Hypostomus is a genus of catfish in the family Loricariidae. They are native to tropical and subtropical South America. H. plecostomus is the popular freshwater aquarium fish formerly known as Plecostomus plecostomus. The taxonomic structure of the Loricariidae is still being expanded by scientists. Hypostomus is a highly species-rich and widely distributed catfish genus. Taxonomy and phylogeny This genus is the type member of its tribe Hypostomini and subfamily Hypostominae. The type species of Hypostomus is H. guacari. With the inclusion of Aphanotorulus, Isorineloricaria and Squaliforma, the genus Hypostomus is by far the largest genus of Loricariidae and the second largest genus of catfish. However, a good way to split up the genus further is unclear. Species level taxonomy of Hypostomus is still poorly known as well as the phylogenetic relationships within and of the genus. It has been shown that the genus does not form a natural group. However, small monophyletic groups are known to exist within the genus Hypostomus, such as the H. cochliodon group. Aphanotorulus and Isorineloricaria are considered separate genera by some authors based on molecular information. Studies conducted with representatives of some genera of Hypostominae showed that within this group, the diploid number ranges from 2n = 52 to 2n = 80. However, the supposed wide karyotypic diversity that the family Loricariidae or the subfamily Hypostominae would present is almost exclusively restricted to the genus Hypostomus and the species from the other genera had a conserved diploid number. Distribution and habitat These species are originate from freshwater habitats of South America and the Caribbean island of Trinidad. They are found throughout most of the range of loricariids except for drainages west of the Atrato River (northwest Colombia). They are essentially ubiquitous throughout their range. Maximum diversity in number of species of Hypostomus occurs in rivers of the Paraná-Paraguay system. Hypostomus species are found in almost all aquatic habitats, from large rivers to small rivulets. The typical habitat would be relatively fast moving water over a shallow gravel bed. Most species are lowland, sluggish stream- and lake-dwellers usually found associated with submerged wood; however, many species may be found among rocks in piedmont to mountain streams with moderate to swift flow. Members of this genus may be found over a range of substrates such mud, detritus, gravel, and sand. Many species spawn in hollows dug into mud banks or within hollow logs. Description and ecology As