No one can figure out how eels have sex - Lucy Cooke

譯者: Lilian Chiu 審譯者: Carol Wang

From Ancient Greece to the 20th century,

從古希臘到二十世紀，

Aristotle, Sigmund Freud, and numerous other scholars

亞里斯多德、佛洛依德， 以及其他數位學者

were all looking for the same thing:

都在找同一樣東西：

eel testicles.

鰻魚的睪丸。

Freshwater eels, or Anguilla Anguilla, could be found in rivers across Europe,

在歐洲各地的河流中

都可以找到淡水鰻魚， 也叫歐洲鰻鱺，

but no one had ever seen them mate.

但沒有人見過牠們交配。

And despite countless dissections,

儘管做過無數次解剖，

no researcher could find eel eggs or identify their reproductive organs.

沒有任何研究者找到鰻魚的卵

或辨識出牠們的生殖器官。

Devoid of data, naturalists proposed various eel origin stories.

在缺乏資料的情況下，

博物學家提出了 各種鰻魚來源的故事。

Aristotle suggested that eels spontaneously emerged from mud.

亞里斯多德指出，鰻魚是 從泥巴中自然冒出來的。

Pliny the Elder argued eels rubbed themselves against rocks,

老普林尼主張鰻魚 會自己磨擦岩石，

and the subsequent scrapings came to life.

刮下的碎屑隨後便有了生命。

Eels were said to hatch on rooftops, manifest from the gills of other fish,

有人說，鰻魚在屋頂上孵化、

是從其他魚類的鰓變成的，

and even emerge from the bodies of beetles.

甚至是從甲蟲的身體中長出來。

But the true story of eel reproduction is even more difficult to imagine.

但關於鰻魚繁殖的 真實故事還更難想像。

And to solve this slippery mystery,

為了解決這個難解之謎，

scholars would have to rethink centuries of research.

學者就得要重新思考 數個世紀的研究。

Today, we know the freshwater eel lifecycle has five distinct stages:

現今，我們知道 淡水鰻魚的生命週期

有五個明確的階段：

larval leptocepheli, miniscule glass eels, adolescent elvers,

葉狀幼蟲、

小玻璃鰻、

未成熟的幼鰻、

older yellow eels, and adult silver eels.

較年長的黃鰻，

及成年的銀鰻。

Given the radical physical differences between these phases,

因為鰻魚在這些階段的 實體差異相當大，

you’d be forgiven for assuming these are different animals.

你很有可能會以為 牠們是不同的動物。

In fact, that’s exactly what European naturalists thought.

事實上，歐洲博物學家 正是這麼以為的。

Researchers were aware of leptocepheli and glass eels,

研究者知道有 葉狀幼蟲和小玻璃鰻，

but no one guessed they were related to the elvers and yellow eels

但沒有人猜到的是，

牠們竟和上游數百公里外的 幼鰻以及黃鰻有關係。

living hundreds of kilometers upstream.

Confusing matters more, eels don’t develop sex organs until late in life.

更讓人困惑的是，

鰻魚要到生命後期 才會發展出性器官。

And the entirety of their time in the rivers of Europe

而牠們在歐洲河流中的這段時間

is essentially eel adolescence.

基本上都還是幼鰻。

So when do eels reproduce, and where do they do it?

所以，鰻魚何時繁殖？

在哪裡繁殖？

Despite its name, the life of a freshwater eel actually begins

雖然淡水鰻魚的名字有「淡水」，

但牠們的生命始於 百慕達三角洲的鹹水。

in the salty waters of the Bermuda Triangle.

At the height of the annual cyclone season,

在每年氣旋季的高峰，

thousands of three-millimeter eel larvae

會有數以千計三公釐長的鰻魚幼蟲

drift out of the Sargasso Sea.

漂出馬尾藻海。

From here, they follow migration paths to North America and Europe—

牠們會從那裡順著遷徙路線， 前往北美和歐洲——

continents that were much closer

在四千萬年前鰻魚 建立這些路線時，

when eels established these routes 40 million years ago.

這兩塊大陸比較靠近。

Over the next 300 days, Anguilla Anguilla larvae ride the ocean currents

在接下來的三百天，

歐洲鰻魚幼蟲便會乘著海洋洋流

6,500 km to the coast of Europe—

到六千五百公里外的歐洲海岸——

making one of the longest known marine migrations.

這是我們已知 最長的海洋遷徙之一。

By the time they arrive, they’ve grown approximately 45 mm,

當牠們抵達時，牠們已經 長大到近四十五公釐，

and transformed into semi-transparent glass eels.

轉變成為半透明的玻璃鰻。

It’s not just their appearance that’s changed.

改變的不只牠們的外表。

If most marine fish entered brackish coastal waters,

大部分的海洋魚類進入到 微鹹的海岸水域時，

their cells would swell with freshwater in a lethal explosion.

牠們的細胞會因為淡水 而膨脹，發生致命的爆炸。

But when glass eels reach the coast,

但當玻璃鰻抵達海岸時，

their kidneys shift to retain more salt

牠們的腎臟會發生轉變， 能保留更多的鹽，

and maintain their blood’s salinity levels.

維持血液中的鹽度。

Swarms of these newly freshwater fish migrate up streams and rivers,

這些新出現的淡水魚類會成群

向溪流及河流的上游遷徙，

sometimes piling on top of each other to clear obstacles and predators.

有時會疊在彼此身上， 以清除障礙和捕食性動物。

Those that make it upstream develop into opaque elvers.

成功到上游的就會發展 成為不透明的幼鰻。

Having finally arrived in their hunting grounds,

終於抵達了狩獵地之後，

elvers begin to eat everything they can fit into their mouths.

幼鰻便開始吃掉任何 能放進牠們口中的東西。

These omnivores grow in proportion to their diets,

這些雜食動物的成長 和牠們的飲食成比例，

and over the next decade they develop into larger yellow eels.

在接下來十年間，牠們 會發展成為更大的黃鰻。

In this stage, they grow to be roughly 80 cm,

在這個階段，牠們 會長到約八十公分，

and finally develop sexual organs.

且終於長出性器官。

But the last phase of eel life— and the secret of their reproduction—

但鰻魚生命的最後一個階段——

以及牠們繁殖的秘密——

remains mysterious.

仍然是個謎。

In 1896, researchers identified leptocepheli as larval eels,

1896 年，

研究者辨識出葉狀幼蟲 就是鰻魚的幼蟲，

and deduced that they had come to Europe from somewhere in the Atlantic.

並推論牠們是從 大西洋的某處來到歐洲。

However, to find this mysterious breeding ground,

然而，若要找到 這塊神秘的繁殖地，

someone would have to perform an unthinkable survey of the ocean

必須要針對小於三十公釐的幼蟲

for larvae no larger than 30mm.

進行一項無法想像的海洋調查。

Enter Johannes Schmidt.

該約翰內斯 · 施密特登場了。

For the next 18 years, this Danish oceanographer

在接下來的十八年間， 這位丹麥海洋學家

trawled the coasts of four continents,

在四塊大陸的海岸進行拖網，

hunting down increasingly tiny leptocepheli.

捕捉越來越多的小葉狀幼蟲。

Finally, in 1921, he found the smallest larvae yet,

終於，在 1921 年，

他在馬尾藻海的南緣

on the southern edge of the Sargasso Sea.

發現了最小的幼蟲。

Despite knowledge of their round trip migration,

儘管科學家了解牠們的來回遷徙，

scientists still haven’t observed mating in the wild,

卻仍然沒有在野外觀察到交配，

or found a single eel egg.

也沒有找到任何一顆鰻魚卵。

Leading theories suggest that eels reproduce

主流的理論指出，鰻魚的繁殖

in a flurry of external fertilization,

是在一系列的外部受精中進行，

in which clouds of sperm fertilize free-floating eggs.

一大群精子會使 自由漂浮的卵子受精。

But the powerful currents and tangling seaweed of the Sargasso Sea

但馬尾藻海有強大的洋流

及糾結的海草， 讓這個理論很難被證實。

have made this theory difficult to confirm.

Researchers don’t even know where to look,

研究者甚至不知道 該研究什麼地方，

since they’ve yet to successfully track an eel

因為他們尚未成功追蹤任何一隻

over the course of its return migration.

在遷徙返程過程中的鰻魚。

Until these challenges can be met,

在這些難題被解決之前，

the eel’s ancient secret will continue to slip through our fingers.

鰻魚的古老秘密

仍然會繼續從我們的指縫中溜走。