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(a) Growth Rate

1.6

a

1.4

1.8

1.2 b*

1.0

1.6

a

b

0.8 0.6 0.4

Feed Efficiency

Thermal Growth Coefficient (TGC)

Off to a good start

1.4 1.2

b*

0.6 0.4

0.0

0.0

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

M-fish V-fish

0.8

0.2

Challenge phase

a*

a

1.0

0.2

Marine phase

(b) Feed Efficiency

Marine phase

Challenge phase

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

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.

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Feed - Douglas Tocher.indd 43

Above: The early stimulus had clear effects. Left: Feed

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16/01/2017 11:46:47

Profile for Fish Farmer Magazine

Fish Farmer Magazine january 2017  

Serving Worldwide Aquaculture Since 1977

Fish Farmer Magazine january 2017  

Serving Worldwide Aquaculture Since 1977

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