This Venomous Fish Has a Sharp Spike Coming From Behind Its Eye

StoneFish
Several types of fish such as this stone fish have spikes that they can erect on their heads. Linda Balon / Flickr

It has taken scientists surprisingly long to find a spike that some venomous fish have coming out of their faces. Now that they know it's there, however, they still don't know exactly what it's for.

Members of the "Scorpaeniformes" group of fish are some of the most insidious venomous animals in the world. The stonefish look like rocks, so you may never see them if you're looking for a snack. But that also means you might not see them in your path, and if you accidentally step on one, you'll get a foot full of painful spines injecting you with venom.

According to new research published in the journal Copeia, scientists have recently discovered that this group of fish has a particularly bizarre physical feature. Right under their eye, they have a mobile "saber," a sharp bone that can pop upwards.

Stonefish are fairly well-studied and are known to be venomous. That means that they inject venom into their enemies to stun or kill them, as opposed to poisonous animals that are dangerous to touch and eat.

Presumably, the fish could use the eye-spike, or lachrymal saber, in defense. Anyone trying to eat a fish like that might get a spine in their throat and cough it up. But according to Smithsonian, the researcher who discovered the saber hasn't been able to trigger a stone fish to erect it. He says he's only seen it protruding in pictures of mail-cheeked fish being eaten.

The spike could be for sexual display — showing off to potential mates. One species even has a glow-in-the-dark lacrymal saber. However, both sexes have the trait, making that theory less likely.

Importantly, this discovery could lead to a better understanding of how the fish family tree is laid out. It's possible that fish with the saber are more closely related than those without, but only DNA sequencing can confirm or deny that theory.