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Why are fish fish-shaped? - Lauren Sallan
https://youtu.be/Cd-artSbpXc
In tropical seas, flying fish leap out of the water, gliding for up to 200 meters,
before dipping back into the sea. In the Indo-Pacific, a hunting sailfish swims up to
110 kilometers per hour. These feats are made possible by a fish’s form—which in
most species is a smooth, long body, fins, and a tail. Lauren Sallan explains why these
features are so common, and what it reveals about fish.
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1.- _______ is an anguilliform swimmer.
AA tuna
BA swordfish
CAn eel
DA salmon
2.- What is one benefit of median and paired fin swimming?
AGreater speed
BFine-tuned movement
CMore efficient constant swimming
DWalking along the bottom
3.- Where are most body and caudal fin swimmers usually found?
AIn open water
BIn complex environments
COn the bottom of the sea floor
DOn reefs
4.- What does a sailfish use its spiny dorsal fin for?

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APropulsion
BLeaping out of the water
CLifting off the bottom of the sea floor
DBraking
5.- What powers swimming in thunniform fishes?
AThe caudal fin
BThe median fins
CThe pectoral fins
DBody undulations
6.- This lesson focuses on the role of fins and body movements in swimming. What
other features of fish shapes might help with movement through water?
7.- This lesson mentions that penguins, dolphins, sea slugs, and squids have all
independently evolved fish-like shapes for moving through water. Where else do we
see these features?
8.- Why are the fins and movements involved with swimming mostly concentrated on
the back half of fishes?
“Fish” is the common term for a wide variety of vertebrates without land-dwelling
ancestors. “Fishes” (the plural of fish when referring to multiple species) therefore
includes everything from clownfish to sharks to jawless lampreys, no matter how
distantly related. Vertebrates with fingers, including humans, penguins, and whales,
are called tetrapods. All tetrapods are descended from a “fish” ancestor with fins
—rather than finger-containing flippers—which existed over 350 million years ago.
Because of this ancestry, some fishes are more closely related to humans than they
are to other fish groups.
Our closest living fishy relatives are the “living fossil” lungfishes and coelacanths.
These are the lobe-finned fishes (Sarcopterygii), which have the equivalent of our
arm bones in their pectoral fins. These specific bones are missing in the 33,000
species of ray-finned fishes(Actinopterygii), such as salmon and tuna. However,
ray-fins share other bones like ours in our skulls, bodies, and jaws. These shared
features mean that ray-finned fishes and lobe-finned fishes (including tetrapods)

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also descend from a common ancestor with these bones. Therefore, they belong to
a larger group (clade) called bony fishes (Osteichthyes).
Sharks and rays, known as cartilaginous fishes (Chondrichthyes), have lost all bones
in their skeletons, and are only distantly related to us and all other fishes. Yet, the
cartilage jaws of sharks show that they also descend from a jawed common
ancestor. Sharks and bony fishes belong to a group known as jawed
fishes (Gnathostomes), which distinguishes them from jawless fishes, like lamprey
and hagfish.
Despite hundreds of millions of years of separate evolution, the vast majority of
“fishes” from all groups, except land-living tetrapods, have retained their essential,
streamlined shapes and fins. They have also evolved the same kinds of aquatic
forms, including reef fishes and eels, throughout the 500-million-year history of
vertebrates.
The study of the function of animal shape is called functional morphology, or
biomechanics. Research on fish biomechanics involves many different scientific
tools. Scientists can observe live fishes in flow tanks, which are special tanks that
use jets to move water over an animal swimming in place; this creates a water “wind
tunnel.” They use light, lasers, and particles to see how fishes can use their fins
and bodies to move water for propulsion or braking. Researchers also produce and
study from models of fishes. These models range from simple shapes to 3D
computer renderings, which can include CT scans or real, working robots.
The results of biomechanics studies are used to understand the diversity of fishes
and their interactions in ecosystems. By comparing fossils with living forms,
scientists have also been able to reconstruct the abilities of fishes that have been
extinct for millions of years. Discoveries from fish biomechanics have been applied
to the designs of everything from aircraft to submarines to swimsuits. Indeed,
many engineering breakthroughs are made possible by scientific research on living
shapes. Evolution is a process that selects the best available solutions to common
problems. By understanding how these solutions work, we can use them to our
advantage.
DISCUSS
To understand fish shapes, scientists uses principles from physics and engineering.
How can studying fishes help with designs for the future? In theory, can we build a
better fish?