The previtellogenetic stages of oogenesis were analysed at the morphocytological level in three species of Nototheniidae and two of Channichthyidae collected in the Ross Sea near the Terra Nova Sound. The aim was to determine whether specific adaptations have occurred in these Antarctic species in response to the particularly severe environmental conditions of their habitat. The data obtained indicate that the previtellogenetic stages of oogenesis in all five species are similar to those observed in other fishes and vertebrates. The observations also reveal the existence in the oocyte cytoplasm of large inclusions of ribonucleoprotein showing a peculiar ultrastructural organization. This finding reinforces the hypothesis that the process of adaptation of notothenioids to the Antarctic seas has involved predominantly ecological diversification.