Horseshoe Leatherjacket

Found singly, pairs, or in large schools, in shallow, too much deeper waters, over off-shore reefs.
Juveniles found sheltering around jetties and piers.
Eastern Indian Ocean - Australia

Filefish can alter their colour and pattern to match their surrounds and so deter predators.
Although closely related to the Triggerfish, their "trigger spine" cannot be locked into place.