The structure and distribution of the parasite assemblages of roaches (Rutilus rutilus L.) along the Odra River against the background of environmental factors
AbstractThe main objective of the study was to trace the multi-directional effect of environmental factors, both natural and anthropogenic, on the distribution and structure of roach (Rutilus rutilus L.) parasite assemblages along the Odra River. A total of 451 roach were caught in seven sites along the whole (854 km) course of the Odra and were subjected to full parasitological section. In all, 68 parasite taxa were isolated and identified; they represented nine higher taxa: Monogenea, Aspidogastrea, Digenea, Cestoda, Nematoda, Acanthocephala, Hirudinea, Crustacea and Bivalvia. The results indicate the effect of environmental factors on the parasite communities associated with roach in the Odra. In a few cases, the observed relationships were fairly clear and explainable, based on the biology, life strategies and developmental types of the analysed groups of parasites. This was especially true of the level of industrialisation and water quality in its broad sense, with respect to nearly all the analysed assemblages, where the effect was mainly executed through the intermediate hosts (aquatic invertebrates), free-living larval stages or, in the case of ectoparasites, directly on adult stages of parasites. The effect of pollution was most often manifested “negatively”, that is decreasing the indices of occurrence to greater or lesser degrees, for example, Digenea, Cestoda, Acanthocephala, Crustacea, bivalve glochidia or intestinal or heteroxenic parasites, endoparasites or crustacean- or mollusc-transmitted parasites. In a few cases the effect was “positive” increasing the indices of occurrence to varying degrees, as seen in, for example, Monogenea or oligochaete-transmitted parasites. Among the remaining factors affecting the roach parasite communities, riverbed partitioning, vicinity of major bird refuges or fish farms, as well as flow velocity can be mentioned. The riverbed partitioning differentiated the indices of occurrence in Digenea and probably also Aspidogastrea. The neighbourhood of bird refuges affected mainly allogenic Digenea and Cestoda, while the presence of fish farms affected the community of Digenea. The flow velocity mainly influenced the distribution of bivalve glochidia and, to a lesser extent, the assemblage of Monogenea. The neighbourhood of the estuary and sea water was also an important factor for the roach parasite community of the lower section of the Odra. The roach inhabiting the lower section of the river migrate to coastal waters and assume parasites from the group of generalists which occur in typically marine hosts. The results indicate also that the relationship between the environmental factors and the parasite assemblages are rarely simple, unequivocal and easy to interpret. Various biotic factors often interact with each other or with abiotic conditions. Their synergistic action may be expressed as weakening the end effect, cancelling each other’s influence, or partially limiting the effect of one of the factors.
|Journal series||Annals of Parasitology, ISSN 2299-0631, e-ISSN 2300-6706, (B 15 pkt)|
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