Dietary Lipid Sources as a Means of Changing Fatty Acid Composition in Fish: Implications for Food Fortification

Abstract

Organisms of vegetal and animal kingdoms can synthesize saturated and monounsaturated fatty acids using carbons from different sources. The major resulting products are palmitic acid (16:0), stearic acid (18:0) and their D9 desaturase products, palmitoleic acid (16:1n-7) and oleic acid (OA, 18:1n-9). However, due to the absence of D12/D15 desaturase enzymes, vertebrates require a dietary source of n-6 and n-3 polyunsaturated fatty acids (PUFAs) to meet their requirements in essential fatty acids (EFA), especially arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) (Fig. 4.1). Thus, once obtained from the diet, linoleic acid (LA, 18:2n-6) is metabolized by elongation and D6/D5 desaturation to ARA. The same desaturases operate for the conversion of α-linolenic acid (LNA, 18:3n-3) to EPA and DHA. However, the conversion of ALA to DHA is low in humans, particularly at the conversion of EPA to DHA [1]. Similarly, when evaluating changes in plasma phospholipid (PL) fatty composition, supplementation of LNA, up to 5 g per day, does not have a significant impact on the PL DHA content [2]. This reinforces the nutritional value of fish, in particular marine oily fish, as virtually the most important source of n-3 long chain PUFA (LC-PUFA) in the human diet [3, 4]. However, global fisheries are in decline, and farmed fish constitute an increasing proportion of fish in the human food basket. Thus, to assure the continuous growing of aquaculture production, the industry is obligated to find suitable alternatives to fish meal and fish oil in fish feeds. Plant products are the obvious choice, but vegetable oils are devoid of n-3 LC-PUFA, and fillet fatty acid composition of farmed fish points towards a reduction in EPA and DHA levels. The sustainable development of aquaculture and the preservation of health benefits of fish consumption represent, thereby, a complex trade-off, and the aim of this chapter is to review recent findings in fish nutrition as a means to assure the production of high quality fish according to the human nutrition guidelines and the concomitant policies for a sustainable utilization of finite marine resources as feed ingredients. Special attention is focused on salmonids and warm marine fish, in particular gilthead sea bream (Sparus aurata), which is now the most important farmed fish in the Mediterranean area.