A number of morphological and reproductive measurements made seasonally on Antarctic toothfish (Dissostichus mawsoni) from mid-December to early April during the 2000/01 to 2004/05 fishing seasons on board the autoliner San Aotea II have been analysed. Results of this study indicate measurable differences in a number of indices from toothfish found on the Ross shelf proper, as distinct from those sampled on the more isolated seamounts and features to the north. These are modal length distribution, sex ratio, fish body condition factor and reproductive development. Dissostichus mawsoni samples from the northern part of the Ross Sea showed that this component of the population had a unimodallength distribution at a consistent peak over all sampling seasons in comparison with the southern group (in which the distribution was multimodal), showed a consistent and significantly higher ratio of males to females, poorer condition and more advanced reproductive development.