Appearance
The yellow boxfish reaches a maximum length of 45 centimetres (18 in). As the name suggests, it is box-shaped. Boxfish are also known for their armored and rigid body called a carapace, covering the head and body. There are openings in the carapace for the mouth, nostrils, gill opening, anus, caudal peduncle, and fins. The rigid body shape provided by the carapace surrounding the body was thought to help the fish stabilize while swimming as the water flows over the body. It was thought to keep them on course in high-flow, turbulent conditions. However, the carapace was found to have little effect on stability. In fact, it was destabilizing, as it increased drag. Instead, the caudal fin is the stabilizing force and acts as a rudder.
