Probing the Secrets of the Eel
By Awake! correspondent in Ireland
EELS baffled Aristotle, the ancient Greek philosopher. However much he examined these smooth-skinned, snakelike fish, he found neither sex organs nor eggs. “The eel,” he said, “is neither male nor female, and can engender nothing.” He concluded: “Eels are derived from the so-called ‘earth’s guts’ that grow spontaneously in mud and in humid ground.”
Modern researchers have solved this particular mystery about the eel. Christopher Moriarty of the Department of the Marine in Ireland explains that while most fish show very distinct eggs, the eel shows no sign of even a small egg. “The ovary of the eel,” he says, “is inconspicuous—almost invisible in young specimens, and forming no more than a whitish, frilled ribbon in more mature ones.”
Since no spawning eel has ever been caught, even up to modern times, you can understand why Aristotle was puzzled. Not having a microscope, he had no way of finding out where eels came from.
While scientists have solved this particular mystery about the eel, they have uncovered others that are still puzzling. Take a look, for example, at the life cycle of the European freshwater eel, and see if it does not intrigue you.
The Mystery of Its Origin
Each spring, millions of tiny eels two or three inches long [5-8 cm]—called elvers—arrive near the shores of Western Europe and North Africa. Where do they come from? Until the 1920’s, no one knew.
However, near the end of the 19th century, a startling discovery was made that contributed to a solution of this mystery. It was observed that the eel, like the frog and the butterfly, starts life in a different form. Biologists discerned for the first time that a slim, transparent fish called leptocephalus, with a tiny head and a body shaped like a willow leaf, metamorphosed, or changed form, to become a tiny transparent larva called a glass eel.
Once the connection between the leptocephalus and the glass eel was made, it was possible to track the eel larvae back to their source. In 1922, Danish oceanographer Johannes Schmidt discovered that the spawning ground of all Atlantic eels is the Sargasso sea, a vast, weed-strewed area of ocean in the North Atlantic. Both the American and the European eels spawn there, and therein lies another mystery.
Take Different Routes
American and European eel larvae go their different ways somewhere near Bermuda. “How they know which way to go when neither has ever seen its ‘home’ is an unanswered question,” says The Fresh & Salt Water Fishes of the World. The book goes on: “For the American eels, the trip is about 1,000 miles [1,600 km]; the journey requires about a year. European eels travel 3,000 miles [5,000 km] or more, their trip taking nearly three years. Equally astonishing is the fact that the growth rates of the two eels [which are almost impossible to tell apart] differ so that each has developed to about the same size by the time they reach their destination.”
Some amazing instinct directs the two types of eels to go their separate ways. Of this mysterious event, the book Fishes of Lakes, Rivers & Oceans says: “How and why they manage this astonishing maneuver is as much a puzzle as their origins were in Aristotle’s time.”
Life in Freshwater
When the growing elvers, now yellow-brown in color, finish their ocean crossing, they instinctively travel upriver to reach the lakes, ponds, and streams where they will grow to maturity over the next 15 years and more. They overcome all obstacles to reach their objective.
The book The Royal Natural History describes “the banks of the rivers being in places black with these migrating little fishes.” It continues: “These young eels have been observed to ascend floodgates of lochs, to creep up water-pipes or drains . . . and they will even make a circuit over a wet piece of ground in order to attain a desirable spot.”
In the River Bann in Northern Ireland, fishermen have laid down elver ladders made of straw at the most difficult part of the river. Here, the elvers climb these ropes into special tanks where they are counted—20,000,000 of them every year!
Transformation and Migration
When the eels reach maturity, something else very mysterious happens. “A series of remarkable changes associated with the onset of maturity take place,” says the book Fishes of the Sea. “The eye increases in diameter and becomes specialized for vision in deep ocean waters; the gut begins to atrophy and the gonads enlarge. The colour also changes from a yellow brown to a silver grey.”
Each autumn, mature eels begin a 3,000-mile [5,000 km] migration back to the Sargasso sea. How they accomplish this remarkable feat of navigation no one knows. They stop feeding and during the six-month journey survive on the fat deposits they have built up.
Biologists say that once back in the deep waters of the Sargasso sea, the female eel lays from 10 to 20 million eggs, and the male fertilizes them. Then the adults die. The fertilized eggs float to the surface and hatch as the leaf-shaped leptocephalus, and the cycle is complete.
Why has no spawning eel ever been caught? “They are no longer feeding, since their digestive organs have wasted away, so they cannot be caught with baited lines,” says Christopher Moriarty. “They spawn at great depths,” he continues, “and since the area of the Sargasso Sea is greater than that of the British Isles, and eels are elusive creatures, they will always have a good chance of escaping fast-moving trawls.”
Perhaps one day all the mysteries surrounding this remarkable creature will be solved. In the meantime, according to researcher Moriarty, when it comes to fascinating fish, ‘the eel is really outstanding.’
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Eel Recipes
While some are revolted by the thought of eating eels, in many parts of the world, they are viewed as a delicacy. Would you like to try eel? Awake! asked a chef in Northern Ireland how to cook the fish. Here are two of his suggestions:
Eel Stew: You will need two medium-sized eels about 20 inches [50 cm] or so in length. They need to be skinned and boned and cut into two-inch [5 cm] pieces. You will also need four tablespoonfuls [60 cc] of olive oil; several crushed garlic cloves; one bouquet garni; juice of one orange; some grated orange rind; a pinch of red chili pepper; a pinch of salt; five fluid ounces [140 cc] of red wine.
Put the olive oil in an earthenware casserole or thick-bottomed pan large enough to hold all the ingredients. Add the crushed garlic, bouquet garni, orange juice and rind, and red chili pepper. Season the pieces of eel with salt, and put them in the casserole. Pour the wine over them, and add enough water to cover the eels. Cook uncovered over a moderate heat for about 30 minutes until the eel is cooked. Serve on heated plates.
Jellied Eels: Put at least a cup of skinned, boned, chopped eels into a saucepan. Add a chopped onion, a carrot, a stick of celery, a bay leaf, some parsley, salt and pepper, and enough water, white wine, or cider to cover the ingredients. Bring this slowly to a boil, and simmer covered for about an hour. Put the cooked eel pieces into a container. Boil the remaining ingredients until they reduce by a quarter, then strain the liquid over the pieces of eel. Discard the vegetables and herbs. Cool the pieces of eel and the liquid to form a jelly. Eat it with lemon juice and buttered toast, just like pâté.
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Did You Know?
The mature female European eel measures about 36 inches [1 m] long, but the male is only half that size.
Some mature eels living in landlocked ponds or lakes never migrate. They can live in such places for 50 years or more.
Eels can survive for 48 hours out of water.
The oldest eel on record was a female named Putte. She died in an aquarium at over 85 years of age.
Eels have an exceptionally keen sense of smell, at least as sensitive as a dog’s.
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Ireland’s River Bann teems with millions of eels