Antarctic icefishes (Channichthyidae) – a unique family of fishes – a review

Icefish are a family of species unique among vertebrates in that they possess no haemoglobin. With the exception of one species, icefish live only in the cold – stable and oxygen – rich environment of the Southern Ocean. It is still questionable how old icefish are in evolutionary terms: they may not be older than 6 MA, i.e. they evolved well after the Southern Ocean started to cool down or they are 15 – 20 Ma old and started to evolve some time after the formation of the Antarctic Circumpolar Current. Certain icefish species, such as Chionobathyscus dewitti, have been found down more than 2,000 m. Icefish have been shown to present organ – level adaptations on different levels to compensate for the ‘disadvantages’ of lacking respiratory pigments. Biological features, such as reproduction and growth, are not unique and are comparable to other notothenioids living in the same environment. Icefish produce large yolky eggs which have a diameter of more than 4 mm in most species. Most icefish species do not attain maturity before they are 5 – 8 years old. Spawning period of most icefish species is autumn – winter. The incubation period spans from 2 months in the north of the Southern Ocean to more than 6 months close to the continent. Growth in icefish to the extent it is known is fairly rapid. They grow 6 – 10 cm in length per annum before they reach spawning maturity. Icefish feed primarily on krill and fish. Some icefish species are abundant enough to be exploited by commercial fisheries, primarily in the 1970’s and 1980’s with Champsocephalus gunnari as the main target species. Most stocks of this species had been overexploited by the beginning of the 1990’s.