Sex- and Regio-Specific Lipid Profiling of Shishamo and Capelin Fish by Nontargeted Liquid Chromatography/Mass Spectrometry

Shishamo smelt (<i>Spirinchus lanceolatus</i>), which is endemic to Hokkaido, Japan, is frequently substituted in markets with morphologically similar capelin (<i>Mallotus villosus</i>) imported from abroad. Lipids are essential nutrients that play important roles in fish authenticity, validation, and nutritional assessment. Although shishamo has long been consumed in Japan, its region-specific lipid distribution and composition are different from those of capelin and have not been well explored. To overcome these gaps, we used untargeted liquid chromatography-mass spectrometry to profile sex- and region-specific lipids in the Japanese <i>S. lanceolatus</i> and Nordic <i>M. villosus</i>. The results revealed that female <i>S. lanceolatus</i> heads exhibited high triacylglycerol (TAG) content, closely resembling roe composition. Docosahexaenoic acid and eicosapentaenoic acid were enriched in the female <i>S. lanceolatus</i> viscera. Multivariate analysis identified monounsaturated fatty acids, such as fatty acid (FA) 22:1 and FA 20:1, as robust discriminatory markers between <i>S. lanceolatus</i> and <i>M. villosus</i>. Overall, sex- and regiospecific differences in lipid composition between the two species were correlated and compared. These lipidomic signatures provide a basis for verifying species authenticity and geographic origin, while highlighting the nutritional lipid potential of <i>S. lanceolatus</i>, particularly from the female viscera.