[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:08.11,0:00:12.24,Default,,0000,0000,0000,,In 1800, the explorer \NAlexander von Humboldt
Dialogue: 0,0:00:12.24,0:00:16.23,Default,,0000,0000,0000,,witnessed a swarm of electric eels\Nleap out of the water
Dialogue: 0,0:00:16.23,0:00:19.83,Default,,0000,0000,0000,,to defend themselves \Nagainst oncoming horses.
Dialogue: 0,0:00:19.83,0:00:24.44,Default,,0000,0000,0000,,Most people thought the story\Nso unusual that Humboldt made it up.
Dialogue: 0,0:00:24.44,0:00:28.80,Default,,0000,0000,0000,,But fish using electricity is more common\Nthan you might think;
Dialogue: 0,0:00:28.80,0:00:32.94,Default,,0000,0000,0000,,and yes, electric eels are a type of fish.
Dialogue: 0,0:00:32.94,0:00:35.12,Default,,0000,0000,0000,,Underwater, where light is scarce,
Dialogue: 0,0:00:35.12,0:00:37.77,Default,,0000,0000,0000,,electrical signals offer ways\Nto communicate,
Dialogue: 0,0:00:37.77,0:00:38.86,Default,,0000,0000,0000,,navigate,
Dialogue: 0,0:00:38.86,0:00:43.69,Default,,0000,0000,0000,,and find—plus, in rare cases, stun—prey.
Dialogue: 0,0:00:43.69,0:00:49.14,Default,,0000,0000,0000,,Nearly 350 species of fish\Nhave specialized anatomical structures
Dialogue: 0,0:00:49.14,0:00:52.81,Default,,0000,0000,0000,,that generate \Nand detect electrical signals.
Dialogue: 0,0:00:52.81,0:00:55.25,Default,,0000,0000,0000,,These fish are divided into two groups,
Dialogue: 0,0:00:55.25,0:00:58.61,Default,,0000,0000,0000,,depending on how much \Nelectricity they produce.
Dialogue: 0,0:00:58.61,0:01:03.59,Default,,0000,0000,0000,,Scientists call the first group\Nthe weakly electric fish.
Dialogue: 0,0:01:03.59,0:01:06.41,Default,,0000,0000,0000,,Structures near their tails \Ncalled electric organs
Dialogue: 0,0:01:06.41,0:01:12.51,Default,,0000,0000,0000,,produce up to a volt of electricity,\Nabout two-thirds as much as a AA battery.
Dialogue: 0,0:01:12.51,0:01:14.60,Default,,0000,0000,0000,,How does this work?
Dialogue: 0,0:01:14.60,0:01:19.07,Default,,0000,0000,0000,,The fish's brain sends a signal through\Nits nervous system to the electric organ,
Dialogue: 0,0:01:19.07,0:01:21.29,Default,,0000,0000,0000,,which is filled with stacks of hundreds
Dialogue: 0,0:01:21.29,0:01:27.26,Default,,0000,0000,0000,,or thousands of disc-shaped \Ncells called electrocytes.
Dialogue: 0,0:01:27.26,0:01:31.44,Default,,0000,0000,0000,,Normally, electrocytes pump out sodium\Nand potassium ions
Dialogue: 0,0:01:31.44,0:01:36.81,Default,,0000,0000,0000,,to maintain a positive charge outside\Nand negative charge inside.
Dialogue: 0,0:01:36.81,0:01:39.92,Default,,0000,0000,0000,,But when the nerve signal arrives\Nat the electrocyte,
Dialogue: 0,0:01:39.92,0:01:43.55,Default,,0000,0000,0000,,it prompts the ion gates to open.
Dialogue: 0,0:01:43.55,0:01:47.71,Default,,0000,0000,0000,,Positively charged ions flow back in.
Dialogue: 0,0:01:47.71,0:01:52.03,Default,,0000,0000,0000,,Now, one face of the electrocyte\Nis negatively charged outside
Dialogue: 0,0:01:52.03,0:01:54.70,Default,,0000,0000,0000,,and positively charged inside.
Dialogue: 0,0:01:54.70,0:01:58.77,Default,,0000,0000,0000,,But the far side \Nhas the opposite charge pattern.
Dialogue: 0,0:01:58.77,0:02:01.42,Default,,0000,0000,0000,,These alternating charges \Ncan drive a current,
Dialogue: 0,0:02:01.42,0:02:06.49,Default,,0000,0000,0000,,turning the electrocyte \Ninto a biological battery.
Dialogue: 0,0:02:06.49,0:02:10.65,Default,,0000,0000,0000,,The key to these fish's powers \Nis that nerve signals are coordinated
Dialogue: 0,0:02:10.65,0:02:15.03,Default,,0000,0000,0000,,to arrive at each cell \Nat exactly the same time.
Dialogue: 0,0:02:15.03,0:02:21.08,Default,,0000,0000,0000,,That makes the stacks of electrocytes\Nact like thousands of batteries in series.
Dialogue: 0,0:02:21.08,0:02:24.32,Default,,0000,0000,0000,,The tiny charges from each one\Nadd up to an electrical field
Dialogue: 0,0:02:24.32,0:02:27.06,Default,,0000,0000,0000,,that can travel several meters.
Dialogue: 0,0:02:27.06,0:02:30.14,Default,,0000,0000,0000,,Cells called electroreceptors\Nburied in the skin
Dialogue: 0,0:02:30.14,0:02:33.12,Default,,0000,0000,0000,,allow the fish to constantly sense\Nthis field
Dialogue: 0,0:02:33.12,0:02:38.02,Default,,0000,0000,0000,,and the changes to it caused \Nby the surroundings or other fish.
Dialogue: 0,0:02:38.02,0:02:40.49,Default,,0000,0000,0000,,The Peter’s elephantnose fish, \Nfor example,
Dialogue: 0,0:02:40.49,0:02:43.67,Default,,0000,0000,0000,,has an elongated chin\Ncalled a schnauzenorgan
Dialogue: 0,0:02:43.67,0:02:46.10,Default,,0000,0000,0000,,that's riddled in electroreceptors.
Dialogue: 0,0:02:46.10,0:02:48.89,Default,,0000,0000,0000,,That allows it to intercept signals\Nfrom other fish,
Dialogue: 0,0:02:48.89,0:02:50.79,Default,,0000,0000,0000,,judge distances,
Dialogue: 0,0:02:50.79,0:02:53.79,Default,,0000,0000,0000,,detect the shape and size\Nof nearby objects,
Dialogue: 0,0:02:53.79,0:02:58.80,Default,,0000,0000,0000,,and even determine whether\Na buried insect is dead or alive.
Dialogue: 0,0:02:58.80,0:03:01.30,Default,,0000,0000,0000,,But the elephantnose\Nand other weakly electric fish
Dialogue: 0,0:03:01.30,0:03:05.40,Default,,0000,0000,0000,,don't produce enough electricity\Nto attack their prey.
Dialogue: 0,0:03:05.40,0:03:08.57,Default,,0000,0000,0000,,That ability belongs \Nto the strongly electric fish,
Dialogue: 0,0:03:08.57,0:03:11.79,Default,,0000,0000,0000,,of which there are only \Na handful of species.
Dialogue: 0,0:03:11.79,0:03:16.39,Default,,0000,0000,0000,,The most powerful strongly electric\Nfish is the electric knife fish,
Dialogue: 0,0:03:16.39,0:03:20.51,Default,,0000,0000,0000,,more commonly known as the electric eel.
Dialogue: 0,0:03:20.51,0:03:25.40,Default,,0000,0000,0000,,Three electric organs span\Nalmost its entire two-meter body.
Dialogue: 0,0:03:25.40,0:03:27.35,Default,,0000,0000,0000,,Like the weakly electric fish,
Dialogue: 0,0:03:27.35,0:03:30.96,Default,,0000,0000,0000,,the electric eel uses its signals\Nto navigate and communicate,
Dialogue: 0,0:03:30.96,0:03:34.68,Default,,0000,0000,0000,,but it reserves its strongest \Nelectric discharges for hunting
Dialogue: 0,0:03:34.68,0:03:40.27,Default,,0000,0000,0000,,using a two-phased attack that susses out\Nand then incapacitates its prey.
Dialogue: 0,0:03:40.27,0:03:43.100,Default,,0000,0000,0000,,First, it emits two \Nor three strong pulses,
Dialogue: 0,0:03:43.100,0:03:46.44,Default,,0000,0000,0000,,as much as 600 volts.
Dialogue: 0,0:03:46.44,0:03:49.73,Default,,0000,0000,0000,,These stimulate the prey's muscles,\Nsending it into spasms
Dialogue: 0,0:03:49.73,0:03:53.04,Default,,0000,0000,0000,,and generating waves \Nthat reveal its hiding place.
Dialogue: 0,0:03:53.04,0:03:55.92,Default,,0000,0000,0000,,Then, a volley of fast, \Nhigh-voltage discharges
Dialogue: 0,0:03:55.92,0:03:59.29,Default,,0000,0000,0000,,causes even more intense \Nmuscle contractions.
Dialogue: 0,0:03:59.29,0:04:03.10,Default,,0000,0000,0000,,The electric eel can also curl up\Nso that the electric fields
Dialogue: 0,0:04:03.10,0:04:07.25,Default,,0000,0000,0000,,generated at each end \Nof the electric organ overlap.
Dialogue: 0,0:04:07.25,0:04:10.94,Default,,0000,0000,0000,,The electrical storm eventually\Nexhausts and immobilizes the prey,
Dialogue: 0,0:04:10.94,0:04:14.89,Default,,0000,0000,0000,,and the electric eel \Ncan swallow its meal alive.
Dialogue: 0,0:04:14.89,0:04:18.55,Default,,0000,0000,0000,,The other two strongly electric fish\Nare the electric catfish,
Dialogue: 0,0:04:18.55,0:04:20.94,Default,,0000,0000,0000,,which can unleash 350 volts
Dialogue: 0,0:04:20.94,0:04:23.91,Default,,0000,0000,0000,,with an electric organ \Nthat occupies most of its torso,
Dialogue: 0,0:04:23.91,0:04:29.47,Default,,0000,0000,0000,,and the electric ray, with kidney-shaped\Nelectric organs on either side of its head
Dialogue: 0,0:04:29.47,0:04:32.85,Default,,0000,0000,0000,,that produce as much as 220 volts.
Dialogue: 0,0:04:32.85,0:04:35.72,Default,,0000,0000,0000,,There is one mystery in the world\Nof electric fish:
Dialogue: 0,0:04:35.72,0:04:39.44,Default,,0000,0000,0000,,why don't they electrocute themselves?
Dialogue: 0,0:04:39.44,0:04:42.15,Default,,0000,0000,0000,,It may be that the size \Nof strongly electric fish
Dialogue: 0,0:04:42.15,0:04:44.80,Default,,0000,0000,0000,,allows them to withstand their own shocks,
Dialogue: 0,0:04:44.80,0:04:48.46,Default,,0000,0000,0000,,or that the current passes out \Nof their bodies too quickly.
Dialogue: 0,0:04:48.46,0:04:53.05,Default,,0000,0000,0000,,Some scientists think that special \Nproteins may shield the electric organs,
Dialogue: 0,0:04:53.05,0:04:57.96,Default,,0000,0000,0000,,but the truth is, this is one mystery \Nscience still hasn't illuminated.