The analysis of the frequencies of chromosome breaks and gaps on the pike - Esox lucius L. individuals from different locations collected in two consecutive years, were showed the highest values that were above the level of spontaneous (under the level of 3%) changes. Frequences of changes in fish Esox lucius L. were higher than the level of the presumed critical zone (3.0-3.5%) at locality of Danube by Visnjica and within the zone by Grocka. In consecutice years in river Tamis by Pancevo, both obtained values of chromosomal changes in this fish also were above the critical zone. Physicochemical water analyses were shown high level of organic contamination and concentration of phenols above MDK values for the 1st, 2nd water categories which argued obtained cytogenetic results. The localities obviously has a risk of being permanent or periodical contaminated with genotoxic agents.

The aim of this study was to assess the water quality of the Gradac, near the town of Valjevo, on an analysis of DNA damage in different tissues of trout (Salmo trutta L. 1758) and barbel (Barbus meridionalis R. 1827). For the detection of genotoxic potential of alkaline comet assay were used three types of tissue, blood liver and gills. Among the parameters available the Olive tail moment was chosen as the most reliable to estimate the damage to DNA molecules. In all tested tissues was detected damage in DNA molecule, where the gills showed the highest sensitivity.

The analysis of breaks and gaps frequences in the fish species Alburnus alburnus from different localities of rivers Kolubara, Sava and Danube, were showed the highest values that were above the presumed critical zone (3.0-3.5% of changes). At some of localities examined in May and October 2008, these values were much more elevated that the level of spontaneous changes normally seen in the controls in laboratory animals and in fish of relatively clean waters. Results that were obtained for these localities indicate to periodical or permanent contamination with genotoxic agents.