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Stable isotope ratios of carbon (13C/12C, δ13C) and nitrogen (15N/14N, δ15N) in snail-host tissue (the foot and hepatopancreas) and trematode parasites on two stages of their life cycle were analyzed. Trophic structure in co-occurring trematode larvae was examined in the following species: five species of cercariae (Echinoparyphium recurvatum, Hypodereum conoideum, Plagiorchis mutationis, Diplostomum chromatophorum and D. volvens) and two species of metacercariae (Cotylurus cornutus and Echinoparyphium recurvatum) within two closely related snail hosts Lymnaea stagnalis and L. tumida using stable isotope analyses. Snail and parasite sampling was conducted in a riverine portion of the Kargat River of the Lake Chany basin, in the south of Western Siberia (54 degrees 37'76"N, 78 degrees 13'07" E), in August 2009. Four out of five studied cercariae species were depleted in 15N as well as in 13C relatively to snail hosts tissues (foot and hepatopancreas), supporting our previously published data for Plagiorchis mutationis and Echinoparyphium recurvatum cercariae. Such fractionation of cercariae is untypical of the commonly observed relationship between consumers and their food. D. chromatophorum cercariae had demonstrated an insufficient enrichment in δ15N volume in relation to the hepatopancreas. Both two species of metacercariae (C. cornutus and E. recurvatum) showed a significant enrichment in δ15N volume relatively to the host tissue consumed (fractionation values ranging from 1.5 to 4 per thousand depending on the species). The differences in δ15N and δ13C volume between cercariae and metacercariae observed in this study illustrate the complexity of the host--parasite trophic relationships. Such isotopic differences between cercariae and metacercariae can probably be explained by selective consumption of specific amino acids or lipids or by changes in metabolism associated with the life cycle of the parasite. The present study represents the first comparative analysis of trophic relationships between the host and the endoparasite at different life cycle stages. It demonstrates the potency of the stable isotope analyses for understanding trophic relationships in multispecies parasite communities.

A comparative analysis of changes of activities of detoxifying and antioxidant enzymes was carried out in the body homogenate of the pond snail Lymnaea stagnalis. Juvenile snails with the shell size of 4-6 mm were infested with cercariae of one (Echinoparyphium aconiatum or E. recurvatum or Moliniella anceps) or two (E. aconiatum +M. anceps or E. aconiatum + E. recurvatum or E. recurvatum + M. anceps) trematode species. It has been revealed that activities of detoxifying and antioxidant enzymes in the body of the snail L. stagnalis change at invasion with trematodes and that the character of the changes depends on the stage of development of the trematodes in the host body, the variant of infestation (monoinvasion or mixed infestation), and the species of the parasite. The first 2 h after penetration of the trematode cercariae into the molluse tissues is accompanied by an increase of activities of the detoxifying and antioxidant enzymes. A long coexistence of metacercariae in the host body (no less than for 13 days) is accompanied by a decrease of activities of non-specific esterases and glutathione-S-transferase and by an increase of superoxide dismutase.

The comparative analysis of esterase changes in homogenates of the snails Lymnaea stagnalis and L. tumida bodies was carried out. Juvenile snails with shell size 2 mm, 3-4 mm, 5-6 mm and 7-8 mm were exposed to cercariae of the trematodes Echinoparyphium aconiatum and/or Moliniella anceps. The esterase activity was detected spectrofotometrically. The highest level of esterase activity in noninfected L. stagnalis was registered in snails with shell size 3-4 mm. The invasion of snails by trematode cercariae results in a change of esterase activity in the tissues of infected snails. The activity of easterases was increased in the infected L. stagnalis snails with shell size 5-8 mm at 2 days post invasion in comparison with control. The decrease of esterase activity in tissues of infected snails L. stagnalis (3-4 mm) and L. tumida (4 mm) was observed at 26 days post invasion by E. aconiatum only. The host size and parasite species was influenced on esterase activity in the snails.

The high percent of the infestation by the trematodes of the families Plagiorchidae and Prosthogonimidae is recorded in the dragonfly Aeschna grandis larvae of the last stage. About 30% of the trematode cysts were melanized. It is established, that the parasitising of the trematodes do not effects on the process of the incapsulation of foreign bodies, but it suppresses partly the formation of oxygen free radicals and phenoloxidase activity in the haemocytes of dragonfly larvae.

Metacercariae of Cyathocotyle bushiensis Khan, 1962 (Digenea) were found in populations of seven species of gastropod snails collected from lakes and rivers in the south of West Siberia (Russia). This is the first record of C. bushiensis in Russia. Five species of snails, Lymnaea stagnalis, L. palustris, L. tumida, Planorbis planorbis (Pulmonata) and Viviparus viviparus (Prosobranchia) were recorded as new hosts for the metacercariae of C. bushiensis. The infection rate of Bithynia tentaculata and Opisthorchophorus (= Codiella) troscheli (Prosobranchia), the main hosts of C. bushiensis metacercariae, was analyzed in regard to the sex and shell length of molluscs. It was revealed that infection rate and mean intensity of metacercariae increases with the shell lengths. Drawings and descriptions of excysted metacercariae from naturally infected snails and adult worms from experimentally infected domestic ducklings are given.

Investigating Mollusca prosobranchia of the Bithyniidae family in the water reservoirs of the Novosibirsk Region in 1994-1998 first revealed that Codiella troscheli had the trematode Metorchis albidus (Braun, 1893). The species affiliation of the trematode was experimentally verified. This paper presents the results of studies of the seasonal and daily emission of M. albidus cercariae and data on their longevity in the environment, on the ability of the cercariae to live in fish and that of metacercariae in the body of a definitive host. The studies have indicated that not only the trematode Opisthorchis felineus, but also C. troscheli may develop in the C. troscheli mollusks, which should be taken into account in both describing the natural foci of opisthorchiasis and diagnosing opisthorchiasis and metorchiasis.

Opisthorchis somatic, metabolic, and tegumental antigens were studied by using immunoblotting. It was shown that among several antigenic components, only the somatic protein with a molecular weight of about 100 kD failed to react with noninvased human sera.