No one can figure out how eels have sex - Lucy Cooke
-
0:07 - 0:10From Ancient Greece to the 20th century,
-
0:10 - 0:14Aristotle, Sigmund Freud,
and numerous other scholars -
0:14 - 0:17were all looking for the same thing:
-
0:17 - 0:20eel testicles.
-
0:20 - 0:26Freshwater eels, or Anguilla Anguilla,
could be found in rivers across Europe, -
0:26 - 0:29but no one had ever seen them mate.
-
0:29 - 0:31And despite countless dissections,
-
0:31 - 0:38no researcher could find eel eggs
or identify their reproductive organs. -
0:38 - 0:44Devoid of data, naturalists proposed
various eel origin stories. -
0:44 - 0:49Aristotle suggested that eels
spontaneously emerged from mud. -
0:49 - 0:54Pliny the Elder argued eels
rubbed themselves against rocks, -
0:54 - 0:57and the subsequent scrapings
came to life. -
0:57 - 1:03Eels were said to hatch on rooftops,
manifest from the gills of other fish, -
1:03 - 1:07and even emerge
from the bodies of beetles. -
1:07 - 1:12But the true story of eel reproduction
is even more difficult to imagine. -
1:12 - 1:15And to solve this slippery mystery,
-
1:15 - 1:19scholars would have to rethink
centuries of research. -
1:19 - 1:26Today, we know the freshwater eel
lifecycle has five distinct stages: -
1:26 - 1:33larval leptocepheli, miniscule glass eels,
adolescent elvers, -
1:33 - 1:37older yellow eels, and adult silver eels.
-
1:37 - 1:41Given the radical physical differences
between these phases, -
1:41 - 1:45you’d be forgiven for assuming
these are different animals. -
1:45 - 1:50In fact, that’s exactly what
European naturalists thought. -
1:50 - 1:54Researchers were aware of leptocepheli
and glass eels, -
1:54 - 1:58but no one guessed they were related
to the elvers and yellow eels -
1:58 - 2:01living hundreds of kilometers upstream.
-
2:01 - 2:07Confusing matters more, eels don’t
develop sex organs until late in life. -
2:07 - 2:10And the entirety of their time
in the rivers of Europe -
2:10 - 2:13is essentially eel adolescence.
-
2:13 - 2:18So when do eels reproduce,
and where do they do it? -
2:18 - 2:23Despite its name, the life
of a freshwater eel actually begins -
2:23 - 2:27in the salty waters
of the Bermuda Triangle. -
2:27 - 2:29At the height of the annual
cyclone season, -
2:29 - 2:32thousands of three-millimeter eel larvae
-
2:32 - 2:35drift out of the Sargasso Sea.
-
2:35 - 2:39From here, they follow migration
paths to North America and Europe— -
2:39 - 2:42continents that were
much closer -
2:42 - 2:46when eels established these routes
40 million years ago. -
2:46 - 2:52Over the next 300 days, Anguilla Anguilla
larvae ride the ocean currents -
2:52 - 2:576,500 km to the coast of Europe—
-
2:57 - 3:01making one of the longest
known marine migrations. -
3:01 - 3:06By the time they arrive, they’ve grown
approximately 45 mm, -
3:06 - 3:10and transformed into semi-transparent
glass eels. -
3:10 - 3:12It’s not just their appearance
that’s changed. -
3:12 - 3:16If most marine fish entered
brackish coastal waters, -
3:16 - 3:21their cells would swell with freshwater
in a lethal explosion. -
3:21 - 3:24But when glass eels reach the coast,
-
3:24 - 3:26their kidneys shift to retain more salt
-
3:26 - 3:29and maintain their blood’s
salinity levels. -
3:29 - 3:34Swarms of these newly freshwater
fish migrate up streams and rivers, -
3:34 - 3:40sometimes piling on top of each other
to clear obstacles and predators. -
3:40 - 3:45Those that make it upstream develop
into opaque elvers. -
3:45 - 3:47Having finally arrived
in their hunting grounds, -
3:47 - 3:51elvers begin to eat everything
they can fit into their mouths. -
3:51 - 3:55These omnivores grow in proportion
to their diets, -
3:55 - 4:00and over the next decade they develop
into larger yellow eels. -
4:00 - 4:04In this stage, they grow
to be roughly 80 cm, -
4:04 - 4:08and finally develop sexual organs.
-
4:08 - 4:13But the last phase of eel life—
and the secret of their reproduction— -
4:13 - 4:16remains mysterious.
-
4:16 - 4:22In 1896, researchers identified
leptocepheli as larval eels, -
4:22 - 4:26and deduced that they had come
to Europe from somewhere in the Atlantic. -
4:26 - 4:29However, to find this mysterious
breeding ground, -
4:29 - 4:33someone would have to perform
an unthinkable survey of the ocean -
4:33 - 4:37for larvae no larger than 30mm.
-
4:37 - 4:39Enter Johannes Schmidt.
-
4:39 - 4:43For the next 18 years,
this Danish oceanographer -
4:43 - 4:45trawled the coasts of four continents,
-
4:45 - 4:49hunting down increasingly
tiny leptocepheli. -
4:49 - 4:54Finally, in 1921, he found
the smallest larvae yet, -
4:54 - 4:58on the southern edge
of the Sargasso Sea. -
4:58 - 5:01Despite knowledge
of their round trip migration, -
5:01 - 5:04scientists still haven’t observed
mating in the wild, -
5:04 - 5:07or found a single eel egg.
-
5:07 - 5:10Leading theories suggest
that eels reproduce -
5:10 - 5:13in a flurry of external fertilization,
-
5:13 - 5:17in which clouds of sperm
fertilize free-floating eggs. -
5:17 - 5:22But the powerful currents
and tangling seaweed of the Sargasso Sea -
5:22 - 5:25have made this theory
difficult to confirm. -
5:25 - 5:27Researchers don’t even know where to look,
-
5:27 - 5:30since they’ve yet to successfully
track an eel -
5:30 - 5:33over the course of its return migration.
-
5:33 - 5:35Until these challenges can be met,
-
5:35 - 5:41the eel’s ancient secret will continue
to slip through our fingers.
- Title:
- No one can figure out how eels have sex - Lucy Cooke
- Speaker:
- Lucy Cooke
- Description:
-
View full lesson: https://ed.ted.com/lessons/no-one-can-figure-out-how-eels-have-sex-lucy-cooke
From Ancient Greece to the 20th century, Aristotle, Freud, and numerous other scholars were all looking for the same thing: eel testicles. Freshwater eels could be found in rivers across Europe, but no one had ever seen them mate and no researcher could find eel eggs or identify their reproductive organs. So how do eels reproduce, and where do they do it? Lucy Cooke digs into the ancient mystery.
Lesson by Lucy Cooke, directed by Anton Bogaty.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:42
lauren mcalpine approved English subtitles for No one can figure out how eels have sex | ||
lauren mcalpine accepted English subtitles for No one can figure out how eels have sex | ||
lauren mcalpine edited English subtitles for No one can figure out how eels have sex | ||
Tara Ahmadinejad edited English subtitles for No one can figure out how eels have sex | ||
Tara Ahmadinejad edited English subtitles for No one can figure out how eels have sex | ||
Tara Ahmadinejad edited English subtitles for No one can figure out how eels have sex | ||
Tara Ahmadinejad edited English subtitles for No one can figure out how eels have sex |