Slippery, slimy and seriously fascinating: Why the American eel still baffles science

Yahoo

25-06-2025

Eels. Just the name can bring shivers to some. Slippery, slimy and wiggly like snakes.
All true, but some of us think they are amazing creatures. Yes, I confess to being enamored of these slippery devils.
According to the Encyclopedia Brittanica, there are more than 800 species of eels in the world, but contrary to popular belief, there is just one species of eel in North America, and that is the American eel
Some may believe that the lamprey eel fits into this category, but they are very different animals.
A lamprey is a cartilaginous fish, meaning no bones. Their mouths are jawless without teeth and are used to attach to other organisms to suck out their body fluids. Now, that brings shivers to me! They have a series of gill holes instead of slits behind their head in which to breathe. Lampreys are anadromous and migrate from the sea into rivers and lakes to spawn.
Despite their appearance, the American eel is a true bony fish, with tiny teeth and an elongated, snakelike body capable of twisting and turning in any direction.
Its body is covered in tiny scales, and its dorsal and caudal fins are fused into two long fins on the top and underside of its body. Their pectoral fins are tiny and located just behind the gill slits on their head. The slime is the mucus layer that protects them from infection.
American eels are catadromous; they spend most of their life in fresh water and migrate to the ocean to spawn.
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Despite intensive research, much about the American eel's lifecycle remains unknown. What we do know is that these eels spend most of their lives in freshwater lakes and streams along North America's Atlantic and Gulf coasts. They can swim into salty estuaries, move over grassy areas, and climb obstacles out of the water to reach streams.
Let's start at the beginning. Scientists regularly find American eel larvae floating in large numbers in the Sargasso Sea. Located about 590 miles east of Florida, the Sargasso is known for its calm, glassy surface and minimal wind. It is believed that adult American eels swim there from North America to breed.
Although eels have been observed swimming toward the Sargasso, they've never actually been seen in the area. Scientists believe they have external fertilization in a spawning frenzy somewhere in the Sargasso Sea. This also has never been observed. Since no one has ever found the adult eels after they spawn, scientists believe that they die immediately after spawning. There is an awful lot we are guessing about these animals.
We do know that they hatch into larval stages and float towards the coast of North America on the Gulf Stream. This can take up to a year, at which time, they metamorphose into glass eels. These are small, transparent eel-like animals that enter streams and estuaries into fresh water, where they once again metamorphose into what we would recognize as an eel. They will spend decades in fresh water and then undergo another metamorphosis. At the time of maturation, they will develop male or female characteristics. Their eyes change to better adapt to the ocean environment, and their digestive tract shrinks while storing fat for their migration back to the Sargasso Sea.
Their life has such a complex turn of events. It gives me a sense of awe that the natural world has so many twists and turns, and still animals survive. Of course, that is without the interference of man.
Eels are a delicacy in Europe but have yet to catch the taste buds of Americans. Something about the sliminess, I should think!
In Maine, 'elvers' are a huge high-profit fishery. Elvers are the tiny-year-old eels that have returned from the Sargasso Sea as glass eels. Elvers are sold to the Asian market to be used as stock for their aquaculture, as eels are a delicacy in Japan. According to the Maine Department of Marine Resources, the price for elvers to commercial fishermen topped $2000 per pound in 2019! They are strictly managed by the Atlantic States Marine Fishery Commission, hoping to avoid what has happened to the Japanese and European eels, which are endangered. The American eel is doing well as they are found throughout the coastal waters of North America, and the juveniles are only fished commercially in Maine and South Carolina.
Some eels travel thousands of miles. How do they know where to go? There are many theories. One, published recently by Dr. Alessandro Cresci, focuses on the European eel. He discovered that they use a combination of moon phases and Earth's magnetic field to guide their migration. This could explain how the American eel finds its way back to the Sargasso Sea.
Having said all this, I would add that the American eel remains one of the ocean's most closely kept mysteries. No one has ever witnessed their spawning. Each February, large numbers of larvae are found in the Sargasso Sea, yet neither adults nor eggs have ever been seen there. Where do they go after leaving the estuaries? Where are their eggs? So many unknowns about our ocean and so much to learn.
Ellen Goethel is a marine biologist and the owner of Explore the Ocean World Oceanarium at 367 Ocean Blvd. at Hampton Beach.
This article originally appeared on Portsmouth Herald: Slippery, slimy and seriously fascinating: Meet the American eel