That description of O. kaianus certainly fits the appearance of the fish that I caught.
I read online somewhere that captures of O. kaianus have been recorded in the Arafura Sea, and interestingly, my specimen was caught in particularly warm water for southern NSW; (22°C, by the temperature sensor on our sounder).
We ended up keeping the fish, as it was suffering from severe barotrauma... I've attached another photo of it, which confirms the presence of a triangular feature on the top of its head.
Can you please help me identify the species of Ostichthys that is in the attached photograph?
Below are some details relating to the fish, which may be of relevance. • Caught 14/01/2012 at Sir John Young Banks, NSW, in ~16m of water. (On the drop-off from 8.5 fathoms; in the vicinity of 34°56.970' S, 150°54.820' E.)
• Fork length approx. 31.5cm.
• Looks similar to O. archiepiscopus, except that the discrete white spots along its body (one on each scale) are small in comparison to the scales, and do not form thick and relatively continuous white bands such as those seen in O. archiepiscopus and O. kaianus.
• Scales rough, and also bearing very fine filaments reminiscent of glochids. (Filaments embed in skin upon handling of the fish, causing subsequent irritation).