Name: Why are fish fish-shaped? - Lauren Sallan
Uploaded: 2018-04-20T06:46:39.000Z
Duration: 4 min 57 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

gliding for up to 200 meters  using wing-like fins,

a hunting sailfish can reach speeds  of 110 kilometers per hour.

That's 11 times faster than Olympic  swimming champion Michael Phelps.

It can then stick up its spiny dorsal fin  like a brake,

Each of these physical feats is made  possible by a fish's form,

which in most species is a smooth,  elongated body, fins, and a tail.

These features are shared across thousands of fish species,

each introducing its own variations on the theme to survive in unique habitats.

What makes these features so commonplace in fish,

and what does it reveal about the more  than 33,000 fish species that inhabit earth's rivers,  lakes, and seas?

according to the type  of motion they favor.

The first is body  and caudal fin driven motion,

and most fish species, about 85%,  fall into this group.

Here, the body and tail  are the primary propelling forces,

with fins mainly playing  a stabilizing and steering role.

This configuration suits  many open-water species,

which need speed, thrust and control for constant, efficient swimming.

their entire bodies undulate to generate  a wave-like motion.

species like salmon and trout,  known as subcarangiforms,

use about two-thirds of their body mass to generate motion,

while carangiform swimmers,  such as mackerel,

Typically, the less of its mass a fish  uses to generate motion,

At the other end of the spectrum from eels are ostraciiform species like boxfish,

In these fish, the tails,  also known as caudal fins, do the work.

A tuna's tail is attached by tendons  to multiple muscles in its body.

forcefully catapulting the bullet-like fish

The second major fish group relies  on median and paired fin motion,

meaning they're propelled through the  water predominantly by their fins.

Fins allow fine-tuned movement  at slow speeds,

so this propulsion  is typically found in fish

Bottom-dwelling fishes, like rays, fall into this group;

using their huge pectoral fins, they can lift themselves swiftly off the sea floor.

That conveniently allows them  to inhabit shallow seas

Similarly, shallow-water flatfish  use their entire bodies

as one big fin to hoist  themselves up off the sand.

so they move around slowly by beating  their wing-like median fins instead.

Similar movements are shared  by many reef species,

Their focus on fins has taken  the demand off their bodies,

many of which have consequently  evolved into unusual and inventive shapes.

There are fishes within both groups  that seem to be outliers.

you'll notice that these  common traits are disguised.

Seahorses, for instance, don't appear  fish-shaped in any conventional way,

yet they use their flexible  dorsal fins as makeshift tails.

A pufferfish may occasionally  look more like a lethal balloon,

but if it needs to swim rapidly, it'll retract its spines.

but really these limb-like  structures are fins,

modified to help them  amble across the sea floor.

so it's become a huge evolutionary  driver of form.

The widespread features of fish  have been maintained across tens of thousands of fish species,

not to mention other  ocean-dwelling animals,

And that's precisely because  they've proven so successful.