Mexico is the southernmost country in North America, and extends into Central America, south of the Isthmus
of Tehuantepec. The northern half of M´exico is located on the Temperate belt and is arid in character (Nearctic),
while the rest is within the Tropical belt (Neotropical). Climate varies from extremely temperate desert in the
north, to tropical humid in the south.M´exico has more than 500 freshwater fish species, about 271 of them country
endemics, and approximately 48 endemics from binational basins. There are still some 30–40 fish species not
yet described. There are 563 fish species colonizing coastal flood plain species. In addition to the numbers of
colonizing fishes, the burden of introduced exotics has also been growing. In 1904, only 4 species were recognized
as exotics; by 1997 the number had increased to 94, and by 2008 to 11
