Nearly all butterfly fish ar fairly small, generally up to 22 centimetres in length. However, the lined butterflyfish grows to 30 cm.Their shape is always a deep-bodied disc, and thin from side to side, with a single dorsal fin. The family name derives from the Greek words for hair and tooth as they have rows of brush-like teeth found in their tiny protruding mouths.
Most adult butterflyfish live as heterosexual couples that swim in tandem around a private patch of reef they have staked a claim over. The majority are coral eaters and stay on coral reefs but a few types form large groups that hang around together in swarms. At dusk they find shelter in a reef recess and become inactive. As they settle in for the night, daytime colours pale and markings change.
Like real butterflies, the fishy versions display impressive body decoration: masks, false eyespots, stripes, bands and checks in a myriad of colours. Many butterflyfish are confused with angelfish, and there are similarities, but angels can be spotted by noting the sharp spine that sits across the lower edge of their gills. Another case of mistaken identity is the Moorish Idol, which is neither a buuterflyfish nor an angel, but the sole representative of the family Zanclidae.