A second species of Ostichthys, O. kaianus is also recorded from Australian waters. It can be separated from O. japonicus by the number of scales along a straight line between the lateral line and the middle of the spiny dorsal fin (2.5 versus 3.5 in O. japonicus). O. kaianus also has an Indo-West Pacific distribution, but in Australia is only known from off the north-west shelf of Western Australia.