The influence of diet protein content (35-45-55%) on growth and lipid composition of muscle and liver of European eel (Anguilla anguilla) was studied for the first time. In control eel, triacylglycerols constituted about 90% of total lipids in muscle and about 40% in liver. Triacylglycerol content in eel muscle significantly increased after two months of treatment with any diet assayed, with independence of protein content and source. In liver, this increase was comparatively higher in herring meal diets. Total phospholipid content in both muscle and liver drastically decreased after one month of all the experimental treatments, although some recuperation was found at the second month. No significant differences in lipid composition of muscle eel were found among the various experimental groups, in spite of the differences observed in the body weight gain.