A number of morphological and reproductive measurements made on Antarctic toothfish Dissostichus mawsoni over the four summer seasons from 2000-01 to 2003-04 aboard the autoliner San Aotea II have been analysed. Summer seasons are defined here as the period from mid December to the beginning of April. 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 differences are fish body condition factor, reproductive development, sex ratio, and length modal distribution. D. mawsoni samples from the northern region showed that this section of the population was more advanced in reproductive development, were in poorer condition, showed a consistent and significant higher ratio of males to females, and showed a unimodal length distribution at a consistent peak over all seasons in comparison with the southern group in which the distribution was multimodal.