). These larval cestodes cause extensive liver damage, resulting in systemic pathologies that include alteration of the physiochemical environment of the intestine. Perch harbour a wide range of intestinal helminths whose occurrence may be potentially influenced by the concurrent presence of T. nodulosus plerocercoids. The present study, using an existing dataset, investigated the effects of T. nodulosus on the infection levels of four common perch helminths – Acanthocephalus lucii, Camallanus lacustris, Proteocephalus percae and Bunodera luciopercae. The prevalences of A. lucii and C. lacustris were significantly reduced in fish infected by T. nodulosus, although the mean intensity of infections remained unaffected for any helminth species, while the mean abundance of C. lacustris was significantly reduced in plerocercoid-affected perch. Differences in site selection and individual interactions between the four helminth species in the intestine of T. nodulosus-infected and non-infected perch were rarely observed.

Here, we evaluate the potential for trace metal accumulation of nine elements (Al, Cr, Mn, Fe, Ni, Cu, As, Cd, and Pb) in the cestodes Proteocephalus macrophallus parasitizing the tucunaré, Cichla kelberi, in the Jacaré-Guaçú River, southeastern Brazil. For metal quantification in the tissues of hosts and parasites, an inductively coupled plasma–mass spectrometer (ICP-MS) was used. All recovered trace metals were in higher amounts in cestodes than in the tissues (muscle, intestine, and liver) of their hosts. The best accumulated element was lead, with concentrations up to 10,000 times higher in parasites than in the liver of the fish hosts. Other well-accumulated elements were cadmium, with concentrations up to 238 times higher in parasites, and aluminum and nickel, with concentrations ranging from 140 to 128 times higher in parasites. In addition, non-infected fish had higher concentrations of cadmium and lead in their tissues than infected fish. In infected fish, the size of the cestodes’ infrapopulations influenced in the concentrations of arsenic, cadmium, and lead in the hosts tissues. In general, specimens of P. macrophallus had a good capacity for metal accumulation for all the analyzed elements, with emphasis on Al, Ni, Cd, and Pb, and therefore could be a useful tool in trace metal bioaccumulation indication.

The occurrence of trophically transmitted intestinal parasites in Arctic charr was analyzed from data material collected over two decades from Lake Takvatn, northern Norway. The main objectives were to investigate (i) between-year variation in parasite infracommunity composition, (ii) between-host variation in infracommunity composition, and (iii) possible interspecific interaction between parasites. The trematode Crepidostomum spp. and the cestode Eubothrium salvelini were most prevalent and had the highest mean intensities whereas the cestodes Proteocephalus sp. and Cyathocephalus truncatus were uncommon taxa. No clear indication of interspecific parasite interactions was evident. By far the most frequent infracommunity composition was E. salvelini co-existing with only Crepidostomum spp. Despite some indications of individual dietary specialization in Arctic charr, this strong species cooccurrence suggests that the majority of fish had been preying on the very different intermediate hosts of both parasites. Overall, even though some sporadic between-year variation was present, no long-term or cyclical variation in infracommunity composition and mean intensity was revealed, suggesting that the host– parasite system is in a steady state. Minor between-year variation was likely the result of changes in habitat and dietary utilization by Arctic charr, possibly linked to documented changes in the fish community structure of the lake.

Here, we report the first record of pleroceroids of the Nearctic tapeworm Proteocephalus ambloplitis (Leidy, 1887) in European fresh waters. The plerocercoids were found encapsulated in the internal organs of the invasive pumpkinseed Lepomis gibbosus (Linnaeus, 1758) in a pond in Bègles Plage, Bordeaux, France. This parasite species was not observed in L. gibbosus collected from two nearby localities, Bordeaux Lac and a pond in the Parc de Fontaudin. Species identification was confirmed using molecular data and morphological characteristics.