Chardonius is an extinct genus of prehistoric freshwater ray-finned fish from the late Aptian or early Albian. It contains a single species, C. longicaudatus, from the Loia Beds of the Democratic Republic of the Congo.
Its taxonomic placement is uncertain, and it has been alternatively classified as a "clupeoid" or a "salmoniform". The latter classification is now thought to be a wastebasket treatment. It is currently considered an indeterminate euteleost.
Morphologically, it is notable for the extreme anterior insertion point of its dorsal fin compared to the anal fin.