Why are fish fish-shaped? - Lauren Sallan

譯者: Lilian Chiu 審譯者: Helen Chang

In tropical seas,

在熱帶海洋中，

flying fish leap out of the water,

飛魚會跳出水面，

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

用類似翅膀的鰭滑翔 200 公尺，

before dipping back into the sea.

然後才落回到海洋中。

In the Indo-Pacific,

在印度洋－太平洋海域，

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

一種獵殺型旗魚的速度 可以高達每小時 110 公里。

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

那比奧運游泳冠軍 麥可·費爾普斯還要快 11 倍。

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

牠能伸出刺狀背鰭來煞車，

grinding to a dead halt, mid-swim.

產生磨擦，從游泳狀態 變成完全靜止。

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

魚類能做到這些身體技藝， 是因為牠們的體形，

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

大多數魚種的體形 是光滑、細長的身體、鰭和尾巴。

These features are shared across thousands of fish species,

數千種魚類有這樣的特徵，

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

為了在獨特的棲息地存活， 每種魚類又有自己的獨特變化。

What makes these features so commonplace in fish,

為什麼魚類常會有這些特徵？

and what does it reveal about the more than 33,000 fish species

對於在地球上的河流、 湖泊，與海洋中超過

that inhabit earth’s rivers, lakes, and seas?

３萬３千種魚類， 這些特徵有什麼意涵？

Fish can be split into two main groups,

魚可以分為兩大類，

according to the type of motion they favor.

分類依據是牠們所偏好的移動方式。

The first is body and caudal fin driven motion,

第一種由身體和尾鰭驅動而移動，

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

大部分的魚類， 約 85％，是這一種。

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

這些魚身和尾巴是主要的推進力，

with fins mainly playing a stabilizing and steering role.

鰭的功能只是在穩定和控制方向。

This configuration suits many open-water species,

這種結構適合許多開放水域的魚種，

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

牠們需要速度、突衝和控制， 滿足經常且有效率的游泳需求。

Eels lie at one extreme of this group.

鰻魚是這一類中的極端例子。

Known as anguilliform swimmers,

牠是鰻式的游泳生物，

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

牠的整個身體會波動， 產生出像水波一樣的動作。

Compared to anguilliform fish,

和鰻魚相比，

species like salmon and trout, known as subcarangiforms,

像鮭魚及鱒魚這類魚種 則是子鰺行式的，

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

用身體質量的 2/3 來產生移動；

while carangiform swimmers, such as mackerel,

而鰺行式的游泳動物，比如鯖魚，

only use about a third.

只會用到 1/3。

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

通常魚在產生移動時 用到的身體質量越少，

the more streamlined its shape.

牠的身體形狀就會越是流線型。

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

如果一端是鰻魚，另一端就是 甲殼式的魚種，如粒突箱魨，

and thunniform swimmers like tuna.

還有鮪行式的游泳動物，如鮪魚。

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

這些魚類的尾巴， 也就是尾鰭，負責移動。

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

鮪魚的尾巴透過 腱和身體的多處肌肉連結。

It powers the body like an engine,

它就像引擎一樣提供動力給身體，

forcefully catapulting the bullet-like fish

把像子彈一樣的魚給強力彈射出去，

to speeds up to 69 kilometers per hour.

速度可高達每小時 69 公里。

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

第二大類的魚，則仰賴 奇鰭和偶鰭來移動，

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

意思就是，牠們主要 是用鰭在水中推進。

Fins allow fine-tuned movement at slow speeds,

鰭讓牠們可以精準地低速移動，

so this propulsion is typically found in fish

會用這種推進方式的魚

that have to navigate complex habitats.

通常需要在複雜的棲息地中游行。

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

底棲魚類，像魟魚，就屬於這一類；

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

靠著巨大胸鰭，牠們就能 將自己從海底敏捷地升起。

That conveniently allows them to inhabit shallow seas

那讓牠們可以很方便地 居住在淺海中，

without being buffeted about by waves.

而不會被海浪給衝擊。

Similarly, shallow-water flatfish use their entire bodies

同樣的，淺水比目魚 會用牠們的整個身體

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

當作一個大鰭， 讓自己能從沙地升起。

Ocean sunfish lack tails,

海洋太陽魚沒有尾巴，

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

所以牠們只能拍打牠們那 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類似的動作，

like the queen angelfish,

比如皇后神仙魚、

surgeonfish,

刺尾鱼，

and wrasse.

以及隆頭魚科。

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

因為牠們用鰭，不需要用到身體，

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

結果，這類魚種當中有許多已經 演化出不尋常且很有創意的形狀。

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

在兩大類當中都有一些魚種 看起來不屬於該類別。

But if you look closer,

但如果你仔細看，

you’ll notice that these common traits are disguised.

會發現這些共通特性 只是藏在偽裝底下。

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

比如海馬，牠們的形狀 不是常見的魚類形狀，

yet they use their flexible dorsal fins as makeshift tails.

但牠們會用牠們的彈性背鰭 來當作臨時代用的尾巴。

A pufferfish may occasionally look more like a lethal balloon,

河豚偶爾看似致命的氣球，

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

但如果牠需要快速游泳， 牠會收回牠的針刺。

Handfish look like they have legs,

長手魚看起來好像有腳，

but really these limb-like structures are fins,

但其實，這些像肢體的結構是鰭，

modified to help them amble across the sea floor.

改造成有助牠們能在海底輕鬆行走。

For fish, motion underpins survival,

對魚而言，移動是生存的基礎，

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

所以，移動是驅使牠們 外形演化的重要因子。

The widespread features of fish have been maintained

魚類有各式各樣的特徵，

across tens of thousands of fish species,

在數萬種魚種中可以看到，

not to mention other ocean-dwelling animals,

更不用說還有其他 住在海洋中的動物了，

like penguins,

像是企鵝、

dolphins,

海豚、

sea slugs,

海參，

and squids.

和章魚。

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

那正是因為事實證明 移動促使身形成功地演化。