Rapeseed oil as an
alternative to marine fish oil in diets of post-smolt Atlantic salmon (Salmo
salar): changes in flesh fatty acid composition and effectiveness of
subsequent fish oil "wash out"
J. Gordon Bell, F. McGhee, P.J. Campbell, J.R.
Sargent-2003
Aquaculture, 218(1-4): 515-528
Abstract:
Duplicate groups of Atlantic salmon post-smolts were
fed five practical-type diets in which the added oil was 100% fish oil
(FO)/0% rapeseed oil (0% RO), 90% FO/10% RO (10% RO), 75% FO/25% RO (25%
RO), 50% FO/50% RO (50% RO) or 100% RO for 16 weeks. After sampling, the
remaining fish were switched to a commercial grower diet containing FO as
the only added lipid for a further 12 weeks. There were no effects of the
inclusion of RO on growth or feed conversion. Fatty acid compositions of
flesh total lipid showed significant increases in 18:1n-9, 18:2n-6 and
18:3n-3 with increasing inclusion of RO. The percentages of flesh 20:5n-3
and 22:6n-3 were significantly reduced in fish fed 10%, 25% and 50% RO,
compared to fish fed 0% RO, and the percentages in fish fed 100% RO were
significantly lower than all other treatments. Following transfer to the FO
washout diet, percentages of flesh 20:5n-3 were not significantly different
among treatments after 4 weeks while percentages of 22:6n-3 were restored
after 12 weeks. However, even after 12 weeks, percentages of flesh 18:2n-6
were still significantly higher in fish previously fed 50% and 100% RO
compared to the other treatments, although the final values were reduced by
48% and 65%, respectively, following the 12-week washout period. This study
suggests that RO is a potential substitute for FO in Atlantic salmon
culture, but that percentages of the n-3 highly unsaturated fatty acid
(HUFA), 20:5n-3 and 22:6n-3, are significantly reduced by feeding RO above
50% of added oil. However, percentages of these two HUFA can be restored by
feeding a diet containing FO for a period of 12 weeks.
(Institute of Aquaculture, University of Stirling, Stirling FK9 4LA,
Scotland, UK,
e-mail: g.j.bell@stir.ac.uk)