Daily and seasonal dynamics of littoral zone fish communities in the lowland Włocławek Reservoir (central Poland), with a special emphasis on alien invasive gobies

The aim of the study was to examine the daily and seasonal dynamics of changes in fish communities in two environmentally different littoral zones of the Włocławek Reservoir (central Poland), i.e., the floodplain (limnic Dobiegniewo site) and lotic area (Murzynowo site). During seasonal catches using trawl nets, in the daily cycle (at 00.00, 06.00, 12.00, and 18.00 hours), the presence of 18 fish species representing 4 families (Cyprinidae, Percidae, Gasterosteidae, Gobiidae) was confirmed. In both localities, the domination of native taxa, such as roach Rutilus rutilus (L.) and Eurasian perch Perca fluviatilis L., in Dobiegniewo (26.6 and 26.6%, respectively) and Murzynowo (13.6 and 22.7%, respectively) of all caught specimens was noted. The quantitative share of three alien invasive gobies, racer goby Neogobius gymnotrachelus (Kessler, 1857), monkey goby Neogobius fluviatilis (Pallas, 1814), and western tubenose goby Proterorhinus semilunaris (Heckel, 1837), varied in the range between 2.7 and 35.3% in samples throughout the season. The results indicate the significant role of gobies in the structure of the sublittoral fish communities of Włocławek Reservoir and the necessity of expansion process studies, as well as the observation of the interactions with native fish species in invaded areas.