Phreatobius is a genus of very small catfishes (order Siluriformes) from tropical South America.

[1][2] Phreatobius has been classified with a number of different families: Clariidae, Plotosidae, Trichomycteridae, Cetopsidae, and Pimelodidae.

[3][6] Phreatobius walkeri, a nomen nudum, is provided by the Guinness Book of World Records, to describe this fish that stays on land for extended periods of time.

[7] Two additional quite distinctive species of Phreatobius, as yet undescribed, are known from the Río Negro basin of Brazil.

[1][2][3] The genus has one of the widest distribution of any hypogean fish genus, with P. sanguijuela from the upper Amazon, some 2000 km from reported locations of P. cisternarum near the Amazon River mouth, and P. dracunculus also approximately 1900 km from the Rio Branco drainage area.