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Component communities of parasites of Phoxinus phoxinus from the Chovju River near Syktyvkar City (Komi Republic) are investigated in seasonal aspect. Material for the study has been collected in May-September 2000 from 90 host specimens of ages 0+-1+. Calculations of diversity indices and other coefficients have been made by two ways -- for metazoan parasites only and for whole parasite community including protozoan species. In both these cases three states of the community have been established, 1) forming community in May-June, 2) completely formed community in the end of June-July, 3) disintegrating community in August, 4) forming community in September. Seasonal dynamics of the component communities in young minnow thus found to be different from that in adult fish hosts.

Influence of adrenaline, hydrocortisone, and prednisolone on the infestation rate of the carp Cyprinus carpio by Dactylogyrus sp. is investigated, according to the analysis of the abudance index of parasites. Introduction of these hormones into experimental fish resulted in the increase of the abudance index of dactylogyrids. Dependence of changes in the investigated parameters on the nature and character of the hormones' influence on the host immune system and metabolic processes is revealed.

Results of the long-term faunistic study of Monogenea from fishes of the Chu River basin are reported. Fauna of Monogenea in the studied area was found to include 51 species of 11 genera and 5 families. Thirteen parasite species occurred in the mountain part of the basin, and 40 species inhabit the valley zone, including 10 species of the Amur faunistic complex probably introduced to Kyrgyzstan together with acclimatized fishes.

Ecological analysis of the helminthofauna of common shrew Sorex araneus L. from Samarskaya Luka (Samara Region) has been carried out. Twenty-three helminth species are found including 3 species of trematodes, 8 cestodes, 10 nematodes, and 2 acanthocephales. Dependence of the structure of helminthofauna on the host age is revealed.

Helminth fauna of Insectivora was investigated in canal banks situated in meliorated territories of Belorussian Polesie during 1996-1999. Thirty-three helminth species were found in the animals examined. Most of the parasites are usual in common shrew Sorex araneus L., which is a predominate insectivore species in canal banks.

The article consist of common results of long standing monogenea researches of Issykkul lake's basin. Monogenea's fauna of the basin includes 46 species. It was discovered for the first time 12 species for the republic, 2 species for Middle Asia. Besides it was described 3 new species for science. About 10 species were discovered into the lake together with hosts during the acclimatization.

A native population of landlocked salmon of the Pista River was investigated in 2000-2002. Adult salmon in Pista River has smallest size among other populations of landlocked salmon in Karelia. Data on the biology and parasite fauna of young salmon are presented. The presence of local salmon populations in lakes of the river system is apparently one of the mechanisms keeping the magnitude of population. The presence of Gyrodactylus salaris, a harmful parasite of the young landlocked salmon, is established in this territory for the first time. This monogenean species is believed to have been introduced into the Pista River via stocking from Finland.

The article is based on the results of helminthological observations made on kittiwake Rissa tridactyla and glaucous gull Larus hyperboreus in 1991-2001 in different areas of the Barents Sea (Eastern Murman coast, Franz Josef Land, Novaya Zemlya, Spitzbergen). 18 helminth species (2 trematodes, 11 cestodes, 4 nematodes, and 2 acanthocephalans) were recorded in the kittiwakes and 19 (3 trematodes, 9 cestodes, 5 nematodes and 2 acanthocephalans) species were recorded in the glaucous gulls. Trematodes were absent in the birds collected at the Franz Josef Land and the northern island of Novaya Zemlya. 3 trematode species, namely Gymnophallus sp. (somateria?), Microphallus sp. 1 (M. pseudopygmaeus), and Cryptocotyle lingua were found in the glaucous gulls of western Spitzbergen. It was supposed that the life cycles of these parasites can be completed there. On the other hand, coastal ecosystems of Arctic archipelagoes turn out to be favourable for the transmission of some cestodes. This is closely connected with the regional traits in the marine bird diet, namely the increase of the amphipod (intermediate hosts of hymenolepidids and some dilepidids) and polar cod (supposed second intermediate host for some tetrabothriids) portion in Arctic. As a result, cestodes are the base of the helminth fauna of kittiwakes and glaucous gulls of the Barents Sea, by their species richness, prevalence and abundance. Nematodes and acanthocephalans were represented by a few species with low infection intensity. The main ecological factors affected the regional difference in the species richness and abundance of the helminths parasitising kittiwakes and glaucous gulls in the Barents Sea are proposed. Those are regional climatic features and regional traits in the behaviour and food priorities of birds, and also the distribution of the helminths intermediate hosts, invertebrates and fishes. The phenomenon of host specificity lowering with respect to the definitive host was recorded in some cestode species (Microsomacanthus diorchis, M. microsoma, and Arctotaenia tetrabothrioides) on the border of their distribution ranges, the coastal ecosystems of Arctic.

The helminth fauna of shrews (Sores araneus, S. caecutiens, S. minutus, S. minutissimus) from the Karelian coast and islands of the Kandalaksha nature reserve was studied. 18 helminth species belonging to 3 taxonomic groups, Trematoda (3), Cestoda (8), and Nematoda (7) were found. The main body of the helminth fauna of shrews is represented by the nematodes species Longistriata codrus, L. didas, and the cestode species Ditestolepis diaphana. Inhabiting of shrews in the insular localities leads to the decrease of the species diversity and the abundance of their helminths. The distribution ranges of the shrew parasites have been outlined more accurately.

Component communities of parasites of gudgeon from the ecologically sustainable reservoirs are studied. The general principle of their organization is established. The material had been collected in the basins of Northern Dvina (41 specimens of gudgeon were dissected) and Mezen (55 specimens of gudgeon were dissected) rivers using generally accepted methods. Errors of regression equations for all individual species groups with their subsequent summation were calculate in order to estimate the state of the component community structure. In different seasons of a year the component community of the parasites of gudgeon from the Ertom river has the same structure, which is determined by the ratio of the biomasses of its comprising species, while it is differs in its species composition, biomasses of the species, leading groups of parasites, and in the dominating species. Thus, several stable seasonal states of the communities of fish parasites can be supposed. Three groups of species distinguished by the ratio of their biomasses are the general for the component communities of the parasites of gudgeon from the basins of Northern Dvina and Mezen rivers. The generalist species is more frequently the dominating species. The group of autogenic species always leads in the community. When methods of parasites collection are violated, the decrease in the number of species groups down to two is recorded. When the materials collected in different periods of a year from an ecologically sustainable reservoir are mixed, the sum of the errors of regression equations become higher than 0.250.

The study of parasites associated with the anadromous mikizha from several rivers of the Western Kamchatka has revealed 44 parasite species. The majority of parasites (59%) belong to marine and estuarine-marine species. Lecithophyllum bothryophorum, Echinorhynchus leidyi and plerocercoids of the family Litobothriidae were found for the first time in anadromous fish entering into Asian continental watersheds. It has been revealed that only a few specimens of the anadromous mikizha feed in fresh waters. Most of feeding fish consume a minor amount of food, and this feeding is occasional. Young forms of intestinal parasites of the freshwater and estuarine-freshwater groups (Neoechinorhynchus spp., Crepidostomum spp., Cucullanus truttae, Eubothrium salvelinf) come into anadromous fishes mainly before their entering in fresh waters.

Gyrodactylus moldovicus sp. n. found on gills, body and in nasal cavities of the European mudminnow (Umbra krameri) differs from G. slovacicus Ergens, 1963 also living on the this host by bigger size of the body, anchors and marginal hooks; from G. cylindriformes Mueller et Van Cleave, 1932 living on the American mudminnow Umbra limi--by bigger size of the body; from G. limi Wood et Mizelle, 1957 also from U. limi--by the form of ventral and dorsal bars and form of marginal hooks. It differs from other freshwater gyrodactylids by special type of marginal hooks which have a hook-like end of the blade. Gyrodactylus moldovicus, G. slovacicus and G. limi have marginal hooks of quite different morphological types. By the morphology of anchors, ventral and sometimes dorsal bars and also morphology of cirrus, G. moldovicus is most related to three species from Cyprininae: G. stankovichi Ergens, 1970, G. longoacuminatus Zitnan, 1964 f. typica and G. shulmani Ling, 1962.

The parasite fauna of the chub mackerel Scomber japonicus Houtuym, 1782 was studied from the neritic areas of Morocco, Western Sahara, Mauritania and from the banks of the Azores Archipelago (the Great Meteor Bank, the Hyeres Bank and the Irving Bank) in 1994-2001. Twenty eight species of parasites of following group have been were found: Coccidia (1 species), Microsporidia (1), Myxosporea (4), Monogenea (4), Cestoda (5), Trematoda (5), Acanthocephala (1) and Nematoda (6). The differences between mackerel parasite fauna in the neritic areas and from of the Azores Archipelago banks were established. Peculiarities of the mackerel parasite fauna in two areas (Morocco--Western Sahara and Mauritania) corroborate the hypothesis that two populations of chub mackerel are available: "Sahara-Moroccan" and "Senegal-Mauritanian". Ontogenetic variability of parasite fauna was related to food demands of mackerel and its feeding habits in the areas Morocco and Mauritania. Kudoa histolytica has negative influence on the commercial value of S. japonicus. These parasites were localized in the muscles of mackerel from Mauritania (40%, TL = 20-25 cm). Parasites being dangerous for human health were presented by larvae of Bolbosoma sp. (occurred on the banks of the Azores Archipelago), Anisakis simplex and Contracaecum sp. (occurred in all areas investigated).

A new species, Gyrodactylus onegensis sp. n., is described from gills of the freshwater sculpin Cottus gobio.

The data on an occurrence of capsalines in marine fishes are analyzed. 33 capsaline species among 55 recently known species are monoxienous, that points to the high specialization of these monogeneans. The majority of species are recorded from three subfamilies of perciform fishes: Scombridae, Istiophoridae, Xiphiidae. Possible factors causing the high specificity in monogeneans are discussed.