In tropical seas, flying fish leap out of the water,
在热带海域，小飞鱼跃出水面，
gliding for up to 200 meters using wing-like fins, before dipping back into the sea.
用翅膀般的鱼鳍，能最远滑行200米，然后再钻入海面。
In the Indo-Pacific, a hunting sailfish can reach speeds of 110 kilometers per hour.
在印度洋，正在捕食的旗鱼速度可高达110千米每小时。
That's 11 times faster than Olympic swimming champion Michael Phelps.
这可比奥运游泳冠军迈克尔·菲利普斯的速度还要快11倍。
It can then stick up its spiny dorsal fin like a brake, grinding to a dead halt, mid-swim.
然后它能竖起带刺的背鳍，像刹车一样，在游泳时慢慢停下来。
Each of these physical feats is made possible by a fish's form,
下面这些身体特征大致形成了鱼类的形状，
which in most species is a smooth, elongated body, fins, and a tail.
在大多数物种中，鱼类拥有光滑细长的躯干、鱼鳍和鱼尾。
These features are shared across thousands of fish species,
成千上万的鱼类都拥有这些特征，
each introducing its own variations on the theme to survive in unique habitats.
而每一中鱼为了在不同的栖息地生存产生了进化差异。
What makes these features so commonplace in fish,
为什么对于鱼类来说这些特征如此常见，
and what does it reveal about the more than 33,000 fish species that inhabit earth's rivers, lakes, and seas?
对于栖息在地球的河流、湖泊以及海洋的超过33000种鱼类，这又揭示了什么？
Fish can be split into two main groups, according to the type of motion they favor.
鱼类可以大致分为两种，按照它们偏好的运动类型划分。
The first is body and caudal fin driven motion, and most fish species, about 85%, fall into this group.
第一种是躯干/尾鳍驱动运动，大多数鱼类，大约85%的鱼类属于这一类型。
Here, the body and tail are the primary propelling forces, with fins mainly playing a stabilizing and steering role.
在这一类中，躯干和鱼尾提供主要的推动力，鱼鳍主要起到保持平衡和调节方向的作用。
This configuration suits many open-water species, which need speed, thrust and control for constant, efficient swimming.
大多数生活在开阔水域的鱼类符合这一构造，在持续高效的游动中，它们需要这一构造保持速度、推力和控制力。
Eels lie at one extreme of this group.
鳗鱼属于这一类型的极端物种。
Known as anguilliform swimmers, their entire bodies undulate to generate a wave-like motion.
作为著名的鳗行式游泳健将，它们的整个身体来回摆动形成波状运动。
Compared to anguilliform fish, species like salmon and trout, known as subcarangiforms,
对比鳗行式鱼类，类似鲑鱼和鳟鱼的鱼类，被称为亚鲹行式，
use about two-thirds of their body mass to generate motion, while carangiform swimmers, such as mackerel, only use about a third.
使用三分之二的体重产生运动，而类似马鲛鱼的鲹行式游泳健将，只使用身体的三分之一。
Typically, the less of its mass a fish uses to generate motion, the more streamlined its shape.
一般来说，越少使用体重产生运动的鱼类，它的形状越靠近流线型。
At the other end of the spectrum from eels are ostraciiform species like boxfish, and thunniform swimmers like tuna.
与鳗行式相反的另一个极端种类是摆动尾鳍推进，比如箱鲀，以及鲔行式游泳健将，比如金枪鱼。

In these fish, the tails, also known as caudal fins, do the work.
这些鱼类依靠尾部，通常称作尾鳍，进行运动。
A tuna's tail is attached by tendons to multiple muscles in its body.
金枪鱼的尾鳍通过筋腱连接着身体多处肌肉。
It powers the body like an engine, forcefully catapulting the bullet-like fish to speeds up to 69 kilometers per hour.
它像发动机一样向身体提供动力，强有力地像子弹一样推进，速度可高达69千米每小时。
The second major fish group relies on median and paired fin motion,
另一种主要的鱼类类型主要依靠中鳍对鳍推进，
meaning they're propelled through the water predominantly by their fins.
意思是它们主要通过鱼鳍在水中推进。
Fins allow fine-tuned movement at slow speeds,
鱼鳍保证低速的微调运动，
so this propulsion is typically found in fish that have to navigate complex habitats.
所以，采用这种推进方式的鱼类，它们通常需要探索复杂的生活环境。
Bottom-dwelling fishes, like rays, fall into this group;
底栖鱼类，像蝠鲼，属于这一类型；
using their huge pectoral fins, they can lift themselves swiftly off the sea floor.
使用巨大的胸鳍，它们能将自己迅速从海底浮起来。
That conveniently allows them to inhabit shallow seas without being buffeted about by waves.
这让它们能够轻而易举地在浅海生存，而不会被海浪击翻。
Similarly, shallow-water flatfish use their entire bodies as one big fin to hoist themselves up off the sand.
同样地，浅海比目鱼使用它们整个身体作为一整个鳍把自己从海沙上抬起来。
Ocean sunfish lack tails, so they move around slowly by beating their wing-like median fins instead.
翻车鱼的尾部比较小，所以它们通过拍击翅膀状的胸鳍缓慢移动。
Similar movements are shared by many reef species, like the queen angelfish, surgeonfish, and wrasse.
很多栖息在礁石的鱼类也使用这种运动方式，像是额斑刺蝶鱼、刺尾鱼以及隆头鱼。
Their focus on fins has taken the demand off their bodies,
它们的鱼鳍起到主要作用，从而减少对躯干的需求，
many of which have consequently evolved into unusual and inventive shapes.
因此它们中的很多种类进化出了罕见的、创造性的形状。
There are fishes within both groups that seem to be outliers.
有些鱼介于两个种类之间，感觉又有点不伦不类的。
But if you look closer, you'll notice that these common traits are disguised.
但如果你仔细观察，你会发现普遍的鱼类特性仍然存在。
Seahorses, for instance, don't appear fish-shaped in any conventional way,
比如说海马，不具备任何传统意义上的鱼类的形状，
yet they use their flexible dorsal fins as makeshift tails.
但是它们能利用它们灵活的背鳍代替尾部。
A pufferfish may occasionally look more like a lethal balloon, but if it needs to swim rapidly, it'll retract its spines.
河豚经常看上去更像是一个致命的气球，但如果它需要快速游走，它会缩回脊柱。
Handfish look like they have legs,
斑点长手鱼看上去像有腿，
but really these limb-like structures are fins, modified to help them amble across the sea floor.
但其实它们像腿一样的结构是鱼鳍，经过改良之后，鱼鳍会帮助它们在海底缓慢爬行。
For fish, motion underpins survival, so it's become a huge evolutionary driver of form.
对鱼类来说，运动是生存的基础，所以也成为了鱼形进化的驱动力。
The widespread features of fish have been maintained across tens of thousands of fish species,
鱼类的普遍特征，在成千上万的鱼类得以维持，
not to mention other ocean-dwelling animals, like penguins, dolphins, sea slugs, and squids.
更不用说其他海栖类动物，像企鹅、海豚、海参以及章鱼。
And that's precisely because they've proven so successful.
而这恰恰是因为这些特征已被证明是如此成功。