flying fish leap out of the water,

飛魚會躍出水面

gliding for up to 200 meters using wing-like fins,

用翅膀似的鰭滑翔近 200 公尺

before dipping back into the sea.

然後才又落下海洋中

In the Indo-Pacific,

在印度洋到太平洋的海域中

a hunting sailfish can reach speeds of 110 kilometers per hour.

一種獵殺型旗魚的速度可以達到時速 110 公里

That's 11 times faster than Olympic swimming champion Michael Phelps.

這個速度比奧運會游泳冠軍 Michael‧Phelps 快上 11 倍

It can then stick up its spiny dorsal fin like a brake,

然後牠能伸出刺狀背鰭來煞車

grinding to a dead halt, mid-swim.

從游泳狀態急煞，變成完全靜止

Each of these physical feats is made possible by a fish's form,

所有的身體技藝都是因為有魚的體型才能辦到

which in most species is a smooth, elongated body, fins, and a tail.

大多數魚種外型是光滑、細長的身體，還有魚鰭跟尾巴

These features are shared across thousands of fish species,

數千種魚類都有這樣的特徵

each introducing its own variations on the theme to survive in unique habitats.

而為了在獨特的棲地生存，各魚種又發展出自己的變化

What makes these features so commonplace in fish,

是什麼原因讓魚類都有這些特徵

and what does it reveal about the more than 33,000 fish species that inhabit earth's rivers, lakes, and seas?

對於地球上河流、湖泊還有海洋中，超過 33,000 種魚類來說，這些特徵又透露了什麼訊息呢？

Fish can be split into two main groups,

魚類可以分成兩大類

according to the type of motion they favor.

根據牠們偏好的移動方式

The first is body and caudal fin driven motion,

第一種是由身體與尾鰭驅動的移動方式

and most fish species, about 85%, fall into this group.

而且大多數魚種，約略 85%，都屬於這一類

Here, the body and tail are the primary propelling forces,

身體與尾巴是牠們主要的推進力

with fins mainly playing a stabilizing and steering role.

而鰭主要扮演的是穩定與控制方向的角色

This configuration suits many open-water species,

這種身體結構適合許多開放水域的魚種

which need speed, thrust and control for constant, efficient swimming.

那裡的魚需要速度、突進能力跟控制力，以滿足經常且有效率的游泳需求

Eels lie at one extreme of this group.

鰻魚就是這一大類的極端魚種

Known as anguilliform swimmers,

牠是鰻行式泳者的代表

their entire bodies undulate to generate a wave-like motion.

牠們整個身體呈現波浪狀起伏，產生水波狀的動作

Compared to anguilliform fish,

相較於鰻行式游泳的魚種

species like salmon and trout, known as subcarangiforms,

像鮭魚、鱒魚那類魚種，則是子鱒行式的游泳方法

use about two-thirds of their body mass to generate motion,

利用身體 3 分之 2 的質量來移動

while carangiform swimmers, such as mackerel,

而鱒行式的泳者，像鯖魚

only use about a third.

只用了 3 分之 1

Typically, the less of its mass a fish uses to generate motion,

通常魚在移動時，用到的身體質量越少

the more streamlined its shape.

牠的身體越呈流線型

At the other end of the spectrum from eels are ostraciiform species like boxfish,

跟鰻魚迥然不同的是甲殼式的魚種，像粒突箱魨

and thunniform swimmers like tuna.

還有鮪行式的泳者，像鮪魚

In these fish, the tails, also known as caudal fins, do the work.

這些魚種的尾巴，也就是尾鰭，負責推進

A tuna's tail is attached by tendons to multiple muscles in its body.

鮪魚的尾巴透過肌腱與身體的多處肌肉連結

It powers the body like an engine,

這使牠的身體像引擎一樣充滿力量

forcefully catapulting the bullet-like fish

能把像子彈一樣的魚用力彈射出去

to speeds up to 69 kilometers per hour.

速度可以達到時速 69 公里

The second major fish group relies on median and paired fin motion,

第二大類的魚種則是仰賴奇鰭和偶鰭來移動

meaning they're propelled through the water predominantly by their fins.

意思是牠們主要是透過鰭在水中推進

Fins allow fine-tuned movement at slow speeds,

鰭可以讓牠們精準地慢速移動

so this propulsion is typically found in fish

所以通常會用這種方式推進的魚

that have to navigate complex habitats.

通常需要在複雜的棲地中航行

Bottom-dwelling fishes, like rays, fall into this group;

底棲魚類，像是魟魚就屬於這一大類

using their huge pectoral fins, they can lift themselves swiftly off the sea floor.

利用牠們巨大的胸鰭，牠們可以把自己迅速地從海底抬升

That conveniently allows them to inhabit shallow seas

這方便牠們居住在淺海地區

without being buffeted about by waves.

而不會被海浪衝擊

Similarly, shallow-water flatfish use their entire bodies

一樣道理，淺水比目魚會把牠們的整個身體

as one big fin to hoist themselves up off the sand.

當做一個大魚鰭，讓自己能從沙地升起

Ocean sunfish lack tails,

翻車魚沒有尾巴

so they move around slowly by beating their wing-like median fins instead.

所以牠們只能透過拍打牠們那像翅膀一樣的奇鰭來緩慢移動

Similar movements are shared by many reef species,

許多珊瑚礁魚種也有相似的動作

like the queen angelfish,

像額斑刺蝶魚 (女王神仙)

surgeonfish,

擬刺尾鯛 (藍倒吊)

and wrasse.

還有隆頭魚科

Their focus on fins has taken the demand off their bodies,

他們都聚焦在鰭上頭，所以不需要注意體型發展

many of which have consequently evolved into unusual and inventive shapes.

結果許多魚種都演化出不尋常、有創意的外型

There are fishes within both groups that seem to be outliers.

這兩大類魚種中，都有一些看起來不屬於該類別的魚種

But if you look closer,

但如果你仔細看

you'll notice that these common traits are disguised.

你會注意到這些共通特徵只是被偽裝起來了

Seahorses, for instance, don't appear fish-shaped in any conventional way,

以海馬為例，牠們的外型不是正常的魚類體型

yet they use their flexible dorsal fins as makeshift tails.

但牠們會用牠們靈活的背鰭作為臨時的尾巴

A pufferfish may occasionally look more like a lethal balloon,

河豚偶爾看起來像顆致命的氣求

but if it needs to swim rapidly, it'll retract its spines.

但如果牠要快速游動，牠會把尖刺收回來

Handfish look like they have legs,

臂鉤躄魚科看起來好像有腳

but really these limb-like structures are fins,

但這些看起來像四肢的構造其實是鰭

modified to help them amble across the sea floor.

改造成能幫助牠們在海底漫步的形狀

For fish, motion underpins survival,

對魚來說，移動是生存的根本

so it's become a huge evolutionary driver of form.

所以移動方式變成驅使牠們外形演進的重要因子

The widespread features of fish have been maintained across tens of thousands of fish species,

魚類最普遍的特徵被保留在成千上萬的魚種中

not to mention other ocean-dwelling animals,

更不用說其他居住在海洋中的動物

like penguins,

像企鵝

dolphins,

海豚

sea slugs,

海參

and squids.

跟烏賊

And that's precisely because they've proven so successful.

那更明確的指出，因為牠們證明了這樣的演化很成功