HOW DOES BOX-SHAPED FISH SWIM?

HOW DOES THE BOX SHAPED FISHES SWIM?

When you imagine a fish, you probably imagine something smooth and sleek that slices right through the water. But there is a handful of fish that just aren't sleek at all… like the boxfish, which is essentially a colorful box with fins. It might seem like exactly the worst shape for fish… but it actually comes with some surprising perks. In general, fish need to be able to cut through the water without a lot of resistance, or drag. That way, they don’t waste too much energy swimming, and they’re quick enough to escape predators. But the boxfish has a rigid skeleton in the shape of a box, which, as you might expect, creates a lot of drag. The odd thing is, despite their shape, boxfish aren’t these lumbering, awkward things. They’re actually pretty agile and good at dodging predators. And that caught scientists’ attention.

 In 2002, a group of researchers used 3D-printed models of these fish to explore how water flowed around them. At first, they focused on little vortices forming off the ends of the fish’s pointed corners. Vortices naturally resist changes in direction, so the researchers thought this was like a self-correcting mechanism that helped the fish stay stable. Which might seem like a pretty clever trick of evolution. And they weren’t the only ones intrigued by the idea that a creature shaped like a box could be both stable and nimble. Engineers at Mercedes-Benz even created a concept car modeled after the boxfish in the 1990s.

 The problem was, the researchers had missed one key detail. If those vortices were having a significant impact on the fish, they would make it too stable to turn quickly and dodge predators. And that clearly wasn’t the case. Observations of boxfish showed that they had no problems making quick maneuvers or darting into their reefs for protection. And in a later study, scientists realized that the vortices weren’t actually that strong compared to the other forces pushing the fish around. In fact, far from being exceptionally stable, these fish proved to be extremely unstable. 

They wobble and topple over really easily. But the scientists realized that, of all things, that’s what makes them so good at navigating It requires a little extra work when they're just swimming from place to place — they have to use their fins to stay upright in the moving water. But when they need to make a quick turn, all it takes is a little push of the fin in the right direction, and their body topples over, letting them turn on a dime. So if a predator shows up, this clumsy-looking fish can be headed in the opposite direction — with almost no effort — before the sleek, faster fish can even turn around. It’s still not a quick swimmer — the boxfish’s drag is at least double that of most other fish, so basically what you’d expect of a swimming box. But it doesn’t really need to swim far; it mostly just moseys around the reef. So the maneuverability is worth the trade-off.

 Sadly, it probably lost its chance to inspire the next Mercedes-Benz, since a high-drag vehicle that easily tips over isn’t the car of the future... but some engineers are still interested in it. Designers of underwater robots or jet planes that need maximum maneuverability might be able to learn something from this fish. So it may still inspire our future technology in spite of itself.