Notothenioidei
Chionodraco hamatus
The subordination of Antarctic fish ( Notothenioidei ) is a group of Perciformes. It represents 75 percent of people living in Antarctic waters fish species. From the outer shape they resemble the bullheads ( Cottidae ) of the Northern Hemisphere. Most are demersal fish, some live in the open water.
Evolution
The Antarctic fish are an example of adaptive radiation, the emergence of countless new species from a parent species by adapting to specific living conditions and the utilization of ecological niches. Geographic isolation and lack of natural enemies favor the fan-out.
Decisive for their adaptation to the inhospitable habitat was probably a key evolutionary innovation during a period of global cooling and the increased glaciation of Antarctica about 35 million years ago. Many fish that had previously lived in the warm southern ocean, became extinct. However, so-called anti -freeze proteins allowed the Antarctic fish survive at temperatures close to freezing, discovered this natural antifreeze in the 1950s. The physical feature is the starting point of the diversification of Notothenioidei. Today the animals are crucial to the diversity of Antarctic marine life in, and predators such as penguins, seals, toothed whales, or they serve as food.
Obviously, further adjustments have made the fish for living conditions near the Antarctic ice sheet is particularly suitable. This includes for example the varying buoyancy of the fish without swim bladders. Closely related species can therefore inhabit diverse marine regions to the deep sea. So the fish always conquered new ecological niches, while potential competitors in the icy surroundings disappeared forever. Today's diversity is thus not only the result of a single key innovation, the emergence of the anti -freeze protein is only one of many factors for the amazing diversification of ancestral species.
System
As next of kin and sister group of the Antarctic fish for a long time were the Aalmutterartigen ( Zoarcoidei ), which usually inhabit the northern cold seas, or the dragon fish ( Trachinoidei ). Today, it is increasingly clear that the sister group of the Antarctic fish are the rights perch ( Percidae ). The Antarctic fish are divided into eight families, about 44 genera and 125 species. Two families who Eleginopsidae and Pseudaphritidae are monotypic.
The following cladogram makes the kinship clear:
Icefish ( Bovichtidae )
Catadromous icefish ( Pseudaphritidae )
Patagonia blennies ( Eleginopsidae )
Antarctic cod ( Nototheniidae )
Antarctic predators ( Harpagiferidae )
Antarctica dragon fish ( Bathydraconidae )
Crocodile ( Channichthyidae )
The first three families do not live in the Southern Ocean, but in the Southern Hemisphere, with the exception of a Eisfischart. 33 Of the 49 species of Antarctic cods are antarctic, antarctica not 16. All species of the last four families are antarctic.