We have studied the chromosomes of 11 of the 15 known species of the notothenioid family Channichthyidae, the specialized whiteblooded Teleosts endemic to the Southern Ocean (ice-fishes). In the female sex, all studied species have the same diploid number of forty eight mostly acrocentric (uniarmed) chromosomes; however there is an interspecific variability in the chromosome morphology, type and quantity of repetitious DNA (usually seen as heterochromatin) localization of silver-stained nucleolar organizers. At least five of the studied species show a multiple sex-chromosome system possibly originated by the translocation of an autosome on an early Y gonosome morphologically similar to the X: the digametic males (2n= 47) show a X1Y X2and the homogametic females (2n= 48) a X1X1X2X2gonosomic constitution. This peculiar sex determining mechanism, otherwise rare in Teleosts, can be considered apomorphic in the same way as other morphofunctional characters usually interpreted as adaptive in these fishes.
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