More than a little box!
The yellow boxfish may be small, but it packs a punch! This little fish is the type species for the genus Ostracion – this means it is the “base” species for the boxfish family and is permanently the first association with the genus. Ostracion means “little box” and describes its cube-like body. Its species name, cubicum, refers to its boxy shape.
Where do they come from?
The yellow boxfish is a common resident in sheltered coastal and offshore coral reefs throughout the Indian Ocean, Pacific Ocean, and southeastern Atlantic Ocean. They eat benthic invertebrates that live on the bottom of the seafloor, like sponges, worms, and crustaceans.
Defence mechanisms
The yellow boxfish secretes a neurotoxin called ostracitoxin in its mucus when stressed, which is deadly to predatory marine fish as it breaks down their red blood cells. This toxic mucus contains Vibrio parahaemolyticus, a bacterium that may play a role in the fish’s defence. Plus, the yellow boxfish’s vibrant yellow and black spots are like a built-in "Don't mess with me!" sign. Juveniles rock even brighter patterns – basically saying, "I’m cute, but don't get any ideas!" to scare off predators before they get too close.
How are they built?
Though the boxfish's rigid, scale-covered body was once thought to stabilise it in turbulent waters, studies show that this shell increases drag, destabilising the fish. Instead, it relies on its caudal (tail) fin as a main stabiliser and rudder. The yellow boxfish is a smart swimmer, using the dorsal, anal, and pectoral fins to manoeuvre. In low speeds, the pectoral and anal fins are more active, and in higher speeds, the dorsal and caudal fins take over. A prominent protrusion (or keel) near the caudal peduncle further helps in stability and control.
How do they move?
Do not let its boxy shape fool you: The yellow boxfish is a very agile swimmer. Its cuboid body creates twisting patterns in the water, which helps it to zoom through coral reefs and avoid predators. The pectoral and anal fins at the leading edge of the body allow it to take sharp corners. This fish’s hydrodynamic shape has already inspired the designs for underwater vehicles of the future! Who knew fish could be trendsetters?
Yellow boxfish can make some noise!
Using muscles in its swim bladder, the yellow boxfish produces hums and clicks. While its cousin, O. meleagris, can also make sounds, the yellow boxfish is known for louder, more frequent clicks. These sounds are believed to help them communicate with each other or warn predators to stay away.
Spotted boxfish versus yellow boxfish
The yellow boxfish can easily be mistaken for the spotted boxfish, Ostracion meleagris. Both have similar boxy-shaped bodies with a spotted pattern, but the yellow boxfish is a bright yellow colour marked with dark spots, whereas the spotted boxfish is darker with white spots.
Fun Fact: Yellow boxfish inspires engineering! The yellow boxfish has inspired designs from Mercedes-Benz's Bionic car to low-drag bridge structures and even more manoeuvrable airships—all thanks to its unique shape and agility!