Antarctica has been a frozen continent for about the last 15-20 million years. In that time, the notothenioid fish have become the dominant group of fish with about 100 new species appearing in the comparative absence of other competing fish. A wide range of lifestyle, size and unusual physiological adaptations are found in this group. We investigated the mechanisms and patterns by which all of ... these notothenioid fish developed, in particular, how significant climate changes are reflected in the pattern of speciation. Individual fish of species common to a number of sites around Antarctica were sampled to look at variation within and between sites and populations (inter and intraspecific variation). Each species caught was identified and photographed (for ID purposes). Fin samples were taken, DNA was isolated and marker regions amplified and analysed. Areas that fish were surveyed from include: Cape Armitage, Cape Roberts, Cape Evans, Cape Hallett (Edisto Inlet) and Cape Christie (near Seebea Hook, Cape Hallett). Some larval fish were recovered after being regurgitated by larger fish and stored whole. A number of Trematomus newnesi were captured, weighed in air and in water (to calculate buoyant density) and the bodies of different sizes were kept for further investigation. Tissue samples were taken to determine the underlying genetic basis of the two morphs.