Manipulation of fatty acid composition of Nile tilapia (Oreochromis niloticus) fillets with flaxseed oil

Nile tilapia (Oreochromis niloticus) is one of the most consumed species among freshwater fish reared in Brazil. However, studies show low levels of n‐3 fatty acids in freshwater fish reared in captivity in comparison with those reared in their natural habitats. The Nile tilapia used in this study were raised in captivity for a period of 5 months and fed varying amounts (0, 1.25, 2.5, 3.75 and 5%) of flaxseed oil as a substitute for sunflower oil (control). No significant differences (P > 0.05) in total lipid (TL) content were found between fillets of tilapia fed the different diets. TL analysis of fatty acid methyl esters by capillary gas chromatography revealed a total of 50 components common to all treatments studied. The major fatty acids present were linoleic acid (18:2n‐6), oleic acid (18:1n‐9) and palmitic acid (16:0). All treatments led to significant % increases in α‐linolenic acid (18:3n‐3), eicosapentaenoic acid (20:5n‐3) and docosahexaenoic acid (22:6n‐3). Increases in both total n‐3 fatty acids and total polyunsaturated fatty acids were observed concomitantly with decreases in total n‐6 fatty acids, resulting in increases in n‐3/n‐6 ratio, with increasing level of flaxseed oil in the feed. Thus feed supplementation with flaxseed oil contributed greatly to raising the nutritional lipid value of Nile tilapia fillets.