Phylogenetic study of the Antarctic fish family Channichthyidae.

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Phylogenetic relationships of the family Channichthyidae had been discussed mainly by their ecological features and osteological characters. Relationships between the jaw structures and stomach contents of the notothenioid fishes including the Channichthyidae were analyzed. The results showed the possibility that the huge biomass of the Antarctic krill enables channichthyid fishes to maintain some paedomorphic characters such as haemoglobinless condition. Based on the cladistic analyzes of these osteological features, 11 genera of this family can be rearranged into 6 groups as, (1) Champsocephalus group, (2) Pagetopsis group, (3) Dacodraco group, (4) Channichthys group, (5) Chaenocephalus group and (6) Chionodraco group. At least in 2 of the 6 groups mentioned above, the Pagetopsis group and Cryodraco group, paedomorphic features were found. The Pagetopsis group is characterized by having fan-shaped large pelvic fins and the second infraorbital bones with ventral expansion. Among the three genera, Pagetopsis shows progenetic character states in body color, shape of the second infraorbital bones and of the third hypobranchial bones, and also in its body size. The genus Cryodraco in the Cryodraco group has long body with low vertical fins and extended rod-like pelvic fins. Its features are usually found in channichthyid larvae. Therefore, these conditions are thought to be neotenic. The white blooded fish family, the Channichthyidae, are convinced to be a monophyletic group. Environmental conditions of habitat of each channichthyid species are considerably similar and some species lives sympatrically. Ecology and behavior of channichthyid species are also similar to each other. Based on above mentioned circumstantial evidences, one of the important process of speciation of the Channichthyidae is thought to be paedomorphosis. Furthermore, the singular character, the lack of hemoglobin, found in all members of this family may also be a result of heterochrony.