Acanthurus nigrofuscus, also known as the lavender tang, brown tang, or spot-cheeked surgeonfish, is a tang from the Indo-Pacific and Hawaii. It commonly makes its way into the aquarium trade. It grows to 21 cm in length. Recently, a huge bacterium discovered in its intestine, Epulopiscium fishelsoni, has been found to grow as large as 600 by 80 μm, a little smaller than a printed hyphen, which controls the pH of its host's gut, thereby influencing its host's ability to digest food and absorb nutrients.