Lagoon Triggerfish (Rhinecanthus aculeatus) ムラサメモンガラ
The Lagoon Triggerfish are locally common in shallow reef areas where there is a lot of sand and rocks.
In Australia they are apparently called Hawaiian triggerfish. They do have them in Hawaii but the state fish of Hawaii is the Rectangular Triggerfish. Both are called Humuhumunukunukuapuaa in Hawaiian.