Ecological characteristics and morphological-genetic differentiation in populations of European mudminnoow (Umbra krameri Walbaum, 1792) from Bačka, Mačva and Semberija

European mudminnow (Umbra krameri Walbaum, 1792) is the only autochthonous and relic species of the genus Umbra present in Europe, and it is endemic for the Danube and Dniester river basins. In scope of its present discontinuous range, due to habitat desiccation and pollution, the populations of European mudminnow significantly decreased during the last decades of the 20th century. For this reason it is listed on the IUCN Red List of Threatened Species as Vulnerable (VU). At the national level, it is listed as Critically Endangered (CR), with a serious threat to be soon extinct. The range of the species in Serbia and in Bosnia and Herzegovina is presented in this dissertation, including a newly recorded population in Serbia (locality Lugomir), along with the results of ecological and morphological-genetic differentiation of the analysed populations, and the threat status at the national level with threat factors and conservation measures. A total of 76 individuals from three populations, two from Serbia (23 individuals from Lugomir and 21 individuals from Bakreni Batar) and one from Bosnia and Herzegovina (32 individuals from Gromiželj), were sampled. Basic geographical parameters (longitude, latitude, altitude) were determined for each locality, along with physical and chemical habitat parameters (width of the water basin, water and silt depth, water and air temperature, pH, electroconductivity, oxygen concentration, oxygen saturation, ammonia, nitrites, phosphates). All sampled individuals were photographed for the purpose of geometric morphometrics analyses, and their total (TL) and standard (SL) body length and body weight were measured for population stucture analyses. Furthermore, gonads were taken for sex determination, digestive tract for diet analysis, scales for age determination, and tissue samples for genetic variability analysis. Species composition of aquatic plants and fishes was determined at all localities, and invertebrates from mud and submersed vegetation were sampled with the aim to determine their diversity and to analyse the diet of European mudminnow. For their physical-chemical parameters and aquatic plant and fish species composition all three studied localities represent typical habitats of European mudminnow. The analysis of invertebrate assemblages showed that representatives of Mollusca, Isopoda, Odonata, Coleoptera, Heteroptera, and Chironomidae were present at all localities. Among the most abundant invertebrates are Isopoda