The brotulas form a family, the Bythitidae, of ophidiiform fishes, also known as viviparous brotulas as they bear live young. They are found in tropical and subtropical waters throughout the world. They are small fishes, around 5 to 10 cm (2.0 to 3.9 in) in length, and live in surface waters or around reefs. A few species are freshwater: for example, the Mexican blind brotula, Ogilbia pearsei, is found in caves and sinkholes in the Yucatán Peninsula, Mexico.