Fatty acid composition of lipid-rich myctophids and mackerel icefish (Champsocephalus gunnari) -: Southern ocean food-web implications

The lipid content, fatty acid composition and calorific value of seven species of mesopelagic deep-sea fish of the family Myctophidae and the mackerel icefish, Champsocephalus gunnari, important in the diet of Southern Ocean marine predators, are presented. Fish were sampled at the Kerguelen Plateau (KP) and Macquarie Ridge (MR) in the Indian and Pacific sectors of the Southern Ocean respectively, to examine geographic variation in lipid compositon. All species of myctophid from KP and Electrona antarctica from MR were high in lipid content (6-18% wet mass), particularly Gymnoscopelus nicholsi (18%) and E. antarctica (15%). The mackerel icefish, and G. fraseri and Protomyctophum tenisoni from MR were generally lower in lipid content (3-5%) and varied significantly in fatty acid composition from KP species. KP myctophids were high in calorific content (9.3 kJ g I wet mass) when compared with icefish (5.4 kJ g 1 wet mass) and other published values for pre items of marine predators such as squid (1.7-4.5 kJ g). KP myctophids were distinguished from each other and from C. gunnari and MR specimens by cluster and discriminant function analysis using six fatty acids (16:0, 18:1omega9, 20:1omega9, 22:1omega11, 20:5omega3, 22:6omega3). Findings presented here highlight trophic links between high-latitude fish and their prey and emphasise the importance of myctophids as a significant energy source for marine predators foraging in the Polar Frontal Zone.