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When you look at a goldfish in a bowl, it’s hard to imagine there’s much going on behind
those googly eyes.
But biologists have found lots of amazing things about fish, like how their swim bladders
let them control buoyancy.
Some fish even take their adaptations to the extreme—almost like they have superpowers.
Take the archerfish, which gets its name from the stealthy way it hunts.
It knocks down insects by spitting out a powerful jet of water, and then its gobbles its prey
up.
First, archerfish collect water in their mouths by making tubes with their tongues.
And then they force it out by squeezing their gill covers closed.
Their aim is so precise that they’ve been seen shooting down insects flying at 25 centimeters
per second, and 2 meters above the water’s surface!
Unlike Superman, archerfish aren’t born with their sharpshooting skills.
Instead, young archerfish hunt in small schools and pick it up through observational learning.
A lot of subtle calculations and practice go into each blast.
For one, light rays bend or refract when they change material, like from air to water.
Different materials are different densities, which changes how light passes through them.
So when light reaches an archerfish’s eyes, it doesn’t see exactly where its prey is.
Kind of like how a pencil looks shifted when you stick it halfway into a glass of water.
To solve this, archerfish have to aim their shot carefully to compensate for the light
refracting.
Exactly how they do this math is still a bit of a mystery though.
Archerfish can adjust how powerful their shot is, too.
For example, for a higher target, they open their mouths longer to let in more water,
and release it a little more slowly.
This makes a more forceful jet of water that lasts longer.
Scientists have even found that archerfish seem to have some visual memory!
In one experiment, researchers showed archerfish two faces on a screen mounted above their
tank — one they wanted the fish to target and one they didn’t.
The fish got a food reward every time they shot water at the target face.
They, then showed the fish the non-target face and some new faces, to test whether they’d
keep ignoring the non-target.
Turns out they could!
Even if the faces were in black and white and the picture was cropped.
Now, this next fish has the ability to hunt using a killer tail-flip.
But not in the water—on land .
The mangrove killifish spends most of its time lurking in warm, muddy waters low in
oxygen and fairly high in hydrogen sulfide — the toxic compound that smells like rotten
eggs.
Those aren’t exactly pleasant conditions, but the killifish tolerates them.
But when the water quality gets too poor, especially if there's too much hydrogen sulfide,
the killifish hightails it out of there and spends up to two months living on land.
If most fish leave water, the thin plates of tissue that make up the gills, called gill
lamellae, collapse.
So they can’t exchange oxygen and carbon dioxide with the environment.
Basically, they can’t breathe.
The killifish avoids this by growing more cells that act like scaffolding in between
their lamellae, known as interlamellar cell masses.
This scaffolding reduces the gills’ surface area and exposure to air, so it protects them
from drying out.
And when they hop back in the water, the cell masses waste away and the gills work regularly
again.
Without functioning gills on land, the killifish relies on its skin for breathing.
Their skin is full of special chemoreceptive neuroepithelial cells that detect when the
fish is in air and trigger those changes in the gills and increase blood flow to help
shuttle chemicals around.
The relatively thin epidermis, or outer layer, is also filled with ion-exchanging cells called
ionocytes.
In exclusively water-dwelling fish, they’re only found in the gills.
Ionocytes help maintain the levels of ions in blood so that a fish’s cells can function
properly.
The killifish’s final trick is a super-powerful tail flip that it uses to hunt on land.
It contracts the muscles on the upper side of its body, making it curl into a “C”
shape.
Then, a wave of contractions forces its tail onto the ground and flips it high into the
air, so it can grab insects high above it.
Now, the tuskfish might be the first example of a fish that uses tools — something we’d
usually associate with the great apes or humans.
Several species of tuskfish like to eat juicy clams.
But the edible part is hidden inside a hard shell.
The tuskfish gets its name from its prominent teeth.
It uses these to grip a clam, swim over to a nearby rock, and smash the shell it by throwing
the clam or flicking its head.
In a way, it’s using a rock like an anvil.
While there’s no one definition of tool use in animals, scientists generally agree
that it has something to do with holding or manipulating an object to alter the environment
or attain a goal.
And researchers have noticed that tuskfish will pick a rock that’s big and solid enough
to break a clam shell, and they’ll use a favorite rock again and again.
Some scientists argue that because the fish are grabbing the clam instead of the rock,
they’re not really using tools.
But fish don’t have any grasping limbs to hold onto tools.
So if a fish held a stone in its mouth, the food would probably float away.
So maybe the way we think about tool use needs to consider an animal’s environment and
anatomy a bit more.
But either way, the tuskfish is still showing off some skills that are more complex than
you might expect.
Thanks for watching SciShow, which is produced by Complexly, a group of people who want to
help humans think about the world we live in more deeply.
If you want to learn more about wildlife, you can check out Animal Wonders, another
one of our channels, at youtube.com/animalwondersmontana.
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