Growth, body composition and nutrient retention efficiency of growing sea bass (Dicentrarchus labrax L) fed fish oil or fatty acid Ca salts

Two hundred and forty sea bass (114.2 +/- 14.4 g, mean +/- SD) were randomly distributed among 12 fibreglass tanks and fed four experimental diets (on an equivalent gross energy and crude protein basis) for 86 days according to a 2 X 2 factorial design: two lipid sources (herring oil (FO) vs. fatty acid Ca salts of herring oil (FAS)) at two lipid levels (3.8% vs. 7.8% ether extract (EE)) with three replicates for each treatment. Protein and organic matter digestibility did not differ among treatments, while crude fat digestibility was slightly higher for the diet FAS38. Final weight, specific growth rate, daily weight gain, daily fat gain and protein efficiency ratio were not affected by lipid source or lipid level, while feed efficiency was significantly better for the diet containing FAS of fish oil at the lower content. In contrast, the hepatosomatic index was significantly lower in fish fed the 7.8% supplemental lipid diets. Body proximate composition, gross energy and protein retention efficiencies were unaffected by the experimental factors. From a practical point of view, it is possible to prepare a complete diet for this species using large amounts of these solid ingredients (see diet FAS78), as the fatty acid composition of the ingredient is more important than its physical state.