Synagrops japonicus is a species of ray-finned fish within the family of Synagropidae. It was described by Döderlein in 1883.
It can be found from Eastern Africa up to the islands of Hawaii. Most of them live at a depth of 100-800 m (330-2600 ft).
They have 10 dorsal spines, 9 dorsal soft rays, 2 anal spines, 7 anal soft rays, and 25 vertebrae. The body is elongated and compressed with large cycloid scales. The body is blackish-brown when young, though after maturing into adults, it becomes paler.