Lipid Class Composition in the Freshwater Pearl Mussel Margaritifera margaritifera from Rivers of the White and Barents Sea Basins

The contents of total lipids (TL) and individual lipid classes were studied in the mantle, foot, and hepatopancreas of the freshwater pearl mussel Margaritifera margaritifera from eight northwestern Russian rivers belonging to the White and Barents Sea basins. Tissue specificity of the lipid composition was observed in the studied tissues; i.e., the hepatopancreas had several times higher contents of TL and dominant lipid classes. A predominance of triacylglycerols among energetic lipids in the hepatopancreas was a distinctive feature of pearl mussels from the Lotta, Sredniy Verman, Mashjoki, and Nautsiyoki rivers, whereas cholesterol esters predominated in mussels from the rivers of the Pyaozero water system, which is further south. Furthermore, the cholesterol/phospholipid ratio (an indicator of the structural and functional state of membranes and a marker of temperature adaptation) was the highest in pearl mussels from the Lotta, Sredniy Verman, Mashjoki, and Nautsiyoki rivers. This may be related to corresponding adaptive changes associated with preparation for the winter period, given a more northern location of the rivers. The results of lipid status analysis in pearl mussels from different habitats may be useful for monitoring studies aimed at preserving and restoring populations of the species in the wild.