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Parasitological research of two landlocked populations of Dolly Varden ( Salvelinus malma ) dwelling the river–lake system in the Uzon caldera (Kamchatka) was done for the first time. Twelve species of fresh-water parasites were found. Charrs from the Lake Tsentral’noe–Shumnaya River were infected by Eubothrium salvelini , Diphyllobothrium ditremum , D. dendriticum , Crepidostomum farionis , Cr. metoecus , Ichthyocotylurus erraticus , Sterliadochona ephemeridarum , Philonema oncorhynchi , and Cucullanus truttae . Charrs from the Lake Dal’nee were infected by Henneguya zschokkei , Chloromyxum coregoni , Proteocephalus longicollis , and Cucullanus truttae . Based on stomachs content and parasites abundance, it was found that charrs from the Lake Dal’nee feed on plankton, and at length more than 12 cm, switch to cannibalism. In the contrast, charrs from the Lake Tsentral’noe and Shumnaya River primarily feed on benthos and rarely on plankton, and no cannibalistic specimens were found.

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.

There is little information on the phylogenetic position and life cycle of family Kathlaniidae. Falcaustra araxiana is a member of this family which infects the large intestine of the European pond turtle (Emys orbicularis). In the present study, morphological data and molecular analyses based on the 18S rDNA were performed on different types of F. araxiana originating from the large intestine and gastric nodules in the turtle. Morphological data revealed both larvae and adult stages in the gastric nodules. In addition, all nematodes recovered in the large intestine were adult worms. GenBank accession numbers KM200715 and KM200716 were provided for adult F. araxiana located in the intestine and stomach, respectively, of E. orbicularis. The results of sequencing proved that these two types are completely similar. Accordingly, it can be hypothesized that nodule formation is a part of the life cycle of the parasite or a survival strategy. Furthermore, F. araxiana develops to the adult stage in the gastric mucosa prior to migrating to the large intestine. Phylogenetic analysis revealed that F. araxiana unexpectedly branched away from other members of the superfamily Seuratoidea (Truttaedacnitis truttae, Cucullanus robustus and C. baylisi) and showed a closer relationship with Paraquimperia africana, a member of the Ascaridoidea. It seems that phylogenetic reconstruction for the present parasite needs more detailed morphology, life cycle and molecular studies.