Tilapia are multi-jawed monsters

Tilapia is a kind of small fish native to lakes and rivers in Africa and the Middle East. You’re probably familiar with it as a cheap farmed fish that’s thin and easy to cook. They’re convenient to farm because they’re omnivores and thus easy to feed – unlike, say, carnivorous salmon. In fact, humans have been farming tilapia since Ancient Egypt.

From the outside (or a packaged fillet), tilapia looks like a pretty typical fish. But don’t let that fool you: tilapia are actually horror movie monsters.

Imagine you’re a tiny fish who’s just been caught by a fearsome tilapia. Your energy is spent, and you know the end is near. In your final moments, as you resign yourself to your fate, the tilapia opens its jaws…

…and then it opens a second set of jaws in its throat.

Chiclids, the family of fish that includes tilapia, have evolved a second set of jaws in their throat, called the “pharyngeal jaws”. These help the fish pull captured prey deeper into their throat, and may be part of why they can eat so many different foods. It’s a trait they share with moray eels and the Xenomorph from the Alien series, though the creator of the latter said the design wasn’t inspired by any particular animal.

Not every chiclid has two sets of teeth. Goldfish, for instance, have the decency to only have teeth on their pharyngeal jaw, not their regular “oral” jaw. But tilapia are fully toothed on both jaws.

Pictured: one of a tilapia’s pharyngeal jaws

Humans have also made an unusual use of our pharynx – at least as far as vertebrates are concerned. The same structure that develops into an extra set of jaws in tilapia instead develops into the hyoid bone in humans and other mammals. The hyoid is notably the only bone in your body not directly connected to any other, and it helps brace your tongue and give it a wider range of motion. It’s present in fossil mammals from 165 million years ago, and may have been evolutionarily useful for baby mammals to swallow milk.

Our distant vertebrate ancestors may also have had teeth in their throats, though they didn’t have jaws in their throat – or even in their mouths. Instead they were jawless fish, like today’s hagfish and lampreys, which have immobile teeth.

There are two main hypotheses about how vertebrate teeth evolved. One is that they evolved “outside-in”, where scales on early fish skin migrated into their mouths. The other is “inside-out”, where hard scales inside the throats of jawless fish migrated forward.

The natural world is full of creatures that seem taken from a horror movie, like parasitic wasps or anglerfish. But we come across tilapia much more often, and they seem so normal. They’re not particularly threatening to us, of course. To a tilapia, maybe a giant two-legged land creature that can flex its tongue around would be just as horrifying – and we do actually eat them fairly often.

So maybe from a cultural perspective, Steven Spielberg was correct in picking a great white shark for his famous 1975 seaside horror film. But if you’re actually afraid of Jaws, then tilapia are twice as scary. Scientifically.

Sources:
https://communities.springernature.com/posts/the-cichlid-oral-and-pharyngeal-jaws-are-evolutionarily-and-genetically-coupled
https://www.pbs.org/wgbh/nova/article/microdocodon-gracilis/
https://doi.org/10.1002%2Fwdev.63