Growth and chemical composition of adult Atlantic salmon ( Salmo salar) fed dry and silage-based diets

Abstract

Atlantic salmon of 1.4 kg mean initial weight were held in four sea pens from September to May. The groups were fed one of four diets based on fish silage (A), a dry pelleted feed (B), a mixed partly defatted fish silage concentrate (C) and concentrated fish silage (D). The percentage of dietary metabolizable energy provided by protein and by lipid varied between 36 and 52%, and between 25 and 48%, respectively. The fish fed diets A and B had the highest final weights, 4.5 and 4.6 kg, respectively. Few differences were found between groups fed diets A, B and D in feed conversion, protein efficiency ratio (PER) and protein productive value (PPV). Fish fed diet C had reduced growth and slightly depressed food and protein conversion. A linear relationship was found between lipid intake and lipid retention in whole fish. The lipid content in fillets and livers reached mean levels of approximately 14 and 6%, respectively. The fillet lipids contained about 20% of ω-3 polyenoic fatty acids which reflected mainly the fatty acid composition of the dietary lipids. Alkaline phosphatase activity in serum showed a significant positive correlation with water temperature. Serum cholesterol level was reduced in the group fed the low lipid content diet (C) while triglyceride levels were not correlated with the lipid contents of the diets.