THE IMPORTANCE OF VARIOUS SPECIES OF MOLLUSCS – SECOND INTERMEDIATE HOSTS – IN MAINTAINING THE CIRCULATION OF POLYCHOSTAL SPECIES OF TREMATODES IN THE WATER BODIES OF THE UKRAINIAN POLISSYA

Abstract

Background. The paper considers the importance of various species of molluscs as second intermediate hosts in the circulation of polyhostal species of trematodes in the Ukrainian Polissya. It was found that the metacercariae of trematodes are concentrated mainly in the most abundant individuals both in a particular water body and in the region as a whole. The specificity of trematodes for a particular intermediate host is determined by the influence of a number of environmental factors. Due to a significant decline in populations of many mollusc species as a result of anthropogenic alteration of the environment, there is a need to determine the species composition of trematode metacercariae in freshwater molluscs in the region, with emphasis on their importance in maintaining local and regional populations of these helminths.
Materials and Methods. The study of trematode metacercariae in gastropods from water bodies of the region was carried out in 2002–2012 and 2022. The molluscs were collected manually or with a net, using conventional methods in malacology. During the study period, more than 50,000 specimens of molluscs from 5 families were examined: Lymnaeidae, Bulinidae, Planorbidae, Bithyniidae and Viviparidae. The morphology of metacercariae was studied on live specimens using vital stains. The extent of invasion was determined during the helminthological dissection of the molluscs. Statistical analysis of the data was performed using Statastica 8.0. The Yates corrected Chi-square test with Bonferroni correction was applied.
Results. Nineteen species of trematode metacercariae, including three species of cercariae, were found in 22 species of molluscs from water bodies in the region. For 9 trematode species, new mollusc species were found to act as a second intermediate host. In 8 out of 16 identified trematode species, the same mollusc species play the role of first and second intermediate host. The findings of the present study indicate that the majority (56.25 %) of the identified trematodes were found in two or more molluscs of different families, acting as second intermediate hosts.
Conclusions. Metacercariae, whose host specificity is usually much broader, are concentrated in the most common mollusc species in the region or even in a particular water body, which are potential second intermediate hosts of these helminths. In the distribution of trematodes at the metacercariae stage, the species composition of mollusc communities and the number of their individual species mainly determine the possibility of a parasite-host encounter.