Differences in Lipid Characteristics Among Populations: Low‐Temperature Adaptability of Ayu, Plecoglossus altivelis

Abstract

The lipid and fatty acid compositions of the total lipids of three cultured populations (migratory between fresh and salt water, Lake Biwa landlocked, and Setogawa River forms) of ayu, Plecoglossus altivelis, were investigated to clarify the difference in lipid characteristics and temperature adaptability among the three groups. Triacylglycerols were the dominant depot lipids of the three populations, while phospholipids, such as phosphatidylcholine and phosphatidylethanolamine, were found to be the major components of the polar lipids, and their lipid classes are similar to each other. The major fatty acids in the triacylglycerols of all specimens were 16:0, 18:0, 16:1n-7, 18:1n-7, 18:1n-9, 18:2n-6 (linoleic acid), 20:5n-3 (EPA, icosapentaenoic acid), and 22:6n-3 (DHA, docosahexaenoic acid), similar to the tissue phospholipids of the three populations, 16:0, 18:0, 16:1n-7, 18:1n-7, 18:1n-9, 18:2n-6, 20:4n-6, EPA, and DHA. All classes had high levels of 18:2n-6, which originates from their dietary lipids. Compared with the lower DHA levels of the triacylglycerols, the higher levels in the phospholipids suggest their selective accumulation or a biosynthetic pathway to DHA as in freshwater fish. Two populations (the migratory and Setogawa River forms) adapted to lower temperatures with comparatively high levels of polyunsaturated fatty acids (PUFA) for their membrane fluidities. With significantly higher levels of n-3 PUFA and total PUFA, the mean DHA content in the lipids of the Setogawa River form (the population that adapted to lower temperatures) was significantly higher than that of the migratory form. From these results, we concluded that the Setogawa River population actively concentrates long-chain PUFA in its polar lipids and has high adaptability to low temperature.

Comparison of Fatty Acid Contents in Major Lipid Classes of Seven Salmonid Species from Siberian Arctic Lakes

“…In the studied freshwater salmonids, TAG percentages varied from 43.4% to 89.7% of the sum of two acyl-containing lipid classes ( Figure 4A). Such high TAG levels may be explained by adaptation of the fish species to low-temperature conditions in the studied arctic lakes [49,50].…”

Seasonal variations in photoperiod affect hepatic metabolism of medaka (Oryzias latipes)

“…However, there was virtually no increase in PUFA under short‐day conditions. Low temperatures during the winter are known to increase the degree of unsaturation of fatty acids to help maintain cell membrane fluidity [21]. Long‐chain PUFAs in polar lipids have been reportedly involved in the high adaptability of ayu ( Plecoglossus altivelis ) to low temperatures, and cold acclimatization has been reported to induce the activity of acyl‐CoA D9 desaturase in carp ( Cyprinus carpio ) liver [22].…”

Evaluation of the impact of seasonal variations in photoperiod on the hepatic metabolism of medaka (Oryzias latipes)

“…However, there was virtually no increase in PUFA under short-day conditions. Low temperatures during the winter are known to increase the degree of unsaturation of fatty acids to help maintain cell membrane fluidity (Xue et al, 2012). Long-chain PUFA in its polar lipids have been reportedly involved in the high adaptability of ayu ( Plecoglossus altivelis ) to low temperatures, and cold acclimatization has been reported to induce the activity of acyl CoA D9 desaturase in carp ( Cyprinus carpio ) liver (Trueman et al, 2000).…”