Arctic and Antarctic fishes
The diversity and adaptations of fishes of the far north and south are treated (Polar regions). Marine shore and continental shelf species down to 200 m from Arctic and Antarctic waters account for about 5.6% of the total fish fauna. The two polar regions contain 538 species of fishes, 289 in the Arctic and 252 in Antarctica (Møller et al. 2005). Only 12 of 214 polar fish genera and 10 of 72 polar fish families are found in both areas. The Arctic region north of 60° in the Pacific (approximately Nunivak Island, Alaska) to Newfoundland and northern Norway in the Atlantic has 20–25% endemism (Briggs 1974) and contains 416 species in 96 families (Eastman 1997). Six groups dominate, comprising 58% of the fish fauna: zoarcoids, gadiforms, cottids, salmonids, pleuronectiforms, and chondrichthyans. Other groups include skates, herrings, greenlings, poachers, snailfishes, pricklebacks, wolffishes, and gunnels. Most of these groups have higher species diversity in the Pacific than in the Atlantic portions of the region (Briggs 1974, 1995).
Antarctica and the surrounding Southern Ocean contain 322 species of fishes in 50 families (Eastman 2005). The immediate Antarctic region has 174 species in 13 families, 88% of which are endemic. Antarctica has a higher level of endemism of fishes and invertebrates than the Arctic Ocean, although the Arctic contains 1.5 times the fish species and twice as many families (Briggs 1974). Of the fishes in the immediate Antarctic region, six families in the suborder Notothenioidei account for 55% of the species and more than 90% of the individuals. Primitive notothenioids, such as the Bovichtidae, occur in southern hemisphere habitats of Australia, New Zealand, and South America. Some families occur in both Antarctica and the surrounding continents (Nototheniidae and Channichthyidae), some occur in Antarctica and nearby oceanic islands such as Las Malvinas (the Falklands) (Harpagiferidae), and one family (Bathydraconidae) is restricted to Antarctica. Of the notothenioids, 97% are Antarctic endemics; even 70% of the non-notothenioids are endemic. Six other families that contribute multiple species to the region are, in order of species diversity (Eastman 2005): snailfishes (70 species), eel pouts (24), skates (eight), and eel cods, deepsea cods, and southern flounders (four species each).
In some cool water species, such as the chub mackerels Scomber japonicus and S. colias, distributions are interrupted by low-latitude regions. Such species are considered to have antitropical distributions, in that they are present in temperate waters on either side of the equator (Hubbs 1952). Other cold water species show tropical submergence, that is, they continue their ranges into tropical regions by submerging, moving into deeper waters that are the same temperature as the cold waters of Arctic and Antarctic regions.