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Mackerel icefish, Champsocephalus gunnari , plays a vital role in the Antarctic marine ecosystem, not only because it is an important prey for higher predators but also because it is the primary predator of Antarctic krill (Euphausia superba), a keystone species in the Southern Ocean. Therefore, elucidating the trophic linkage between C. gunnari and its exclusive prey can provide a model for the trophic relationship between a predator and its prey in cold environments. Stomach contents analysis showed that E. superba was the predominant prey of C. gunnari in terms of quantity (99.3%) and quality (99.9%) during winter at South Georgia. E. superba had a similar fatty acid profile to that of C. gunnari , with a high proportion of short-chain monounsaturated fatty acids (MUFA) and a lower proportion of long-chain MUFA. However, C. gunnari was more likely to retain polyunsaturated fatty acids, especially docosahexaenoic; E. superba tended to accumulate saturated fatty acids and MUFA. This reflects the fact that fatty acids, when transferred from low trophic level to higher levels, are accumulated in the predator selectively, according to their relative content in the diet and their physiological and ecological function in the predator. • Diet of Champsocephalus gunnari in South Georgia during winter was examined using stomach content and fatty acids analyses. • E. superba is the predominant prey of C. gunnari in South Georgia during winter. • E. superba and C. gunnari shared similar fatty acid profile. • C. gunnari retains polyunsaturated fatty acids, but E. superba accumulates saturated and monounsaturated fatty acids. • Study provide insight for predator-prey relationship in the Southern Ocean during data-limited season. [ABSTRACT FROM AUTHOR]