They're long and slithery, and they're not very colorful.
他们（体态）修长并且（皮肤）黏滑，但不是非常色彩斑斓。
But they do have a strange beauty of their own.
但是它们有其独特的魅力。
Their sinuous, nocturnal movements through the water are mesmerizing to watch.
它们夜间蜿蜒从水中游过，看起来让人着迷。
And though they may resemble underwater snakes, eels are, in fact, a very interesting type of fish.
即使他们像水下的蛇，但事实上鳗鱼是一种非常有趣的鱼。
There are several things about eels that make them unique besides their elongated shape and limbless bodies.
除了它们修长无四肢的身体，有几个特征让鳗鱼独具一格。
For one thing, eels have the ability to breathe through their skin.
第一个，鳗鱼可以透过它们的皮肤来呼吸。
Some can even leave the water and move over land for short periods.
有些鳗鱼甚至可以离开水在陆地上存活一小段时间。
And, unlike most migratory fish, such as salmon,
不像大多数迁徙性鱼类，比如鲑鱼，
which spawn in fresh water but live their adult lives in salt water,
它们在淡水中产卵，但是成年时期生活在盐水中，
eels of the genus Anguilla migrate in the opposite direction, spawning and breeding in oceans and seas,
安圭拉属的鳗鱼以相反的方向迁徙，它们在海洋中产卵和繁殖，
while spending most of their intervening time in fresh water.
而大部分的时间生活在淡水中。
If we were to take one such fresh water eel and follow its life story,
如果我们跟随一条淡水鳗鱼来了解它的生活故事，
it would be born in the middle of the North Atlantic Ocean, about a thousand miles east of Bermuda.
那就是它出生于北太西洋中，游到百慕达的东部约1000英里的地方。
This area, called the Sargasso Sea, forms the western part of a subtropical gyre, a giant whirlpool in the middle of the ocean.
这个区域，称为马尾藻海，也就是亚热带环流的西半部，在海洋中有一个巨大的漩涡。
Our eel, let's call it Eli, would begin as one of ten to twenty million tiny eggs, carried by a female eel,
我们称这条鳗鱼为伊莱，当雌鳗鱼带着这个千万分之一的小卵时，它的生命由此开始，
hatching into a transparent leaf-shaped thing that looks nothing like an adult eel.
然后孵化成透明且叶子形状的东西，这看起来一点也不像鳗鱼。
Eli starts to drift in ocean currents,
伊莱随着海潮漂流，
predominantly the Gulf Stream towards either Europe or North America, depending on its particular species.
顺着墨西哥湾流的方向，依种类的不同游向欧洲或北美洲。
Upon reaching the coast, Eli is about two inches long,
当到达岸边时，伊莱大约有两英寸长了，
looking more eely but still transparent, known at this stage as a glass eel.
这时形状看起来比较像鳗鱼，但仍然是透明的身体，这个时期，大家称它为玻璃鳗。
But within a couple of days in fresh water,
但生活在淡水的几天后，
Eli's skin becomes pigmented a brownish-black, now looking more like that of an adult eel.
伊莱的皮肤变成无光泽的黑褐色，这时看起来比较像鳗鱼。
You might notice that we haven't mentioned anything about Eli's gender yet.
你也许注意到有一件事我们还没提到，那就是伊莱的性别。
That's because this is only determined once an eel enters fresh water, though nobody is sure exactly how that happens.
这是因为性别是在鳗鱼进入淡水时的情况而定，没有人能确切知道真实的状况。

Most of the eels that stay in the estuaries and brackish water become males,
大部分的鳗鱼会停留在出海口，带有微咸的水域让鳗鱼变成雄性，
while those that go upstream become females, growing up to two to three times bigger than their future mates.
而那些往河流上游游去的鳗鱼则变成雌性，雌鳗鱼会长到比未来的配偶还要大上两至三倍。
In this case, it turns out that Eli was actually short for Elaine.
在这个情况下，伊莱变成是伊莱恩。
As a female eel, Elaine will be quite solitary for most of her life in the stream, eating whatever falls in the water:
作为一条雌鳗鱼，伊莱恩在大部分时间独来独往地生活于淡水河中，它吃任何掉入水中的东西：
grasshoppers, crickets, small fish, insect larvae, frogs, baby birds, almost anything she can get her mouth around.
蚱蜢，蟋蟀，小鱼，幼虫，青蛙，雏鸟，任何她嘴巴能轻易取得的东西。
And she will grow quite big, up to four feet long and weighing as much as thirteen pounds.
她可以长得相当大，直到四英尺长，重量达十三磅。
We don't know exactly how fresh water eels know when it's time to return to the ocean, but something calls to them.
我们无法确切得知在淡水中生活的鳗鱼是如何知道要在何时回到海洋的，一定有某种力量在召唤它们。
And their fall migration is one of the largest unseen migrations on the planet.
它们的秋季迁移是地球上前所未见的大迁移之一。
As Elaine leaves fresh water for the ocean, she undergoes a shocking metamorphosis.
当伊莱恩离开淡水游往海洋，她经历一个令人惊讶的蜕变。
Her eyes enlarge by about ten times, her skin gets thicker, and her fins get larger.
她的眼睛变大十倍，皮肤变得比较厚，鳍也变得更大。
These are most likely adaptations for their upcoming ocean travel,
这是为了适应它将在海洋中的旅程所做的变化，
and Elaine seamlessly makes the transition from fresh to salt water, which would be toxic for most other fish.
从淡水到咸水的过程中，伊莱恩悄悄地做了转变，但咸水对大部分的鱼类来说是有害的。
Once Elaine leaves the mouth of the fresh water streams, she will disappear completely from human view.
一旦伊莱恩离开淡水河口，她就完全消失在人类的视线中。
No one has witnessed, or been able to follow, an adult eel on their migration, nor do we know how deep they spawn.
没有人目睹或跟踪一条成人鳗鱼的迁移，我们不知它们在多深的海域产卵。
But it's assumed that they can follow some signs that they can detect,
假设它们能够侦测信号，然后随着这些信号游回海洋，
such as a thermal barrier between ocean currents or a salinity front,
比如洋流之间的热障或是盐度，
in order to return to the same area of the ocean where they were born.
这是为了回到它们出生的海洋。
Because we don't even know exactly what happens during an eel's migration,
我们不是很了解在鳗鱼迁移当中发生了什么事，
we can only imagine what the actual breeding looks like.
我们只能想象繁殖的情况。
But the common hypothesis is that Elaine and thousands, or hundreds of thousands, of other eels gather in large,
一般的假设是：伊莱恩和数千个或成千上万的其他鳗鱼聚集成一大群，
intertwined masses and release their eggs and sperm in a giant orgy known as panmixia.
互相纠缠在一起，尽情地进行随机交配，然后产出卵子和精子。
A couple of days after the eggs are laid, they hatch, and the cycle begins again.
卵被生下的几天后，它们孵化了，然后又再次循环这个过程。
And because we've never seen the adult eels returning up the fresh water rivers,
因为我们从没目睹过成年鳗鱼游回淡水河的情形，
we must assume that, having completed their long and roundabout journey,
所以我们必需如此假设：在完成长途且曲折的旅程后，
these amazing and mysterious creatures finally die there, in the same place where they were born.
这些神奇且神秘的生物，最后消逝在它们出生的海洋中。
Goodbye, Elaine! It was a pleasure knowing you.
再见，伊莱恩！很高兴认识你。