Impact of n-3 fatty acid chain length and n-3/n-6 ratio in Atlantic salmon (Salmo salar) diets

A feeding trial was carried out to test the impact of n - 3 fatty acid chain length and n - 3/n - 6 ratio in diets for Atlantic salmon, according to a 2 x 4 factorial design. Two dietary fat sources: fish oil (FO), rich in long chain EPA and DHA and linseed oil (LO) rich in linolenic acid were replaced by increasing levels of sunflower oil (SO) rich in linoleic acid: 0, 25, 50 and 75%. Thus eight experimental diets were produced containing either a combination of FO and SO (100:0; 25:75, 50:50 and 25:75) or a combination of LO and SO (100:0; 25:75, 50:50 and 25:75). Diets were fed to duplicate tanks of Atlantic salmon weighing approximately 220 g (initial stocking density 10 kg/m(3)). The effects of the diets on performance, fat digestibility, muscle and liver fatty acid composition were determined after 12 weeks of feeding. No differences in growth were observed. Fat digestibility was affected by the concentration of saturated fatty acid in the diet, and was lower in fish fed the FO based diets. However, the progressive replacement of FO by SO led to a linear increase (P<0.01) of fat digestibility. Fatty acid composition in muscle and liver was significantly altered by experimental diets. The progressive inclusion of SO in the diet led to a linear increase (P<0.01) in total n - 6 fatty acids in the muscle however, the source of dietary n - 3 affected (P<0.01) the accumulation pattern of these fatty acids having a more marked response in fish fed the FO based diets. Total n - 3 HUFA concentrations where higher (P<0.01) in muscle and liver of fish fed FO based diets, and linearly (P<0.01) decreased with increasing dietary SO inputs. However, total n-3 fatty acid concentration was higher in fish fed the LO based diets (P<0.01). The present study suggest that LO is a potential fat source in Atlantic salmon feeding having no detrimental effects on fish growth, health and feed conversion. (C) 2007 Elsevier B.V. All rights reserved.