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The effects of substitution of dietary fish oil with vegetable oils on the growth, tissue lipid composition, metabolism and health of European sea bass

The first trials with European sea bass in Cadiz, Spain involved feeding juvenile bass of ~90g diets containing 100% FO, 60% LO, 60% RO or 60% OO to triplicate groups for a period of 34 weeks. In the second dietary trials, bream were fed 100% FO or two different 60% blends of rapeseed/linseed and palm oils (60% VO blends A & B) to replicate groups for 64 weeks from initial weight of 5g. In both trials fish were grown to market size and were then fed a FO finishing diet for a further 14 weeks (trial I) or 20 weeks (trial II).

In sea bass, replacement of up to 60% of FO with VO had no detrimental effects on growth or feed conversion. Flesh and liver lipid content were unaffected by dietary lipid but flesh fatty acid concentrations closely reflected diet fatty acid concentrations, with DHA tending to be conserved. In sea bass fed 60% VO, DHA & EPA were reduced by ~50%. In general, reduction of DHA and EPA was less in fish fed diets with low PUFA contents, e.g. olive oil, and the VO blend than in fish fed diets high in PUFA. DHA and EPA could be restored to > 90% of their values in FO fish, in sea bass, by feeding a FO finishing diet for 14-20 weeks. The duration of the finishing diet period was dependent on fish size, growth rate, and dietary DHA and EPA contents. Our results suggest that oils most suited as FO substitutes should be high in monoenes, contain saturate levels similar to those in the fish being fed and be low in C18 PUFA, especially 18:2n-6, as this fatty acid is poorly oxidised and difficult to remove using finishing diets.

Using blends of VO, no clear effects on beta-oxidation capacity were found in any of the species. In sea bass, hepatocyte HUFA synthesis was very low, ~ 5- to 20-fold lower than in salmon. In sea bass, HUFA synthesis was increased by dietary VO in enterocytes but not hepatocytes. Trends were observed for dietary VO to increase delta-6 FAD in sea bass liver; however, this was only significant for one of the 60% vegetable oil blends tested.

Sea bass showed reduced macrophage phagocytic activity when fed 60% VO. Arachidonic acid - derived prostaglandin production was reduced in sea bass fed VO diets, although this was less affected when feeding a VO blend than by single VO replacement diets. When using a single VO to replace FO, a number of immune parameters (haematocrit, leucocyte numbers, macrophage respiratory burst) were altered by dietary treatment, in sea bass. However, when a VO blend was chosen to replace FO, immune functions were not affected up to 60% replacement in sea bass.

Reported by

Universidad de Cadiz
Departmento de Biologia Animal, Campus del Rio San Pedro
11510 Puerto Real, Cadiz
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