High and low fat diets, leucine and DHA influence growth, gene expression and fatty acid composition of different tissues in Atlantic salmon (salmo salar L)

Abstract

The main goal of this master thesis project was to examine how protein to lipid ratio in the diets, and DHA and leucine in combination, interact and affect the energy utilization for growth and lipid and protein deposition in Atlantic salmon (Salmo salar L) in the early freshwater phase. Leucine was chosen because it is known to be higher in certain plant meal ingredients than in fish meals and DHA was chosen because it is found in fish oil and not existent in plant oils and therefore reduced in modern fish diets. Both leucine and DHA are known to influence the lipid metabolism in animals. Atlantic salmon was fed 6 different diets supplemented with leucine and DHA with a high- or normal-fat dietary content. Whole body, in addition to tissue samples of liver, muscle and adipose were analyzed for fatty acid composition. A microarray analysis was performed on liver, muscle and adipose tissues to study the different gene expressions related to the lipid metabolism in the fish. The fish grew from 4 g to 22 grams during the trial and the fat, protein, leucine or DHA levels in the diet did not influence the growth. The protein to fat ratio in the feed affected however the whole body protein and fat contents of the fish, with higher protein and less fat in the low fat dietary groups. Dietary leucine did not increase protein and muscle growth, but affected the liver fat deposition negatively in combination with high fat diet.