In 1800, the explorerAlexander von Humboldt
witnessed a swarm of electric eelsleap out of the water
to defend themselvesagainst oncoming horses.
Most people thought the story so unusual that Humboldt made it up.
But fish using electricity is more commonthan you might think;
当然 带电的鳗鱼只是其中的一种 在水下
and yes, electric eels are a type of fish. Underwater,
where light is scarce,
electrical signals offer waysto communicate, navigate,
并寻找 或是在极少情况下 电晕猎物
and find—plus, in rare cases, stun—prey.
Nearly 350 species of fishhave specialized anatomical structures
that generateand detect electrical signals.
These fish are divided into two groups,
depending on how muchelectricity they produce.
Scientists call the first groupthe weakly electric fish.
Structures near their tailscalled electric organs
produce up to a volt of electricity,
about two-thirds as much as a AA battery.
How does this work?
The fish’s brain sends a signal
through its nervous system to the electric organ,
which is filled with stacks of hundreds
or thousands of disc-shapedcells called electrocytes. Normally,
electrocytes pump out sodiumand potassium ions
这样 外环境带正电 内部环境带负电
to maintain a positive charge outsideand negative charge inside.
But when the nerve signal arrivesat the electrocyte,
it prompts the ion gates to open.
Positively charged ions flow back in. Now,
one face of the electrocyteis negatively charged outside
and positively charged inside.
But the far sidehas the opposite charge pattern.
These alternating chargescan drive a current,
turning the electrocyteinto a biological battery.
The key to these fish’s powers is
that nerve signals are coordinated
to arrive at each cellat exactly the same time.
That makes the stacks of electrocytes act like thousands of batteries in series.
The tiny charges
from each one add up to an electrical field
that can travel several meters.
Cells called electroreceptorsburied in the skin
allow the fish to constantly sensethis field
and the changes to it caused by the surroundings or other fish.
The Peter’s elephantnose fish,for example,
has an elongated chincalled a schnauzenorgan
that’s riddled in electroreceptors.
That allows it to intercept signalsfrom other fish,
judge distances, detect the shape and sizeof nearby objects,
and even determine whethera buried insect is dead or alive.
But the elephantnoseand other weakly electric fish
don’t produce enough electricityto attack their prey.
That ability belongsto the strongly electric fish,
of which there are onlya handful of species.
The most powerful strongly electricfish is the electric knife fish,
more commonly known as the electric eel.
Three electric organs spanalmost its entire two-meter body.
Like the weakly electric fish,
the electric eel uses its signals to navigate and communicate,
but it reserves its strongestelectric discharges for hunting
利用双相攻击进行试探 之后捕猎食物 首先
using a two-phased attack that susses out and then incapacitates its prey. First,
it emits twoor three strong pulses,
as much as 600 volts.
These stimulate the prey’s muscles,sending it into spasms
and generating wavesthat reveal its hiding place. Then,
a volley of fast,high-voltage discharges
causes even more intensemuscle contractions.
The electric eel can also curl up so
that the electric fields
generated at each endof the electric organ overlap.
The electrical storm eventuallyexhausts and immobilizes the prey,
and the electric eelcan swallow its meal alive.
The other two strongly electric fishare the electric catfish,
which can unleash 350 volts
with an electric organthat occupies most of its torso,
and the electric ray,
with kidney-shaped electric organs on either side of its head
that produce as much as 220 volts.
There is one mystery in the worldof electric fish:
why don’t they electrocute themselves?
It may be that the sizeof strongly electric fish
allows them to withstand their own shocks,
or that the current passes outof their bodies too quickly.
Some scientists think that specialproteins may shield the electric organs,
but the truth is, this is one mystery science still hasn’t illuminated.