Lipidome of Endemic Fish Comephorus dybowskii (Scorpaeniformes, Comephoridae) in Lake Baikal Plays an Essential Role in Maintaining Organism Homeostasis Due to Biomembrane Modifications and Metabolic Consistency

The lipid and fatty acid composition of the little Baikal oilfish (Comephorus dybowskii Korotneff, 1905) was studied to identify the features of its biochemical adaptation to the environmental conditions of Lake Baikal. Multivariate analysis of lipid classes and FA profiles revealed reproducible clustering patterns in both muscle tissue and whole-body samples, indicating the presence of distinct physiological states differing in membrane organization and lipid metabolism. Lipid-class variability was primarily associated with sphingomyelin, cholesterol esters, phosphatidylinositol, and lysophosphatidylcholine, suggesting the coordinated regulation of membrane structure. The fatty-acid profiles were mainly presented by variations in saturated, monounsaturated, and long-chain polyunsaturated fatty acids, with muscle tissues characterized by a relatively longer carbon chain (ACL = 19 vs. 18 I whole body) and unsaturation (UI = 1.98–2.76 vs. 1.64–2.53 in whole body). At the same time, comparative analysis demonstrated low correspondence between lipid and FA profiles, indicating partially independent adaptive mechanisms. The experimental transfer of fish from their natural habitat to controlled conditions resulted in the significant remodeling of both lipid and FA compositions, including increases in acylglycerols, membrane phospholipids, and monounsaturated fatty acids, together with a decline in long-chain n-3 polyunsaturated fatty acids. The results suggest that lipid classes and fatty acids represent complementary but functionally distinct levels of biochemical adaptation contributing to the maintenance of membrane organization and metabolic homeostasis in C. dybowskii, revealing a previously undescribed multi-level organization of lipid-related adaptive responses in this endemic deep-water fish.