The fishes in this order are commonly called bony tougues, which contains arawanas, elephantfishes and knifefishes.
Arawanas (Family Osteoglossidae)Arawanas (or Arowanas), commonly called Dragonfishes, belong to Family Osteoglossidae. There are 7 species - 3 South American, 1 African, 1 Asian and 2 Australian.
There are 2 species in Singapore, both introduced.
The Asian Arawana (Scleropages formosus) has been suggested to split into 4 separate species1, but they are treated as a single species here. There is even a fifth Asian species suggested2.
The Silver Arawana (Osteoglossum bicirrhosum) is one of the South American arawanas and is an introduced species here.
Knifefish (Family Notopteridae)The Clown Knifefish (Chitala ornata) is an introduced freshwater species in Singapore.
References1. Asian Arawana split
2. Myanmar Arawana