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The trophic niches of Arctic charr and brown trout differ when the species occur in sympatry . Their trophically transmitted parasit es are expected to reflect these differences. Here , we investigate how the infections of Diphyllobothrium dendriticum and Diphyllobothrium ditremum differ between charr and trout. These tapeworms use copepods as their first intermediate hos ts and fish can become infected as second intermediate hosts by consuming either infected copepods or infected fish . We examined 767 charr and 368 trout for Diphyllobothrium plerocercoids in a subarctic lake. The prevalence of D. ditremum was higher in charr (61.5 %) than in trout , (39.5 %), but the prevalence of D. dendriticum was higher in trout (31.2 %) than in charr (19.3 %). Diphyllobothrium spp. intensities were elevated in trout compared to charr, particularly for D. dendriticum . Large fish with massive parasite bur dens were responsible for the high Diphyllobothrium spp. loads in trout. We hypothesize that fish prey may be the most important source for the Diphyllobothrium spp. infection s in trout, whereas charr predominantly acquire Diphyllobothrium spp. by feeding on copepods . Our findings support previous suggestions, that the ability to establish in a second piscine host is greater for D. dendriticum than for D. ditremum .

Between April and June 2009, 1,075 feral rainbow trout from 10 different lakes involved with aquaculture activities in Los Lagos Region, Chile, were inspected for Diphyllobothrium species. All viscera and muscles of the fish were examined using stereomicroscopy; pyloric cecae and stomachs infected with plerocercoids were checked by histology and scanning electron microscopy. Plerocercoids of Diphyllobothrium dendriticum were confirmed by PCR and sequencing of COI and 18S rRNA + ITS1 + 5.8S rRNA + ITS2 genes for the first time in Chile. Overall prevalence of plerocercoids of D. dendriticum was 9.2% (99/1,075) in Los Lagos Region and 17.4% (99/570) for Chiloe Island. Plerocercoids were not detected in the continental lakes of the Los Lagos Region (Chapo, Rupanco, and Llanquihue). Tarahuín Lake exhibited a prevalence of 50.9% (81/159), Cucao Lake 5.1% (4/79), Natri Lake 4.7% (5/107), Huillinco Lake 3.6% (5/138), and San Antonio Lake 66.7% (4/6). Abundance was 1.1 plerocercoid larvae per fish (1,169 larvae/1,075 fish). All the plerocercoids were found encysted in the viscera of the fish. Plerocercoids were 10.9 ± 3 (7–16) mm long by 0.4 ± 0.2 (0.2–0.6) mm wide. The scolex was enlarged, with 2 bothria and a frontal pit. The body was covered with short capilliform filitriches, 4–6 mm long. The Chilean COI and 18SrRNA + ITS1 + 5.8SrRNA + ITS2 gene sequences indicated 96.34–96.52% and 99% similarity with D. dendriticum sequences, respectively. Diphyllobothrium dendriticum is reported for the first time in freshwater ecosystems as far as 43°S on Chiloe Island. These findings and previous reports of plerocercoids of Diphyllobothrium spp. in farmed rainbow trout at Tarahuín Lake support the putative life cycle of this parasite in lakes of southern Chile where there are aquaculture activities.

Parasite prevalence in predatory mammals is influenced by numerous factors including diet, sex, season, and habitat. We examined the effect of such factors on the prevalence of gastrointestinal helminths in North American river otters (Lontra canadensis) in Yellowstone Lake, Yellowstone National Park. Otters in this ecosystem have recently experienced a decline in their main prey, Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri), and have, in turn, increased consumption of alternative foods. Helminths were found in 13.2% of otter fecal samples. The dominant parasite was a Diphyllobothrium sp. (Diphyllobothrium ditremum or Diphyllobothrium dendriticum), a cestode acquired from cutthroat trout. Truttaedacnitis truttae and Contracaecum spp. nematodes were incidental parasites in otter feces, and acanthocephalan eggs were found in 1 sample. The prevalence of trout remains and a Diphyllobothrium sp. in otter feces was higher during the cutthroat trout spawning season. A Diphyllobothrium sp. was more prevalent in the feces of female otters. There was no relationship between annual declines in the frequency of trout in otter feces and prevalence of parasites. Helminth prevalence and species richness in Yellowstone otters was low and likely reflects low predator densities and few intermediate hosts. This is the first study reporting the helminth fauna of river otters in the Greater Yellowstone Area and confirms the otter as a definitive host for Diphyllobothrium sp. in this region.

The present study addresses the morphological features of cisco, round whitefish and grayling. These fish species are the most abundant representatives of Coregonidae and Thymallidae in the eastern part of Lake Sobachye. The local cisco (Coregonus sp.) is closer to vendace (Coregonus albula) than to least cisco (Coregonus sardinella) in its diagnostic features. Ciscoes with a low number of vertebrae (the average number significantly below 60) were previously found in the Khantayka River and Khatanga River basins. C. sardinella is a cisco with a high number of vertebrae (more than 60 on average), which inhabits all basins, along with cisco populations that have a low number of vertebrae. Analysis of mitochondrial DNA polymorphism (mtDNA) of the cisco (Coregonus sp.) from Lake Sobachye showed a significant similarity between this population and the cisco from European water bodies (C. albula). The basic meristic traits of the round whitefish (Prosopium cylindraceum) from Lake Sobachye and other lakes of the Putorana Plateau are considered in the present study. The round whitefish in the water bodies of the Norilo-Pyasinskaya system is represented by a single population. All known groups of the Taymyr round whitefish are rightfully considered as typical representatives of the \"Arctic\" group. Thus, there is no reason to distinguish between the \"Arctic\" and \"Boreal\" groups. The round whitefish in the water bodies of the Norilo-Pyasinskaya system is represented by river and lake-river forms. For the first time, complete morphological characterization of the Siberian grayling (Thymallus arcticus) has been given for this region. Research ofparasite fauna of cisco, round whitefish, Siberian grayling and whitefish (Coregonus lavaretus) showed that Lake Sobachye is a site of diphyllobothriasis. The cestode Diphyllobothrium dendriticum carriers are whitefish (C. lavaretus) and cisco (Coregonus sp.). Compared with the results of previous studies, the rate offish infestation with parasites associated with the zooplanktonic organisms has increased: the prevalence of cisco by D. dendriticum has increased from 73% (2002-2004) to 96%, and the average intensity ofparasitic infestation has increased from 4 to 8 individuals.

Toxaphene, an organochlorine pesticide, is the major contaminant of Arctic charr (Salvelinus alpinus) in the Canadian Arctic. The objective of this study was to investigate the combined effects of toxaphene exposure and infection by the larval stage of the cestode Diphyllobothrium dendriticum on fish growth, nutritional composition, and hematology. Hatchery-reared Arctic charr were subjected to one of four treatments: (1) oral administration of corn oil (control); (2) single oral dose of 10 microg/g wet wt toxaphene dissolved in corn oil; (3) exposure to 15 larval D. dendriticum; and (4) exposure to toxaphene and D. dendriticum in combination. The experiment was run for 104 days. Mean final toxaphene concentrations in charr muscle were 0.121, 0.336, 0.131 and 0.458 microg/g wet wt in each treatment group, respectively. Exposure to toxaphene and D. dendriticum decreased fish growth and condition as well muscle lipid and protein content. However, toxaphene did not increase the susceptibility of Arctic charr to parasite infection. Overall, 25 of 40 fish (62.5%) exposed to larval D. dendriticum became infected. Parasitized charr had decreased hematocrits and increased lymphocyte:erythrocyte ratios. Although total blood cell counts were decreased in all treatments compared with controls, differential leucocyte counts were unaffected. Our results suggest that toxaphene does not moderate Arctic charr resistance to D. dendriticum and there is no contaminant-parasite interaction at environmental levels.

Individual Arctic charr (Salvelinus alpinus) from Fjellfrosvatn, northern Norway, could be categorized by their stomach contents as zooplanktivores or benthivores. Feeding specialization among these fish was evident from negative correlations between helminths transmitted by pelagic copepods (Diphyllobothrium dendriticum and D. ditremum) and those transmitted by the benthic amphipod Gammarus lacustris (Cystidicola farionis and Cyathocephalus truncatus). Occurrences of parasite species acquired from the same types of invertebrate were positively correlated in the fish. Strong relationships among habitat use, diet, and helminth infections among the Arctic charr indicated persistent foraging patterns involving long-term habitat use and feeding specialization. The distribution of all parasite species was highly aggregated in the fish samples, measured by the exponent k of the fitted negative binomial distributions (range: 0.5-7.5) and the variance-to-mean ratios (s2/[xmacr] , range: 5-85). Charr specializing on either copepods or Gammarus predominantly contributed to high-intensity class intervals within the overall frequency distributions of the corresponding parasite species. Such fish had low infection intensities of helminths transmitted by other prey organisms. The detailed analyses of the parasite frequency distributions for fish with different habitat or feeding preferences evidently show how heterogeneity in trophic behavior contributes strongly to the commonly observed aggregation of helminths among hosts under natural conditions.

A parasitological study was performed of chars of the genus Salvelinus inhabiting Lake Kronotskoe (Kamchatka Peninsula)— S. malma, S. albus, S. schmidtii , and S. kronocius , as well as of juvenile Salvelinus spp. Twenty-three species of parasites, including six species new for the lake, Hennequya zschokkei, Protteocephalus longicollis, Diphyllobothrium dendriticum, Crepidostomum sp., Echinorhynchus salmonis , and Paracanthobdella livanowi , were found. With consideration of published data, in chars of this water body, 28 species of parasites were recorded, including seven species ( N. cf. pungitius, B. luciopercae, Crepidostomum sp., Cr. fausti, Cr. cf. cooperi, Eubothrium crassium , and Proteocephalus sp.), whose presence or species identification in the lake ecosystem need confirmation. Two species ( N. rutili and Diphyllobothrium sp.) are removed from the list. Parasites common for all species of chars were revealed. They include Myxobolus arcticus, E. salvelini, D. ditretum, Crepidostotum sp., Cr. farionis, Cr. metoecus, Cystidicola farionis, Cucullanus truttae, Philonema oncorhynchi , and Salmincola carpionis . Cluster analysis of the fauna of parasites of different species of chars demonstrated considerable differences in infestation, which indicates differences between them in preference for food items and occupied biotopes and thereby supports the ecological differentiation of chars in the basin of Lake Kronotskoe. S. albus and S. kronocius are most similar in parasitofauna, which is determined by their predation; S. malma as a benthophage is infected by the same species of parasites, but considerably less intensively. Extremely high indices of population numbers of some parasite species are considered as a manifestation of the Krebs cycle in parasites under the conditions of an isolated lake.

Composition of fatty acids (FA) was studied in bacteria Vibrio anguillarum, total and lysosomal lipids of cestodes Eubothrium crassum and Diphyllobothrium dendriticum, and roe of the roach Rutilus rutilus, carp Cyprinus carpio, and salmon Salmo salar. Bacteria collected from different geographic zones but cultivated under the similar conditions have been found to maintain the FA spectra peculiarities substantially corresponding to temperature conditions of their habitat region. Unsaturation of total lipids in D. dendriticum, determined from the ratio between saturated, monoenoic, and polyenoic acids was higher than that of lysosome membrane lipids. This phenomenon might be due to pre-adaptation of the lipid FA composition of eggs produced in huge amounts by a parasite to low temperatures of environment, in which embryos are to be developed. Quantitative ratios of lipid FA in the roach, carp, and salmon roes correspond to the spawning thermal tolerance diapason specific of some particular fish species and to some extent do not depend on real temperature conditions existing at the moment of development.

The free radical nitric oxide (NO) has emerged as a simple and unique signalling molecule that can serve as neurotransmitter, paracrine substance or hormone. NO is a gas, formed by various neuronal cells, both centrally and peripherally. NO regulates cyclic GMP synthesis. The production of NO can be detected using the NADPH diaphorase (NADPH-d) histochemical stain for nitric oxide synthase (NOS). NOS was detected in two parasitic flatworms, Diphyllobothrium dendriticum and Hymenolepis diminuta, and two free-living flatworms, Planaria torva and Girardia tigrina. The staining for NOS was very strong in the nervous system of both parasitic worms. The main nerve cords, the transverse ring commmissures, nerves in association with the musculature, especially the cirrus musculature and sensory nerve endings showed NADPH-d staining. The NADPH-d staining in the free-living flatworms was much weaker. Still NOS activity was found in the neuropile of the brain and in association with the pharynx musculature. The demonstration of NOS in flatworms, indicates that NO is an old signal molecule in evolutionary terms.

Five cDNAs (pDidact2-pDidact6), representing different actin genes, were isolated from a Diphyllobothrium dendriticum cDNA library, and the DNA as well as the putative amino acid sequences were determined. The corresponding Didact2 and Didact4 genes code for peptides 376 amino acids long, with molecular weights 41,772 and 41,744 Da, respectively, while the deduced Didact3 protein is 377 amino acids long and weighs 41,912 Da. The pDidact5 and -6 cDNAs lack nucleotides corresponding to three to six amino acids at the amino-terminus. Two of the five cDNAs contain the conventional AATAAA as the putative polyadenylation signal, one has the common variant ATTAAA, whereas the hexanucleotide AATAGA is found 15 and 18 nucleotides, respectively, upstream of the poly(A) site in two of the cDNAs. Phylogenetic studies including 102 actin protein sequences revealed that there are at least four different types of cestode actins. In this study three of these types were found to be expressed in the adult D. dendriticum tapeworm. Structurally the cestode actin groupings differ from each other to an extent seen only among the metazoan actins between the vertebrate muscle and cytoplasmic isoforms. In the phylogenetic trees constructed, cestode actins were seen to map to two different regions, one on the border of the metazoan actins and the other within this group. It is, however, difficult to say whether the cestode actins branched off early in the metazoan evolution or if this position in the phylogenetic tree only reflects upon differences in evolutionary rate.