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  • From Ancient Greece to the 20th century,

    譯者: Lilian Chiu 審譯者: Carol Wang

  • Aristotle, Sigmund Freud, and numerous other scholars

    從古希臘到二十世紀,

  • were all looking for the same thing:

    亞里斯多德、佛洛依德, 以及其他數位學者

  • eel testicles.

    都在找同一樣東西:

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

    鰻魚的睪丸。

  • but no one had ever seen them mate.

    在歐洲各地的河流中

  • And despite countless dissections,

    都可以找到淡水鰻魚, 也叫歐洲鰻鱺,

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

    但沒有人見過牠們交配。

  • Devoid of data, naturalists proposed various eel origin stories.

    儘管做過無數次解剖,

  • Aristotle suggested that eels spontaneously emerged from mud.

    沒有任何研究者找到鰻魚的卵

  • Pliny the Elder argued eels rubbed themselves against rocks,

    或辨識出牠們的生殖器官。

  • and the subsequent scrapings came to life.

    在缺乏資料的情況下,

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

    博物學家提出了 各種鰻魚來源的故事。

  • and even emerge from the bodies of beetles.

    亞里斯多德指出,鰻魚是 從泥巴中自然冒出來的。

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

    老普林尼主張鰻魚 會自己磨擦岩石,

  • And to solve this slippery mystery,

    刮下的碎屑隨後便有了生命。

  • scholars would have to rethink centuries of research.

    有人說,鰻魚在屋頂上孵化、

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

    是從其他魚類的鰓變成的,

  • larval leptocepheli, miniscule glass eels, adolescent elvers,

    甚至是從甲蟲的身體中長出來。

  • older yellow eels, and adult silver eels.

    但關於鰻魚繁殖的 真實故事還更難想像。

  • Given the radical physical differences between these phases,

    為了解決這個難解之謎,

  • you'd be forgiven for assuming these are different animals.

    學者就得要重新思考 數個世紀的研究。

  • In fact, that's exactly what European naturalists thought.

    現今,我們知道 淡水鰻魚的生命週期

  • Researchers were aware of leptocepheli and glass eels,

    有五個明確的階段:

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

    葉狀幼蟲、

  • living hundreds of kilometers upstream.

    小玻璃鰻、

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

    未成熟的幼鰻、

  • And the entirety of their time in the rivers of Europe

    較年長的黃鰻,

  • is essentially eel adolescence.

    及成年的銀鰻。

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

    因為鰻魚在這些階段的 實體差異相當大,

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

    你很有可能會以為 牠們是不同的動物。

  • in the salty waters of the Bermuda Triangle.

    事實上,歐洲博物學家 正是這麼以為的。

  • At the height of the annual cyclone season,

    研究者知道有 葉狀幼蟲和小玻璃鰻,

  • thousands of three-millimeter eel larvae

    但沒有人猜到的是,

  • drift out of the Sargasso Sea.

    牠們竟和上游數百公里外的 幼鰻以及黃鰻有關係。

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

    更讓人困惑的是,

  • continents that were much closer

    鰻魚要到生命後期 才會發展出性器官。

  • when eels established these routes 40 million years ago.

    而牠們在歐洲河流中的這段時間

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

    基本上都還是幼鰻。

  • 6,500 km to the coast of Europe

    所以,鰻魚何時繁殖?

  • making one of the longest known marine migrations.

    在哪裡繁殖?

  • By the time they arrive, they've grown approximately 45 mm,

    雖然淡水鰻魚的名字有「淡水」,

  • and transformed into semi-transparent glass eels.

    但牠們的生命始於 百慕達三角洲的鹹水。

  • It's not just their appearance that's changed.

    在每年氣旋季的高峰,

  • If most marine fish entered brackish coastal waters,

    會有數以千計三公釐長的鰻魚幼蟲

  • their cells would swell with freshwater in a lethal explosion.

    漂出馬尾藻海。

  • But when glass eels reach the coast,

    牠們會從那裡順著遷徙路線, 前往北美和歐洲——

  • their kidneys shift to retain more salt

    在四千萬年前鰻魚 建立這些路線時,

  • and maintain their blood's salinity levels.

    這兩塊大陸比較靠近。

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

    在接下來的三百天,

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

    歐洲鰻魚幼蟲便會乘著海洋洋流

  • Those that make it upstream develop into opaque elvers.

    到六千五百公里外的歐洲海岸——

  • Having finally arrived in their hunting grounds,

    這是我們已知 最長的海洋遷徙之一。

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

    當牠們抵達時,牠們已經 長大到近四十五公釐,

  • These omnivores grow in proportion to their diets,

    轉變成為半透明的玻璃鰻。

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

    改變的不只牠們的外表。

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

    大部分的海洋魚類進入到 微鹹的海岸水域時,

  • and finally develop sexual organs.

    牠們的細胞會因為淡水 而膨脹,發生致命的爆炸。

  • But the last phase of eel lifeand the secret of their reproduction

    但當玻璃鰻抵達海岸時,

  • remains mysterious.

    牠們的腎臟會發生轉變, 能保留更多的鹽,

  • In 1896, researchers identified leptocepheli as larval eels,

    維持血液中的鹽度。

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

    這些新出現的淡水魚類會成群

  • However, to find this mysterious breeding ground,

    向溪流及河流的上游遷徙,

  • someone would have to perform an unthinkable survey of the ocean

    有時會疊在彼此身上, 以清除障礙和捕食性動物。

  • for larvae no larger than 30mm.

    成功到上游的就會發展 成為不透明的幼鰻。

  • Enter Johannes Schmidt.

    終於抵達了狩獵地之後,

  • For the next 18 years, this Danish oceanographer

    幼鰻便開始吃掉任何 能放進牠們口中的東西。

  • trawled the coasts of four continents,

    這些雜食動物的成長 和牠們的飲食成比例,

  • hunting down increasingly tiny leptocepheli.

    在接下來十年間,牠們 會發展成為更大的黃鰻。

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

    在這個階段,牠們 會長到約八十公分,

  • on the southern edge of the Sargasso Sea.

    且終於長出性器官。

  • Despite knowledge of their round trip migration,

    但鰻魚生命的最後一個階段——

  • scientists still haven't observed mating in the wild,

    以及牠們繁殖的秘密——

  • or found a single eel egg.

    仍然是個謎。

  • Leading theories suggest that eels reproduce

    1896 年,

  • in a flurry of external fertilization,

    研究者辨識出葉狀幼蟲 就是鰻魚的幼蟲,

  • in which clouds of sperm fertilize free-floating eggs.

    並推論牠們是從 大西洋的某處來到歐洲。

  • But the powerful currents and tangling seaweed of the Sargasso Sea

    然而,若要找到 這塊神秘的繁殖地,

  • have made this theory difficult to confirm.

    必須要針對小於三十公釐的幼蟲

  • Researchers don't even know where to look,

    進行一項無法想像的海洋調查。

  • since they've yet to successfully track an eel

    該約翰內斯 · 施密特登場了。

  • over the course of its return migration.

    在接下來的十八年間, 這位丹麥海洋學家

  • Until these challenges can be met,

    在四塊大陸的海岸進行拖網,

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

    捕捉越來越多的小葉狀幼蟲。

From Ancient Greece to the 20th century,

譯者: Lilian Chiu 審譯者: Carol Wang

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B2 中高級 中文 TED-Ed 鰻魚 幼蟲 淡水 繁殖 歐洲

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

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    林宜悉 發佈於 2020 年 12 月 15 日
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