Rough Triggerfish

Found in large schools, over shallow coastal waters, as well as deep, steep outer reef slopes.
Circumglobal

Triggerfish have a hard spine Dorsal Fin that can be locked.
When sleeping this spine is used to wedge them into place in a crevasse and so deter predators from pulling them out of their bed!
The spine is also held erect as a warning to other fish to stay away.
Several large Titans blow shallow depressions in the sand for nesting and if approached will raise this spine as a warning, if ignored they may charge, even divers! especially the Titan Triggerfish who will take a tasty bite. Beware.