The concentration of mercury, fatty acids and lipid quality indices were determined in three species of fish (European eel, Anguilla anguilla Linnaeus, 1758, Eurasian perch, Perca fluviatilis Linnaeus, 1758 and roach, Rutilus rutilus Linnaeus, 1758). The fish were caught from a reservoir in the Warmia and Mazury region located near Olsztyn (north-eastern Poland). Mercury content was determined by atomic absorption thermal decomposition using Milestone DMA-80 (Italy), whereas fatty acids were measured by gas chromatography using a 7890A Agilent Technologies chromatograph. The total mercury concentration had the following sequence: European perch (0.297 mg/kg) > European eel (0.160 mg/kg) ≈ roach (0.100 mg/kg) (P<0.05). A positive correlation was found between the mercury content and size (the body weight and total length) of these fish (P<0.0001). Based on the THQ, HI (<1.0) and BRQ (1.063), it was concluded that the fish does not pose a health risk and is fit for human consumption. Similarly, low AI and TI values (<1) are beneficial to human health related to reducing the risk of ischemic heart disease. A low OFA index of C12+C14+C18 and a high index of C18+UFA also indicate that these fish are safe from a nutritional point of view. The fatty acid indices HH (32.10–74.30), NVI (0.83–2.14), DI(18) (65.50–89.28), DI(16) (18.45–32.96), UI (131.93–278.64) and PI (88.60–314.90) were also studied. However, higher PUFA/SFA and de minimis EPA+DHA/Hg ratios compared to the recommended ratios suggest further research in this area is needed.
