Effects of Dietary α-Linolenic Acid (18:3n-3)/Linoleic Acid (18:2n-6) Ratio on Fatty Acid Metabolism in Murray Cod (Maccullochella peelii peelii)

Abstract

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 C₁₈ 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.

LC‐PUFA Biosynthesis in Rainbow Trout is Substrate Limited: Use of the Whole Body Fatty Acid Balance Method and Different 18:3n‐3/18:2n‐6 Ratios

“…Accordingly, previous studies using radio-labelled fatty acids in Atlantic salmon hepatocytes observed that the overall level of LC-PUFA synthesis from 18:2n-6 was less than half of that from 18:3n-3, irrespective of the diet [40,41]. Similarly, using the whole body fatty acid balance method, a 3.2-fold greater D-6 desaturase affinity toward 18:3n-3 over 18:2n-6 was recorded in Murray cod [22,42]. In the present study, an almost identical relationship between substrate availability and D-6 desaturase activity was shown (Fig.…”

“…or 18:2n-6 (i.e soybean oil, sunflower oil, etc.) have been studied in fish in detail [14][15][16], studies focusing on a sliding 18:3n-3/18:2n-6 ratio are relatively scarce and limited to a few species, including: Coho salmon (Oncorhynchus kisutch) [17]; Milkfish (Chanos chanos) [18]; silver perch (Bidyanus bidyanus) [19]; Eurasian perch (Perca fluviatilis) [20]; yellow catfish (Pelteobagrus fulvidraco) [21]; and Murray cod (Maccullochella peelii peelii) [22,23]. An early study on rainbow trout also assessed the effect of various 18:3n-3/18:2n-6 ratios in juvenile fish from 0.4 to 4 g of body weight [24].…”

Impact of dietary fatty acids on muscle composition, liver lipids, milt composition and sperm performance in European eel

“…In this regard, PRO-EEL2 diet had a 2-fold higher EPA content in comparison to PRO-EEL3 and the DAN-EX diets, however the milt samples of these three experimental groups after induced maturation did not show any differences in EPA percentage. Recently, studies have suggested a preferential utilization of dietary EPA as an energy source for sperm (Senadheera et al, 2011;Al-Souti et al, 2012;Wing-Keong et al, 2013); thus, it could be related to higher sperm motility for the fish fed diets with a high percentage of this fatty acid and producing sperm with higher EPA levels. Baeza et al (2014) suggested the existence of a synthesis of PUFA in the liver (especially EPA) from their precursors to be sent to the testis to increase sperm energy for motility and highlighted the importance of EPA during spermatogenesis.…”

Preliminary Validation of a High Docosahexaenoic Acid (DHA) and -Linolenic Acid (ALA) Dietary Oil Blend: Tissue Fatty Acid Composition and Liver Proteome Response in Atlantic Salmon (Salmo salar) Smolts

“…Limited or negligible bioconversion of ALA to n-3 LC-PUFA has been attributed to high availability of either substrate (ALA) or end-product (DHA). Whereas excessive C 18 fatty acids can affect elongation activities by limiting the ability of delta-6-desaturase to act on C 24 and consequently restraining DHA production [56, 57], the high abundance of n-3 LC-PUFA, particularly DHA rather than EPA, can limit their possible biosynthesis due to an inhibitory effect on delta-6-desaturase and Elovl-2-like elongase enzymes [58–60]. ALA bioconversion has been reported to reach 25% of total net intake in Atlantic salmon fed a diet with full replacement of fish oil with Camelina oil [13, 55]; although ALA concentration was similar to that of TOFX diet (~ 20% total fatty acid), DHA was approximately 10-fold lower than in TOFX diet.…”