There is a constant need to monitor mercury pollution in the environment, especially in water, due to the methylation of Hg and its increased bioavailability. Fish are a good indicator material, but the lethal method of sampling for testing could be replaced by a non-lethal one. The aim of the study was to determine the mercury content in selected tissues of freshwater fish species, commonly consumed in Poland, to check whether fish scale testing will be an alternative to lethal testing for mercury contamination. Crucian carp (Carassius carassius), tench (Tinca tinca), and perch (Perca fluviatilis) were obtained from a breeding pond in Knyszyn (Podlaskie Voivodeship, Poland). Mercury was analyzed in the skeletal muscles and liver (samples for the lethal method) and scales (samples for the non-lethal method). The AMA 254 mercury analyzer was used, and the method based on atomic absorption spectrometry with thermal decomposition of the sample in a flow of oxygen was applied. The obtained results confirm the phenomenon of mercury biomagnification in the tissues of the tested fish and emphasize that even low concentrations in the natural environment can accumulate in living organisms. The highest mercury contents occurred in the species occupying a higher link in the trophic chain (perch). However, the mercury content in the muscles of the fish tested for consumption did not exceed the mercury content limits specified in the law (Commission Regulation (EU) 2023/915), i.e., up to 0.50 mg kg-1. Scales can be an interesting indicator of environmental pollution with Hg, but their value was significantly lower compared to their concentration in the muscle and liver of perch, tench, and crucian carp.