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in tropical seas flying fish leap out of
the water gliding for up to 200 meters
using wing-like fins before dipping back
into the sea in the indo-pacific a
hunting sailfish can reach speeds of 110
km/h that's 11 times faster than Olympic
swimming champion Michael Phelps it can
then stick up its spiny dorsal fin like
a brake grinding to a dead halt mid swim
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
fish can be split into two main groups
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
eels lie at one extreme of this group
known as Anguilla form swimmers their
entire bodies undulate to generate a
wave-like motion
compared to Anguilla form fish species
like salmon and trout known as sub
Karanga forms use about two-thirds of
their body mass to generate motion while
Karanga form swimmers such as mackerel
only use about 1/3 typically the less of
its mass a fish uses to generate motion
the more streamlined its shape
at the other end of the spectrum from
eels are ostracized pcs like box fish
and fun of form swimmers like tuna in
these fish the tails also known as
caudal fins do the work
a tunas tail is attached by tendons to
multiple muscles in its body it powers
the body like an engine forcefully
catapulting the bullet lake fish to
speeds up to 69 km/h 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 that have to navigate complex
habitats bottom-dwelling fishes like
rays fall into this group using their
huge pectoral fins they can lift
themselves swiftly off the seafloor that
conveniently allows them to inhabit
shallow seas without being buffeted
about by waves
similarly shallow water flatfish use
their entire bodies as one big fin to
hoist themselves up off the sand ocean
sunfish lack tails so they move around
slowly by beating their wing-like median
fins instead similar movements are
shared by many reef species like the
Queen angelfish surgeonfish
and wrasse 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 but if you look closer
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
hand fish look like they have legs but
really these limb like structures are
fins modified to help them amble across
the seafloor for fish motion underpins
survival so it's become a huge
evolutionary driver of
the widespread features of fish have
been maintained across tens of thousands
of fish species not to mention other
ocean dwelling animals like penguins
dolphins sea slugs and squids and that's
precisely because they've proven so
successful love science check out this
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