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Most of us don’t really give fish scales a second thought, but for some fish, the scales of others can make for a tasty snack.

Hosted by: Olivia Gordon

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[♪ INTRO].

You're probably pretty familiar with the Hollywood image of piranhas. The water starts churning, and suddenly an unlucky animal is nothing but a bare skeleton.

And yeah, piranhas can definitely do some damage, but most of them aren't these ferocious monsters. They eat lots of different things, and many piranhas — along with other tropical fish — have evolved one pretty creative feeding strategy: they steal scales off of other fish. The act of eating another fish's scales is known as lepidophagy.

Part of the reason this is a thing at all is that scales can actually be a pretty good food source— they're high in protein and important minerals, and they're easy to come by. If you're a fish, anyway. No one even has to die in the process!

Fish can just do a drive-by and scrape off some scales to go. That said, most scale-eating species don't only eat scales. For the most part, they just go in for a nibble when competition for resources gets stiff.

They eat scales to supplement their regular diet. And they're not too discriminating. If they need a bite to eat, they'll steal scales off just about anyone–even fish from their same species!

As for how they go about it, they have a few different methods. Some fish use stealth to snag scales, or speed to grab 'n' go. Some bite scales off cleanly, while others scrape or chew them loose.

No matter what the fish's method of choice is, a special diet calls for special tools. And some fish have adaptations precisely for eating scales. For example, typical piranhas have wide jaws that give them excellent leverage for deshingling the side of a passing fish.

And certain African cichlids are so ready for scale-snacking that their mouths even grow at an angle. These fish can be left- or right-mouthed, and they'll typically come at a fish from their dominant side and use their mouths to twist off scales. Meanwhile, the wimple piranha has opted for a more… straightforward tactic.

It approaches a fish from the side, then uses its blunt face to basically T-bone its victim at full speed with its mouth open. The collision knocks scales loose, and the piranha then catches them as they sink. Seems like overkill, but whatever works, I guess.

However they do it, these fish are able to get the nutrition they need through a uniquely renewable resource. Because the best part is, scales grow back! It's probably a little unpleasant to get T-boned by a piranha, but in general, the fish that get their scales stolen or smashed off just bounce back fine.

Turns out, losing scales and regrowing them is a natural part of fish life. So as weird of a tactic as it is, lepidophagy probably evolved as a strategy for when food sources are low. Scales are plentiful, and this way, small predatory fish that can't find enough smaller prey can always graze on larger fish that are too big to take down.

It's a niche these fish can really thrive in, and it makes them unique among even their closest relatives. So while it may be a fish-eat-fish world most of the time, some tropical predators have found a more peaceful way to coexist. Thanks for watching this episode of SciShow!

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