Growth, digestibility and fatty acid utilization in large Atlantic salmon (Salmo salar) fed varying levels of n-3 and saturated fatty acids

Dietary fatty acids strategies of metabolic relevance were studied in large Atlantic salmon. Fish with an average weight of 1.8 kg were fed four experimental diets with the same basal composition but coated with different oils, according to a 2 x 2 factorial design. The two factors were the level of saturated fatty acids (SAFA) in the diet (30% or 19% of the total fatty acids) and the level of n-3 fatty acids (35% or 20%). The oils used were a pure fish oil (herring oil), or combinations of the fish oil with a n-3 fatty acid concentrate and/or palm stearin rich in SAFA. All diets contained the same concentration of fat, protein and carbohydrates. Productive measurements were recorded and apparent digestibility coefficients (ADC) of fat and selected fatty acids calculated. Heart muscle mitochondrial L-3-hydroxyacyl-CoA dehydrogenase (L3HOAD), and liver glucose 6-phosphate dehydrogenase (GOD) and malic enzyme (ME) were used as markers to determine the effects of dietary fat type on fat catabolism and synthesis, respectively. Significant differences in growth were observed among fish fed the different diets, with the specific growth rate (SGR) being higher in the groups fed diets with low levels of n-3 fatty acids (P < 0.003). Fat digestibility was highest in fish fed the low saturated-low fatty acid n-3 diet (93.31%) and lowest in fish fed the high saturated-high n-3 diet (79.11%). All enzymatic activities were higher in the groups fed the diets with low levels of n-3 fatty acids. Dietary polyunsaturated fatty acids (PUFA) were negatively correlated with all enzymatic activities. Monounsaturated fatty acids (MUFA) positively correlated with both the ME and L3HOAD activities, especially 16:1n-7, 20:1 and 22:1, which showed the highest Pearson correlation coefficients. Dietary SAFA negatively correlated with enzymatic activities, except 14:0, which positively correlated with ME (r=0.95; P<0.0001), and L3HOAD (r=0.81; P<0.0002). The results of this study suggest that the lipid metabolism of large Atlantic salmon is readily influenced by the fatty acids supplied in the diet according to their unsaturation and chain length. Dietary 16:1n-7, 20:1 and 22:1 are preferred substrates for heart mitochondrial p-oxidation. (C) 2003 Elsevier Science B.V. All rights reserved.