Study of the diets of two coexisting species- invasive Chinese sleeper (Perccottus glenii Dybowski, 1877) and native European perch (Percafluviatilis Linnaeus, 1758)

In Poland, the Chinese sleeper Perccottus glenii is one of the alien fish species which, by effectively competing with native species, may contribute to the weakening of their population and a reduction of the biodiversity. The aim of this paper is to study the diets of two coexisting species: the native European perch Perca fluviatilis and the invasive Chinese sleeper. The fish were collected from a watercourse used for draining water from a fishing farm, located in the Nida River water system (Poland), using the electro-fishing method. The captured fish were killed, preserved in a 4% formaldehyde solution and the stomachs of the fish were dissected. Then, based on the materials collected from these stomachs, the abundance and taxonomic rankings of the individual diet components (quantity of individuals in the individual taxa) were determined. The overlap of the P. fluviatilis and P. glenii feeding spectra was studied using a principal component analysis (PCA). The analysis of the data collected demonstrated that the diets of these two species overlaps considerably. At the same time, the analysis of the major diet components showed that the niche used by P. fluviatilis is broader than that used by P. glenii. It seems that, due to its high level of plasticity, P. fluviatilis is able to withstand the pressures of P. glenii and is also able to limit its abundance. Both species frequently choose fish as their prey, including juvenile common carp Cyprinus carpio Lin-naeus, 1758, which indicates that together with native predators, P. glenii may pose a considerable threat to farmed juvenile Cyprinidae.