Fish oil supplementation suppresses resistance exercise and feeding-induced increases in anabolic signaling without affecting myofibrillar protein synthesis in young men.

Fish oil (FO) supplementation potentiates muscle protein synthesis (MPS) in response to a hyperaminoacidemic-hyperinsulinemic infusion. Whether FO supplementation potentiates MPS in response to protein ingestion or when protein ingestion is combined with resistance exercise (RE) remains unknown. In a randomized, parallel group design, 20 healthy males were randomized to receive 5 g/day of either FO or coconut oil control (CO) for 8 weeks. After supplementation, participants performed a bout of unilateral RE followed by ingestion of 30 g of whey protein. Skeletal muscle biopsies were obtained before and after supplementation for assessment of muscle lipid composition and relevant protein kinase activities. Infusion of L-[ring-(13)C6] phenylalanine was used to measure basal myofibrillar MP Sat rest (REST), in a nonexercised leg following protein ingestion (FED) and following RE and protein ingestion (FEDEX).MPS was significantly elevated above REST during FEDEX in both the FO and CO groups, but there was no effect of supplementation. There was a significant increase in MPS in both groups above REST during FED but no effect of supplementation. Supplementation significantly decreased pan PKB activity at RESTin the FO group but not the CO group. There was a significant increase from REST at post-RE for PKB and AMPKα2 activity in the CO group but not in the FO group. In FEDEX, there was a significant increase in p70S6K1 activity from REST at 3 h in the CO group only. These data highlight that 8 weeks of FO supplementation alters kinase signaling activity in response to RE plus protein ingestion without influencing MPS.

DHA Supplementation Alone or in Combination with Other Nutrients Does not Modulate Cerebral Hemodynamics or Cognitive Function in Healthy Older Adults.

A number of recent trials have demonstrated positive effects of dietary supplementation with the omega-3 polyunsaturated fatty acids (n-3 PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on measures of cognitive function in healthy young and older adults. One potential mechanism by which EPA, and DHA in particular, may exert these effects is via modulation of cerebral hemodynamics. In order to investigate the effects of DHA alone or provided as one component of a multinutrient supplement (also including Gingko biloba, phosphatidylserine and vitamins B9 and B12) on measures of cerebral hemodynamics and cognitive function, 86 healthy older adults aged 50-70 years who reported subjective memory deficits were recruited to take part in a six month daily dietary supplementation trial. Relative changes in the concentration of oxygenated hemoglobin and deoxygenated hemoglobin were assessed using Near Infrared Spectroscopy (NIRS) during the performance of cognitive tasks prior to and following the intervention period. Performance on the cognitive tasks was also assessed. No effect of either active treatment was found for any of the NIRS measures or on the cognitive performance tasks, although the study was limited by a number of factors. Further work should continue to evaluate more holistic approaches to cognitive aging.

The effect of dietary n-3/n-6 polyunsaturated fatty acid ratio on salmonid alphavirus subtype 1 (SAV-1) replication in tissues of experimentally infected rainbow trout (Oncorhynchus mykiss).

Salmon pancreas disease (SPD) is one of the most commercially significant viral diseases of farmed Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) in Europe. In this study, the potential for dietary mitigation of the disease using different polyunsaturated fatty acid (PUFA) profiles was assessed in rainbow trout. We experimentally infected fish with salmonid alphavirus subtype 1 (SAV-1), the causative agent of SPD. These fish were fed two diets with different n-3/n-6 PUFA ratio (high omega 3, 3.08, and high omega 6, 0.87). We assessed the influence of the diets on the fatty acid composition of the heart at 0 days post infection (d.p.i.) (after 4 weeks of feeding the experimental diets prior to SAV-1 infection), and sampled infected and control fish at 5, 15 and 30d.p.i. Viral E1 and E2 glycoprotein genes were quantified by two absolute real-time PCRs in all the organs sampled, and significantly lower levels of the virus were evident in the organs of fish fed with high omega 6. Characteristic pathological lesions were identified in infected fish as early as 5d.p.i., with no significant differences in the pathology lesion scores between the two dietary regimes. This study shows that decreasing the n-3/n-6 PUFA ratio in experimental diets of rainbow trout changes the fatty acid content of the fish, and is associated with reduced SAV-1 replication in rainbow trout.

Nutritional quality of salmon products available from major retailers in the UK: content and composition of n-3 long-chain PUFA.

In the present study, salmon products available from UK retailers were analysed to determine the levels of n-3 long-chain PUFA (LC-PUFA), a key determinant of nutritional quality. There was a wide variation in the proportions and absolute contents of EPA and DHA in the products. Relatively high contents of 18 : 1n-9, 18 : 2n-6 and 18 : 3n-3, characteristic of vegetable oils (VO), were found in several farmed salmon products, which also had generally lower proportions of EPA and DHA. In contrast, farmed salmon products with higher levels of 16 : 0 and 22 : 1, characteristic of fish oil (FO), had higher proportions of EPA and DHA. Therefore, there was a clear correlation between the levels of VO and FO in feeds and the proportions of n-3 LC-PUFA in products. Although wild salmon products were characterised by higher proportions of n-3 LC-PUFA (20-40%) compared with farmed fish (9-26%), they contained lower total lipid contents (1-6% compared with 7-17% in farmed salmon products). As a result, farmed salmon products invariably had higher levels of n-3 LC-PUFA in absolute terms (g/100 g fillet) and, therefore, delivered a higher 'dose' of EPA and DHA per portion. Overall, despite the finite and limiting supply of FO and increasing use of VO, farmed salmon continue to be an excellent source of and delivery system for n-3 LC-PUFA to consumers.

Interactions between dietary docosahexaenoic acid and other long-chain polyunsaturated fatty acids on performance and fatty acid retention in post-smolt Atlantic salmon (Salmo salar).

A study with varying dietary inclusion levels (1, 5, 10, 15 and 20 g kg(-1)) of docosahexaenoic acid (DHA; 22:6n-3) was conducted with post-smolt (111 ± 2.6 g; mean ± S.) Atlantic salmon (Salmo salar) over a 9-week period. In addition to the series of DHA inclusion levels, the study included further diets that had DHA at 10 g kg(-1) in combination with either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), both also included at 10 g kg(-1). An additional treatment with both EPA and DHA included at 5 g kg(-1) (total of 10 g kg(-1) long-chain polyunsaturated fatty acids, LC-PUFA) was also included. After a 9-week feeding period, fish were weighed, and carcass, blood and tissue samples collected. A minor improvement in growth was seen with increasing inclusion of DHA. However, the addition of EPA further improved growth response while addition of ARA had no effect on growth. As with most lipid studies, the fatty acid composition of the whole body lipids generally reflected that of the diets. However, there were notable exceptions to this, and these implicate some interactions among the different LC-PUFA in terms of the fatty acid biochemistry in this species. At very low inclusion levels, DHA retention was substantially higher (~250%) than that at all other inclusion levels (31-58%). The inclusion of EPA in the diet also had a positive effect on the retention efficiency of DHA. However, EPA retention was highly variable and at low DHA inclusion levels there was a net loss of EPA as this fatty acid was most likely elongated to produce DHA, consistent with increased DHA retention with additional EPA in the diet. Retention of DPA (22:5n-3) was high at low levels of DHA, but diminished with increasing DHA inclusion, similar to that seen with DHA retention. The addition of EPA to the diet resulted in a substantial increase in the efficiency of DPA retention; the inclusion of ARA had the opposite effect. Retention of ARA was unaffected by DHA inclusion, but the addition of either EPA or ARA to the diet resulted in a substantial reduction in the efficiency of ARA retention. No effects of dietary treatment were noted on the retention of either linolenic (18:3n-3) or linoleic (18:2n-6) acids. When the total n-3 LC-PUFA content of the diet was the same but consisted of either DHA alone or as a combination of EPA plus DHA, the performance effects were similar.

Effect of functional feeds on fatty acid and eicosanoid metabolism in liver and head kidney of Atlantic salmon (Salmo salar L.) with experimentally induced heart and skeletal muscle inflammation.

Heart and Skeletal Muscle Inflammation (HSMI) is an emerging viral disease caused by a novel Atlantic salmon reovirus (ASRV) affecting farmed fish. Primary symptoms associated with HSMI include myocardial and skeletal muscle necrosis indicating a severe inflammatory process. Recently, we applied the concept of clinical nutrition to moderate the long-term inflammatory process associated with HSMI in salmon subjected to experimental ASRV challenge. The use of functional feeds with lower lipid (hence energy) content reduced the inflammatory response to ASRV infection and the severity of associated heart lesions. The aim of the present study was to elucidate possible mechanisms underpinning the observed effects of the functional feeds, focussing on eicosanoid and fatty acid metabolism in liver and head kidney. Here we show that liver was also a site for histopathological lesions in HSMI showing steatosis reflecting impaired lipid metabolism. This study is also the first to evaluate the expression of a suite of key genes involved in pathways relating diet and membrane phospholipid fatty acid compositions, and the inflammatory response after ASRV infection. The expression of hepatic Δ6 and Δ5 desaturases was higher in fish fed the functional feeds, potentially increasing their capacity for endogenous production and availability of anti-inflammatory EPA. Effects on mobilization of lipids and changes in the LC-PUFA composition of membrane phospholipids, along with significant changes in the expression of the genes related to eicosanoid pathways, showed the important role of the head kidney in inflammatory diseases caused by viral infections. The results from the present study suggest that clinical nutrition through functional feeding could be an effective complementary therapy for emerging salmon viral diseases associated with long-term inflammation.

Vitamin C enhances vitamin E status and reduces oxidative stress indicators in sea bass larvae fed high DHA microdiets.

Docosahexaenoic acid (DHA) is an essential fatty acid necessary for many biochemical, cellular and physiological functions in fish. However, high dietary levels of DHA increase free radical injury in sea bass (Dicentrarchus labrax) larvae muscle, even when vitamin E (α-tocopherol, α-TOH) is increased. Therefore, the inclusion of other nutrients with complementary antioxidant functions, such as vitamin C (ascorbic acid, vitC), could further contribute to prevent these lesions. The objective of the present study was to determine the effect of vitC inclusion (3,600 mg/kg) in high DHA (5% DW) and α-TOH (3,000 mg/kg) microdiets (diets 5/3,000 and 5/3,000 + vitC) in comparison to a control diet (1% DHA DW and 1,500 mg/kg of α-TOH; diet 1/1,500) on sea bass larvae growth, survival, whole body biochemical composition and thiobarbituric acid reactive substances (TBARS) content, muscle morphology, skeletal deformities and antioxidant enzymes, insulin-like growth factors (IGFs) and myosin expression (MyHC). Larvae fed diet 1/1,500 showed the best performance in terms of total length, incidence of muscular lesions and ossification degree. IGFs gene expression was elevated in 5/3,000 diet larvae, suggesting an increased muscle mitogenesis that was confirmed by the increase in the mRNA copies of MyHC. vitC effectively controlled oxidative damages in muscle, increased α-TOH larval contents and reduced TBARS content and the occurrence of skull deformities. The results of the present study showed the antioxidant synergism between vitamins E and C when high contents of DHA are included in sea bass larvae diets.

Effects of genotype and dietary fish oil replacement with vegetable oil on the intestinal transcriptome and proteome of Atlantic salmon (Salmo salar).

BACKGROUND: Expansion of aquaculture requires alternative feeds and breeding strategies to reduce dependency on fish oil (FO) and better utilization of dietary vegetable oil (VO). Despite the central role of intestine in maintaining body homeostasis and health, its molecular response to replacement of dietary FO by VO has been little investigated. This study employed transcriptomic and proteomic analyses to study effects of dietary VO in two family groups of Atlantic salmon selected for flesh lipid content, 'Lean' or 'Fat'. RESULTS: Metabolism, particularly of lipid and energy, was the functional category most affected by diet. Important effects were also measured in ribosomal proteins and signalling. The long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis pathway, assessed by fatty acid composition and gene expression, was influenced by genotype. Intestinal tissue contents of docosahexaenoic acid were equivalent in Lean salmon fed either a FO or VO diet and expression of LC-PUFA biosynthesis genes was up-regulated in VO-fed fish in Fat salmon. Dietary VO increased lipogenesis in Lean fish, assessed by expression of FAS, while no effect was observed on ß-oxidation although transcripts of the mitochondrial respiratory chain were down-regulated, suggesting less active energetic metabolism in fish fed VO. In contrast, dietary VO up-regulated genes and proteins involved in detoxification, antioxidant defence and apoptosis, which could be associated with higher levels of polycyclic aromatic hydrocarbons in this diet. Regarding genotype, the following pathways were identified as being differentially affected: proteasomal proteolysis, response to oxidative and cellular stress (xenobiotic and oxidant metabolism and heat shock proteins), apoptosis and structural proteins particularly associated with tissue contractile properties. Genotype effects were accentuated by dietary VO. CONCLUSIONS: Intestinal metabolism was affected by diet and genotype. Lean fish may have higher responsiveness to low dietary n-3 LC-PUFA, up-regulating the biosynthetic pathway when fed dietary VO. As global aquaculture searches for alternative oils for feeds, this study alerts to the potential of VO introducing contaminants and demonstrates the detoxifying role of intestine. Finally, data indicate genotype-specific responses in the intestinal transcriptome and proteome to dietary VO, including possibly structural properties of the intestinal layer and defence against cellular stress, with Lean fish being more susceptible to diet-induced oxidative stress.

Selenium inclusion decreases oxidative stress indicators and muscle injuries in sea bass larvae fed high-DHA microdiets.

The objective of the present study was to determine the effect of Se inclusion in high-DHA and vitamin E microdiets (5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight; 5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight supplemented with Se) in comparison with a control diet (1 g DHA/100 g dry weight and 150 mg vitamin E/100 g dry weight) on sea bass larval growth, survival, biochemical composition, malonaldehyde (MDA) content, muscle morphology and antioxidant enzymes (AOE), insulin-like growth factors (IGF) and myosin expression. For a given DHA and vitamin E dietary content, Se inclusion favoured larval total length and specific growth rate, and reduced the incidence of muscular lesions, MDA contents and AOE gene expression. In contrast, IGF gene expression was elevated in the 5/300 larvae, suggesting an increased muscle mitogenesis that was corroborated by the increase in mRNA copies of myosin heavy chain. The results of the present study denoted the beneficial effect of Se not only in preventing oxidative stress, as a glutathione peroxidase cofactor, but probably due to other as yet unknown physiological functions.

Transcriptomic analyses of intestinal gene expression of juvenile Atlantic cod (Gadus morhua) fed diets with Camelina oil as replacement for fish oil.

For aquaculture of marine species to continue to expand, dietary fish oil (FO) must be replaced with more sustainable vegetable oil (VO) alternatives. Most VO are rich in n-6 polyunsaturated fatty acids (PUFA) and few are rich in n-3 PUFA but Camelina oil (CO) is unique in that, besides high 18:3n-3 and n-3/n-6 PUFA ratio, it also contains substantial long-chain monoenes, commonly found in FO. Cod (initial mass ~1.4 g) were fed for 12 weeks diets in which FO was replaced with CO. Growth performance, feed efficiency and biometric indices were not affected but lipid levels in liver and intestine tended to increase and those of flesh, decrease, with increasing dietary CO although only significantly for intestine. Reflecting diet, tissue n-3 long-chain PUFA levels decreased whereas 18:3n-3 and 18:2n-6 increased with inclusion of dietary CO. Dietary replacement of FO by CO did not induce major metabolic changes in intestine, but affected genes with potential to alter cellular proliferation and death as well as change structural properties of intestinal muscle. Although the biological effects of these changes are unclear, given the important role of intestine in nutrient absorption and health, further attention should be given to this organ in future.

Diet × genotype interactions in hepatic cholesterol and lipoprotein metabolism in Atlantic salmon (Salmo salar) in response to replacement of dietary fish oil with vegetable oil.

The present study investigates the effects of genotype on responses to alternative feeds in Atlantic salmon. Microarray analysis of the liver transcriptome of two family groups, lean or fat, fed a diet containing either a fish oil (FO) or a vegetable oil (VO) blend indicated that pathways of cholesterol and lipoprotein metabolism might be differentially affected by the diet depending on the genetic background of the fish, and this was further investigated by real-time quantitative PCR, plasma and lipoprotein biochemical analysis. Results indicate a reduction in VLDL and LDL levels, with no changes in HDL, when FO is replaced by VO in the lean family group, whereas in fat fish fed FO, levels of apoB-containing lipoproteins were low and comparable with those fed VO in both family groups. Significantly lower levels of plasma TAG and LDL-TAG were measured in the fat group that was independent of diet, whereas plasma cholesterol was significantly higher in fish fed the FO diet in both groups. Hepatic expression of genes involved in cholesterol homeostasis, ß-oxidation and lipoprotein metabolism showed relatively subtle changes. A significantly lower expression of genes considered anti-atherogenic in mammals (ATP-binding cassette transporter A1, apoAI, scavenger receptor class B type 1, lipoprotein lipase (LPL)b (TC67836) and LPLc (TC84899)) was found in lean fish, compared with fat fish, when fed VO. Furthermore, the lean family group appeared to show a greater response to diet composition in the cholesterol biosynthesis pathway, mediated by sterol-responsive element-binding protein 2. Finally, the presence of three different transcripts for LPL, with differential patterns of nutritional regulation, was demonstrated.

Using a fingertip whole blood sample for rapid fatty acid measurement: method validation and correlation with erythrocyte polar lipid compositions in UK subjects.

It is well accepted that n-3 long-chain PUFA intake is positively associated with a range of health benefits. However, while benefits have been clearly shown, especially for CVD, the mechanisms for prevention/benefit are less understood. Analysis of plasma and erythrocyte phospholipids (PL) have been used to measure the status of the highly unsaturated fatty acids (HUFA), especially EPA (20 : 5n-3) and DHA (22 : 6n-3), although the time and complexity of the process places limitations on the sample numbers analysed. An assay has been developed using whole blood, collected by finger prick, and stored on absorbant paper, subjected to direct methylation and fatty acids quantified by automated GC. Tests on fatty acid stability show that blood samples are stable when stored at - 20°C for 1 month although some loss of HUFA was seen at 4°C. A total of fifty-one patients, including twenty-seven who consumed no fatty acid supplements, provided a blood sample for analysis. Concentrations of all major fatty acids were measured in erythrocyte PL and whole blood. The major HUFA, including EPA, DHA and arachidonic acid (ARA; 20 : 4n-6), as well as the ARA:EPA ratio and the percentage n-3 HUFA/total HUFA all showed good correlations, between erythrocyte PL and whole blood. Values of r2 ranged from 0.48 for ARA to 0.95 for the percentage of n-3 HUFA/total HUFA. This assay provides a non-invasive, rapid and reliable method of HUFA quantification with the percentage of n-3 HUFA value providing a potential blood biomarker for large-scale nutritional trials.

Genotype-specific responses in Atlantic salmon (Salmo salar) subject to dietary fish oil replacement by vegetable oil: a liver transcriptomic analysis.

BACKGROUND: Expansion of aquaculture is seriously limited by reductions in fish oil (FO) supply for aquafeeds. Terrestrial alternatives such as vegetable oils (VO) have been investigated and recently a strategy combining genetic selection with changes in diet formulations has been proposed to meet growing demands for aquaculture products. This study investigates the influence of genotype on transcriptomic responses to sustainable feeds in Atlantic salmon. RESULTS: A microarray analysis was performed to investigate the liver transcriptome of two family groups selected according to their estimated breeding values (EBVs) for flesh lipid content, 'Lean' or 'Fat', fed diets containing either FO or a VO blend. Diet principally affected metabolism genes, mainly of lipid and carbohydrate, followed by immune response genes. Genotype had a much lower impact on metabolism-related genes and affected mostly signalling pathways. Replacement of dietary FO by VO caused an up-regulation of long-chain polyunsaturated fatty acid biosynthesis, but there was a clear genotype effect as fatty acyl elongase (elovl2) was only up-regulated and desaturases (Δ5 fad and Δ6 fad) showed a higher magnitude of response in Lean fish, which was reflected in liver fatty acid composition. Fatty acid synthase (FAS) was also up-regulated by VO and the effect was independent of genotype. Genetic background of the fish clearly affected regulation of lipid metabolism, as PPARα and PPARß were down-regulated by the VO diet only in Lean fish, while in Fat salmon SREBP-1 expression was up-regulated by VO. In addition, all three genes had a lower expression in the Lean family group than in the Fat, when fed VO. Differences in muscle adiposity between family groups may have been caused by higher levels of hepatic fatty acid and glycerophospholipid synthesis in the Fat fish, as indicated by the expression of FAS, 1-acyl-sn-glycerol-3-phosphate acyltransferase and lipid phosphate phosphohydrolase 2. CONCLUSIONS: This study has identified metabolic pathways and key regulators that may respond differently to alternative plant-based feeds depending on genotype. Further studies are required but data suggest that it will be possible to identify families better adapted to alternative diet formulations that might be appropriate for future genetic selection programmes.

High levels of vegetable oils in plant protein-rich diets fed to gilthead sea bream ( Sparus aurata L.): growth performance, muscle fatty acid profiles and histological alterations of target tissues.

The feasibility of fish oil (FO) replacement by vegetable oils (VO) was investigated in gilthead sea bream (Sparus aurata L.) in a growth trial conducted for the duration of 8 months. Four isolipidic and isoproteic diets rich in plant proteins were supplemented with L-lysine (0.55 %) and soya lecithin (1 %). Added oil was either FO (control) or a blend of VO, replacing 33 % (33VO diet), 66 % (66VO diet) and 100 % (VO diet) of FO. No detrimental effects on growth performance were found with the partial FO replacement, but feed intake and growth rates were reduced by about 10 % in fish fed the VO diet. The replacement strategy did not damage the intestinal epithelium, and massive accumulation of lipid droplets was not found within enterocytes. All fish showed fatty livers, but signs of lipoid liver disease were only found in fish fed the VO diet. Muscle fatty acid profiles of total lipids reflected the diet composition with a selective incorporation of unsaturated fatty acids in polar lipids. The robustness of the phospholipid fatty acid profile when essential fatty acid requirements were theoretically covered by the diet was evidenced by multivariate principal components analysis in fish fed control, 33VO and 66VO diets.

Effects of partial substitution of dietary fish oil with blends of vegetable oils, on blood leucocyte fatty acid compositions, immune function and histology in European sea bass (Dicentrarchus labrax L).

Within a decade or so insufficient fish oil (FO) will be available to meet the requirements for aquaculture growth. Consequently, alternative sources are being investigated to reduce reliance on wild fish as a source of FO. Vegetable oils (VO) are a feasible alternative to FO. However, it is important to establish that alternative dietary lipids are not only supplied in the correct quantities and balance for optimal growth, but can maintain immune function and prevent infection, since it is known that the nutritional state of the fish can influence their immune function and disease resistance. A way of maintaining immune function, while replacing dietary FO, is by using a blend of VO rather than a single oil. In this study, juvenile European sea bass (Dicentrarchus labrax) were fed diets with a 60 % substitution of FO with a blend of rapeseed, linseed and palm oils. Two oil blends were used to achieve a fatty acid composition similar to FO, in terms of energy content, and provide a similar balance of SFA, MUFA and PUFA. Fish were fed the diets for 64 weeks, after which time growth and fatty acid compositions of liver and blood leucocytes were monitored. The impact of the dietary blends on selected innate immune responses and histopathology were also assessed, together with levels of plasma prostaglandin E2. The results suggest that potential exists for replacing FO with a VO blend in farmed sea bass feeds without compromising growth, non-specific immune function or histology.

Authenticating production origin of gilthead sea bream (Sparus aurata) by chemical and isotopic fingerprinting.

Recent EU legislation (EC/2065/2001) requires that fish products, of wild and farmed origin, must provide consumer information that describes geographical origin and production method. The aim of the present study was to establish methods that could reliably differentiate between wild and farmed European gilthead sea bream (Sparus aurata). The methods that were chosen were based on chemical and stable isotopic analysis of the readily accessible lipid fraction. This study examined fatty acid profiles by capillary gas chromatography and the isotopic composition of fish oil (delta(13)C, delta(18)O), phospholipid choline nitrogen (delta(15)N) and compound specific analysis of fatty acids (delta(13)C) by isotope ratio mass spectroscopy as parameters that could reliably discriminate samples of wild and farmed sea bream. The sample set comprised of 15 farmed and 15 wild gilthead sea bream (Sparus aurata), obtained from Greece and Spain, respectively. Discrimination was achieved using fatty acid compositions, with linoleic acid (18:2n-6), arachidonic acid (20:4n-6), stearic acid (18:0), vaccenic acid (18:1n-7) and docosapentaenoic acid (22:5n-3) providing the highest contributions for discrimination. Principle components analysis of the data set highlighted good discrimination between wild and farmed fish. Factor 1 and 2 accounted for >70% of the variation in the data. The variables contributing to this discrimination were: the fatty acids 14:0, 16:0, 18:0, 18:1n-9, 18:1n-7, 22:1n-11, 18:2n-6 and 22:5n-3; delta(13)C of the fatty acids 16:0, 18:0, 16:1n-7, 18:1n-9, 20:5n-3 and 22:6n-3; Bulk oil fraction delta(13)C; glycerol/choline fraction bulk delta(13)C; delta(15)N; % N; % lipid.

Tailoring of Atlantic salmon (Salmo salar L.) flesh lipid composition and sensory quality by replacing fish oil with a vegetable oil blend.

Atlantic salmon (Salmo salar L.) juveniles were fed either 100% fish oil (FO), 75% vegetable oil (VO), or 100% VO throughout their life cycle to harvest weight followed by a finishing diet period when all groups were fed 100% FO. The two experimental VO diets were tested at two different locations (Scotland and Norway) against the same control diet (100% FO). The VO blend was composed of rapeseed oil, palm oil, and linseed oil using capelin oil as a control for fatty acid class compositions. Flesh fatty acid profiles were measured regularly throughout the experiment, with the times of sampling determined by changes in pellet size/lipid content and fish life stage. Growth and mortality rates were not significantly affected by dietary fatty acid compositions throughout the life cycle, except during the seawater winter period in Norway when both growth and protein utilization were increased in salmon fed 100% VO compared to 100% FO. Flesh fatty acid composition was highly influenced by that of the diet, and after the finishing diet period the weekly intake recommendations of very long chain n-3 polyunsaturated fatty acid (VLCn-3 PUFA) for human health were 80 and 56% satisfied by a 200 g meal of 75% VO and 100% VO flesh, respectively. No effect on flesh astaxanthin levels was observed in relation to changing dietary oil sources. Sensory evaluation showed only minor differences between salmon flesh from the dietary groups, although prior to the finishing diet period, flesh from 100% VO had less rancid and marine characteristics and was preferred over flesh from the other dietary groups by a trained taste panel. After the finishing diet period, the levels of typical vegetable oil fatty acids in flesh were reduced, whereas those of VLCn-3 PUFA increased to levels comparable with a 100% FO fed salmon. No differences in any of the sensory characteristics were observed between dietary groups. By blending VOs to provide balanced levels of dietary fatty acids, up to 100% of the fish oil can be replaced by the VO blend without compromising growth or flesh quality. At the same time, 75% of the dietary fish oil can be replaced without compromising flesh VLCn-3 PUFA content, thereby providing a beneficial nutritional profile for human consumption.

Fatty acid metabolism in Atlantic salmon (Salmo salar L.) hepatocytes and influence of dietary vegetable oil.

Isolated hepatocytes from Atlantic salmon (Salmo salar), fed diets containing either 100% fish oil or a vegetable oil blend replacing 75% of the fish oil, were incubated with a range of seven (14)C-labelled fatty acids. The fatty acids were [1-(14)C]16:0, [1-(14)C]18:1n-9, 91-(14)C]18:2n-6, [1-(14)C]18:3n-3, [1-(14)C]20:4n-6, [1-(14)C]20:5n-3, and [1-(14)C]22:6n-3. After 2 h of incubation, the hepatocytes and medium were analysed for acid soluble products, incorporation into lipid classes, and hepatocytes for desaturation and elongation. Uptake into hepatocytes was highest with [1-(14)C]18:2n-6 and [1-(14)C]20:5n-3 and lowest with [1-(14)C]16:0. The highest recovery of radioactivity in the cells was found in triacylglycerols. Of the phospholipids, the highest recovery was found in phosphatidylcholine, with [1-(14)C]16:0 and [1-(14)C]22:6n-3 being the most prominent fatty acids. The rates of beta-oxidation were as follows: 20:4n-6>18:2n-6=16:0>18:1n-9>22:6n-3=18:3n-3=20:5n-3. Of the fatty acids taken up by the hepatocytes, [1-(14)C]16:0 and [1-(14)C]18:1n-9 were subsequently exported the most, with the majority of radioactivity recovered in phospholipids and triacylglycerols, respectively. The major products from desaturation and elongation were generally one cycle of elongation of the fatty acids. Diet had a clear effect on the overall lipid metabolism, with replacing 75% of the fish oil with vegetable oil resulting in decreased uptake of all fatty acids and reduced incorporation of fatty acids into cellular lipids, but increased beta-oxidation activity and higher recovery in products of desaturation and elongation of [1-(14)C]18:2n-6 and [1-(14)C]18:3n-3.

Environmental and dietary influences on highly unsaturated fatty acid biosynthesis and expression of fatty acyl desaturase and elongase genes in liver of Atlantic salmon (Salmo salar).

Highly unsaturated fatty acid (HUFA) synthesis in Atlantic salmon (Salmo salar) was known to be influenced by both nutritional and environmental factors. Here we aimed to test the hypothesis that both these effectors involved similar molecular mechanisms. Thus, HUFA biosynthetic activity and the expression of fatty acyl desaturase and elongase genes were determined at various points during an entire 2 year production cycle in salmon fed diets containing either 100% fish oil or diets in which a high proportion (75% and 100%) of fish oil was replaced by C18 polyunsaturated fatty acid-rich vegetable oil. The results showed that HUFA biosynthesis in Atlantic salmon varied during the growth cycle with peak activity around seawater transfer and subsequent low activities in seawater. Consistent with this, the gene expression of Delta6 desaturase, the rate-limiting step in the HUFA biosynthetic pathway, was highest around the point of seawater transfer and lowest during the seawater phase. In addition, the expression of both Delta6 and Delta5 desaturase genes was generally higher in fish fed the vegetable oil-substituted diets compared to fish fed fish oil, particularly in the seawater phase. Again, generally consistent with this, the activity of the HUFA biosynthetic pathway was invariably higher in fish fed diets in which fish oil was substituted by vegetable oil compared to fish fed only fish oil. In conclusion, these studies showed that both nutritional and environmental modulation of HUFA biosynthesis in Atlantic salmon involved the regulation of fatty acid desaturase gene expression.

Highly unsaturated fatty acid synthesis in vertebrates: new insights with the cloning and characterization of a delta6 desaturase of Atlantic salmon.

Fish are an important source of the n-3 highly unsaturated fatty acids (HUFA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids that are crucial to the health of higher vertebrates. The synthesis of HUFA involves enzyme-mediated desaturation, and a delta5 fatty acyl desaturase cDNA has been cloned from Atlantic salmon (Salmo salar) and functionally characterized previously. Here we report cloning and functional characterization of a delta6 fatty acyl desaturase of Atlantic salmon and describe its genomic structure, tissue expression, and nutritional regulation. A salmon genomic library was screened with a salmon delta5 desaturase cDNA and positive recombinant phage isolated and subcloned. The full-length cDNA for the putative fatty acyl desaturase was shown to comprise 2106 bp containing an open reading frame of 1365 bp specifying a protein of 454 amino acids (GenBank accession no. AY458652). The protein sequence included three histidine boxes, two transmembrane regions, and an N-terminal cytochrome b5 domain containing the heme-binding motif HPGG, all of which are characteristic of microsomal fatty acid desaturases. Functional expression showed that this gene possessed predominantly delta6 desaturase activity. Screening and sequence analysis of the genomic DNA of a single fish revealed that the delta6 desaturase gene constituted 13 exons in 7965 bp of genomic DNA. Quantitative real-time PCR assay of gene expression in Atlantic salmon showed that both delta6 and delta5 fatty acyl desaturase genes, and a fatty acyl elongase gene, were highly expressed in intestine, liver, and brain, and less so in kidney, heart, gill, adipose tissue, muscle, and spleen. Furthermore, expression of both delta6 and delta5 fatty acyl desaturase genes in intestine, liver, red muscle, and adipose tissue was higher in salmon fed a diet containing vegetable oil than in fish fed a diet containing fish oil.