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Imagine you're walking along a rocky beach when, out of the blue, you see this forearm-length fish charge straight into the shallows. We're talking water that's less than 10 centimeters deep, where a fish that big could easily end up beached. After a moment, the animal kind of flops its way back into deeper water, and then it does it all over again.

This is exactly what fish researchers saw off the coast of Saudi Arabia in May 2018, so they started recording. And it turns out it wasn't just any old fish; it was a titan triggerfish, a voracious and smart marine hunter, and what they had witnessed was the animal flexing its brainpower to snag crabs from the shore.

Venturing into very shallow water might seem like a poor choice for any fish, but that triggerfish was no fool. It had spotted a tasty treat just out of its reach, so it figured out how to reach it, which might sound pretty clever, because it is. And it's right in line with what ichthyologists know about triggerfishes.

For example, in the 1970s, German biologist Hans Fricke tested the problem-solving abilities of three yellow-spotted triggerfish he decided to call Odonus, Flip, and Berta. He showed Odonus a delicious sea urchin, and then put it in a glass dish under an opaque lid. And it didn't take the fish long to suss out the new materials and solve the problem to reach the treat.

So Fricke stepped up the difficulty. This time, the urchin went under a mesh container that had to be lifted or tipped. Then, he let Flip and Berta have a go at it. Once again, the fish got their rewards, but each solved the problem slightly differently. And they remembered what they learned. When he moved the set up to a new area and re-tried the test, they both reached the urchin much faster. To Fricke, that indicated they were smart enough to generalize their knowledge to new scenarios.

On other dives, Fricke observed what appeared to be evidence for social learning in a different triggerfish species. In other words, the fish seem to learn from one another. He came across five different individuals in a small area that all ate urchins in a totally unique way. Instead of flipping them over with jets of water like most triggerfish, they first bit off the spines, then hauled the urchins up towards the surface so they could nibble at the soft undersides as the denuded animals fell. It seemed unlikely that each of them figured this out separately, so Fricke concluded it was probably one fish's idea, and then the other four watched and copied the behavior.

Now, the researchers aren't sure if the beaching triggerfish they saw figured out its clever hunting tactic all by itself or learned it from another fish, but no one has reported anything like it in any triggerfish species. And, either way, it shows that the titan has some pretty impressive smarts, and that may be because it's got a big brain.

See, the part of the fish brain called the telencephalon is relatively large in triggerfishes, and studies have linked larger telencephalons with better problem-solving abilities, at least in some species. Researchers have even suggested that, if we really want to understand how cognitive abilities evolve, we should study fish instead of the "smarter" animals like primates. That's because fish are much more varied in their abilities, environments, and social interactions than primates are. So the clever tricks of triggerfish aren't just cool to watch. They could also help teach us a lot about how intelligence evolves.

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