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5 Interesting Facts About the Yellow Box Fish

In the wild, the yellow boxfish (known scientifically as Ostracion argus or tuberculatus) lives in coral and rocky reefs in the Indo-Pacific ocean. It is a stunning, if quirky, looking sea creature. Though it may look funny, you wouldn’t want to laugh and upset it if you were a neighbor on the reef! No, it doesn’t have razor-sharp teeth, but, trust me, you don’t want to be besties with a yellow boxfish!

Let’s explore 5 interesting facts about these little yellow spotted fish.

1. They don't stay yellow

Though it’s called the “yellow” boxfish, this denizen of warm seas doesn’t stay bright yellow with rich black spots. As it ages, the spots fade and the color becomes far more muted – more a bluey-gray with yellow patches. The adults have lots of small black spots on the tail but those on the body become less distinct.

The ones you may see in captivity are mostly quite small, but in the wild when fully grown they can achieve a length of between 15 and 18 inches (38 to 46 centimeters).

2. They’ll eat anything they can fit in their little mouths

Unlike many fish, the mouth is tiny but big enough for their omnivorous diet. Though a staple is marine algae that they scrape off the coral, they like a good mix on their menu. Tubeworms, sponges, crustaceans, mollusks, and fish – pretty much anything that can fit between their puckered lips, in fact.

3. Annoying a yellow boxfish is the last thing a fish will do

This one’s the real killer – literally! You don’t want to stress a yellow boxfish in any way. If one becomes alarmed or is threatened, it reacts – by blowing itself up to appear more dangerous and releasing a cloud of ostracitoxin, AKA pahutoxin, a powerful toxin that will kill any fish in the immediate surroundings.

By the way, this unique fish toxin is also lethal to other yellow boxfish (and themselves!) – one reason why they are pretty solitary.

4. Their box shape comes from rigid bony plates

Ostracitoxin is not their only defense system. Their boxlike body is formed from rigid bony plates with holes to allow their mouth, eyes, fins, and tail to operate. Any predator that tries to gobble up a yellow boxfish is going to be severely disappointed. If they don’t get zapped by the poison, and they almost certainly will, they will certainly need a trip to the dentist!

5. You might not want one in your aquarium

It has become popular to keep yellow boxfish in a home saltwater aquarium, but it is not really advisable. For a start, ostracitoxin is a powerful toxin and if your yellow boxfish becomes alarmed you could find all life in your marine aquarium wiped out, including the yellow boxfish… Plus, you can only have one, as out of breeding season they don’t really get along. And guess what happens when they bicker!

They are very easily upset, too. Turning on lights or just walking past could be enough for them to push the ostracitoxin button. So, though the yellow boxfish is a fascinating and attractive animal, it may be best to enjoy it in its natural environment by scuba diving rather than keeping one in captivity. This goes for all the other cute forms of Ostraciidae, such as cofferfish, cowfish, and trunkfish.

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