Ancistrus is a genus of nocturnal freshwater fish in the family Loricariidae of order Siluriformes, native to freshwater habitats in South America and Panama. Fish of this genus are common in the aquarium trade where known as bushynose or bristlenose catfish. Sometimes, they are called bushynose or bristlenose plecos instead, but this may lead to confusion as “pleco” usually is used for Hypostomus plecostomus and a few of its close relatives but is also classed and or sold as a pleco by most places.
Ancistrus is one of the widest ranging genera of the family, and representatives are found throughout the range of Loricariidae. Many species are found in the rivers and floodplain areas of the Amazon Basin, but there are also species elsewhere in tropical South America, as well as two species, A. centrolepis and A. chagresi in Panama. Three species are true troglobites: A. cryptophthalmus, A. galani and A. formoso. These are the only known loricariids showing adaptions for a subterranean lifestyle with reduced pigmentation (appearing overall whitish) and eyes.