The blacknosed butterflyfish or barberfish (Johnrandallia nigrirostris) (from the Spanish names, El Barbero or Mariposa Barbero, "the barber" or "butterfly barber"), is a species of fish in the family Chaetodontidae, the butterfly fishes.

It is found in the East Pacific, specifically around the Galápagos Islands and in the Sea of Cortez, and it sometimes acts as a cleaner fish.

[5] It is the only member of the genus Johnrandallia, named after the ichthyologist John E. Randall, but in the past it was commonly placed in Chaetodon.

It is marked with black bands along the base of its dorsal fin, and on its snout and forehead.

It will remain at cleaning stations where infested fishes come to have various crustaceans and other ectoparasites removed.