Ochmacanthus is a genus of pencil catfishes native to South America. These species are distributed in South America. O. alternus and O. orinoco originate from the Rio Negro and Orinoco River basins of Brazil and Venezuela. O. batrachstoma inhabits the Paraguay River basin in Brazil. O. flabelliferus lives in river drainages in Guyana and Venezuela. O. reinhardtii is known from the Amazon River basin in Brazil and drainages in French Guyana.