Name: 【TED-Ed】為什麼魚會長得那副魚樣？(Why are fish fish-shaped? - Lauren Sallan)
Uploaded: 2018-11-05T21:01:10.000Z
Duration: 4 min 57 s

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

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,

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,

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？

according to the type  of motion they favor.

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

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

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,

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

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

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

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

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,

so this propulsion  is typically found in fish

所以通常會用這種方式推進的魚

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

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

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

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

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

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

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

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