Specialisations of swimming muscles in the pelagic antarctic fish Pleuragramma antarcticum

The distribution and ultrastructure of muscle-fibre types has been investigated in adult and juvenile specimens of the pelagic high-antarctic silverfish Pleuragramma antarcticum Boulenger, 1902 collected from the South Shetland Islands during the winter of 1984/1985. Two main fibre-types were identified in araldite-embedded material. The axial musculature was mainly composed of poorly vascularised, largediameter muscle fibres which were densely packed with myofibrils (volume density 81 and 72% for adults and juveniles, respectively). These ultrastructural characteristics are typical of fast-twitch fibres. The number of capillaries ner unit cross-sectional area and the volume density of mito