The type species is Ancistrus cirrhosus. This genus is the largest genus within the tribe Ancistrini. The name ancistrus derives from the Greek 'agkistron' meaning hook - a refernence to the form of the cheek odontodes. The genera Pristiancistrus, Thysanocara and Xenocara are now synonyms of Ancistrus.
Ancistrus species show all the typical features of the Loricariidae. This includes a body covered in bony plates and a ventral suckermouth. The feature most commonly associated with the genus are the fleshy tentacles found on the head in adult males; females may possess tentacles along the snout margin but they are smaller and they lack tentacles on the head. Tentacules, tentacles directly associated with odontodes, develop on the pectoral fin spine of the males of some species. Males also have evertable cheek odontodes which are less developed or absent in females. They also lack odontodes along the snout. In comparison with a typical plec, a bristlenose is typically shorter (15 cm or less), more flattened and fatter with a comparatively wider head. Colouration is typically mottled brown, grey or black. Small white or yellow spots are common.
Ancistrus is one of the widest ranging genera of the family, and representatives are found throughout the range of Loricariidae. They are found throughout rivers and floodplain areas of the Amazon River in South America. There are also some species, A. cryptophthalmus and A. formoso, that live in caves.
These fish are often kept by aquarists as they are dutiful algae-eaters and smaller in adult size than the common plecos usually seen in petshops. They are hardy animals, tolerant to a wide range of water conditions, breeding easily in captivity, compatible with most other freshwater fish, and come in many beautiful colors and patterns. Historically commonly available species of Ancistrus were Ancistrus dolichopterus and Ancistrus temminckii, other species are now available though exact identification is difficult. Size is up to 15 cm (male), 12 cm (female), recommended temperature 23-27 degrees Celsius, lifespan up to 12 years. Feeding is easy, bristlenoses will graze on algae and other surface growing organisms as well as eating algae wafers or tablets, flake food, squash, spinach, cucumber, zucchini, green beans and peas. Sexing is very easy as the female will occasionally have bristles around the edge of the chin and the male will have them up the center of the head. Breeding is also possible: Males attract female to small cave or hollow, then guard eggs after fertilization through hatching (4-8 days) until fry are free swimming (4-6 days after hatching), the aquarist need only supply a suitable cave, food, and one of each sex. Like other plecs benefit from the addition of bogwood, which they will rasp at and use as a hiding place - in the absence of other plant matter (sources of fibre) wood may be essential to the survival of these fish in the aquarium when fed on typical high protein fish food. Caution should be taken with the spines (odontodes) - although the risk of personal injury is small with this genus the hooked nature of the odontodes means that a bristlenose may become trapped in non-natural material such as sponge filters and netting.
Taken from WikipediA