Tennent's Surgeonfish

Found singly, or in schools, over silty waters, around slopes, in lagoons, outer reefs and seaward reefs.

Surgeonfish have a blade like spine in the tail that points outwards when bent, unicorns have two hook-like plates along the tail, these are used for defence and are as sharp as a surgeons scalpel, hence the name "Surgeonfish".
Some species are venomous.