Fatty acids of polar lipids in heart tissue are good taxonomic markers for tropical African freshwater fish

Abstract

The fatty acid profiles in total, neutral and polar lipids in the heart tissues of five freshwater fish species (Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus, marbled lungfish Protopterus aethiopicus, Bagrus docmak and African catfish Clarias gariepinus) from Lakes Victoria and Kyoga were determined chemometrically by methanolysis of the lipid extracts and gas chromatography of the resulting methyl esters. The analytical data were treated using multivariate principal component analysis. In neutral and polar lipids palmitic acid (16:0) and stearic acid (18:0) were the dominant saturated fatty acids. The polyunsaturated fatty acids in the polar lipid fraction ranged from 33% to 56% and in the neutral lipid fraction from 23% to 30%, dominated by arachidonic acid (20:4n6) and docosahexaenoic acid (22:6n3). The amount of cholesterol in the neutral fraction was 57–89 mg g⁻¹ lipid. The amount of plasmalogen was 12–27 mg g⁻¹ and 14–37 mg g⁻¹ lipid in the polar fraction and total lipid, respectively. In the principal component plots, the fish species from the two lakes were distinguished by fatty acid profiles in neutral, polar and total lipid from the heart tissue. However, polar lipid fractions were better markers of fish species and populations than the neutral fraction and total lipids. Heart tissues have low lipid levels dominated by polar lipids (phospholipids), with polyunsaturated fatty acids as the principal components. The dominance of genetically controlled phospholipids in the heart tissue makes heart tissue most suitable for differentiating between species and populations.

Keywords:

• cholesterol
• fish
• gas chromatography
• lipid
• phospholipid
• plasmalogens
• principal component analysis