The Role of Lipids in the Life History of the Antarctic Silverfish Pleuragramma antarctica

Abstract

A unique characteristic of the pelagic Antarctic silverfish Pleuragramma antarctica is the massive accumulation and storage of lipids in special oil sacs. The enormous lipid deposition beyond 50% of body dry mass functions primarily as buoyancy aid compensating for the missing swim bladder in these fishes, although the depot lipids could also serve as energy reserves. The lipid signature clearly reflects the life cycle of P. antarctica. Trophic marker fatty acids of the early larval and post-larval stages reveal feeding preferences on phyto- and zooplankton, mainly copepods, which these stages utilize for rapid somatic growth without special lipid storage. The juvenile stages tend to feed on calanoid copepods, while the adults shift to krill (Euphausia superba, E. crystallorophias) as major food items. The findings from fatty acid trophic markers are in accordance with gut content analyses. Juveniles to adults exhibit a pronounced lipid deposition, namely triacylglycerols, in the oil sacs. These triacylglycerols are composed of unmodified dietary fatty acids, but may also partially be synthesized de novo. This substantial lipid accumulation not only represents a key adaptation of P. antarctica to life in the pelagic realm. It is also of major importance as high-quality and high-energy food for other marine vertebrates such as seabirds and seals and ultimately ensures an efficient energy flow through the lipid-based high-Antarctic food web.