Fatty acid content of the dorsal muscle—an indicator of fat quality in freshwater fish

Abstract

In 56 samples of freshwater fish, most were low in fat, ≤ 5% of dry weight (D.W.), and the sum of all fatty acids (ΣFA) was about 2% of D.W. Trout, whitefish, and grayling had the highest content of the long‐chained FA. of ω3 type, EPA and DHA (1·7–2·6% of D.W.). Two large, low‐fat pikes with ΣFA of about12–3% of D.W. and a medium‐fat whitefish had the highest ω3/ω6 ratios, 8–9, whereas the fattiest fishes, eels from two lakes and the Baltic (ΣFA =17–26% of D.W.) had lower ω3/ω6 ratios, 1·1–1·8 (ω3 and ω6 FA are two important series of FA). The results indicate that ΣA controls the content of saturated FA (SAFA) and monounsaturated FA (MUFA), whereas the polyunsaturated FA (PUFA) was independent of ΣFA after a break point of about 10%ΣFA of D.W. The P/S ratio (PUFA/SAFA) and the PUFA/ΣFA ratio decreased with increased ΣFA, whereas the ω3/ω6 ratio showed no clear correlation to ΣFA. The difference in fatty acid patterns lay between low‐fat and high‐fat fishes, rather than between marine and freshwater fishes. The variation, both within and between species of the separate FA is small in fish with similar ΣFA content. Also, low‐fat and medium‐fat fishes tend to be more dietarily favourable than high‐fat fishes, when considering the latest criteria for high nutritional value to humans. Abbreviations used in the text: FA, fatty acids; ΣFA, sum of all FA; AA, arachidonic acid (20 : 4ω6); EPA, eicosapentaenoic acid (20 : 5ω3); DHA, docosahexaenoic acid (22 : 6ω3); SAFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; D.W., dry weight; F.W. fresh weight; CV, coefficient of variation; ω3 FA, series of PUFA with the first double bond located at carbon number 3; ω6 FA, series of PUFA with the first double bond located at carbon number 6. The fatty acids are described by three numbers, x:ywz, where x=number of carbon atoms, y=number of double bonds, and z=position of the first double bond counted from the methyl end of the molecule.

Size-related dietary changes observed in young-of-the-year pumpkinseed (Lepomis gibbosus): stomach contents and fatty acid analyses

“…All samples in this study were in concordance with those of many freshwater fishes, characterized by higher x6 PUFA and high levels of oleic and palmitoleic acids (Ahlgren et al 1994;Andrade et al 1995;Zenebe et al 1998a;Kozlova and Khotimchenko 2000). The x3/x6 ratio in marine species varies between 4.7 and 14.4, while it varies between 0.5 and 3.8 in freshwater species (Henderson and Tocher 1987;Ahlgren et al 1994;Abd Rahman et al 1995). Here, x3/x6 ratio in L. gibbosus did not exceed 3.1, and it tended to decrease (but not significantly) with fish size (Table 4).…”

“…Ecol (2011) 45:23-33 29 It is assumed that FA composition has a higher content in x6 PUFA in freshwater than in marine fishes, since freshwater prey, mainly terrestrial and/or aquatic insects and benthic organisms, are rich in these PUFA (Henderson and Tocher 1987). All samples in this study were in concordance with those of many freshwater fishes, characterized by higher x6 PUFA and high levels of oleic and palmitoleic acids (Ahlgren et al 1994;Andrade et al 1995;Zenebe et al 1998a;Kozlova and Khotimchenko 2000). The x3/x6 ratio in marine species varies between 4.7 and 14.4, while it varies between 0.5 and 3.8 in freshwater species (Henderson and Tocher 1987;Ahlgren et al 1994;Abd Rahman et al 1995).…”

From Aquatic to Terrestrial Food Webs: Decrease of the Docosahexaenoic Acid/Linoleic Acid Ratio

“…A dietary-influence of DHA and EPA concentrations linked to fish consumption has already been documented for American minks kits fed on a fish-oil supplemented diet [4]. Indeed, DHA is abundant in both marine and freshwater fishes [14,19]. Although freshwater fishes can also be a source of ALA [8,25,26] the high concentration of this FA observed for the European polecat (7.3% of TFAW) is probably not completely due to fish consumption.…”

“…Consequently, each type of food web shows a ''typical'' fatty acid profile [17,18]. In aquatic food webs n-3 PUFAs dominate over n-6 PUFAs by a factor of 5-20 [17,19]. The opposite is true for terrestrial food webs where n-6 PUFAs are more abundant than n-3 PUFAs [20].…”

Changes in some components of the muscle lipids of three freshwater fish species under natural extreme cold and temperate conditions

“…Three representative commercial size specimens of each species were used for the gas chromatography (GC) analysis. Before each analysis, the fish was thawed, and a 20-g sample was taken from the dorsal muscle along the lateral line, which is an indicator of fat quality in freshwater fish (Ahlgren et al 1994). …”