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Objective of research. To study the species composition of the parasite fauna and the infestation rate of the spiny loach Cobitis taenia Linnaeus, 1758 from Saratov Reservoir.Materials and methods. The material was collected in the Mordovo-Kol’tsovsky area of the Reservoir (the middle part of the reservoir) in 2009 and 2014–2015. Fishing was carried out by a hydrobiological net. Totally 47 individuals of spiny loach were investigated by the method of full parasitological autopsy. Collection, fixation and office studies were carried out using the standard technique; diagnostics of species composition of parasites — by identification guides. To estimate the rate of fish invasion, we used the common parasitological indices: extensity of invasion, intensity of invasion and the index of abundance of parasites.Results and discussion. 7 species of parasites belonging to 5 classes: Monogenea — 1, Cestoda — 1, Trematoda — 3, Nematoda — 1, Bivalvia — 1 were found in the spiny loach Cobitis taenia Linnaeus from Saratov Reservoir.The species composition of parasites and the level of host infestation directly depend on the lifestyle and nutrition of fishes. Eating the infected benthic and weed bed invertebrates (oligochaetes, larvae and adult insects), the spiny loach becomes infected with 3 species of helminths.4 species of parasites infect the host using the active infestation way. Most of the parasites found in fish from different families and groups are wide specific. The parasite fauna includes 1 species, narrow specific for the spiny loach (monogenea Gyrodactylus latus Bychowsky, 1933) and 1 species specific for loaches (fam. Cobitidae) — metacercariae of Holostephanus cobitis Opravilova, 1968. For 4 species of parasites, the spiny loach is the final (definitive) host, for 3 — intermediate. The dominant species in the composition of the parasite fauna C. taenia is the trematode H. cobitidis (mtc.); the extensity of infection with it reaches 97,9%, the abundance index is 10,8 ind.Fluke larvae infect fishes (using the active way) penetrating through the skin. The most pathogenic for spiny loach parasites are the monogenea G. latus, metacercariae of trematodes H. cobitidis and Paracoenogonimus ovatus Katsurada, 1914, the larva of the nematode Raphidascaris acus Bloch, 1779.

Objective of research. Data on the species composition of the fauna of multicellular parasites and the infection rates of the pope ruffe Gymnocephalus cernuus Linnaeus, 1758 from Mordovian floodplain of the Saratov reservoir (the middle part) are pesented. Materials and methods. 53 ruffe individuals were investigated in spring and summer 2012 – 2015 by incomplete parasitological post-mortem examination (Bykhovskaya-Pavlovskaya, 1985). 19 species of multicellular parasites belonging to 7 classes: Monogenea - 1, Cestoda - 1, Trematoda - 11, Nematoda - 3, Acanthocephala - 1, Bivalvia - 1, Crustacea – 1 were registered. The largest group are flukes; more than half of species (8) are larval forms, which is the result of bottom living of the host. The significant diversity of larval stages of helminths (8 species of trematodes and 2 species of nematodes) shows the involvement of the ruffe as an intercalary, supplementary and/or reservoir host in the circulation of parasites in fish, birds and mammals. 7 species of parasites infest the ruffe on the food chain; 12 species – using the active infestation way. Results and discussion. The studied parasite fauna contains one species narrowly specific for the ruffe (monogenea D. amphibothrium (Wagener, 1857) and 2 species typical for percoid fishes (cestoda Proteocephalus percae (Müller, 1780) and trematoda Bunodera luciopercae (Müller, 1776). 2 alien species Nicolla skrjabini (Iwanitzky, 1928) (marita) and Apophallus muehlingi (Jägerskiöld, 1898) (mtc.) whose natural habitat is limited by the rivers of the Azov-Black Sea and Baltic Sea were registered in the fauna of multicellular parasites of the ruffe from the Saratov reservoir. The most common ruffe parasites are Diplostomum and Ichthyocotylurus metacercariae metacercaria infesting fish by penetrating through the body covers. These metacercariae as well as Apophallus muehlingi metacercariae are pathogenic to fish.