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Feed – Research

BY DOUGLAS R TOCHER, MICHAEL CLARKSON AND JOHN F TAYLOR

Off to a good start Programming salmon to improve utilisation of sustainable feeds

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tudies in mammals and humans have shown that dietary influences exerted at critical developmental stages in early life, such as neonatal and weaning nutrition, may have long-term consequences on physiological functions in later life. This phenomenon is known as ‘nutritional programming’ and has been studied mainly in mammalian models in relation to diseases that are currently prevalent, such as metabolic syndrome and diabetes. However, the concept of metabolic programming was also likely to exist in fish as it was known that the function of some metabolic pathways in juveniles depended upon specific nutritional signals during early larval stages. This, therefore, raised the possibility of being able to influence specific key metabolic pathways or functions in juvenile fish, for example to improve the use of alternative feed ingredients and thus promote the development and application of sustainable feeds in aquaculture. As a consequence, validating the concept of nutritional or metabolic programming in farmed fish species became an important part of the recently completed EU FP7 project, ARRAINA (Advanced Research Initiatives for Nutrition and Aquaculture). In practical terms, nutritional programming involves giving the fish a nutritional ‘stimulus’ early in life that will enable the fish to have an improved response to a similar ‘challenge’ later in life. Figures (Nutritional programming) At the Institute of Aquaculture, University of Stirling, we investigated the concept in Atlantic salmon with our stimulus/challenge being a feed with very low levels of the marine ingredients, fishmeal and fish oil, and, consequently, very low levels of the omega-3 long-chain polyunsaturated fatty acids, EPA and DHA. The trial design involved initially feeding two triplicated groups of salmon fry for three weeks from first feeding with either a stimulus diet (V),

STIMULUS

3 weeks

MARINE PHASE

15 weeks

Below: Identical diets after the first three weeks

CHALLENGE PHASE

Diet M Diet V

6 weeks Fig. 1

42 Fig.1. Trial design

Feed - Douglas Tocher.indd 42

containing just 10 per cent fishmeal and no fish oil, or a marine diet (M), containing 80 per cent fishmeal and four per cent fish oil (Fig. 1). The isoenergetic feeds were both 57 per cent crude protein and 12 per cent crude lipid, formulated by Dan Leeming (BioMar UK) and manufactured at the BioMar TechCentre, in Brande. After the short stimulus phase, all fish were fed the marine M diet for 15 weeks (marine phase) before all fish were challenged by being fed the V diet for a further six weeks (challenge phase) (Fig. 1). Therefore, it is important to note that in the entire six-month trial the fish had almost identical nutritional histories apart from the first three-week period when they were fed either the M or V diets, termed M-fish or V-fish, respectively. Growth performance, feed intake, feed efficiency, and nutrient retentions were determined in the marine and challenge phases of the trial. The early nutritional stimulus had clear, significant effects on fish growth and feed efficiency. In the marine phase, the M-fish showed the higher thermal growth coefficient and feed efficiency but, in the challenge phase, this was completely reversed with the V-fish showing significantly higher growth and feed efficiency (Fig. 2). The effects on growth were not dependent upon feed intake, which was not different between the M- and V-fish during either marine or challenge phases. However, protein, lipid and energy retentions were all significantly higher in V-fish during the challenge phase (Fig. 3). This was the reverse of that observed during the marine phase when protein, lipid and energy retentions were all greater in the M-fish. It should be noted that the stimulus/challenge

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