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What you're looking at
isn't some weird x-ray.
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It's actually a baby yellow tang surgeonfish
at two months old.
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And you thought your childhood
was awkward.
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But here is the same fish as an adult,
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a beautiful inhabitant of the
Indian and Pacific Oceans' coral reefs
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and one of the most popular captive fish
for salt water aquariums.
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Of the 27,000 known fish species,
over a quarter live on coral reefs
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that make up less than 1%
of the Earth's surface.
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But prior to settling down in this
diverse tropical environment,
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baby coral reef fish face the difficult
process of growing up on their own,
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undergoing drastic changes,
and the journey of a lifetime
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before they find that reef to call home.
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The life cycle for most of these fish
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begins when their parents spew
sperm and eggs into the water column.
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This can happen daily, seasonally,
or yearly depending on the species,
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generally following lunar or
seasonal tidal patterns.
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Left to their fate, the fertilized eggs
drift with the currents,
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and millions of baby larvae
hatch into the world.
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When they first emerge,
the larvae are tiny and vulnerable.
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Some don't even have gills yet
and must absorb oxygen
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directly from the water
through their tissue-thin skin.
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They may float in the water column
anywhere from minutes to months,
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sometimes drifting thousands of miles
across vast oceans,
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far from the reefs where they were born.
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Along the way, they must
successfully avoid predators,
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obtain food, and ride the right currents
to find their way to a suitable adult habitat,
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which might as well be a needle
in vast haystack of ocean.
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So, how did they accomplish this feat?
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Until recently, marine biologists thought of
larval fish as largely passive drifters,
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dispersed by ocean currents
to distant locales.
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But in the last 20 years,
new research has suggested
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that larvae may not be
as helpless as they seem,
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and are capable of taking
their fate in their own fins
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to maximize their chances of survival.
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The larvae of many species are
unexpectedly strong swimmers,
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and can move vertically in the water column
to place themselves in different water masses
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and preferentially ride certain currents.
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These fish may be choosing the best routes
to their eventual homes.
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When searching for these homes,
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evidence suggests that larvae navigate
via a complex suite of sensory systems,
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detecting both sound and smell.
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Odor, in particular, allows larvae to
distinguish between different environments,
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even adjacent reefs,
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helping guide them toward their
preferred adult habitats.
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Many will head for far-flung locales
miles away from their birth place.
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But some will use smell
and other sensory cues
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to navigate back to the reefs
where they were born,
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even if they remain in the
larval stage for months.
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So, what happens when larvae
do find a suitable coral reef?
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Do they risk it all in one jump
from the water column,
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hoping to land in exactly
the right spot to settle down
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and metamorphose into adults?
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Not exactly.
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Instead, larvae appear to have
more of a bungee system.
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Larvae will drop down in the water column
to check out a reef below.
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If conditions aren't right,
they can jump back up
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into higher water masses and ride on,
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chancing that the next reef
they find will be a better fit.
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But this is the point
where our knowledge ends.
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We don't know the geographic movements
of individual larva for most species.
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Nor do we know which exact environmental
cues and behaviors they use
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to navigate to the reefs
they will call home.
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But we do know that these tiny trekkers
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are more than the fragile
and helpless creatures
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science once believed them to be.
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The secret lives of baby fish
remain largely mysterious to us,
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unknown adventures waiting to be told.