(a) Growth Rate
0.8 0.6 0.4
Thermal Growth Coefficient (TGC)
Off to a good start
diets were not essential fatty acid (EFA) deﬁcient as they were formulated with rapeseed oil and so the levels of linolenic (18:3n-3) and linoleic (18:2n-6) acids far exceeded the reported EFA requirement levels (~ 1 g/ Kg diet) of Atlantic salmon. However, the V diets contained only very low levels of EPA and DHA, around 0.3 g/Kg, tenfold lower than in the M diet (3 g/Kg).
(b) Feed Efficiency
At this point it is important to remind ourselves that the only diﬀerence between V- and M-ﬁsh is that the V-ﬁsh were exposed to this low level for just three weeks at the beginning of the trial. However, this short exposure had a huge impact on fatty acid metabolism in the ﬁsh, with EPA and DHA retentions being considerably higher in V-ﬁsh compared to M-ﬁsh in the challenge phase (Fig.4.). As expected, retention of DHA was far greater than that of EPA, irrespective of dietary history. The results of this study suggested that the ability of salmon to grow and thrive on a diet with very high levels of substitution of ﬁshmeal and ﬁsh oil, far exceeding current replacement levels, was improved by exposing the ﬁsh very brieﬂy to this feed early in life, speciﬁcally ﬁrst feeding. The fact that growth and feed eﬃciency were both affected without any signiﬁcant eﬀects on feed intake highlights that this was not due simply to diﬀerences in palatability and/or eﬀects on appetite between the diets. This, and the results of the nutrient retention analyses, clearly suggested that the eﬀects were at a metabolic and/ or physiological level and, therefore, would appear to validate the concept of nutritional programming. The precise biological mechanisms whereby the nutritional programming event can be eﬀectively ‘stored’ until later in life could
Fig. 2. Growth rate and feed efficiency during the marine and challenge phases.
means ± SEM 3) based nutritional history during the stimulus phase (M-fish Theare early nutriti onal(nsti=mulus hadonclear, “Data signiﬁcant eﬀects on ﬁsh growth and or V-fish). Superscripts denote significant differences (p 0.05) between dietary history and feed eﬃciency ” asterisks denote significant differences between feeding phases.
Feed - Douglas Tocher.indd 43
Above: The early stimulus had clear eﬀects. Left: Feed
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