Gilthead seabream juveniles were fed on either a fish oil (FO)-containing diet or a diet containing a 50 : 50 blend of FO and Echium oil (EO) to determine the effect of EO on growth, plasma parameters and tissue lipid compositions. After 4 months of feeding, there was a significant increase of 18 : 2n-6 and a reduction of approximately 25% of 20 : 5n-3 in the flesh of fish fed the EO diet. At this point, half of the fish that fed on EO were returned to the FO diet as a third treatment and the trial continued with the three groups for a further 3 months. At the end of the experiment, food intake, survival, growth and plasma parameters were not affected by the inclusion of dietary EO. However, hepatosomatic index (HSI), total lipid and triacylglycerol contents of muscle decreased in fish fed the EO diet. Feeding the EO diet resulted in significant increments of potentially health-promoting fatty acids such as 18 : 3n-6, 18 : 4n-3 and 20 : 3n-6 but reduced n-3 highly unsaturated fatty acids, particularly 20 : 5n-3. When EO-fed fish were returned to the FO diet, tissue lipid contents and HSI tended to increase, but 18 : 2n-6 and 20 : 5n-3 levels were not fully restored to the levels of fish fed the FO diet for the entire trial. Furthermore, the fatty acids present in EO, which may promote beneficial health effects, were reduced.

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