Summary:

River monitoring for the status and species composition of ichthyofauna is one of the forms of open water fisheries management. Research conducted on 10 selected for maintenance works of small rivers was to determine the composition and density of native and invasive fish and estimating the European Fish Index (EFI +) to assess the ecological status of designated sites in these rivers located in the Vistula and Oder basin. A total of 1405 fish, belonging to 24 species, were captured. Native species predominated, however, 19% of the fish caught were invasive species. The most common species was roach (Rutilus rutilus), but the most numerous was the gudgeon (Gobio gobio). At the researched stations, the maximum value of the EFI+ amounted to 0.868. After division into classes according to the value of the EFI + index, the majority of investigated sites where fish were found (24 of 28 sites), the EFI + value was between 0.00 to 0.40. This relatively small value indicated a poor condition of fish habitats, which was confirmed by low classes of ecological status at individual sites. Only in the case of the 1st position in the Tywa river and the 3rd position in the Czarna-Cedron river, there was a water quality class 2. Class 3 was determined at station 3 in the Tywa River. As many as 15 sites have found class 5, which determines the poor condition of fish habitats and low biodiversity.