PREVITELLOGENESIS IN ANTARCTIC FISHES - COMPARISON WITH TEMPERATE SPECIES

The previtellogenetic stages of oogenesis were analysed at the morphoc ytological level in three species of Nototheniidae and two of Channich thyidae collected in the Ross Sea near the Terra Nova Sound. The aim w as to determine whether specific adaptations have occurred in these An tarctic species in response to the particularly severe environmental c onditions of their habitat. The data obtained indicate that the previt ellogenetic stages of oogenesis in all five species are similar to tho se observed in other fishes and vertebrates. The observations also rev eal the existence in the oocyte cytoplasm of large inclusions of ribon ucleoprotein showing a peculiar Ultrastructural organization. This fin ding reinforces the hypothesis that the process of adaptation of notot henioids to the Antarctic seas has involved predominantly ecological d iversification.