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In 1800, the explorer Alexander von Humboldt witnessed a swarm of electric eels
1800年，探险家亚历山大·冯·洪堡看到了一群电鳗
leap out of the water to defend themselves against oncoming horses.
为了避免被过河的马踩伤而跳出水面的瞬间。
Most people thought the story so unusual that Humboldt made it up.
大多数人认为这个离奇的故事是洪堡编造出来的。
But fish using electricity is more common than you might think; and yes, electric eels are a type of fish.
但鱼类使用电的现象比你想象中更为普遍；而且，电鳗确实是一种鱼。
Underwater, where light is scarce,
在光线微弱的水底，
electrical signals offer ways to communicate, navigate, and find -- plus, in rare cases, stun -- prey.
电信号可以被用来交流、导航和定位--偶尔甚至会用来攻击--猎物。
Nearly 350 species of fish have specialized anatomical structures that generate and detect electrical signals.
大概有350种鱼拥有能产生及探测电信号的能力的特殊的身体结构。
These fish are divided into two groups, depending on how much electricity they produce.
依据它们产生电信号的量，这些鱼可以被分成两组。
Scientists call the first group the weakly electric fish.
科学界称第一组为弱电鱼类。
Structures near their tails called electric organs produce up to a volt of electricity,
它们尾部有被称为电能器官的结构，能产生一伏特的电力，
about two-thirds as much as a AA battery. How does this work?
相当于一个AA电池三分之二的电量。其中的原理是什么呢？
The fish's brain sends a signal through its nervous system to the electric organ,
这类鱼的大脑通过神经系统给电能器官送出信号。
which is filled with stacks of hundreds or thousands of disc-shaped cells called electrocytes.
电能器官充满了成百上千个被称作发电细胞的盘状细胞。
Normally, electrocytes pump out sodium and potassium ions to maintain a positive charge outside and negative charge inside.
通常，发电细胞会释放钠离子和钾离子来保证細胞外部呈正电，内部呈负电。
But when the nerve signal arrives at the electrocyte, it prompts the ion gates to open.
但当神经系统信号到达发电细胞时，离子通道会被打开。
Positively charged ions flow back in.
呈正电的离子开始涌回细胞。
Now, one face of the electrocyte is negatively charged outside and positively charged inside.
现在，发电细胞的外部呈负电，内部呈正电。
But the far side has the opposite charge pattern.
而其另一边的正负电情况却相反。
These alternating charges can drive a current, turning the electrocyte into a biological battery.
这些互相交替的正负结构能够形成电流，让发电细胞变成生物电池。
The key to these fish's powers is that nerve signals are coordinated to arrive at each cell at exactly the same time.
这些鱼具有这个能力的关键是它们神经系统的协调性，信号能在最恰当的时刻被发出。
That makes the stacks of electrocytes act like thousands of batteries in series.
这会使堆叠的电解质变成上千个串联的电池组。
The tiny charges from each one add up to an electrical field that can travel several meters.
每个电池释放出的少量电量积累成一个可以延伸到几米外的电磁场。
Cells called electroreceptors buried in the skin allow the fish to constantly sense this field
鱼的皮肤下有能让它察觉磁场的电感应器细胞，
and the changes to it caused by the surroundings or other fish.
因此它能感受到周围环境或其它鱼类造成的磁场的变化。
The Peter's elephantnose fish, for example,
拿弯颌象鼻鱼来举例，
has an elongated chin called a schnauzenorgan that's riddled in electroreceptors.
它们的下巴叫做schnauzenorgan，很长，且长满电感应器。
That allows it to intercept signals from other fish, judge distances,
这会让这类鱼能够和其它鱼交换信号，计算距离，
detect the shape and size of nearby objects, and even determine whether a buried insect is dead or alive.
估计附近物体的形状和大小，甚至能知道一个埋起来的虫子是死是活。
But the elephantnose and other weakly electric fish don't produce enough electricity to attack their prey.
但是象鼻鱼和其它弱电鱼类无法产生足够的电量去攻击猎物。
That ability belongs to the strongly electric fish, of which there are only a handful of species.
使用电捕食是强电鱼类的专长，只有少数几种鱼属于这一类。
The most powerful strongly electric fish is the electric knife fish, more commonly known as the electric eel.
最强有力的带电鱼是电刀鱼，俗称电鳗。
Three electric organs span almost its entire two-meter body.
它们两米长的身子基本被三个带电器官占满。
Like the weakly electric fish, the electric eel uses its signals to navigate and communicate,
和弱电鱼一样，电鳗使用信号来导航和交流，
but it reserves its strongest electric discharges for hunting using a two-phased attack
但是它最强的电流是留给捕食用的，它们的进攻分为两步，
that susses out and then incapacitates its prey.
定位猎物以及使猎物瘫痪。
First, it emits two or three strong pulses, as much as 600 volts.
首先，它会释放出两至三道强有力的，高达600伏特的电流。
These stimulate the prey's muscles, sending it into spasms and generating waves that reveal its hiding place.
这些电波会刺激猎物的肌肉导致其痉挛，还会产生显示猎物的藏匿地点的反射电波。
Then, a volley of fast, high-voltage discharges causes even more intense muscle contractions.
接着，电鳗会释放一系列快速的高压电流，导致更严重的肌肉收缩。
The electric eel can also curl up so that the electric fields generated at each end of the electric organ overlap.
电鳗还会在放电时弯曲身体，使身体两端产生的电场重叠和加强。
The electrical storm eventually exhausts and immobilizes the prey, and the electric eel can swallow its meal alive.
电流风暴最终使猎物筋疲力尽，无法动弹，电鳗就可以把猎物生吞下去。
The other two strongly electric fish are the electric catfish,
另外两个强大的发电鱼，其中之一是发电鲶鱼
which can unleash 350 volts with an electric organ that occupies most of its torso,
它可以利用占据它大部分躯干的发电器官释放350伏特的电流，
and the electric ray, with kidney-shaped electric organs on either side of its head that produce as much as 220 volts.
另一种则是鳐鱼，可以在它头的两侧、形状像肾的发电器官中，产生220伏特的电流。
There is one mystery in the world of electric fish: why don't they electrocute themselves?
在发电鱼的世界中有一个谜团：为什么它们不会把自己电死？
It may be that the size of strongly electric fish allows them to withstand their own shocks,
这可能是因为强电鱼的大小使他们能够承受自身发出的电流，
or that the current passes out of their bodies too quickly.
或者是电流会很快地通过它们的身体。
Some scientists think that special proteins may shield the electric organs,
一些科学家认为，有些特殊的蛋白质保护了发电器官，
but the truth is, this is one mystery science still hasn't illuminated.
但是事实上，这是一个至今仍未解释清楚的神秘科学。
