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You might think that fish ride the undercurrents with all their buds to avoid the hungry mouths of predators - safety in numbers, right? But, it turns out, there’s more to consider when asking why fish swim in schools.

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When it comes to synchronized swimming, nothing is more impressive than schooling fish.  Hundreds or even thousands of them will choreograph their movements without a singular leader telling them what to do. And you might think you know why: because schooling helps fish avoid being eaten.  But that’s only part of the story.

To really understand schooling, you don’t just have to think about biology you also have to dive deep into psychology and into physics. There are technically two types of fish crowds: schools and shoals.  Schools are highly coordinated groups that seem to move like a single organism, while shoals are looser, less organized gatherings that can be huge, like the size of a city. Still, despite their differences, both of these benefit fish beyond reducing the odds they will disappear into a hungry mouth.  You see, studies find that communal fish have lower metabolic rates than loners.

That means they use less energy going about their day to day lives, so they’re healthier and have more stamina.  In fact, researchers have found that fish living in groups have higher growth rates, and their bodies are in better condition than isolated fish. And that is where psychology and physics come into play.  Scientists have long suspected that shoals and schools protect fish from predators because it’s helpful to have a lot of eyes scanning for danger.  Plus, it can be difficult for predators to target individual fishes in a blurry mass of fins and tails.  But it isn’t just scientists who know there’s safety in numbers. The fish know it too.  In 2016, researchers found that fish living in groups were calmer and less stressed than solo fish.  And less stress means less energy spent stressing, so there’s more available for things like growth and reproduction.  But stress reduction isn’t the only way schools help fish save energy.

There’s also fluid dynamics. When fish swim in schools, their endurance levels are two to six times greater than when they’re traveling alone.  So for many years, it was thought that it’s easier for fish to swim in a school for the same reason it’s easier for birds to fly in a V formation.  Essentially, the lead bird creates changes in air currents, so the other birds face less wind resistance. But to create the same effect, fish would have to form specific patterns and maintain certain distances from each other like birds do.  And, I don’t know if you’ve ever, like, watched fish before, but they don’t do that.  Problem is, it’s really hard to measure flow patterns and energy use in wild fish.

So scientists couldn’t figure out what actually goes on with them. Then, for a 2020 study, scientists came up with a solution: robots. The researchers made robots that look like carp, they put them in a tank, and measured their swimming patterns more than 10,000 times.  Based on this, they made predictions about how schooling fish optimize their speed and energy use.

Then, they tested those predictions on free-swimming goldfish.  They found that by beating their tails out of sync with the fishes in front of them when they’re close, and matching their tail beats when farther away, these animals could capitalize on the small vortexes of moving water made by other fish.  So, they save energy by constantly adjusting the rhythm of their tail beats and by chilling out with a bunch of their best buds.  And that means fish always benefit from schooling, even if there isn’t a predator in sight.  Thanks for asking! If you find yourself wondering about things like this a lot, I bet you’d enjoy other Quick Question episodes, like Can Soda Save a Dying Fish? So maybe watch that one next!

And you might consider clicking the subscribe button and ringing the notification bell. That way, you catch every episode we make.  [♪ OUTRO].