Trichogenes claviger

Trichogenes claviger, also known as the Caetés catfish (Portuguese: bagre-de-caetés), is a critically endangered species of ray-finned fish belonging to the family Trichomycteridae, the pencil catfishes. This species is endemic to streams in the Atlantic Forest of Brazil. It was discovered early in 2010 and scientifically described later that year. One of three species within the genus Trichogenes, it is restricted to an area of 16 km² (6.2 sq mi) in the Caetés forest, a mountainous area in the Brazilian state of Espírito Santo. When discovered, the rainforest in which it occurs was unprotected and threatened by deforestation. A private nature reserve has since been established, allowing visitors to see the fish in its habitat.

A small fish, T. claviger is up to 51 mm (2.0 in) in length. A series of black dots runs along the side of the body, distinguishing it from related species. Males have a bony protrusion from the gill area (the opercular process) that is elongated and club-like, a feature that inspired the name of the species (claviger – 'club-bearing'). The opercular process in T. claviger is the only known secondary sex characteristic in pencil catfishes, and might have evolved for sexual signaling; it is also used by the fish to climb up net walls when caught. The mouth is terminal (faces forwards rather than being upturned or downturned); this feature is also found in the species' closest relative, T. beagle, but absent in all other members of their family. This fish is known to gulp air from the water surface; when carrying air, the body tilts downward. The species lives in small, shaded, and slow-moving streams in the rainforest, and mostly feeds on insects that have fallen on the water surface. It is the only fish in its habitat.