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The Pacific saury Cololabis saira (Brevoort, 1856) is one of the important target species of commercial fisheries. Food manufacturers and consumers encounter problems due to the infection of the saury by acanthocephalans, which are quite difficult to clean out completely during on-board catch processing. Infection of C. saira was not studied on a regular basis, therefore, our knowledge about the parasites of saury is fragmentary. This paper contains infection indices (only acanthocephalans) of the Pacific saury caught in the Kuril Islands area (Russian Exclusive Economic Zone) in 2015.

Parasitological investigations of 529 specimens of 7 fish species from the water basins of the Khabarovsk Territory in 2009-2013 revealed the high extensity (11.7 to 100%) and intensity (as many as 9341 larvae per fish) of invasion with N. s. schikhobalowi metacercaria in salmonlike fishes from the mountain tributaries (Khor, Anyui, and Manoma) of the Amur river. The examined specimens of four salmonlike fish species (Thymallus tugarinae, Hucho taimen, Brachymystax tumensis and B. lenok) showed an increase in all indicators of infestation: invasion extensity (IE), invasion intensity (II), and abundance index (AI) with age. Moreover, IE peaked just in a 3-4-year-old fish (and in 1-year-old B. lenok) and further remained virtually unchanged. N. s. schikhobalowi metacercaria accumulated in the fish trunk with age, by maintaining their viability. With very high II, practically 100% infestation in B. lenok makes the population run the maximum risk of Nanophyetus infection with the dietary intake of this fish species if it is not disinfected. Examination of the distribution of N. s. schikhobalowi metacercaria in the trunk of Thymallus tugarinae showed that over 50% of larvae were detectable in the kidneys. This peculiarity of their localization could propose a simple method to determine II for Nanophyetus larvae in salmonlike fishes. Recommendations for reducing the risk of human infection with trematodes are given.

Malacofaunal and ichthyoparasitological studies were conducted in the floodplain-river ecosystem in the middle course of the Amur River. The studies covered its channels and tributaries, such as Big and Small Bira, Bidzhan, In, and Vertoprashikha Rivers, in the Birobidzhan, Leninskoye, and Smidovich districts of the Jewish Autonomic Region in the second half of August 2011. It was established that there were biotopes of the mollusk Parafossalurus manchouricus, the first intermediate host of Clonorchis sinensis, in the exosystems of the In, Bira, and Bidzhan Rivers. Sporadic P. manchouricus specimens were found in the Bidzhan channel in the vicinity of its estuary and on the flooded bank of the In River. The bay of the Bira River (the town of Birobidzhan) exhibited a biotope of P. manchouricus with a mollusk population density of 180 to 300 specimens/m2. Seven of 16 examined fish species showed metacercariae of Clonorchis. Among them there were not only Cyprinidae, but also representatives of other families and orders. The two-year-olds of orca-skripuns (Pseudobagrus fulvidraco), orca-whips (Tachysyrus ussuriensis), and Brazhnikov's orsas (Liocassis braschnikowi) were infected with C. sinensis metacercariae. Clonorchis metacercariae were first detected in Amur sleepers (Percottus glehni). This fish species has not been heretofore recorded as the second intermediate host ofC. sinensis. The highest invasion extent for C. sinensis metacercariae was revealed in Amur bitterlings (Rhodeus sericeus) born during the current year. In the biotopes ofdifferent water reservoirs, it changed from 10.0 to 48.0%. In 4 of 6 water reservoirs, Amur bitterlings were found to have larvae of this species of trematodes. The invasion rates were in the range from 1 to 4 metacercariae per fish. Only in individual cases, they were as great as 28 parasitic larvae per fish.

Fishes, such as ide (Leuciscus idus), dace (Leuciscus leuciscus), carpbream (Abramis brama), roach (Rutilus rutilus), and muvarica (Alburnus alburnus), with different frequency and rate of invasion and abundance index were infested with larvae of O. felineus, M. bilis, and P. truncatum. There were the highest rates of fish infection with P. truncatum larvae in the subtaiga zone (the south of the region) and with O. felineus metacercariae in the northern subtaiga and taiga zones. In research, experimental, and clinical studies, the nosological entity opisthorchiasis is a parasitic cenosis consisting of 2-3 co-members requiring their specific identification, which allows therapeutic measures to be more effectively implemented among the population of a hyperendemic focus.

The study was undertaken in 1996-1999 to examine 255 fishes of 15 species from the Bug River for their helminthic larve that are a serious hazard to human health. The larvae of 6 species of these parasites were found. Their fish infection rates were 38.8%; Eleven species were found to act as their hosts species. Among helminths there were the trematoda Opisthorchis felineus (Rivolta, 1884) that is of medical significance. Metacercariae were detected in 2 roaches from 95 caught in the Bug River in the vicinity of the village of Domachevo, Brest Region.

The influence of the T. nodulosus plerocercoid invasion on the liver of the intermediate fish hosts (perch) was studied. The water, protein, glycogen and glucose contents was examined in adult worms inhabiting the intestine of definitive hosts (pike), the rate of glucose accumulation along the strobile of parasite and an ability of adult worms to hydrolyze the main nutrients was also investigated. As a result of the plerocercoid infection, the glucose and glycogen contents in the liver of perch juveniles decreased, while the wet weight of liver increased. It was found, that the water and protein contents from the anterior to posterior section of strobile in T. nodulosus adults was not significantly different, while the glucose contents and the rate of its accumulation decreased. The data confirming the possibility to realize the final stages of protein and carbohydrate hydrolisis with the participation of membrane digestion on the surface of helminths and proving the ability of cestodes. The problems of relations of T. nodulosus with intermediate and definitive hosts at the level of the whole organisms are discussed.

Relations of PKX [vector of proliferative kidney disease (PKD)] of reared and wild Salmonoidea and Tetraspora bryozoides, the only genus and species of Myxozoa found in fresh water Bryozoa, is discussed using recent publications. Both organisms were found in several European countries as well as in North America. It seems that PKX is a Bryozoa parasite which do not undergo full cycle of sporulation in fish.

Experiments were made to infect young Ophiocephalus argus, the fish of prey delivered from eastern Asia in the Amu-Dar'ya River basin, outside the area of the broad tapeworm Diphyllobothrium latum. The dalags were infected mainly by ingesting the local copepods Arctodiaptomus salinus, the experimentally invaded larvae of the broad tapeworm. The latter larvae were obtained from the development of eggs of the helminth isolated from strobilae from the patients treated in Perm Province. D. latum plerocercoids lived in the dalags nearly 3 weeks, then they died and lysed. Thus, the dalag cannot be a supplementary host of D. latum.

Five species of trematodes: Metagonimus yokogawai, M. katsuradai, Centrocestus armatus, Nanophyetus salmincola schikhobalowi and Paragonimus westermani ichunensis which are able to infect man have been found to develop with the participation of mollusks of the Juga genus from the rivers of the Maritime Territory. Some epizootiological aspects of the infections caused by these trematodes are considered in the paper.

Helminthological investigation of the Irtysh-Karaganda Canal area was performed in the summer of 1989. In 9 storage ponds on the Shiderta and Olenta rivers 900 fish individuals, whose size was suitable for fishery have been examined, samples of water have been taken and the epidemiological assessment of modern conditions of opisthorchiasis agent circulation have been presented. The whole canal is at present favourable in view of opisthorchiasis infection. Local cases of infection are associated with fish from Shiderta and Olenta rivers.

Materials reflecting opisthorchiasis infection in fish in the Novosibirsk region were analyzed. On the basis of fish population estimation and studies on its invasion with Opisthorchis felineus (Rivolta, 1884) it was shown that a considerable part in maintaining opisthorchiasis foci is played by Leucaspius delineatus. It is numerous, can easily acclimatize itself in natural water bodies, inaccessible for predatory animals, easily infected with Opisthorchis larvae, and therefore can play an important role in formation of new opisthorchiasis foci during amelioration of Kulunda and Baraba forest-steppe.

The data concerning biological peculiarities of spores of Myxosoma cerebralis obtained by the author and other researchers are summarized. The life cycle of M. cerebralis is well adapted to the seasonal cycle of the host owing to the fact that the infectivity of the spores is attained only after 4 months of aging in water and that the spores are highly resistive to freezing and drying. No sexual process during 4 month aging was observed. It is supposed that the maturity of spores depends to a great extent on the ability of polar capsules for extrusion.

The list of intermediate hosts of Bunodera luciopercae is given. In Lake Syamozero they are represented by crustaceans Heterocope, Ophryoxus. Data on their role in the ration of juvenile perch are given. Diurnal dynamics of the ratio between infected and noninfected plankton in feeding and the process of the formation of fish infection have been studied.