•

EEL

by

CARL L. HUBBS

Reprinted from Encyclopaedia Britannica C)I963 by ENCYCLOPAEDIA BRITANNICA, INC. g i°0°' 5 /6

EEL, the name that is properly applied to any fish of the order long dorsal fin and the anal fin are joined around the end of the Anguilliformes (Apodes). The true eels are all elongate in form tail to form, with the greatly reduced caudal fin, a single soft-rayed and lack all trace of the pelvic fin (hence the name Apodes, mean- vertical fin. The gill openings are small; the gas bladder has a ing without feet, or, in this case, pelvic fins). The smooth, muscu- duct to the esophagus. Compared with other fishes, the eel's lar, snakelike body, usually scaleless (but with embedded scales vertebrae are greatly increased in number; the face bones, includ- in a few species) and covered with a copious supply of mucus, ing the jawbones, are reduced in number. All eels pass through a renders eels very difficult to grasp. In most species the very protracted larval stage, known as the leptocephalus, in which the

Printed in 13. S. A. EEL much compressed and generally elongate body is glassy-clear; and anal fins, are also widely distributed in warm coastal waters, these larvae commonly reach a length of more than six inches; along with the little worm eels (generally less than a foot long) one five-foot-long larva has been thought to represent the young and members of other families. Various eels occur on the bottom of a gigantic eel that may have been the basis for reports of sea in deep water—among them Synaphobranchus, with the gill slits serpents. united below; and Simenchelys, a blunt-headed eel, which, like the Fresh-Water Eels.—Best known and of greatest commercial hagfishes, burrows into other fishes to consume the muscle. Still importance are the fresh-water eels, family Anguillidae, of Europe other and even more bizarre eels inhabit the cold black mid-depths (Anguilla anguilla), eastern North America (Anguilla rostrata) of the ocean. Prominent among these are the snipe eels (Nemich- (fig. 1), Japan (Anguilla japonica) and various countries bordering the western Pacific, New Zealand and the Indian ocean (other species of Anguilla). The fresh-water eels utilize streams, ponds and estuaries for their growth and development, but like all other eels, they breed and pass through their larval life in the sea. Some if not all migrate long distances from the mouth of streams to the breeding waters. Thus the European eel, after forsaking the stream in which it developed, migrates, .using as yet unknown clues, to an oceanic area southeast of Bermuda, where it is assumed that it TRENT DAVIDSON spawns and dies. The spawning area, long a mystery, was deter- FIG. I.-AMERICAN EEL (ANGUILLA ROSTRATA), EASTERN NORTH AMERICA mined by a great Danish scientist, Johannes Schmidt, through a prolonged and famous study of the distribution of the larvae of different size-classes. He further discovered that the American eel breeds in an overlapping area, and that the leptocephalus larva of the European eel, which drifts slowly to Europe in the Gulf Stream, requires three years to reach the stage of transformation known as the elver, at which stage the young eel runs into streams to start its period of growth and development in fresh water. (In the middle ages, long before the remarkable life history of the European eel had been deciphered, it was thought that this fish was spontaneously generated from mud.) The American eel, which has a shorter journey in the open sea, passes through its BY COURTESY OF CARL L. HUBBS larval life in a single year. FIG. 2.-BOBTAIL SNIPE EEL (CYEMA ATRUM ), OF MARINE MID-DEPTHS Fresh-water eels are highly esteemed for food, especially in Europe and Japan. Large numbers are caught, and are consumed thyidae), in which the threadlike jaws are rough with tiny teeth either fresh or smoked. The main fishing in Europe is for "silver that entangle the prey and the body cavity is extremely short. The eels," the stage in which the eels, rich in fats, are starting their excessively elongate tail region is extended into a long filament, journey downstream toward the sea. In Japan, and to a lesser except in the bobtail snipe eel, Cyema atrum (fig. 2). extent in Europe, eels are reared for the market in ponds. The name eel is often applied to many other eel-shaped (an, Marine Eels.—In the oceans, particularly in warm seas, several liform) fishes. For example, the lamprey (q.v.) is often c hundred known marine eels represent many types and live in di- lamprey eel, and the hagfish (q.v.) is also called slime-eel. verse habitats. The most conspicuous eels of the coral reefs are so-called spiny eels and their relatives are deep-sea fishes belo the morays (family Muraenidae), which are sharp-toothed, large- to the order Notacanthiformes (Heteromi). The electr' mouthed and often vicious fishes, much feared by skin divers. (q.v.) is not an eel at all, but is more closely allied with cat Morays lack the pectoral as well as the pelvic fins and have the minnows, etc., in an entirely different order. gill openings reduced to pores. The snake eels (Ophichthidae), in See also FISH; and references under "Eel" in the Index vol which the finless tail tip projects beyond the ends of the dorsal (C. L. H