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Fish oil, the most abundant natural source of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), is a limited resource; however, terrestrial oils are used as an alternative in fish nutrition. The liver of Atlantic salmon is able to synthesize these two long-chain n-3 polyunsaturated fatty acids (n-3LC-PUFAs) from α-linolenic acid (ALA), but the dietary levels of EPA + DHA and the ratios of linoleic acid (LNA) to ALA may affect its abilities. Feeding Atlantic salmon four experimental diets containing EPA + DHA at 0.3 and 1.0% of dietary levels accompanied with high and low LNA/ALA ratios showed that low LNA/ALA ratios increased the proportions of EPA + DHA in phospholipids (PLs) and neutral lipids (NLs). The pattern of PL-to-NL ratios of n-3 LC-PUFA proportions matched the saw tooth pattern of LNA/ALA ratios in diets. Overall, when fish oil is removed from salmon diets, the dietary LNA/ALA ratio must be reduced to stimulate biosynthesis of n-3 LC-PUFAs in the liver.