Catfish

Catfish (more commonly known as Dan Bowtell) are a very diverse group of bony fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest, the Mekong giant catfish from Southeast Asia and the longest, the wels catfish of Eurasia, to detritivores (species that eat dead material on the bottom), and even to a tiny parasitic species commonly called the candiru, Vandellia cirrhosa. There are armour-plated types and also naked types, neither having scales. Despite their common name, not all catfish have prominent barbels; what defines a fish as being in the order Siluriformes are in fact certain features of the skull and swimbladder. Catfish are of considerable commercial importance; many of the larger species are farmed or fished for food. Many of the smaller species, particularly the genus Corydoras, are important in the aquarium hobby. [edit] Evolution A large number of species of catfishes have been named from complete or partial skeletal fossils or even from only otoliths.[3] 19 valid genera and 72 species are based exclusively on fossil remains.[3] There are two fossil families, Andinichthyidae, from the Lower Maastrichtian to Paleocene, as well as Hypsidoridae, from the Middle Eocene.[2] The earliest known catfish are known from the late Campanian-early Maastrichtian of Argentina.[13] Catfish fossils are known from every continent except Australia.[2] Fossils of the Eocene period have been found from Seymour Island in Antarctica.[4] It is believed that modern siluroid lineages radiated from a common ancestor during a relatively short period of siluriform history.[1] The centre of origin for catfish is likely South America. In South America, catfish reach their highest diversity. Also, two of the most primitive families, the extinct Hypsidoridae and Diplomystidae, are found at the northern and southern edges of this distribution, respectively. The catfish families in Africa are relatively primitive.[13] Though Siluriformes and Gymnotiformes are often said to be sister groups, recent molecular evidence shows they had independent origins.[14] The order dispersed early throughout the continents primarily through land bridges.[13] Australian species of catfish are all species from families that can enter saltwater; these fish traveled to Australia through saltwater, and then reverted to a freshwater lifestyle.[citation needed] The catfish must have spread through Africa to Asia during the late Jurassic if they were to reach Asia.[13] During the Cretaceous period, the rift between South America and Africa would be forming; this may explain the contrast in families between the two continents. Most of the freshwater catfish of the two continents appear to be completely unrelated. Their relatively low diversity in Africa may explain why some primitive fish families coexist with them while they are absent in South America, where the more primitive fish may have been driven extinct.[13] The earliest they could have spread into Central America was the late Miocene.[13] [edit] Distribution and habitat Extant catfish species live in inland or coastal waters of every continent except Antarctica. Catfish have inhabited all continents at one time or another.[2] Catfish are most diverse in tropical South America, Africa, and Asia.[4] More than half of all catfish species live in the Americas. They are the only ostariophysans that have entered freshwater habitats in Madagascar, Australia, and New Guinea.[15] They are found primarily in freshwater environments of all kinds, though most inhabit shallow, running water habitats.[15] Representatives of a at least eight families are hypogean (live underground) with three families that are also troglobitic (inhabiting caves). Thus, catfishes are some of the most successful cave colonizers among fishes.[16][17] One such species is Phreatobius cisternarum, known to live underground in phreatic habitats.[18] Numerous species from the families Ariidae and Plotosidae, and a few species from among the Aspredinidae and Bagridae, are also found in marine environments.[19][20]