Replacement of Dietary Fish Oils by Alpha‐Linolenic Acid‐Rich Oils Lowers Omega 3 Content in Tilapia Flesh

Abstract

A 20-week feeding trial was conducted to determine whether increasing linolenic acid (18:3n-3) in vegetable oil (VO) based diets would lead to increased tissue deposition of 22:6n-3 in Nile tilapia (Oreochromis niloticus). Five isonitrogenous and isoenergetic diets were supplemented with 3% of either linseed oil (LO), a mixture of linseed oil with refined palm olein oil (PO) (LO-PO 2:1) and a mixture of refined palm olein oil with linseed oil (PO-LO 3:2) or with fish oil (FO) or corn oil (CO) as controls. The PO-LO, LO-PO and LO diets supplied a similar amount of 18:2n-6 (0.5% of diet by dry weight) and 0.5, 0.7 and 1.1% of 18:3n-3, respectively. Increased dietary 18:3n-3 caused commensurate increases in longer-chain n-3 PUFA and decreases in longer-chain n-6 PUFA in the muscle lipids of tilapia. However, the biosynthetic activities of fish fed the LO-based diets were not sufficient to raise the tissue concentrations of 20:5n-3, 22:5n-3 and 22:6n-3 to those of fish fed FO. The study suggests that tilapia (O. niloticus) has a limited capacity to synthesise 20:5n-3 and 22:6n-3 from dietary 18:3n-3. The replacement of FO in the diet of farmed tilapia with vegetable oils could therefore lower tissue concentrations of 20:5n-3 and 22:6n-3, and consequently produce an aquaculture product of lower lipid nutritional value for the consumer.

Fatty acid profile of fillet, liver and mesenteric fat in tilapia (<i>Oreochromis niloticus</i>) fed vegetable oil supplementation in the finishing period of fattening

“…Opposite results were described by SHAPIRA et al (2009), where farmed mango tilapia (Sarotherodon galilaeus galilaeus) fed increased n-3 PUFA in the form of linseed showed moderate increases in the n-3 long chain PUFA proportion, supporting the capacity for n-3 PUFA transformation and accretion. Our result confirms the report of Karapanagiotidis et al (2007), that tilapia (Oreochromis niloticus) has a limited capacity to synthesize EPA and DHA from dietary ALA precursor. Agaba et al (2005) reported that freshwater fish were found to effectively metabolize C18 PUFA to highly unsaturated fatty acid, but the pattern of activity shown by the elongases from tilapia was found to be slightly unusual in that the activity towards C20:5n-3 was equal to that towards C18:4n-3 and it had the highest activity towards C20:4n-6.…”

“…The main reason for this decrease is a combination of a decreasing market availability of fish oil from capture fisheries, increasing market cost and increased global use of cheaper plant and animal alternative lipid sources (Tacon & Metian 2008). Several publications (Ng et al 2001, Visentainer et al 2005, De Souza et al 2007, Karapanagiotidis et al 2007, Tonial et al 2009, Szabó et al 2009) demonstrated that the use of different vegetable oils (palm oil, linseed oil, sunflower oil) could substitute a significant amount of dietary fish oil without compromising fish growth and feed utilisation efficiency. However, apart from economically acceptable growth the post-harvest quality of farmed fish is an important aspect that should be taken into consideration when evaluating the suitability of vegetable oils as possible dietary fish oil alternatives (Ng & Bahurmiz 2009).…”

“…However, apart from economically acceptable growth the post-harvest quality of farmed fish is an important aspect that should be taken into consideration when evaluating the suitability of vegetable oils as possible dietary fish oil alternatives (Ng & Bahurmiz 2009). In case of the fillet fatty acid composition Tocher et al (2002) and Karapanagiotidis et al (2007) reported that tilapia has a limited hepatic capacity to elongate and desaturate 20:5n-3 and 22:6n-3 from dietary ALA precursor. By feeding vegetable oil containing diets, the desaturation and elongation of ALA is generally insufficient to compensate for the lack of EPA and DHA in the vegetable oil source, leading ultimately to compromised fatty acid composition.…”

Effect of different dietary lipid levels on growth performance, slaughter yield, chemical composition, and histology of liver and intestine of pikeperch, Sander lucioperca

“…Nonetheless, the content of MUFA (and oleic acid) in the body of pikeperch might be linked to the tendency of fish to store these acids as an energy source and/or to the synthesis of monoenoic acids in the fish tissues (Karapanagiotidis et al, 2007). However, the apparent selection against metabolism of some fatty acids might also be due to MUFA content in fish tissue (Bell et al, 2003).…”

Effect of dietary fish meal replacement by poultry by-product meal on muscle fatty acid composition and liver histology of fry of Nile tilapia, Oreochromis niloticus (Actinopterygii: Perciformes: Cichlidae)

“…It is important for the feed to contain balanced levels of polyunsaturated fatty acids and highly unsaturated fatty acids. So, a number of studies have been performed to evaluate the effects of alternative protein sources used in fi sh feeds as FM substitutes on fi sh fatty acid composition (Maina et al 2003, Dias et al 2005, Gümüş and Erdogan 2010, Nogueira et al 2012, Gümüş and Aydin 2013, Parés-Sierra et al 2014, and also the effects of different lipid sources used in fi sh feeds as energy sources (Stubhaug et al 2005, Ruyter et al 2006, Karapanagiotidis et al 2007. Although the differences in the amounts of corn oil in the diet were slight, the high level of linoleic acid in corn oil affected the lipid metabolism and fatty acid bioconversion and or accumulation (Stubhaug et al 2005).…”