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The changes of perch parasite fauna during the different phases of water level cycle recurrense were viewed, and the periods of fish enzootic forming were discovered.

Postembryonic development of Bursaphelenchus mucronatus has been studied. First molt takes place within the egg-shell, and three subsequent molts after hatching. Structure of all juvenile stages are described, as well as molting juveniles and adults. Juvenile stages differ in genital primordium structure, copulatory structures primordial and the body length. In juveniles of 3rd and 4th stage the sex of juvenile was distinguished: male juveniles have cloacal primordium, whereas female juveniles have vulval primordium. Adults differ from juveniles in presence of vulva in females and spicules in males. The key to identify juvenile stages and their sex is given. Male has the terminal bursal flap and 3 pairs of iail papillae: pi anadanal; p2 and p3 at the bursal flap base: p2 close to mid-line of the ventral body surface, p3 located laterally to p2 at the same level. Unpaired papilla is present on the upper cloacal lip, on the ventral mid-line.

Data on all known currently trematodes, revealed in insectivores and muride rodents from the Middle Volga region are generalised and analysed in article. The description and original drawings of 10 parasites species are given. 2 helminth species (Brachylecithum rodentini, Corrigia vitta) were specified for micromammals from Volga basin for the first time. The new hosts were marked for 2 parasites (B. rodentini, Quinqueserialis wolgaensis).

The helminths fauna of common spaedfoot Pelobates fuscus (Laurenti, 1768) and moor frog Rana arvalis Nilsson, 1842 has been studied at their joint habitation. The stuff was collected in 1998—2002, 2004—2006 years in several regions (republic Mordovia, Samara and Saratov areas). The processing of a stuff is conducted by a method of full helmintologic dissecting. The fauna of helminths considerably differs. For common spaedfoot only 13 species of helminths was detected which also parasitized moor frog (for moor frog 23 species) are detected. The index Jaccar demonstrated mean resemblance structure of helminths and varied from 0.25 till 0.69, and the index Morisite - from 44.58 of % till 74.51 of %. The communities of parasites of common spaedfoot was characterized by low values of an index of Shannon, but the high indexes of an index Simpson, whereas for moor frog tracked the return tendence.

Life cycles of two species of echinostomes Echinochasmus japonicus Tanabe, 1926 and E. beleocephalus (Linstow, 1873) have been studied. In Primorye region the first intermediate hosts E. japonicus are snails of genus Boreoelona, E. beleocephalus develops in Parafossarulus. Second iintermediate hosts are freshwater fish and tadpole of frog Rana dubowskii. Encysted cercariae of E. beleocephalus also were found in tissue of first intermediate hosts. Experimental definitive host for both species were Gallus gallus dom. chickens.

Tumours occurrence of minnow and tumour parameters are found to be greatest at the end of june — the first part of july. Black tumours give metastases, while gray tumours are separated from the neighboring tissue by a capsule. The stroma of the tumour is pierced through by fungal hyphae of Fusarium solani (Mart.) App. et Wr. The minnow living the first year (the end of it) and the second year (the beginning of it) suffers tumours more frequently. The minnow taken from the Saitanovka river estuary (the cordon place, abundant in Equisetum, which is the motorboats anchorage) was found to be most affected by tumours.