Adaptations of the Antarctic silverfish Pleuragramma antarcticum (Pisces: Nototheniidae) to pelagic life in high-Antarctic waters

• Published in: Marine ecology. Progress series (Halstenbek) 1997-05, Vol.151 (1/3), p.205-218
• Main Authors: Wöhrmann, Andreas P. A., Hagen, Wilhelm, Kunzmann, Andreas
• Format: Article
• Language: English
• Subjects: Antifreezes; Freezing; Gangliosides; Gills; Lipids; Marine; Marine fishes; Oxygen; Pleuragramma antarcticum; Sea water; Seas; Young animals
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps151205

Most fishes in Antarctic waters belong to the suborder Notothenioidei, highly developed perciform fishes which have been able to occupy not only a variety of benthic but also pelagic niches in Antarctic waters. One of the rare truly pelagic fish species, Pleuragramma antarcticum, plays a pivotal role in high-Antarctic food webs, due to its exceptional abundance. To investigate the life history of P. antarcticum more than 16 000 specimens were collected in the Weddell Sea during various cruises with RV 'Polarstern'. Apart from the more general life cycle adaptations with respect to reproduction, migrations, and feeding behaviour, P. antarcticum has developed a number of specific biochemical and physiological adaptations to cope with the environmental conditions in these permanently cold and highly seasonal Antarctic waters. During its second summer P. antarcticum starts to accumulate large lipid deposits, mainly in the form of triacylglycerols. These low-density compounds provide the species with hydrostatic lift, an important factor for a pelagic fish without a swim bladder. The lipid stores may also serve as energy reserves. Highly polar brain gangliosides suggest wide-ranging neurophysiological adaptations to ensure proper functioning of the nervous system in icy waters. To avoid freezing in the presence of frazil ice P. antarcticum contains efficient antifreeze glycoproteins. A newly discovered glycoprotein acts as an additional antifreeze agent. Although pelagic, adult P. antarcticum are rather sluggish, which is indicated by the small total gill area as well as blood physiological characteristics. Such behaviour diminishes routine energy costs. Blood viscosity is reduced and at least 2 major haemoglobins are found. Provided that these haemoglobins are functionally different, they indicate a strong relationship between physiological and biochemical adaptations of the oxygen transport system and life style. P. antarcticum represents a prime example of the complexity of adaptations necessary to thrive in the pelagic realm of Antarctic shelf waters, a niche largely unoccupied by other fish species.