ISSN 1995-0829, Inland Water Biology, 2011, Vol. 4, No. 1, pp. 78–89. © Pleiades Publishing, Ltd., 2011. Original Russian Text © Zh.N. Dugarov, N.M. Pronin, L.D. Sondueva, T.G. Burdukovskaya, M.D. Batueva, S.V. Pronina, 2011, published in Biologiya Vnutrennikh Vod, No. 1, 2011, pp. 86–97. 78 INTRODUCTION Dogel’ commenced studies on the dependence that parasitic fauna has on the age of the host [4, 5]; this direction was then continued by many researchers, in particular, when studying the fish in Lake Vrevo (Len- ingrad oblast) under the guidance of Strelkov [17]. The first study of the age-related changes of the host in par- asitic fauna was performed in the population of perch Perca fluviatilis L. in Lake Gusinoe [13]. When the general concept of parasite communities was formed [20, 21] and the methods for assessing ecological diversity were developed [12], the number of papers on the parasite communities and the factors influencing them increased. In particular, these works include the studies of the dependence that parasite communities have on the age of the yellow perch Perca flavescens Mitchill [23], some tropical fish (Stegastes nigricans Lacepède, Dascyllus aruanus L., and Ceph- alopholis argus Bloch et Schneider [24]), minnow Phoxinus phoxinus (L.) [8], and others. A study of the roach parasite communities from the Cherkalov Sor Bay of Lake Baikal using a minimal sample (14 roach individuals) [16] did not make it possible to detect the effect of spatial factor and host age. However, an anal- ysis of the effect that these particular factors have on the distribution of only one parasite species, Aspido- gaster conchicola Baer in the mussel Colletopterum spp. populations from different regions of Lake Baikal, provided new data on the biology and chorology of the host population [9]. The goal of this work was to analyze the changes in parasite communities in different age groups of roach populations in two aquatic bodies of the same basin. MATERIALS AND METHODS The parasite communities in roach were studied in the Chivyrkuiskii Bay of Lake Baikal (May–August 1998–2005; 221 roach individuals) and the Selenga River Estuary (May 2002; 75 roach individuals). The Chivyrkuiskii Bay is in the southern end of Lake Baikal and is separated from the lake by the Svyatoi Nos Pen- insula. The Selenga River Estuary is the only classical freshwater estuary in the world and consists of numer- ous creeks, lakes, dead arms, etc. Roach of various ages were caught for parasitological examination in one of the small creeks (Gusevskaya Creek) in the southern part of the estuary. The following definitions of parasite communities were used in this work: infracommunity, comprising all the parasites (of all species) in a host individual, and component community, comprising all the infracom- munities in a given host population [3, 15, 19, 22]. In addition to these types of communities, one more level of communities was considered when analyzing the distribution of parasites in a roach population, namely, Dependence that the Community Structure of the Roach Rutilus rutilus (L.) Parasites Has on the Host Age Zh. N. Dugarov a , N. M. Pronin a , L. D. Sondueva a , T. G. Burdukovskaya a , M. D. Batueva a , and S. V. Pronina b a Institute of General and Experimental Biology, Siberian Branch, Russian Academy of Sciences, ul. Sakh’yanovoi 6, Ulan-Ude, 670047 Russia e-mail: zhar-dug@biol.bscnet.ru b Buryat State University, ul. Smolina 24a, Ulan-Ude, 670000 Russia Received September 3, 2009 Abstract—The changes that take place in the structure of the parasite communities of two roach populations as the hosts grow older have been studied in the Chivyrkuiskii Bay of Lake Baikal and the estuary of the Selenga River. The parasite communities are analyzed at the levels of host individuals (infracommunities), host age groups (sets of infracommunities), and host population (component community). The number of parasite species regularly increases as the roaches age in both aquatic bodies, whereas the evenness of the par- asite communities decreases. The Berger–Parker dominance index of the parasite communities changes with the roach age in different directions, increasing in the Chivyrkuiskii Bay and decreasing in the estuary of the Selenga River. The changes in the Shannon diversity index for sets of infracommunities of roach parasites are the opposite of those in the Berger–Parker index. Keywords: structure of parasite communities, roach, Chivyrkuiskii Bay of Lake Baikal, Selenga River Estuary. DOI: 10.1134/S1995082911010044 PARASITOLOGY OF HYDROBIONTS