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Thanuthong T.,Deakin University | Thanuthong T.,Songkhla Rajabhat University | Francis D.S.,Australian Institute of Marine Science | Manickam E.,Monash University | And 4 more authors.
Aquaculture | Year: 2011

This study aimed to gain a better understanding of the metabolic fate of dietary fatty acids in rainbow trout, with a specific focus on the effect of varying total C 18 PUFA level. Fish were fed a control fish oil based diet or one of five experimental fish oil deprived diets formulated with a constant 1/1 ratio of 18:3n-3/18:2n-6 and varying total C 18 PUFA levels for a period of 7weeks. The transcriptional changes of the δ-6 desaturase and elongase enzymes in direct comparison to in vivo fatty acid bioconversion, estimated using the whole-body fatty acid balance method, were analysed. The main findings were that i) the efficiency of δ-6 desaturase was negatively affected by C 18 PUFA availability, but the total apparent in vivo enzyme activity was directly proportional to C 18 PUFA substrate availability; ii) δ-6 desaturase had a greater affinity towards n-3PUFA than n-6PUFA; iii) excessive C 18 PUFA substrate availability could limit the availability of δ-6 desaturase to act on C 24 fatty acid; iv) the elimination of dietary n-3LC-PUFA (enzyme products) up-regulated the transcription rate of δ-6 desaturase; but v) the total apparent in vivo enzyme activity was directly and positively affected by substrate availability, and not product presence/absence nor the extent of the enzyme transcription rate. © 2011 Elsevier B.V. Source

Turchini G.M.,Deakin University | Francis D.S.,Australian Institute of Marine Science | Senadheera S.P.S.D.,Deakin University | Senadheera S.P.S.D.,National Institute of Fisheries and Nautical Engineering | And 4 more authors.
Aquaculture | Year: 2011

Within the context of fish oil replacement in aquaculture, the modification of fillet fatty acid make-up and the maximisation of omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA; namely eicosapentaenoic acid - EPA - 20:5n-3, and docosahexaenoic acid - DHA - 22:6n-3) deposition are attracting increasing interest. The present study investigated these aspects by testing fish oil and four different vegetable oils (selected for their extreme fatty acid composition: palm oil, olive oil, sunflower oil and linseed oil) in a feeding trial consisting of a grow-out and finishing period using juvenile Murray cod. Minimal/no effect on growth performance was recorded. The dietary treatment largely affected the fillet fatty acid make-up, which was to some extent, diluted by the finishing period. The overall fatty acid composition of the alternative oil used (i.e. saturated, monounsaturated and polyunsaturated fatty acids - SFA, MUFA and PUFA, respectively) was found to have a significant effect on the final n-3 LC-PUFA content of cultured fish. It was shown that MUFA, and to a lesser extent SFA, can have a form of "omega-3 sparing effect", whereby an abundant availability of dietary MUFA and SFA can decrease the catabolism of n-3 LC-PUFA and result in a greater deposition rate of these health-promoting fatty acids into fish fillets. © 2011 Elsevier B.V. Source

Senadheera S.D.,Deakin University | Senadheera S.D.,National Institute of Fisheries and Nautical Engineering | Turchini G.M.,Deakin University | Thanuthong T.,Deakin University | And 2 more authors.
Journal of Agricultural and Food Chemistry | Year: 2011

Global shortages in fish oil are forcing the aquaculture feed industry to use alternative oil sources, the use of which negatively affects the final fatty acid makeup of cultured fish. Thus, the modulation of fatty acid metabolism in cultured fish is the core of an intensive global research effort. The present study aimed to evaluate the effects of various dietary α-linolenic acid (ALA, 18:3n-3)/linoleic acid (LA, 18:2n-6) ratios in cultured fish. A feeding trial was implemented on the freshwater finfish Murray cod, in which fish were fed either a fish oil-based control diet or one of five fish oil-deprived experimental diets formulated to contain an ALA/LA ratio ranging from 0.3 to 2.9, but with a constant total C 18 PUFA (ALA+LA) content. The whole-body fatty acid balance method was used to evaluate fish in vivo fatty acid metabolism. The results indicate that dietary ALA was more actively β-oxidized and bioconverted, whereas LA appears to be more efficiently deposited. LA was β-oxidized at a constant level (∼36% of net intake) independent of dietary availability, whereas ALA was oxidized proportionally to dietary supply. The in vivo apparent Δ-6 desaturase activity on n-3 and n-6 PUFA exhibited an increasing and decreasing trend, respectively, in conjunction with the increasing dietary ALA/LA ratio, clearly indicating that this enzymatic activity is substrate dependent. However, the maximum Δ-6 desaturase activity acting on ALA peaked at the substrate level of 3.2186 (μmol g fish -1 day -1), suggesting that additional inclusion of ALA is not only wasteful but counterproductive in terms of n-3 LC-PUFA production. Despite a constant total supply of ALA+LA, the recorded total in vivo apparent Δ-6 desaturase activity on both substrates (ALA and LA) increased in synchrony with the ALA/LA ratio, peaking at 1.54, and a 3.2-fold greater Δ-6 desaturase affinity toward ALA over LA was recorded. © 2011 American Chemical Society. Source

Thanuthong T.,Deakin University | Thanuthong T.,Songkhla Rajabhat University | Francis D.S.,Australian Institute of Marine Science | Senadheera S.P.S.D.,Deakin University | And 3 more authors.
Lipids | Year: 2011

Five experimental diets with constant total C18 PUFA and varying 18:3n-3/18:2n-6 ratios were fed to rainbow trout over an entire production cycle. The whole-body fatty acid balance method demonstrated a clear trend of progressively reduced fatty acid bioconversion activity along the n-3 and n-6 pathways, up to the production of 20:5n-3 and 20:4n-6, respectively. This suggests that the pathway exhibits a "funnel like" progression of activity rather than the existence of a single rate limiting step. The production of 22:5n-3 and 22:6n-3 was more active than that of 20:5n-3. However, despite this trend in reduced apparent in vivo net enzyme activity, the efficiency of the various bioconversion steps (measured as % of bioconverted substrate) confirmed an opposing trend. A 3.2-fold higher Δ-6 desaturase affinity towards 18:3n-3 over 18:2n-6 and an 8-fold greater Δ-5 desaturase affinity towards 20:4n-3 over 20:3n-6 were recorded. The main results of the study were that (1) rainbow trout are quite efficient at bioconverting 18:3n-3 to 22:6n-3, and (2) the LC-PUFA biosynthetic pathway is substrate limited. Fillet n-3 LC-PUFA concentrations increased with the increasing dietary supply of 18:3n-3. Despite an almost identical dietary supply of n-3 LC-PUFA, originating from the fish meal fraction of the diets, the fillets of trout fed the diet richest in 18:3n-3 were 2-fold higher in n-3 LC-PUFA than fish fed low 18:3n-3 diets. Nevertheless, fillets of trout fed a fish oil control diet contained more than double the amount of n-3 LC-PUFA compared to fish fed the diets richest in 18:3n-3. © 2011 AOCS. Source

Senadheera S.P.S.D.,Deakin University | Senadheera S.P.S.D.,National Institute of Fisheries and Nautical Engineering | Turchini G.M.,Deakin University | Thanuthong T.,Deakin University | And 2 more authors.
Aquaculture | Year: 2010

The objective of the present study was to evaluate the effect of different dietary α-linolenic acid (ALA, 18:3n-3) to linoleic acid (LA, 18:2n-6) ratios, while employing 100% fish oil deprived diets, on growth performance and flesh fatty acid composition of Murray cod, and subsequent finishing (wash-out) efficiency. The ALA/LA ratios of the five experimental diets were gradually increased from 0.3 to 2.9, with a constant total content of ALA. +. LA of 51%. Fish oil was used for the sixth diet (control), which was also used during the finishing period. It was shown that an increased dietary ALA/LA ratio does not impair growth performance or the tissue lipid concentration of Murray cod. However, the dietary ALA/LA ratio significantly impacts on the final fatty acid make-up and nutritional quality of the fish fillet. In particular, the fillets of fish fed with higher ALA/LA ratios (hence receiving more dietary ALA) recorded significantly higher concentrations of EPA and DHA (eicosapentaenoic acid, 20:5n-3, and docosahexaenoic acid, 22:6n-3, respectively). High dietary LA content, however, was shown to have significant negative impacts on the efficiency of a finishing strategy. Interestingly, it was observed that, on average, only 10% of the total EPA and DHA provided during the finishing period via the fish oil-based diet was retained and deposited into the fish fillet. Additionally, the deposition of EPA and DHA during the finishing period was shown to be affected by previous feeding history, with fish previously fed high LA diets depositing significantly lower amounts of these fatty acids in comparison to fish previously fed a diet rich in ALA. © 2010 Elsevier B.V. Source

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