The purpose of this study was to investigate the effect of freshwater rearing on the fatty acid profiles of the whole body and muscle tissue of the European sea bass (Dicentrarchus labrax). Half of initial fish were gradually acclimated to freshwater (FW) kept at the same temperature to salt water and grown in same conditions as their counterparts in saltwater (SW). The decrease in salinity caused an increase in the percentages of 18:1n - 9, 24:1n - 9, 18:3n - 3, 18:2n - 6 and decrease in the percentages of 14:0, 15:0, 20:0, 21:0, 20:5n - 3 and 22:6n - 3 both in the whole body and in the muscle tissue fatty acid profiles. The lipids of FW-reared fish contained significantly (P < 0.01) higher percentages of 18:2n - 6 and 18:3n - 6 than that of SW-reared fish. However, percentages of 20:5n - 3 and 22:6n - 3 fatty acids decreased significantly (P < 0.05) compared with those of salt water-reared European sea bass. There was a clear trend of decrement in the percentages of n - 3 PUFA fatty acids due to the decrease in water salinity. However, the percentages of n - 6 PUFA fatty acids were also increased with the decrease in water salinity. We concluded that the FW acclimation is followed by changes in certain lipid classes of sea bass muscle tissue and whole body samples. n - 3/n - 6 PUFA ratios were characteristic to previously reported ratios for both FW- and SW-reared European sea bass. In addition, EPA/DHA ratios were basically similar for the fish reared in both SW and FW indicating the equal nutritional value of the final products in terms of providing PUFA's for human nutrition.