So as dads, when you go fishing you spend a lot of time thinking about how to get the fish to bite,

but you don't really think about how mechanically the fish do the bite. Does that make any sense?

So today on Smarter Every Day we're gonna go to James Cook University in Australia, and look at how a fish bite takes place in slow motion using a Phantom camera.

You're getting Smarter Every Day.

[ music ]

OK, so, how do fish eat.

So they suck food in, but they have to generate that flow right?

- Oh you talking to me?

- Yes I am, Dr Seymour.

- I'm trying to do two things at once here.

- Alright so we've got a big tank of.. barramundi? Am I saying that right Richard?

- Mm hmm.

- Why do you have a stick and a string here?

- OK this is the stick of death. This is what we use to feed everything with.

So if we hold that over the tank on the water, then you'll be able to focus on that, and you'll be able to see the barramundi come up and [sucking sound].

- OK, got it.

- Here he comes, gone!

[ music ]

(Destin) So how do they actually create that flow inwards?

Are they, like increasing the chest cavity somehow?

- It's the buccal cavity or the mouth.

- Say what?

- The buccal cavity, the mouth. So they'll open their operculum, which are the gill flaps, and they open their mouth wide, and that sucks the water in,

so they're basically producing a vacuum in behind it.

- Buccal cavity.

- Yep.

- When they open their mouth, why does flow not come in the gills?

- Because they open the front first. So you'll have a look, and you'll see it on the high speed, they'll open here, and then that'll go.

And they'll push.. all the water then comes out through the back of the gills.

When you see it on the high speed it will make sense.

- So that's how they.. No way.

- Yeah yeah!

- OK I just had that moment where I figured it out.

- Dong!

- Yeah, so the fish opens his mouth, and he starts flow in, so you have fluid momentum going in, and then he still has momentum going in, and if he doesn't get rid of that somehow it'll push him backwards.

- Yep.

- So when it goes in, after he gets it in his mouth, then he opens his gills and he releases that momentum.

- Yes.

- Shut up! I've been fishing my whole life and I didn't know that.

- And you'll see it on the high speed.

- Really?

- Yeah yeah.

[ music ]

- Alright. Dude that's awesome!

- Do it out here in the light.

Woah!

- So the fish is coming up to the food, and instead of accelerating the whole body to grab the food, fish have a very complex mouth, where they can throw the jaws forward.

So instead of throwing the whole body mass forward, at the last moment you have this very complex mouth with all these bones that just opens up,

so it closes that gap with the prey a lot quicker and a lot easier.

(Destin) OK so he doesn't have to accelerate the mass of his whole body, just the front jaws.

- No just the jaws, and so when the jaws are thrown forward as Jamie explained, it's creating this huge volume and the water has to rush into it.

And then out through the gills. And so you've got this suction feeding.

- That's awesome.

- Suction feeders, ram feeders you can call them.

- That's awesome, really.

- That's good.

- Do all fish do this?

- No. Only a few fish actually suck their prey in. Because these guys don't have teeth as such.

- OK, so teach me the terminology. So there's the buccal cavity..

- Which is the mouth, yep.

- They open the buccal cavity and then they open the gills..

- Or it's the opercular flap, so the gill is behind this flap. So when that's closed off, the only entrance is in through the mouth.

Water sucks in, then you've gotta get rid of it somewhere, so you then open that out and it'll all blow through the back here.

- Because you have to dissipate momentum.

- OK, James Cook University just taught me something about how fish eat, and I'm assuming you..

- Does this work on like your goldfish in your aquarium?

- Yeah, same sort of thing.

- When you put the flakes in, you're gonna see him open his mouth and then open the operculum..

- Mm hmm.

- And dissipate that over the pectoral fin. Yeah. You're getting Smarter Every Day.

I'm Destin, have a good one.

Have you caught anything yet?

- No sir.

- Do you enjoy it anyway?

- Yes sir.

- Do you wish we had an audio book to listen to?

- Yes sir.

- Which one?

- Captain Nemo.

- Pull, pull! Pull son! Pull it!

- I got a fish!

- There you go!

- Keep reeling it in!

- Alright, OK.

-It still has a worm in his mouth. He Does! Let's let him eat that worm.

(Destin) So this is what happens. He opens his mouth right here, the water gets pulled into his mouth and then he opens his gills after that and he shoots the water out of that. Does that make sense?

- Yes sir.

- Hold on tight, don't be scared. You ready? Now slowly let him back in the water.

There you go.

Alright, so that's how fish eat. If you are interested in supporting more fishing trips and more episodes of Smarter Every Day, you can support us by going to audible.com/smarter and getting a free audio book.

Does that sound good to you?

- Yes sir.

- What audio book do you recommend?

- Umm.. 20,000 Leagues Under the Sea.

- That's right. Where do we listen to that?

- In the car.

- That's right. So if you're interested in helping Smarter Every Day, go to audible.com/smarter, download a free audio book, you can get 20,000 Leagues Under the Sea, and you can help Smarter Every Day, it'd be a real good thing.

Anyway, thank you very much. You want to say thank you?

- Thank you!

- Anyway I'm Destin..

- And bye!

- And bye. I'm Destin, you're getting Smarter Every Day, have a good one.