This study aimed to analyse whether regular swimming exercise affects skeletal muscle membrane lipid composition of fish. Common carps (Cyprinus carpio L., n=2x12 control vs. trained) were exercised 30 minutes/ day in an artificial water flow at 0.6 m/s standard velocity. After 35 days fast-twitch type muscle samples were taken and phospholipid Fatty Acid (FA) composition was determined with column chromatography and subsequent gas chromatography. Training significantly decreased the proportion of myristic (C14:0), margaric (C17:0) and arachidonic (C20:4 n6) acids and the total n6 FA proportion, while increased the proportion of behenic acid (C22:0). The fillet malondialdehyde content (indicative of the in vivo lipid peroxidation) decreased significantly in the trained group. These novel results on carp are mostly consonant with those gained so far only in homeothermic vertebrates.