The Castle's conger (Gnathophis castlei) is an eel in the family Congridae (conger/garden eels). It was described by Emma Stanislavovna Karmovskaya and John Richard Paxton in 2000. It is a marine, deep water-dwelling eel which is known from Queensland, Australia, in the western central Pacific Ocean. It dwells at a depth range of 131-366 metres. Males can reach a maximum total length of 34.2 centimetres. The species epithet refers to Peter Henry John Castle.