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Here, we present the results of a large-scale fish rescue prior to the building of flood protection structures along a stretch of the River Svratka running through Brno city centre (Moravia, Czech Republic). During this demanding and unique event, 5,861 fish, with a total weight of 1,951 kg, were caught and successfully transferred downstream. A total of 21 species of fish were recorded, of which two were protected species and two non-native to the Czech Republic. The dominant species caught (i.e. > 10%) were chub (Squalius cephalus), nase (Chondrostoma nasus), roach (Rutilus rutilus) and vimba bream (Vimba vimba), making up 85% of the catch. While this stretch of the Svratka supported a type-specific fish community dominated by rheophilic species, the occurrence of many species was supported through stocking by the Moravian Anglers Association. The length-frequency distribution of individual fish species suggests there has been a lack of recruitment over a relatively long period. This is most likely linked with hydropeaking from the Brno reservoir water power plant, with daily sharp fluctuations in flow in a river channel lacking shallow bankside areas and refuges with slowflowing water preventing fish fry survival. [ABSTRACT FROM AUTHOR]

While fish communities have been studied in Czech reservoirs for decades, monitoring has increased since implementation of the EU Water Framework Directive (2000 / 60 / EC). Despite this, many smaller drinking water reservoirs have yet to be surveyed. Between May and July 2016, we undertook a pilot-study examining the fish communities of five Moravian reservoirs (Ludkovice, Bojkovice, Hubenov, Nová Říše and Landštejn). Fish were sampled using boat electrofishing along the littoral zone and Nordic gill nets in the pelagic zone. Both methods were evaluated separately and combined as CPUE and relative abundance and biomass ( %). Nineteen fish species and one hybrid were recorded, with roach Rutilus rutilus dominating overall by abundance, but carp Cyprinus carpio, pike Esox lucius and wels Silurus glanis dominating by biomass in electrofishing samples. Predatory species represented up to 60 % of biomass in the combined sample, with an F / C index ranging from 0.5 - 3, implying a high abundance of predators. Electrofishing tended to underestimate the abundance of bleak and ruffe, while gill nets underestimated the biomass of predatory species. In some reservoirs, the abundance of pike and wels was high (though it is difficult to say if these fish were stocked or the result of natural reproduction). In others (e.g. Landštejn), zander Sander lucioperca were not registered by either sampling method, despite intensive stocking. Overall, gill netting alone appears inadequate for gaining a true picture of the fish community in reservoirs and we suggest a combination of electrofishing and gill netting in future. [ABSTRACT FROM AUTHOR]