Characteristics of lipid composition differences between cultured and wild ayu (Plecoglossus altivelis)

The lipid levels and fatty acid compositions of the muscle and liver of ayu (sweetfish), Plecoglossus altivelis, and those of its stomach contents were investigated to clarify the difference in the lipid characteristics between aquacultured and wild samples. The lipid levels of the cultured P. altivelis (2.0–3.7%) were significantly higher than were those of the wild ones (1.1–1.4%). Triacylglycerols were the dominant depot lipids of both the cultured and wild samples, while phospholipids were the major components in the polar lipids. The major fatty acids in the muscle and liver triacylglycerols were 14:0, 16:0, 16:1n-7, 18:1n-9, 18:2n-6 (linoleic acid for cultured), 18:3n-3 (linolenic acid for wild), 20:5n-3 (icosapentaenoic acid), and 22:6n-3 (docosahexaenoic acid for cultured). In spite of similar levels of many fatty acids for cultured and wild triacylglycerols, the cultured samples had markedly higher levels of 18:1n-9, 18:2n-6, and 22:6n-3 while the wild ones had significantly higher levels of 18:3n-3 and 20:5n-3, which originate from their dietary lipids. The ratio (RLA/LN) of linoleic acid (18:2n-6) to linolenic acid (18:3n-3) in the cultured samples was markedly higher than were those of the wild samples, and we can easily determine whether P. altivelis is cultured or wild by fatty acid analysis. Moreover, a significant difference in the long-chain PUFA levels, between the cultured and wild samples, was found: higher 22:6n-3 levels were found in the cultured samples while higher 20:5n-3 and 22:5n-3 levels were observed in the wild ones. This finding suggests a limitation of desaturation enzymes in P. altivelis and high 22:6n-3 levels in artificial feedstuff lipids.