Why fish are better at breathing than you are - Dan Kwartler

譯者: Lilian Chiu 審譯者: 麗玲 辛

In 2019, Eliud Kipchoge finished a Vienna marathon

2019 年，

埃利烏德‧基普喬蓋在維也納 跑完了一場馬拉松，

in one hour, 59 minutes, and 40 seconds.

只用了一小時五十九分鐘四十秒。

This staggering time broke the two-hour barrier

這令人驚嘆的成績 打破了兩小時障礙，

that most runners previously deemed impossible.

先前大部分跑者都認為 這是不可能辦到的。

However, some researchers weren't as surprised.

但是，有些研究人員 並沒有那麼驚訝。

Recent studies investigating if humans could maintain such a high pace

近期有些研究在探究人類 是否能維持這麼高的步速，

for the length of a marathon had found that elite runners

跑完馬拉松全程， 結果發現，菁英跑者

can take in twice as much oxygen as non-runners.

能攝入的氧氣量是非跑者的兩倍。

And it’s likely that this superhuman ability played a role in Eliud’s victory.

很有可能，這種超人能力 促成了埃利烏德的勝利，

But when it comes to breathing efficiently,

但，談到有效地呼吸，

not even the best runners in the world can compete with the average fish.

連世界上最好的跑者 也比不上一般的魚類。

That’s right— you’re looking at some of the best breathers on Earth;

沒錯——你現在看到的就是 一些地球上最厲害的呼吸高手；

which actually makes sense when you consider how little oxygen there is

這其實合情合理，想想看

在牠們的水生環境中 氧氣是多麼稀少。

in their aquatic environments.

Fish can breathe in a variety of ways,

魚類有數種呼吸的方式，

but the most common is through the use of gills.

但最常見的是用鰓來呼吸。

These branching organs typically come in four pairs,

這些分支器官通常有四對，

all enclosed in gill chambers.

都被包裏在鰓室中。

These chambers are protected by opercle, or gill covers,

保護鰓室的是鰓蓋，

which are just as essential to underwater breathing as the gills themselves.

對於水下呼吸而言， 鰓蓋和鰓本身同等重要。

When most fish take a breath,

大多數魚類在呼吸時，

they first close these covers and take a gulp of water.

牠們會先關上鰓蓋，吸入一口水。

Then, they open their opercle,

接著，牠們會打開鰓蓋，

creating a pressure differential that pulls water through the gills,

創造出壓力差，引導水穿過鰓，

which are composed of thread-like filaments spaced evenly along a gill arch.

鰓是由線狀的鰓絲組成，

鰓絲沿著鰓弓均勻排列，

These filaments are covered in countless small blood vessels called capillaries,

鰓絲上覆蓋著無數 小血管，稱為毛細血管，

in addition to tiny extensions known as gill lamellae

以及微小的延伸物，稱為鰓小片，

which further increase the gill’s surface area.

鰓小片可進一步增加鰓的表面積。

When water passes over these capillaries,

當水經過這些毛細血管時，

the membrane is thin enough for the fish’s red blood cells

薄膜夠薄，薄到能讓魚的紅血球

to pull dissolved oxygen from the water into the bloodstream.

把溶解在水中氧拉到血液中。

And just like when we breathe with our lungs,

就像我們用肺來呼吸一樣，

this process releases carbon dioxide,

這個過程也會釋放二氧化碳，

which passes out into the water through the open gill cover.

打開的鰓蓋讓二氧化碳被排到水中。

This technique only works underwater—

這個技巧只有在水中才有用——

on the surface, the pressure differential created by opening and closing gill covers

在水面上，打開和關閉 鰓蓋所產生的壓力差

isn’t strong enough to pull in sufficient air.

沒有強到可以吸入足夠的空氣。

But under the surface, it’s remarkably efficient.

但在水面下，效率就非常高。

Inside the lamellae, blood flows in the opposite direction to the water,

在鰓小片內，

血流的方向和水相反，

creating a counter-current system that optimizes gas exchange.

創造出一個逆流系統， 能優化氣體交換。

In fact, gills can absorb roughly 75% of the oxygen passing through them;

事實上，

鰓可以吸收約 75％ 通過鰓的氧氣；

that’s twice the percentage of oxygen our lungs extract from a breath of air.

我們的肺從吸入的空氣中 取得的氧氣百分比只有其一半。

Fish also breathe much more frequently than we do.

魚類的呼吸也比我們頻繁。

The average adult human breathes 12 to 18 times a minute,

一般的成年人每分鐘 呼吸十二到十八次，

while most fish pull water over their gills

而大部分魚類把水吸入鰓中的頻率

anywhere from 20 to 80 times a minute.

是每分鐘二十到八十次。

Those numbers would raise even a marathoner’s eyebrows.

連馬拉松跑者都會 對這些數字感而震驚。

Thanks to this fast, frequent, and efficient breathing

由於有這種快速、頻繁， 且有效的呼吸方式，

fish process far more oxygen than we do.

魚類能處理的氧氣量遠超過我們。

It's also why some species can live at great depths.

這也是為什麼有些魚種 可以在深海中生活。

Bodies of water get most of their oxygen from the surface,

水體中的氧氣多半來自水面，

where O2 dissolves into the water and begins circulating.

在水面上，氧氣會溶解 到水中，並開始循環。

But further down, there are oxygen minimum zones,

但在水中更深處，還有最低含氧區，

with concentrations as low as 0.5 milligrams of oxygen per liter.

濃度低至每公升只有 零點五毫克的氧氣。

To get the oxygen they need,

為了取得必要的氧氣，

fish living at these depths rely on increased gill ventilation

生活在深海中的魚類 需要增加鰓的通氣量，

and hearts that pump high volumes of oxygenated blood throughout the body.

且心臟要能將大量 含氧的血液打到全身。

Even with these tricks, sometimes there's still not enough oxygen to go around,

即使有這些花招， 有時氧氣還是不夠用，

forcing fish to adapt more extreme solutions.

迫使魚類適應更極端的解決方案。

For example, the Australian lungfish lives in a habitat

例如，澳洲肺魚生活的棲息地

where the water level drops precipitously in August and September,

在八月和九月時水位會急劇下降，

making it almost impossible to survive with gills alone.

光靠鰓幾乎不可能生存。

Fortunately, these fish have gills and lungs.

幸運的是，這些魚類有鰓也有肺。

Using their long, thin limbs,

使用細長的肢體，

they can lift their mouths above the surface and take deep breaths of air,

牠們可以將嘴巴抬出水面，

深吸空氣，

allowing them to survive out of the water for several days.

可以不靠水就存活數天。

And other species of lungfish can survive above ground even longer

還有其他種類的肺魚， 可以在地面上生存更久，

in cocoons of mud and mucus.

靠的是用泥巴和黏液形成的繭。

Fortunately, for most fish these extreme adaptations aren’t necessary.

幸運的是，大多數的魚類 並不需要這些極端的適應。

After all, 71% of Earth is covered in H2O,

畢竟，地球表面 有 71% 被水覆蓋，

giving these aquatic animals plenty of room to flaunt their gills’ skills.

讓這些水中動物有很多空間 來炫耀牠們的魚鰓技能。