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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 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.