Oneknife Unicornfish

Found singly or in large schools, patrolling steadily over reefs, in search of plankton, close to drop-offs, reef edges, and slopes, over outer lagoons 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.