Habitats and Density of the Invasive Topmouth Gudgeon (Pseudorasbora parva Schlegel) in Small Polish Watercourses, in the Light of Threats to the Habitats of Native Species of Fishes

Abstract

The newly introduced species (alien species) can become invasive and pose a serious economic and ecological threat, causing changes in the habitats of native species, while competing with native species, they can affect the density and biodiversity within the ecosystem. One of the invasive species of fish in Europe is the topmouth gudgeon (Pseudorasbora parva Schlegel, 1842). The aim of this study was to assess the habitats of selected topmouth gudgeon’s populations in terms of basic hydrological and physicochemical characteristics, as well as to determine the density of the species and the potential impact of the population on native species in small Polish watercourses. Three small watercourses in Odra catchment (Myśla and Wardynka river) and Wisla (Molnica river) were selected for the study, where electrofishing were conducted and water samples were taken for hydrochemical analysis. Among the 9 surveyed sites, the topmouth gudgeon was caught on the 5th. On the Myśla River, it was located on two sites, the same on the Molnica river and on the 1 site on the Wardynka river. In total, 550 fishes (belonging to 10 species) were caught on these 5 sites, including 388 topmouth gudgeon, which accounted for over 70% of the fishes caught. Although the physicochemical conditions of the tested watercourses are not optimal for this invasive species, the increase of density and further colonization of the topmouth gudgeon can be expected, and thus already observed in other watercourses, the impact on indigenous species and habitats occupied by it.