The banded butterflyfish (Chaetodon striatus) is a species of marine ray-finned fish, a butterflyfish found in the tropical western Atlantic Ocean from Brazil to Bermuda. Common names include the banded butterflyfish, the butterbun, the butterflyfish, the Portuguese butterfly, the school mistress and the banded mariposa. The name is derived from the dark vertical bands on the fish's body. This, combined with a vertical, black bar through the eye, is an antipredator adaptation, the bands disrupting the body's outlines.