Total lipids, lipid class and fatty acid compositions were studied to elucidate their role in the life cycle strategies of the Antarctic silverfish Pleuragramma antarcticum, one of the few truly pelagic fish species in the Antarctic realm. Various size groups (larvae to juveniles, 10-105 mm length) of this notothenioid fish have been collected in the southern Weddell Sea during different seasons (mainly spring: October/November and summer: January/February). Total lipid data of P. antarcticum revealed little variation between the seasons. Lipid levels were largely determined by the developmental stage and size, with lower lipid levels (<20% of dry mass DM) found in the larvae (10-16 mm) and intermediate concentrations in the younger juveniles, which increased strongly to maximum amounts of lipid (>40%DM) in the older juveniles (>55-105 mm). Lipid class composition was clearly related to total lipid levels, with neutral lipids (triacylglycerols) comprising <20% of total lipid (%TL) in the younger lipid-poor specimens and >65%TL in the older lipid-rich fishes. Triacylglycerols and phospholipids showed an inverse relationship. Hence, the relative importance of these polar lipids, typically components of biomembranes, decreased with increasing lipid and triacylglycerol levels. Principal fatty acids were 14:0, 16:0, 18:1(n-9), 18:1(n-7), 20:5(n-3) and 22:6(n-3). Elevated portions of the long-chain mono¬unsaturated fatty acids, 20:1 and 22:1, in the lipid-rich specimens suggest the ingestion of two dominant calanoid copepod species, the wax ester-rich Calanoides acutus and the triacylglycerol-rich Calanus propinquus. They are the only species known to biosynthesize larger amounts of these monounsaturated compounds in high-Antarctic waters, which may therefore serve as dietary marker fatty acids for higher trophic levels. Apparently, wax ester moieties (fatty acids and alcohols) ingested with prey, e.g. copepods, are converted to triacylglycerols via fatty acids or metabolized by P. antarcticum. We discuss the function of these high-energy and low-density lipid compounds as energy reserve and/or buoyancy aid in this swimbladderless fish species.