Many natural freshwater ecosystems, especially in the north eastern Macedonia, are polluted with heavy metals, which are released by active mines. Long-term exposure to high levels of dissolved metals might result in increased metal bioaccumulation in organs of aquatic organisms, and consequently might cause various sub-toxic and toxic effects. The aim of this study was to assess the health of Vardar chub (Squalius vardarensis) inhabiting mining impacted rivers Zletovska and Kriva, in comparison with chub from the reference Bregalnica River. It was done by use of indicators of tissue damage (histopathology of liver and gonads) and general indicators of exposure to environmental stressors (condition factor, organo-somatic indices and external/internal macroscopic lesions). Histological assessment of gonads revealed good reproductive health in all three rivers, indicating high tolerance of gonads to contaminant exposure. Contrary, several external/internal lesions were more pronounced in chub from severely metal contaminated Zletovska River. Prevalence of hepatic lesions was also higher in mining impacted rivers (in Kriva, 70%; in Zletovska, 59%) compared to Bregalnica River (38%). The spectrum of histological lesions observed in chub liver varied from non-specific minor degenerative conditions, such as lymphocyte infiltration, fibrosis, parasites, granulomas and lipidosis, to extensive and/or more severe changes such as bile duct proliferation, necrosis, megalocytosis, light-dark hepatocytes and hepatocytes regeneration. The results of histopathological investigation for all three rivers showed clear signs of water contamination, especially prominent in mining influenced rivers. More research efforts should be devoted to study of environmental conditions and metal contamination in the mining impacted rivers worldwide, especially of their effects on health of local ichthyofauna.

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Exceptional natural value of karst rivers, as well as their potential as a source of drinking water supply, contributes to the importance of developing strict environmental protection. Although most of its watercourse is proclaimed national park, Krka River is impacted by technological and municipal wastewaters, which are released without proper purification only 2 km upstream of the park border. In order to assess water ecological status of the Krka River, vulnerability of karst ecosystem and potential threat to the Krka National Park, spatial and temporal variability of physico-chemical and microbiological water parameters, as well as concentrations of 25 total dissolved metals/metalloids were evaluated. All parameters indicated deteriorated water quality near the wastewater influences, which was for certain metals and bacterial counts even comparable to other world rivers of technological/rural catchment. Downstream location pointed to purification processes in karst river, although nutrients and conductivity were still in a range below good water quality and Al, Co, Fe, Li, Mn, Ni, Sr, Ti, and Zn levels remained comparable to their levels in the pollution impacted area, especially in autumn, indicating season-dependent processes. Presented data provided background status and identified pollution influences in the karst riverine system which indicated potential risk for protected area and a need for comprehensive water quality assessment.

26The assessment of general condition of fish in the moderately contaminated aquatic environment was performed 27 on the European chub (Squalius cephalus)

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