Annual cycles in chemical composition of the body, liver, gonads, red and white muscles were determined for two medium fat sculpins, COTTOCOMEPHORUS GREWINGKI and C. INERMIS, endemic to Lake Baikal. Their total lipid content ranged from 3 to 9% during the year. The content of defatted dry substance was 14-17%, similar to the protein content of the other Baikalian cottoid fishes. The prespawning period was characterized by a positive lipid and protein balance in both species. In C. GREWINGKI the liver performed largely a metabolic function, whereas in C. INERMIS it served also as a storage site for lipid reserves. During spawning, total body lipids of females of both species showed a two- to threefold decrease. Males of C. GREWINGKI guarding nests deplete greatly their total body lipids, which decrease seven- to ninefold by the time of larval hatching in comparison with the prespawning period, and constitute 1-2%. After spawning, lipid reserves of females C. GREWINGKI were quickly restored to the initial level (from about 3 to 9%) and maintained during the long sexual maturation period. In C. INERMIS total body lipids increased only twofold in comparison to those observed during the spawning period.

A study was made of the lipid class composition in liver, gonads, red and white muscles of C. GREWINGKI and C. INERMIS. The main lipid classes were triacylglycerols and phospholipids. The highest levels of triacylglycerol (81.8%) were found in males C. INERMIS liver, and the phospholipid (38.3%) in males testes of both species. The main phospholipid classes were phosphatidylcholine and phosphatidylethanol- amine, which varied in examined organs and tissues in both fish species from 44.3 to 78.7%, and from 16.8 to 42.1%, respectively.

A study was made of the fatty acid composition of polar and neutral lipids in liver, gonads and red and white muscles of two fish species C. GREWINGKI and C. INERMIS and of the crustacea EPISCHURA BAICALENSIS, Sars (Copepoda) and MACROHECTOPUS BRANICKII, Dybowski (Amphipoda). A high level of polyunsaturated (n-3) series fatty acids, unusual for freshwater fish, was detected. According to the fatty acid ratio (n-3)/(n-6) in polar lipids, the Baikal fish occupy an intermediate place between freshwater and marine fishes and, in regard to neutral lipids, they refer to typically freshwater species. It is shown that 22:6(n-3), 16:0, 18:1 are the main components of fatty acids of these fish and crustacea and, among them, 22:6(n-3) is dominant. In the spawning period, in comparison with that of sexual maturation, the 22:6(n-3) content of polar lipids decreases in the liver; the content of 16:1 decreases in neutral lipids and the content of C18 of polyunsaturated fatty acids increases in the liver and red muscles in both species. The fish C. GREWINGKI and C. INERMIS have an identical fatty acid composition, although their main foods E. BAICALENSIS and differ in fatty acid composition.