The time course of fish oil wash-out follows a simple dilution model in gilthead sea bream (Sparus aurata L.) fed graded levels of vegetable oils

The aim of the study was to determine whether changes in the tissue fatty acid (FA) profile follows a simple test dilution model after changing the dietary oil sources in gilthead sea bream. A 14-month trial was conducted with juvenile fish of 18 g initial body weight fed either a fish oil-based diet (FO diet) or vegetable oils replacing 33% (33VO) and 66% (66VO) of fish oil. The trial included 3 months feeding a fish oil finishing diet to follow the restoration of the FA profile with the FO diet. Fish oil replacement with/without a finishing phase of fish oil re-feeding did not affect growth and all groups reached 520–531 g body weight. Changes in body composition with weight gain did not modify the FA profile of fish continuously fed FO, 33VO or 66VO diets. Increased amounts of oleic acid (18:1n−9), linoleic acid (18:2n−6) and linolenic acid (18:3n−3), in combination with reduced proportions of n−3 long chain polyunsaturated FAs, were found with the partial replacement of fish oil. Hence, multivariate component analysis highlighted a gradient of fish oil load determined by the total intake of fish oil over the entire production cycle. The simple dilution model was a good descriptor of these tissue FA changes, and excellent correlations between observed and predicted values were found at the end of finishing period in fish grow out with either 33VO or 66VO diets.