Our paper presents the results of a study on the concentrations of total (Hgtotal), organic (CH3Hg+) and inorganic (Hginorg) mercury in freshwater fish from the Vistula Lagoon, coastal waters of the Baltic Sea.  Mercury assays were performed on tissues (muscle, skin, gills) and internal organs (heart, spleen, liver, gastrointestinal tract, gonads) of pikeperch, common roach, and common bream. The distributions of Hgtotal, CH3Hg+, and Hginorg depending on fish species, tissue, or organ and bioaccumulation in tissues and biomagnification in the trophic chain were determined. Interspecific and intraspecific differences in mercury concentrations occurred in fish tissues and organs. Muscles of pikeperch, bream and roach accumulated the highest concentration of CH3Hg+, Hginorg dominating in the gastrointestinal tract of bream and roach. The concentration gradations of Hgtotal and CH3Hg+ depending on fish species were as follows: pikeperch > common roach > common bream. For Hginorg, the gradations were as follows: common bream > common roach > pikeperch. The type of food was a determining criterion for the distribution of mercury forms in the tissues and organs of the fish studied, and quantifiable confirmation of this was the different values of the L:M coefficient (Hginorg in the hepatic tissue : CH3Hg+ in muscle). Differences in Hgtotal, CH3Hg+, and Hginorg concentrations in fish tissues and organs were linked with the food the fish consume, their position in the trophic chain and biomagnification in the food chain.

24.2.2019