Slender Unicornfish

Found in large schools in areas with strong current over steep outer reef drop-offs of coastal reefs.
Sometimes display a white patch around pectoral fin.

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.