Enigmatic eel in the Rock

StoryImage( ‘/Images/Story//img-rFNZDQDXOT.jpg’, ‘Photo by Dr. Robert Hedeen’, ‘The complicated life cycle of the eel adds to its mystique.’);

A photo in a recent issue of the local daily newspaper of a large eel caught in the Rock River was of considerable interest. Several people have told me they had heard of someone catching an eel from the river, but they personally had not had that experience. Elizabeth Mullen in her 1992 The Fishes of Winnebago County, Illinois reports the presence of these mysterious fish in three unidentified tributaries of the river, and confirms they are certainly not common denizens of the waters in our area.

One of the interesting tales about eels is the story of their migration. It has taken scientists many years to discover the details of the eel’s life cycle. Even now, the story is not complete, but what has been discovered makes an exciting scientific saga.

Many people know several species of fish, such as the salmon, striped bass, and herring, live in salt water and return to their birthplace in fresh water to reproduce, but many do not know that a few fish reverse the procedure and breed in the ocean and return to fresh water to mature. The enigmatic eel is in the latter category

Perhaps it is appropriate that fresh-water eels, about which so many fish yarns have been spun, should have unusual breeding habits. These “snaky” fish become sexually mature when they are several years old, and shortly thereafter start downstream toward the sea. Eventually, large numbers of them congregate in a common breeding ground in the Atlantic Ocean in an area southwest of Bermuda called the Sargasso Sea. Here they spawn, and, having fulfilled their biological duty, die in a short time.

The fertilized egg does not hatch into a creature resembling a miniature eel, but into a flattened, leaf-like, small larva called a leptocephalus (slender head, in Latin). The larvae somehow find their way back to shore, but before they are physiologically able to enter fresh water, they must change into another juvenile form called an elver. The elvers swim upstream and remain in fresh or brackish water until they become mature, in some cases requiring up to 20 years.

Curiously enough, the American and European eels, although different species, use the same breeding grounds and frequently intermingle. Yet, the integrity of each type is not violated. An American eel has never been found in European waters and vice versa.

The larva of the American eel requires about a year to reach the shores of North America, and the timing of the transformation from leptocephalus to elver is synchronized with the travel time. The European leptocephalus requires about three years reaching the mouths of the rivers of Europe to change into the elver form. Apparently the eel’s sense of direction is well developed, as an American eel that made a right turn at Cuba would find itself in the embarrassing position of changing into a fresh water form in mid Atlantic, and a European eel that turned left would have to wait off American shores for two years before it was capable of entering fresh water.

Another interesting thing about eels is their ability to leave the water and travel overland for considerable distances. The skin is heavily laden with slippery mucus, and this facilitates their movement overland around barriers to their migration such as dams. They occur in almost every watershed in Illinois except those that drain into Lake Michigan, and they have been found as far north as rivers and streams in the Dakotas.

Eels are not a popular food item in this country except among certain ethnic groups, but in other parts of the world, they are considered a delicacy. In northern Europe, especially along the coast, smoked eel is preferred; while farther inland it is either boiled with dill or served cold in aspic. Residents of the Baltic region smoke the eel first and then fry it in butter.

I once ordered smoked eel served in a heavy wine sauce at a wayside inn in the Bordeaux region of France. Frankly, I can’t remember how the eel tasted, but I do recall the sauce was delicious.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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