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Sometimes when a fish 
is reeled up to the surface

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it will appear inflated,

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with its eyes bulging out of their sockets

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and its stomach 
projecting out of its mouth,

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as if its been blown up like a balloon.

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This type of bodily damage,
caused by rapid changes in pressure,

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is called barotrauma.

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Under the sea, pressure increases
by 14.7 pounds per square inch

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for every 33 foot increase in depth.

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So, take the yelloweye rockfish,

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which can live as deep as 1800 feet,

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where there's over 800 pounds of pressure
on every square inch.

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That's equivalent to the weight of a
polar bear balancing on a quarter.

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Now, Boyle's gas law states

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that the volume of a gas
is inversely related to pressure.

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So, any air-filled spaces,
like a rockfish's swim bladder,

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or human lungs,

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will compress as they descend deeper

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and expand as they ascend.

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After a fish bites a fisherman's hook
and is quickly reeled up to the surface,

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the air in its swim bladder 
begins to expand.

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Its rapid expansion actually forces
the fish's stomach out of its mouth,

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while the increased internal pressure
pushes its eyes out of their sockets,

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a condition called exophthalmia.

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Sometimes rockfish eyes will even have
a crystallized appearance

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from corneal emphysemas,

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little gas bubbles 
that build up inside the cornea.

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Thankfully, a scuba diver doesn't have
a closed swim bladder to worry about.

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A diver can regulate pressure in her lungs
by breathing out as she ascends,

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but must be wary of other laws of physics
that are at play under the sea.

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Henry's law states that the amount 
of a gas that dissolves in a liquid

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is proportional to its partial pressure.

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The air a diver breathes is 78% nitrogen.

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At a higher pressure under the sea,

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the nitrogen from the air in a scuba tank

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diffuses into a diver's tissues in greater
concentrations than it would on land.

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If the diver ascends too quickly,

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this built up nitrogen 
can come out of solution

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and form microbubbles in her tissues,
blood and joints,

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causing decompression sickness,
aka the bends.

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This is similar to the fizz 
of carbon dioxide coming out of your soda.

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Gas comes out of solution 
when the pressure's released.

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But for a diver, the bubbles
cause severe pain

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and sometimes even death.

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Divers avoid falling victim to the bends
by rising slowly

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and taking breaks along the way,
called decompression stops,

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so the gas has time to diffuse 
back out of their tissues

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and to be released through their breath.

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Just as a diver needs decompression,

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for a fish to recover, 
it needs recompression,

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which can be accomplished 
by putting it back in the sea.

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But that doesn't mean that fish
should just be tossed overboard.

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An inflated body will float

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and get scooped up by a hungry sea lion
or pecked at by seagulls.

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There's a common myth

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that piercing its stomach 
with a needle will let air escape,

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allowing the fish to swim 
back down on its own.

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But that is one balloon
that shouldn't be popped.

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To return a fish properly to its habitat,

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fisherman can use 
a descending device instead

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to lower it on a fishing line
and release it at the right depth.

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As it heads home and recompression
reduces gas volume,

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its eyes can return 
to their sockets and heal,

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and its stomach can move back into place.

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This fish will live to see another day,

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once more free to swim, eat, reproduce
and replenish the population.