query: How many species of fish have been identified?
passage: Diversity of fish
Fish are very diverse animals and can be categorised in many ways. This article is an overview of some of ways in which fish are categorised. Although most fish species have probably been discovered and described, about 250 new ones are still discovered every year. According to FishBase, 33,100 species of fish had been described by April 2015.[5] That is more than the combined total of all other vertebrate species: mammals, amphibians, reptiles and birds.
passage: Mississippi River
About 375 fish species are known from the Mississippi basin, far exceeding other North Hemisphere river basin exclusively within temperate/subtropical regions, except the Yangtze. Within the Mississippi basin, streams that have their source in the Appalachian and Ozark highlands contain especially many species. Among the fish species in the basin are numerous endemics, as well as relicts such as paddlefish, sturgeon, gar and bowfin.