Persistent organochlorine pollutants (POPs) like polychlorinated biphenyls (PCBs) and DDT residues (DDTs) can still be a problem for the aquatic environment and the human health. PCBs and DDTs were determined in three freshwater fish species: common carp (Cyprinus carpio), catfish (Silurus glanis), pike-perch (Sander lucioperca) and two marine fish: shad (Alosa pontica pontica) and grey mullet (Mugil cephalus). The freshwater fish samples were collected from the Danube River and from Black Sea, Bulgaria in 2010. The POPs were analyzed in order to investigate the presence of PCBs and DDTs in fish species from Danube River and compared the results to the levels in marine fish species from Black Sea. The fifteen congeners of PCBs, p,p’-DDT and its two main metabolites p,p’-DDE and p,p’-DDD were determined by capillary gas chromatography system with mass spectrometry detection. DDTs were the predominant contaminants in investigated species, with the p,p’- DDE contributing to more than 67% to the total DDTs. In freshwater fish concentrations of DDTs were found from 19.2 to 30.3 ng/g ww and PCBs concentrations - from 6.2 to 12.6 ng/g ww. The highest levels of PCBs and DDTs were determined in shad. The levels of DDTs and PCBs were determined lower than those found in similar fish species from other aquatic ecosystems.