Marine Biology
eels, american, silver

American Eel

eels, american, silver
Effie Moore Salem's image for:
"American Eel"
Caption: eels, american, silver
Image by: rach2k
© creative commons

The American eel is an ugly and slimy little creature that resembles a flattened snake in some respects but it has a most interesting life cycle. And not only that, it has secrets about its overall life that scientists have yet to unravel. And if that’s not enough to make this combination salt and fresh water marine creature interesting, it’s a food delicacy in Europe and Asia. The European variety Aguilla aguilla is almost the same as the American variety, Aguilla rostrata but genetically there are small differences in coloring, and possibly in shape and in actions.   

Both varieties of eel are born in the Sargasso Sea in the Atlantic Ocean.  This area of the ocean is peculiar in that masses of Sargasso grass that grows deep down in the ocean form mats that float. This sea is in the Bermuda Triangle off of the shores of the Carolinas notorious for sinking ships. Many have sailed into this strip of ocean to disappear and never be heard from again.

As unlikely as it appears, eels are hatched in this area and then they migrate to fresh water areas while maturing. When in the stage to give birth they begin the trek homeward to the Atlantic and the females undergo bodily changes. They gradually turn themselves into a large egg pouch bag that can hold as many as a million eggs. On their journey to Europe the newly hatched eels ride the currents. Generally their journey will take about three years.

The American larvae is hatched in the same way as the European variety but being closer to land and to fresh water lakes and streams they often have even been found in the Great Lakes.

They don’t swim, they drift in the currents but if landed in grass or on rocks they can twist and turn themselves to get free from entanglements. Where they eventually end up has much to do with the currents and in what direction they take. They’ve been found in the Gulf of Mexico, as far north as Greenland and in the other direction, in the West Indies. Some eels remain in estuaries and in salt marshes.  

Larvae, first and second stage of life cycle

As baby eels they are about two inches long, worm like, and will continue developing. All creatures are born with some kind of natural protection and the eel’s protection is its slime. From their skin they produce copious amounts of mucous which makes them difficult from other creatures to hold on to them.

In their second stage of development they lose their silvery look and develop their pigmentation which nearly resembles their adult stage of growth. In this second stage, they’re called yellow eels and this designation means they’re yet too immature to create new life. Completion of their life cycle will take anywhere from five to twenty years.

Nocturnal habits

They come out at night to eat and to search for food; Small fish, insects, worms, crawfish and snails are gourmet food to them. During the day they remain out of sight by burrowing in the ocean floor sediment. This is probably because intense light disturbs them or it could also be for safety; most other sea creatures feed during the daytime and use their eyes in searching for food.

Size of eels when grown

Females are larger than males and weigh in at three or four pounds when fully mature: Males, with smaller chores only reach about a foot or a foot and a half. The larger body mass of the female is for the purpose of carrying and nurturing eggs. There are exceptions: Landlocked eels sometimes grow to five and six feet and weigh up to ten or fifteen pounds.

At maturity

In their final stage of development transformation takes place as they begin their journey back to where they were hatched, back to the Sargasso Sea. It seems as if nature has programmed this habitat specifically for eels and this particular arrangement of grasses that hold on to the ells as currents and swift waters batter them about.

This too is where the mystery begins. The whole pilgrimage toward their nesting ground is never observed by scientists.  And precisely how this pilgrimage takes places is unknown to them but it happens again and again. The journey toward home begins in the fall, as early as August but reaches its peak in September and November. A few stragglers may wait until December but most mature eels have already moved out by then.  Downstream they head as if by clockwork and into the ocean they disappear.

Changes during maturity

Eels lose their yellow color and develop silvery looks to their exteriors. Their reproductive organs grow and fat deposits form which become the fueling sources for their long journey toward their hatching grounds. They’ve eaten all they can eat and their gut becomes useless and degenerates.

These changes have been necessary to help them adapt to their new salt water habitat. Their eyes change, become larger and their eyes change from being light sensitive to red while they were in the fresh water environment, to blue light sensitive in the salt water environment.  Their bodies change and become more adaptable at swimming in deeper water levels.

At home

When this fateful trip is over no one knows for sure, but the evidence that the eel arrived home is evident by a new breed of hatchling come spring. In the meantime, the female gives over herself to her brood. The male is more active but both die after the spawning is over. The new hatchlings are silver in color. The new generation is seen as a willow leaved shaped eel while in the larvae stage.  

As the yellow eels migrate downstream, they are caught in nets by fishermen who are out to catch them for human food. The most valuable type of eels for commercial use is the silver eels because they have more fat content. These are shipped live to Europe for their gourmet dining tables. 

More about this author: Effie Moore Salem

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