In this study we attempted to determine the effect of various feeding methods (bottom and surface feeding) used in the hatchery, on the survival and growth rates of hatchery-reared sea trout (Salmo trutta trutta L.) in the wild. Rearing was performed in two variants: a bottom-fed group (BFG) and a surface-fed group (SFG). At the end of the rearing time, we observed that BFG fish gathered at the bottom of tank, as opposed to SFG fish, which swam in the whole water column. After 4 weeks of rearing, the fish were released into two similar streams. After about 2 months the fish were captured and the foodbase of the streams were examined. 30 fish from each group have been randomly selected for stomach contents analysis. In the shallow stream the growth rates were better for the BFG fish than the SFG and also a significantly higher number of typical benthic taxa was found in stomachs of the BFG fish than the SFG fish. In the deeper stream more food was found in the stomachs of the SFG fish than in the BFG fish. The analyzed results showed that factors such as stream depth, current velocity, and turbulence can also affect the rearing success of juvenile salmonids in hatchery streams. Bottom feeding fish during rearing has a positive impact only on the fish in shallow watercourses, where there is no turbulence, and the food is not carried by the current drift or washed out from the bottom into the drift.

The threats to small urban streams lead to a decrease in their water quality and dysregulate their ecological balance, thereby affecting the biodiversity and causing degradation of indicators that determine the ecological potential. The aim of our study was to determine the impact of abiotic conditions induced by intensive human activity on the community structures of invertebrates (zooplankton and macroinvertebrates) in the small urban stream Bukówka in the Szczecin agglomeration (NW Poland). This stream exhibits the same characteristics as a large river, in which the mass of live organic matter increases with their length. The composition of invertebrates (zooplankton and macroinvertebrates) was strongly influenced by the changes caused by humans in the stream bed. The construction of small reservoirs and bed regulation in this small urban streams had a similar effect on the quality of the water and ecological potential as in large rivers, but at a lower scale.

The aim of this study was to make a comparative analysis of macrozoobenthos composition at different sites at selected sections of lower the Odra River with relation to different physicochemical factors. The observations were made on the lower section of Odra River at five study sites: two of them were localized in the main channel, one in the left branch of river, another one in the channel carrying post-cooling water from Dolna Odra power plant, and the last one was in the channel connecting both branches of Odra River. At all sites, 26 taxa were found representing by: Bivalvia, Gastropoda, Oligochaeta, Hirudinea, Malacostraca and Insecta. The greatest biodiversity and the highest abundance of zoobenthos organisms were noted in the channel joining the two branches of the river, site 5, characterised by the lowest water flow rates and the densest coverage of the macrophytes at the bottom. Temperature was the sole parameter to be studied that affected the composition of benthic invertebrates. A clearly negative impact of temperature on the diversity of invertebrates was observed only in the channel with post-cooling water discharged from the power plant.