Harenaichthys is an extinct genus of osteoglossiform fish that lived in Mongolia during the Late Cretaceous and was found in the Nemegt Formation. The type species is H. lui and is based solely on the holotype, which consists of partial skull parts, isolated and articulated centra, and an articulated caudal fin preserved together within a single sandstone block. The monospecific assemblages of Harenaichthys were affected by the high altitude of their habitat and the fossils show signs of pathologies caused by diseases while the animals were still alive.