The Yellow Boxfish (Ostracion cubicus) is a well-loved fish for its cute looks and bright appealing colouration. A small fish, reaching a maximum size of about 45cm, it’s body is comprised of a hard external skin, which is formed by many fused scales, creating a sort of ‘armour’ to protect against predators. The name ‘box-fish’ is quite clearly derived from this anatomy!
To provide further protection, the body also has spines on the body-ridges. It doesn’t stop there though… It has long been known that many animals use colour as a warning for predators to stay away. This is called aposematism. A classic example of this can be seen in snakes which have brightly coloured bands, indicating that they are venomous, or butterflies with bright spots, warning that they are distasteful, or even poisonous.
Well, the yellow boxfishes bright pigment is a perfect example of aposematism. They have a toxin that covers their entire skin. When they are threatened, they can eject it in a cloud through specialised skin cells and swim quickly away. The toxin acts to burst red blood cells in the victim, which will eventually die, because it cannot obtain enough oxygen to survive. Cute but deadly!
Finally, although small, this little fish plays an important role on the reef. Spending most of its day foraging and grazing on algae, it makes up an important part of the fish on the reef which keep our coral healthy by preventing algae overgrowth. Why don’t you head out for a snorkel and see if you can spot one of these critters?