WEBVTT - How Do Eels Reproduce? 0:00:01.800 --> 0:00:06.920 Welcome to brain Stuff, a production of I Heart Radio. Hey, 0:00:06.960 --> 0:00:11.440 brain Stuff, Lauren vogel Bomb here online. It's become a 0:00:11.520 --> 0:00:16.440 frequently asked question. How do eels, those long, writhing fish 0:00:16.560 --> 0:00:18.960 you might have seen an aquarium or on a menu, 0:00:19.520 --> 0:00:25.000 go about making eel babies? How to eels reproduce for real? 0:00:25.320 --> 0:00:28.560 People have studied these creatures for literally thousands of years, 0:00:28.600 --> 0:00:31.320 but even after all this time, some aspects of their 0:00:31.320 --> 0:00:35.560 breeding lives are still shrouded in mystery. And to get 0:00:35.600 --> 0:00:38.839 these skinny on eel reproduction for the articles, episode is 0:00:38.840 --> 0:00:42.440 based on how Stuff Works. Spoke with an expert, Caroline Derriff, 0:00:42.560 --> 0:00:45.760 an ecologist at the Norwegian Institute of Marine Research who 0:00:45.760 --> 0:00:51.040 studies the habits of these incredible fish. Okay, first off, 0:00:51.320 --> 0:00:55.480 calling something an eel doesn't make it one necessarily, no 0:00:55.600 --> 0:00:59.320 doubt you've heard of the South American electric eel. Despite 0:00:59.440 --> 0:01:02.960 common name, that dramatic fish isn't really an eel. It's 0:01:03.000 --> 0:01:08.720 a Bizarro carp relative that's classified as a knife fish. 0:01:08.880 --> 0:01:13.080 The order Anguilliforms contains all of the world's true eels. 0:01:13.520 --> 0:01:16.720 There are more than eight hundred species from Mora's you know, 0:01:16.880 --> 0:01:20.839 Ursula's sidekicks from the little Mermaid to the aptly named spaghetti. 0:01:20.920 --> 0:01:26.000 Eels usually slender and elongated a true eels do not 0:01:26.160 --> 0:01:29.679 have pelvic fins, which are twin appendages often found on 0:01:29.720 --> 0:01:34.119 the underbellies of other fish. Eels can be scaleless, Many 0:01:34.160 --> 0:01:38.560 species feel slippery to the touch, and salt water is 0:01:38.600 --> 0:01:42.440 the preferred habitat for the majority of eels. However, there 0:01:42.480 --> 0:01:46.600 are nineteen species of so called freshwater eels or anglid, 0:01:47.080 --> 0:01:50.120 which spend some stages of their lives in fresh water. 0:01:50.960 --> 0:01:53.880 They spawn in the ocean, that is, the adults produce 0:01:53.960 --> 0:01:56.960 eggs and sperm, and then the resulting babies hatched there, 0:01:57.880 --> 0:02:01.120 but they grow in freshwater before turning to the sea. 0:02:03.120 --> 0:02:05.680 Saying that these fish have a complex life cycle is 0:02:05.760 --> 0:02:09.360 a little bit of an understatement. If it survives to 0:02:09.440 --> 0:02:12.600 reach sexual maturity, a freshwater eel will have gone through 0:02:12.800 --> 0:02:17.279 five distinct stages. With each new phase, the animal experiences 0:02:17.360 --> 0:02:22.239 both a physical transformation and shift in lifestyle. Derec explained. 0:02:22.639 --> 0:02:26.720 The first stage is called the leptocephalus larva. They're called 0:02:26.800 --> 0:02:33.120 leptocephalus because lepta means leaf and cephalis means head. True 0:02:33.120 --> 0:02:36.400 to the name, the newborn larva have leaf shaped bodies 0:02:36.440 --> 0:02:40.639 that appear broad and flattened in profile in biological jargon. 0:02:40.760 --> 0:02:46.560 Their bodies are laterally compressed, being nearly transparent. They're also 0:02:46.800 --> 0:02:50.600 very well camouflaged. Imagine trying to recover a lost contact 0:02:50.720 --> 0:02:55.200 lens from the bottom of a swimming pool. Leptocephalus larva 0:02:55.320 --> 0:02:59.799 are ocean going animals. Eventually, though instinct pushes them defined 0:03:00.080 --> 0:03:03.000 change in scenery, which is where the change into the 0:03:03.000 --> 0:03:07.600 second phase of the life cycle occurs. Derriff said, they 0:03:07.639 --> 0:03:11.760 migrate for great distances. They drift through the gulf stream, 0:03:11.840 --> 0:03:14.760 and then when they reach the continental shelf, they metamorphos 0:03:14.840 --> 0:03:19.560 into glass eels. A glass eels are still more or 0:03:19.639 --> 0:03:24.160 less transparent, but they're longer and skinnier by comparison, and 0:03:24.320 --> 0:03:27.520 they're attracted to fresh water, so they head inland by 0:03:27.560 --> 0:03:31.440 traveling up rivers, and that brings us to life stage 0:03:31.520 --> 0:03:35.560 number three, a yellow eels. Unlike the transparent larva and 0:03:35.600 --> 0:03:39.280 glass eels, these guys have body pigment with a yellowish 0:03:39.320 --> 0:03:42.600 overall complexion. But it's not the last color change that 0:03:42.600 --> 0:03:45.600 the fish will go through. A Derff said, oh, when 0:03:45.640 --> 0:03:49.160 they're ready, they become silver eels, which is like puberty. 0:03:49.400 --> 0:03:51.680 We often call them silver because they have a silver 0:03:51.760 --> 0:03:55.320 belly and a black dorsal area. It's an adaptation to predation. 0:03:57.280 --> 0:04:00.720 Many fish have the space of color pattern. When from below, 0:04:00.960 --> 0:04:03.840 their silver bellies blend in with the brighter light coming 0:04:03.880 --> 0:04:07.240 from the surface, and when viewed from above, their darker 0:04:07.240 --> 0:04:12.400 backs blend in with the dimmer water below. But this 0:04:12.520 --> 0:04:16.599 change in eels doesn't happen overnight. Transitioning from a yellow 0:04:16.600 --> 0:04:19.520 eel to a silver eel can take twenty or thirty years. 0:04:20.279 --> 0:04:23.480 Once the process finally ends, they return to their roots 0:04:23.560 --> 0:04:28.000 and head seaward. Only then can the eels attain sexual maturity, 0:04:28.360 --> 0:04:32.400 the fifth and final stage in their life cycle. However, 0:04:32.920 --> 0:04:35.880 we don't know much about the reproductive stage of angle 0:04:35.920 --> 0:04:39.080 at eels because no one has ever caught a sexually 0:04:39.160 --> 0:04:43.480 mature eel alive in the wild. Likewise, no one has 0:04:43.480 --> 0:04:47.600 observed these eels spawning in their natural habitat. The scientists 0:04:47.600 --> 0:04:50.400 have yet to catch wild angleids in the act, if 0:04:50.440 --> 0:04:55.640 you will, whatever happens out there. Experts think freshwater eels 0:04:55.760 --> 0:04:59.719 die shortly after mating. The laboratory researchers have managed to 0:05:00.200 --> 0:05:03.400 sexual maturity in silver eels by injecting them with hormones. 0:05:03.880 --> 0:05:08.200 But after the transition their health declines, and Dereff said 0:05:08.560 --> 0:05:12.320 the bones become decalcified like a woman during menopause. It's 0:05:12.360 --> 0:05:16.960 super interesting, actually, and then their digestive tract their gut regresses. 0:05:18.600 --> 0:05:21.560 Maybe that's just as well a breeding age. Freshwater eels 0:05:21.640 --> 0:05:24.440 get together in places where their usual food options like 0:05:24.520 --> 0:05:28.000 insects and small fish are probably rare or non existent. 0:05:30.000 --> 0:05:32.560 Out in the Atlantic Ocean, there's a region called the 0:05:32.600 --> 0:05:38.120 Sargasso Sea. Unlike the Mediterranean, the Red and most other seas, 0:05:38.120 --> 0:05:41.600 this one is not bordered by any land masses. Instead, 0:05:41.839 --> 0:05:46.560 its borders are formed by strong ocean currents. Both American 0:05:46.720 --> 0:05:50.480 and European species of freshwater eels come here to reproduce. 0:05:51.120 --> 0:05:54.200 A research suggests that they might use magnetic fields as 0:05:54.240 --> 0:05:58.280 a navigation tool. The European eel has the longest path 0:05:58.360 --> 0:06:02.560 to travel. Some individ jewels transverse around five thousand miles 0:06:02.640 --> 0:06:07.520 or eight thousand kilometers to get there from Norway, half 0:06:07.560 --> 0:06:10.159 a world away. The freshwater eels that live in and 0:06:10.200 --> 0:06:13.000 around the Pacific Ocean have spawning areas of their own. 0:06:13.839 --> 0:06:16.119 The Japanese eel is thought to breed at a site 0:06:16.120 --> 0:06:20.120 west of the Mariana Islands. Other species could be procreating 0:06:20.160 --> 0:06:26.320 somewhere between New Caledonia and Fiji. Eels release their eggs 0:06:26.400 --> 0:06:30.560 underwater to be fertilized by clouds of expelled sperm that 0:06:30.600 --> 0:06:34.040 goes for both freshwater eels and the non freshwater species 0:06:34.160 --> 0:06:38.719 such as the aforementioned moras and conger eels, speaking of 0:06:38.720 --> 0:06:41.880 which a derec explained that we know even less about 0:06:41.880 --> 0:06:45.640 conger eels than anglids when it comes to reproduction. She said, 0:06:46.000 --> 0:06:48.480 but we think there is at least a spawning area 0:06:48.680 --> 0:06:53.160 in the Mediterranean Baby. Hopefully future research will shed some 0:06:53.240 --> 0:07:01.479 light on their private lives. Today's episode is based on 0:07:01.480 --> 0:07:04.120 the article how do eels reproduce? On how stuff works 0:07:04.160 --> 0:07:07.279 dot Com, written by Mark Mancini. Brain Stuff is production 0:07:07.320 --> 0:07:09.400 of I Heart Radio in partnership with how stuff works 0:07:09.400 --> 0:07:12.120 dot Com and is produced by Tyler Clang. Four more 0:07:12.160 --> 0:07:14.760 podcasts from my heart Radio, visit the iHeart Radio app, 0:07:14.880 --> 0:07:17.720 Apple Podcasts, or wherever you listen to your favorite shows.