3 Things Fish Shouldn’t Be Able to Do

3 Things Fish Shouldn’t Be Able to Do


[ INTRO ] 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. [ OUTRO ]

14 thoughts on “3 Things Fish Shouldn’t Be Able to Do

  1. Sometimes it's easy to things going on inside their heads . It depends on the size of tank the smaller the take the less sentient fish seems. Maybe it's stercrazy or less brain activity

  2. How do they do those calculations, you ask? Uh… have you never estimated the soon-to-be location of an object in motion? If you play flight combat games, you’re doing this a lot. Animals do this all the time.

    Humans underestimate other animals SO much. Actually, it’s more that humans overestimate their uniqueness and specialness a LOT. We have very few truly unique features. One of those is formalized language.

  3. As for the tusk fish, perhaps tool usage could be delineated LIGNUISTICALLY: the fish "uses the rock…"! Whether it uses the rock as a hammer OR an anvil, doesn't seem to make that much difference…to me. This is a well-made series of presentations. Thank you.

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