Fatty acid metabolism in European sea bass (Dicentrarchus labrax): effects of n-6 PUFA and MUFA in fish oil replaced diets

Abstract

Monounsaturated fatty acids (MUFA)-rich and n-6 polyunsaturated fatty acid (n-6 PUFA)-rich vegetable oils are increasingly used as fish oil replacers for aquafeed formulation. The present study investigated the fatty acid metabolism in juvenile European sea bass (Dicentrarchus labrax, 38.4 g) fed diets containing fish oil (FO, as the control treatment) or two different vegetable oils (the MUFA-rich canola/rapeseed oil, CO; and the n-6 PUFA-rich cottonseed oil, CSO) tested individually or as a 50/50 blend (CO/CSO). The whole-body fatty acid balance method was used to deduce the apparent in vivo fatty acid metabolism. No effect on growth performance and feed utilization was recorded. However, it should be noted that the fish meal content of the experimental diets was relatively high, and thus the requirement for n-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) may have likely been fulfilled even if dietary fish oil was fully replaced by vegetable oils. Overall, relatively little apparent in vivo fatty acid bioconversion was recorded, whilst the apparent in vivo β-oxidation of dietary fatty acid was largely affected by the dietary lipid source, with higher rate of β-oxidation for those fatty acids which were provided in dietary surplus. The deposition of 20:5n-3 and 22:6n-3, as % of the dietary intake, was greatest for the fish fed on the CSO diet. It has been shown that European sea bass seems to be able to efficiently use n-6 PUFA for energy substrate, and this may help in minimizing the β-oxidation of the health benefiting n-3 LC-PUFA and thus increase their deposition into fish tissues.

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“…In a similar study on sea bass, Izquierdo et al (2003) reported that the replacement of 60% of fish oil with linseed oil (n-3 PUFA-rich), soybean oil (n-6 PUFA-rich), rapeseed oil (MUFA-rich) and a mixed-blend did not negatively impact on fish performance, when high lipid content (25%) diets were evaluated. As in many instances, this result is similar to a number of the other earlier studies with European sea bass and salmonids where the complete replacement of dietary fish oil with alternative vegetable oils has resulted in no affect on fish growth performance (Guillou et al, 1995;Tocher et al, 2000;Torstensen et al, 2000;Bell et al, 2001, Mourente et al, 2005bTurchini et al, 2011b;Eroldoğan et al, 2012;Eroldoğan et al, 2013).…”

“…However, in marine fish feeds the use of vegetable oils as the sole lipid source is limited by the low ability of these species to convert α-linoleic (LA,) and linolenic (LNA,, abundant in many plant oils, into arachidonic (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA,. Thus, the partial replacement of fish oil by vegetable oils would be only possible when these fatty acids are present in the diets in sufficient levels to meet essential fatty acid requirements, which can generally be achieved when fishmeal is included in the diet in the range of 30 -50% Benedito-Palos et al, 2008;Ng and Gibon 2010;Eroldoğan et al, 2013).…”

“…elongase, Δ-6 desaturase and Δ-5 desaturase) involved in the desaturation and elongation of C 18 fatty acids have been reported (Mourente et al, 2005a;. However, previous studies have demonstrated that the dietary fish oil component of the diet can be substituted to levels of 50-60% Mourente et al, 2005 b;Richard et al, 2006) and 100% (Eroldoğan et al, 2012;Eroldoğan et al, 2013). However, one of the principal effects of fish oil substitution is the unavoidable and detrimental impact on the final fillet concentrations of long chain omega-3 fatty acids (n-3 LC PUFA) and the modification of specific fatty acid digestibility.…”

“…Of the oils available for utilization in aquafeed formulations, several studies have investigated the potential inclusion of those rich in MUFA or other n-6 PUFA ( Torstensen et al, 2004;Stubhaug et al, 2007;Turchini and Francis, 2009) However, specific and direct comparisons of these two types of oils are scarce in relation to individual fatty acid digestibility. A recent study with sea bass demonstrated that the apparent in vivo β-oxidation of dietary fatty acids was significantly affected by the dietary lipid source (Eroldoğan et al, 2013). However, the fatty acid or lipid digestibility in terms of dietary PUFA/HUFA ratio has always been reported as none or minimal (Eroldoğan et al, 2013;Francis et al, 2007).…”

“…A recent study with sea bass demonstrated that the apparent in vivo β-oxidation of dietary fatty acids was significantly affected by the dietary lipid source (Eroldoğan et al, 2013). However, the fatty acid or lipid digestibility in terms of dietary PUFA/HUFA ratio has always been reported as none or minimal (Eroldoğan et al, 2013;Francis et al, 2007).…”