Hephaestus carbo has a deep body which is oblong and oval in shape and also slightly compressed.

The ventral profile is evenly curved from the tip of the lower jaw to the anus.

The juveniles are more colourful than the adults and have bright yellow to orange markings with a reddish-orange ring around the eye.

[4] They prefer the upper reaches of coastal river drainage systems where the water temperatures is always in excess of 15 °C (59 °F).

[2] Hephaestus carbo was first formally described in 1916 as Terapon carbo by the Australian zoologists James Douglas Ogilby and Allan Riverstone McCulloch with the type locality given as the upper waters of the Gregory River in Queensland.