Johnius amblycephalus was first formally described as Umbrina amblycephala in 1855 by the Dutch physician, herpetologist and ichthyologist Pieter Bleeker with its type locality given as Ambon Island.

[7] Johnius amblycaphalus has its dorsal fin supported by a total of 11 spines and between 23 and 26 soft rays while the anal fin is supported by 2 spines and 7 soft rays.

The rear edge of the caudal fin can be truncate, rhomboidal or s-shaped.

The overall colour is black or dark brown on the back and whitish or pale yellow on the sides and belly.

[2] Johnius amblycephalus is found in the Indo-Pacific region where it occurs from the Persian Gulf to Papua New Guinea, north to southern China and Taiwan and south to Australia.