Investigations were conducted for fat content and fatty acids composition of six of the most frequently fished species inhabiting the Vistula Lagoon (bream, roach, perch, pikeperch, herring, and eel). Fat content of the fish examined ranged from 0.39 to 29.77%, whereas fatty acids composition range was as follows: saturated fatty acids (SFA) 25.1–29.4%, monounsaturated fatty acids (MUFA) 22.3–52.2 %, and polyunsaturated fatty acids(PUFA) 18.5–52.2%. Among the SFAs, palmitic acid dominated (C16:0). Oleic acid (C18:1) had the greatest share of the MUFAs. PUFAs had a high share of acids from the n-3 family, especially of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. A high share of these acids was confirmed in the fats of pikeperch (33.25%) and perch (31.02%). The total contents of EPA and DHA in 100 g of muscle tissue of the fish examined in the current study was as follows: eel – 2.11 g; herring – 0.62 g; bream – 0.33 g; roach – 0.19 g; perch – 0.16 g; and pikeperch – 0.14 g (the recommended daily dose for healthy persons is 0.5 g). At the recommended minimum value of 0.45, the ratios of n-6/n-3 (0.18 – 0.55) and PUFA/SFA (0.63 – 2.04) were advantageous in the fats of the fish examined.