Fish assemblage in the Úpoř brook was observed. The stream was inhabited by 13 fish species and Lampetra planeri. The abundance reached the mean value of 12175 spec.ha-1 and the mean biomass 395 kg.ha-1. Salmo trutta dominated, Cottus gobio was also very abundant and inhabited preferably riffles as well as Barbatula barbatula. Leuciscus cephalus and L. leuciscus were resident in pools. Other species occurred occasionally. Preferences in habitat and microhabitat use were evaluated using RDA and FE test. Two first axes of RDA explain 27.8% of total variability of all species, and 95.3% of relationship between the species and the environmental variables. These factors significantly correlated with the axes: distance from the mouth, maximum depth, presence of mud, presence of stones as shelters, presence of rocky shelters, and presence of the deposits. The character of substrates was the most important factor influencing the distribution of S. trutta, L. cephalus, L. leuciscus and B. barbatula, whereas C. gobio were greatly influenced by character of shelters. Also the distance from the mouth play a role in distribution of two last species. Seasonal changes in habitat preference of C. gobio were recorded.
Seven populations (Oľšava/Hornád R., Oľšava/Topľa R., Ublianka R., Ondava R., Ipeľ R., Malý Dunaj R. and Vlára R.) of Balcan spined loach were subjected to phylogenetic analysis based on variability of the cytochrome b gene and mitochondrial specific marker. They were separated in to five groups but these groups were represented by specimens from different populations. Genetic distances among populations and among groups were quite low. Subsequently, analysis of relations among our groups and sublineages of Danubian-Balkanian complex of Sabanejewia was made. the first four groups were genetically close to sublineage III, while the fifth one to the sublineage IV. These findings agree with the conclusion about conspecificity of analysed Danubian-Dniester populations belonged to monotypic S. balcanica. Phylogenetic analysis showed that the most suitable populations for the restoration of this species in the Bečva River are populations dwelling the Ipeľ and Vlára rivers.