Adaptation of lipid metabolism, tissue composition and flesh quality in gilthead sea bream (Sparus aurata) to the replacement of dietary fish oil by linseed and soyabean oils

Abstract

Linseed (LO) and soyabean (SO) oils were evaluated as fish-oil (FO) substitutes in the diets of marketable-sized gilthead sea bream (Sparus aurata). Practical diets were designed factorially with the lipid added as follows (%): FO 100, LO 60þ FO 40, LO 80þFO 20, SO 60þFO 40, SO 80þ FO 20. The effects of experimental diets on growth, fatty acids patterns in liver and muscle, flesh quality variables and activities of selected enzymes involved in lipid synthesis and catabolism were determined at the end of a 7-month trial. Fatty acid composition of liver and muscle generally reflected the fatty acid composition of the diets. The n-3 PUFA levels were significantly reduced by the inclusion of vegetable oils. This tendency was more pronounced for EPA than for docosahexaenoic acid. The n-3:n-6 fatty acid ratio reached the lowest values in fish fed the SO diets; this was associated with a higher liver lipid deposition. No differences were found in fillet texture and pH. However, under conditions of forced peroxidation, muscles from fish fed the SO diets had lower peroxidation levels. Vegetable oil substitution decreased lipogenesis in liver and this effect was greatest at the highest substitution level. In contrast, muscle b-oxidation enzymes had increased activities with vegetable oil substitution. Thus, the lower hepatic lipogenesis was correlated with an increased lipid utilisation in muscle. It is concluded that growth and lipid metabolism were affected by experimental diets. Sea bream: Vegetable oil: Lipid metabolism: Flesh quality: Essential fatty acidsAs the preferred lipid source in commercial diets for cultured fish, the demand for fish oil (FO) for aquatic feeds is increasing. Despite the most optimistic projections forecast, a global demand for aquaculture of about 1·90 million tonnes for the year 2015, production of FO seems to have reached a maximum at about 1·20 million tonnes per year, this value decreasing markedly during El Niño years (Food and Agriculture Organization, 2002). Since that production has to be shared with other uses, such as feeds for broilers and piglets and for pharmacology, there is a great interest in searching for alternative lipid sources in commercial fish feeds.It has been shown in salmonids that FO can be replaced by certain types of vegetable lipid sources by up to 80-100 % without compromising fish growth, but affecting tissue lipid composition and metabolism (Torstensen et al.

Effects of dietary fish oil substitution by Echium oil on enterocyte and hepatocyte lipid metabolism of gilthead seabream (Sparus aurata L.)

“…There was also a trend for DHA and EPA to decrease but not in a significant way. In many other trials, fish fed VOs displayed significant reductions in n-3HUFA together with increased C 18 fatty acids in liver (Rodríguez et al, 2002;Menoyo et al, 2004;Mourente et al, 2005;Bell et al, 2006;Almaida-Pagán et al, 2007) and enterocytes Mourente et al, 2005;Almaida-Pagán et al, 2007) of different marine fish. Nevertheless, in seabass fed a balanced blend of VOs, enterocytes were capable at regulating fatty acid levels, with C 18 fatty acids not increasing greatly, and EPA and DHA levels relatively maintained (Mourente et al, 2005).…”

“…The inclusion of VOs in carnivorous fish diets is often associated with increased fat contents and lipid droplets in liver and enterocytes, usually when substitution is over 75% (Rodríguez et al, 2002;Caballero et al, 2003;Menoyo et al, 2004;Francis et al, 2007), or at lower levels of substitution when an unbalanced fatty acid profile is provided (Caballero et al, , 2004Menoyo et al, 2004). Nevertheless, when the substitution level is not too large (50-75 %) and the fatty acid profile of the VO is well balanced, fat deposition in enterocytes and liver is not reported (Caballero et al, 2004;Mourente et al, 2005;Francis et al, 2007).…”

“…In this sense, up to 50-70% substitution of FO by VO has been reported to maintain the correct growth and health of some marine fish species including seabream and seabass Montero et al, 2003;Menoyo et al, 2004;Mourente et al, 2005;Benedito-Palos et al, 2007;Díaz-López et al, 2009;Fountoulaki et al, 2009). However, research is now focused at identifying VOs or blends that avoid excessive deposition of fat and LA, provide a good n-3/n-6 HUFA ratio, and maximize potential for conversion of C 18 n-3PUFA to EPA and DHA.…”

“…Therefore, HUFA are essential fatty acids (EFA) for marine fish, and are important as structural components of cell membranes Marsh, 2008), eicosanoids precursors (Tocher, 2003;Bell et al, 2006;Villalta et al, 2007) and regulators of gene expression (Zheng et al, 2005;Miller et al, 2008;Leaver et al, 2008). The fatty acid profile of VO, together with this poor ability of marine fish to convert C 18 polyunsaturated fatty acids (PUFA) to HUFA, lead to important changes in the fatty acid composition of flesh of fish fed VOs, which include decreased n-3 HUFA and increased fat and LA contents Menoyo et al, 2004;Bell et al, 2006;Benedito-Palos et al, 2007;Díaz-López et al, 2009;Fountoulaki et al, 2009). Excessive consumption of VO and,has been related to some detrimental effects on health of fish (McKenzie, 2001;Sargent et al, 2002;Montero et al, 2003Montero et al, , 2008.…”

“…Gilthead seabream, Sparus aurata L., is the most important marine fish species in Mediterranean and Canarian aquaculture, and several studies have shown that it can generally be grown well on diets with FO partially replaced by VO Caballero et al, 2003Caballero et al, , 2004Menoyo et al, 2004;Benedito-Palos et al, 2007;Díaz-López et al, 2009;Fountoulaki et al, 2009). However knowledge of seabream lipid metabolism is still incomplete compared to other fish species, such as salmonids, turbot, and seabass Rodríguez et al, 2002;Mourente et al, 2005;Bell et al, 2001Bell et al, , 2002Bell et al, , 2006Tocher et al, , 2004Fonseca-Madrigal et al, 2006).…”