This work studies the phospholipid and fatty acid composition in hake brain and spinal cord and in sea bass brain. Fluorescence anisotropy of phospholipid vesicles labeled with 1,6-diphenyl hexatriene was measured to investigate the associated dynamic properties. In all tissues studied, phosphatidylcholine and phosphatidylethanolamine were the major constituents with minor contributions of phosphatidylserine, phosphatidylinositol and sphingomyelin. Fatty acids belong to the n-9 and n-3 series exclusively. Phosphatidylinositol from hake spinal cord and phosphatidylethanolamine and phosphatidylserine from hake brain contain the greatest percentages of eicosa-5,8,11,14,17-pentaenoic (20:5) and docosa-4,7,10,13,16,19-hexaenoic (22:6), respectively. For all fractions studied the total content of saturated fatty acids increases in the order of hake spinal cord, hake brain, sea bass brain together with a decrease in the sum of monounsaturated fatty acids. The comparison between fluorescence anisotropy values and fatty acid composition clearly demonstrates that saturated acids and 20:5 and 22:6 exert a rigidizing effect.