Practice English Speaking&Listening with: How Do Sharks and Rays Use Electricity to Find Hidden Prey? | Deep Look

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We live in a world full of electric fields.

Animals, plants -- even the earth itself -- creates them. But only a handful of creatures

can actually sense them.

Sharks -- also rays and skates... a whole group, animals called elasmobranchs -- can

actually detect electricity

Maybe it's like feeling the presence of someone hiding in a dark room.

A different way of experiencing their world - an extra sense that we don't have.

And for sharks and rays? an extra edge for finding their prey.

The discovery of this exceptional sense dates back three hundred years -- long before the

discovery of electricity -- to a man named Stefano Lorenzini.

Lorenzini was a doctor with a passion for anatomy, who one day found himself dissecting

a ray. ...which is where he noticed the strangest

thing:

tiny pores that dotted the rays skin.

He drew a picture. It shows how each pore led to a tube full of goo, and each tube

ended in a little pouch.

Those little round pouches reminded him of ancient roman flasks, called ampullae, so

thats what he called them.

But when it came to the function of those ampullae, Lorenzini was stumped.

Three hundred years later, were still figuring out exactly how electroreception

works... and a big part of that is studying what makes

these electrical fields in the first place.

Every time a fish opens its mouth to breathe it exposes its mucus membranes to the salty

water, creating a tiny voltage that disappears every time the mouth closes.

At Florida Atlantic University, scientists are actually able to measure this phenomenon.

That repeating on off pattern is an electric frequency, carried easily through salt water.

2 hertz. 2 breaths a second.

Stingrays like these can tune in to that same frequency, like a radio channel.

Take a close look at a stingray, and you can see those pores.

They lead to long canals, that cluster together.

When an electric charge enters a pore, it travels through the highly conductive gel

in the canal to the ampulla... where special cells detect the current and send a message

along nerves to the brain.

Thats how stingrays can spot prey hidden beneath them, even though their eyes are

on top of their heads.

But the ampullae arent just for hunting.

Pores on the rays back also let it know if someones trying to sneak up on it from

behind.

Here, the researchers place diodes on the floor of a tank-- replicating the same electric

frequency as a breathing fish.

They flip the current from circle to circle, and the ray strikes at the active target.

Maybe by studying how this sense works we can learn better ways to coexist with these

ancient creatures. Find new ways to keep them out of our nets and away from our surfers.

Of course none of this really explains what its like to feel electricity.

Is it as simple as flipping a switch on and off?

or as varied and subtle as smell or taste?

A whole spectrum of experiences hidden to the rest of us.

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