The ecological concept of parasitism as a general biology phenomenon underlies the understanding of the role of parasites in terrestrial and aquatic ecosystems. The review gives an account of the current positioning of parasitology in the system of biological sciences, the subject and tasks of ecological parasitology. We relate the history of the science school in parasitology at the Institute of Biology KarRC RAS, which took shape under the leadership of pupils of the founder of the Russian school in ecological parasitology, outstanding scholar from Leningrad V. A. Dogiel. Major stages and areas of research and methodological approaches to the study of parasites and host-parasite relationships are described, covering a wide range of objects: blood-sucking arthropods, parasites of fish, birds, mammals, and plants. Studies deal with the formation and dynamics of parasitic communities in natural and disturbed terrestrial and aquatic ecosystems (eutrophication, industrial pollution, alien species invasions, aquaculture). The results of these studies are of high theoretical significance and have been published in monographs and in articles in Russian and international journals. Practical recommendations are widely applied in nature management, veterinary and agricultural practices, and are annually published in the Republic of Karelia State Report on the Environment. Today, the science school in ecological parasitology in Karelia is represented by qualified specialists, who investigate a wide range of both basic and applied topics, including those of special relevance for the region.

Herein, data on rainbow trout infections with the copepod Caligus lacustris in cage aquaculture on Lake Ladoga is presented. Caligus lacustris (n = 127 ex.) were collected from a farm in Lake Ladoga housing cage-reared rainbow trout to describe the size–age and sex structure of the copepod population. Morphological features of the copepods were evaluated according to 10 characters with terminology proposed by Kabata and Gusev (J Linn Soc (Zool) 46(309):155–207, 1966). To determine the phylogenetic position of C. lacustris within the genus Caligus, fragments of the cytochrome c oxidase subunit 1 mitochondrial gene (COI, 645 bp) and 18S rRNA gene (1617 bp) were sequenced. An increase of parasite prevalence was observed as the lake was warming up from July to September. The morphological features of the crustacean’s larval and adult stages, characterized by specific parameters of quantitative traits, are described. Three COI haplotypes and only one 18S rRNA haplotype of C. lacustris were identified among five samples. Based on 18S rRNA analysis (resolution of the COI tree was poor), we can conclude that the clade containing C. lacustris, and the aforementioned sister species, appears as an early radiation of the genus Caligus. The development of freshwater aquaculture contributes to the transfer of the native parasite C. lacustris to farmed rainbow trout.

Аннотация: Изучена фауна паразитов европейской корюшки Osmerus eperlanus (L.) -промыслового вида рыб Ладожского озера.Проведен сравнительный анализ изменений паразитофауны европейской корюшки за многолетний период.Установлено, что структурная перестройка в паразитофауне ладожской корюшки проявляется в снижении видового богатства за счет исчезновения типичных видов паразитов олиготрофных озер.Состав руководящего комплекса паразитов ладожской корюшки формируют эвригостальные виды с широким кругом хозяев.Изменение численности и структуры зоопланктона и зообентоса (кормовой базы ладожской корюшки

This paper offers a summary of the data on parasites of European smelt based on own collections and materials published in journal reviews, scientific papers, conference proceedings and theses. The system of parasitic organisms published in Catalogues of parasites of freshwater fishes of North Asia [Pugachev, 2001-2004] is used, taking into account new studies on the systematics of infusorians and trematodes. Other groups of parasites are considered within the frameworks of widely used classifications. The species structure of European smelt and its ecological forms follow the classification by L. Berg [1948] and Yu. Reshetnikov [Atlas ..., 2003]. Altogether 65 species/taxa of parasites have been recorded from the distribution range of European smelt (Conoidasida - 1, Haplophasea – 2, Ichthiosporea - 1, Myxosporidia - 1, Phyllopharyngea - 1, Oligohymenophorea – 3, Monogenea - 1, Cestoda - 9, Trematoda - 11, Nematoda - 19, Palaeacanthocephala - 7, Hirudinea - 1, Bivalvia - 1, Crustacea - 7). Each parasite species is briefly described; the species occurrence in different smelt ecoforms, sources for species records (provenance and author) are stated. For higher taxa, we analyzed the taxonomic diversity of smelt parasites, their zoogeographic zoning and distribution, as well as specificity, distinctive morphological, biological and ecological traits.

The parasite fauna of LakeOnegocommercial fish species – vendace, Coregonus albula L., and smelt, Osmerus eperlanus L., was studied. The prevalence, abundance distribution and age structure of the cestode Proteocephalus longicollis (Zeder, 1800) in vendace were determined. Seasonal variations of Eubothrium crassum (Bloch, 1779) infection in vendace were traced, and the role of vendace in the life cycle of this cestode was identified. A comparative analysis of long-term changes in the parasite fauna of vendace and smelt was carried out. The species diversity of helminths and its structure proved to be relatively stable. Changes were mainly observed in the intensity of infection. These results suggest that the two major plankton-feeders, vendace and smelt, quite successfully coinhabitLakeOnego.