Replacement of Fish Oil with Rapeseed Oil in Diets of Atlantic Salmon (Salmo salar) Affects Tissue Lipid Compositions and Hepatocyte Fatty Acid Metabolism

Abstract

Duplicate groups of Atlantic salmon post-smolts were fed five practical-type diets in which the added lipid was 100% fish oil [FO; 0% rapeseed oil (0% RO)], 90% FO + 10% RO (10% RO), 75% FO + 25% RO (25% RO), 50% FO + 50% RO (50% RO) or 100% RO, for a period of 17 wk. There were no effects of diet on growth rate or feed conversion nor were any histopathological lesions found in liver, heart, muscle or kidney. The greatest accumulation of muscle lipid was in fish fed 0% RO, which corresponded to significantly lower muscle protein in this group. The highest lipid levels in liver were found in fish fed 100% RO. Fatty acid compositions of muscle lipid correlated with RO inclusion in that the proportions of 18:1(n-9), 18:2(n-6) and 18:3(n-3) all increased with increasing dietary RO (r = 0.98-1.00, P < 0.013). The concentrations of eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic acid [22:6(n-3)] in muscle lipid were significantly reduced (P < 0.05), along with total saturated fatty acids, with increasing dietary RO. Diet-induced changes in liver fatty acid compositions were broadly similar to those in muscle. Hepatic fatty acid desaturation and elongation activities, measured using [1-(14)C] 18:3(n-3), were increased with increasing dietary RO. Limited supplies of marine fish oils require that substitutes be found if growth in aquaculture is to be maintained such that fish health and product quality are not compromised. Thus, RO can be used successfully as a substitute for fish oil in the culture of Atlantic salmon in sea water although at levels of RO >50% of dietary lipid, substantial reductions occur in muscle 20:5(n-3), 22:6(n-3) and the (n-3)/(n-6) polyunsaturated fatty acid (PUFA) ratio, which will result in reduced availability of the (n-3) highly unsaturated fatty acids that are beneficial for human health.

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

“…Increased HUFA synthesis has been described mainly in freshwater fish and salmonids fed VO diets at different levels of substitution (Bell et al, 2001Tocher et al, , 2004Zheng et al, 2005;Stubhaug et al, 2005;Fonseca-Madrigal et al, 2006). Some of these trials also used EO, or even borage oil from the same plant family in salmonids (Tocher et al, 1997.…”

“…Much information of the biosynthetic pathways of HUFA synthesis and other aspects of fatty acid metabolism has been obtained by incubating isolated fish cells with radiolabeled fatty acids (Bell et al, 2001Rodríguez et al, 2002;Tocher et al, , 2004Mourente et al, 2005;Fonseca-Madrigal et al, 2006;Almaida-Pagán et al, 2007). Therefore, the aim of the present study was to evaluate the effects of 50% substitution of dietary FO by EO, in gilthead seabream lipid profile and fatty acid metabolism in isolated hepatocytes and enterocytes.…”

“…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. In this sense, there are several studies demonstrating that dietary VOs induce the conversion of LA to ARA, and LNA to EPA and DHA in both hepatocytes and enterocytes in salmonids, although total n-3 HUFA levels are still significantly decreased in flesh and liver (Bell et al, 2001Tocher et al, , 2004Fonseca-Madrigal et al, 2006). However, HUFA synthesis is very low and generally not increased by dietary VOs in marine fish (Mourente et al, 2005;Almaida-Pagán et al, 2007).…”

“…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). Thus, neither HUFA synthesis, nor β-oxidation processes have been investigated in gilthead seabream.…”

The use of genetic engineering techniques to improve the lipid composition in meat, milk and fish products: a review

“…However, in fish, as in other vertebrates, this conversion, especially in marine species, is limited, mainly due to the insufficient efficiency of desaturase activity. Therefore, the body lipids of farmed fish fed diets supplemented with vegetable oils contain significantly less EPA and DHA than the meat of wild fish of the same species (Bell et al, 2001). Thus, transgenesis techniques aimed to overexpress enzymes synthesising n-3 LCPUFAs in fish can greatly increase the dietetic value of the meat from farmed fish.…”