A Box Shaped Nuke - Can Boxfish wipe out an aquarium?

In my earlier life, I was set on becoming an ichthyologist, but it just wasn’t meant to be. However, one of the families of fish I took great interest in during my time of study was Ostraciidae commonly known as boxfish. 

I have always had a soft spot for the order Tetraodontiformes and kept many of the species throughout the years, but boxfish has always been a favourite.

I was advised to keep in mind the same thing whenever I bought a new boxfish at a local fish store.

1. When they are stressed, they produce a deadly toxin that kills everything in the aquarium.
2. Toxicity excretes from their bodies into the aquarium as the ejected protective mucus sheds if they die, again killing everything in the aquarium.
3. There's always a tale of caution about someone's cousin's uncle's brother-in-law's best friend who had a boxfish that wiped out everything from fish to hermit crabs.

Ostracion cubicus one of the most common boxfish found in the aquatic trade.  

In my lifetime I have personally kept 18 boxfish and have imported 1000’s of them with no issues. This does not mean the claims of aquarium wipeouts are not true. However, researching endlessly on the Ostraciidae family and its Pahutoxin I came to the conclusion that it’s not a myth but more of a stretched truth. 

Yes, boxfish have the ability to wipe out their fellow fish mates but to wipe out everything in the aquarium including invertebrates from the initial excretion just would not be possible.

The Boxfish toxin Pahutoxin is haemolytic and works by rupturing red blood cells. When the boxfish excretes its toxin to deter a predator, the damage is done by the toxin attacking the red blood cells in the gills. The predator now turned victim can no longer exchange oxygen and carbon dioxide, resulting in death.

Boxfish have a small tolerance to the toxin, and the vastness of the ocean thins excretions immensely when expelled in the wild. In an aquarium, the toxin is merely cycled without a destination, eventually killing all the fish. Due to its limited tolerance, the boxfish would not be immune and would succumb to the same fate as the other aquarium fish.

The scenario of boxfish poisoning themselves, I believe is the basis of the myth that dead boxfish can cause wipeouts. The myth goes on an assumed fact that the Pahutoxin is part of the boxfishes mucus layer created by a glycoprotein called mucin, which is then ejected into the water upon its death.

Yes, the protective mucus does discharge itself when the boxfish dies, but the toxin is not present in the protective mucus. The toxin has to be actively synthesised by the fishes mucous gland, and that synthesis can only happen when the boxfish is alive.

I mentioned earlier that it was not possible for Pahutoxin to completely wipe out an aquarium, invertebrates and all. This is because if the toxin was released into an aquarium and went unnoticed, invertebrates would survive the excretion.

The reason being Pahutoxin would not affect creatures like corals or an anemone is because they have no circular system or blood, they extract oxygen directly from the water through their outer cells. 

Invertebrates such as crabs would also be safe from the toxin as they have no red blood cells. Instead, their blood is made up of a copper-based substance called hemocyanin.

Triactis producta would not feel the effects of the toxin due to its copper-based blood.

Tell-tale sign the boxfish has released Pahutoxin mucus into the aquarium is soap-like foam collecting on the surface of the aquarium and your protein skimmer going nuts. 

This is due to the mucus being hydrophobic and positively charged, making it visible to the naked eye. It will almost appear like colourless washing up liquid floating around in the water.  

Do not rely on absorbing filter materials like activated carbon to remove the toxic mucus from the aquarium, as they cannot absorb it due to the hydrophobic tail structure of the toxin.

So there you have it, is the boxfish a nuke like the myth says? No, defiantly not, but it could still potentially cause havoc in the aquarium. The release of the toxin is a deterrent and is triggered in extreme circumstances.  

The likelihood of your aquarium fish being wiped out by a boxfish is slim, and if the event of the boxfish discharging its toxin does occur, swift intervention and large water changes can avoid a total disaster. 

I will say this, keep boxfish with peaceful inhabitants, they are hardy fish once settled and are capable of handling themselves. Keeping boxfish with peaceful tankmates you are lowering the risk of toxin discharge and after all, why rock the boat?