Rheophilic fish in oxbow lakes of the Warta River – the effect of environmental conditions on habitat selection

Oxbow lakes are typical elements of meandering watercourses and are considered to be key components of floodplains of natural rivers. A permanent connection with the river promotes the use of these water bodies by ichthyofauna as spawning grounds, shelter for fry, feeding and wintering grounds. The aim of this study was to determine which rheophilic species inhabit oxbow lakes and how environmental conditions affect habitat selection and fish behavior. Analyses were conducted on six oxbow lakes of the Warta River in the Koło-Poznań section. Fish and water samples were collected for three years, in spring, summer and late autumn. Variation in environmental conditions in the analyzed water bodies results in a considerable diversity of the ichthyofauna, including rheophilic species, in individual seasons of the year. In the course of the study, nine rheophilic fish species were recorded, including four from the lithophilic reproductive guild having the highest environmental requirements. Relative abundance of rheophilic species in the dominance structure ranged from 0 to 100%, depending on the reservoir and seasons, with an average of 7% for all catches. For comparison, their relative abundance in the adjacent parts of the river was 12 and 23%.