EEL, the name given generally to fishes of the order Apodes, and particularly to the common or fresh-water eel of Europe (Anguilla anguilla). The Apodes are soft-rayed fishes with a duct to the air-bladder, elongate, with small gill-openings, with out pelvic fins, and generally with long dorsal and anal fins con fluent with the reduced caudal. The congers and the morays (Muraena) are well known members of this large group of marine fishes, all of which have compressed transparent pelagic larvae, known as Leptocephali.
Anguilla anguilla is found on the coasts and in the rivers of western Europe and the Mediterranean countries. It has an elongate, subcylindrical body, covered with small oblong scales embedded in the slimy skin, and arranged in little groups at right angles to each other; the mouth is terminal, with bands of pointed teeth ; the back is greenish or brownish, the sides generally yellowish. The eels inhabit not only rivers and lakes but small brooks and isolated ponds ; they are also found in harbours and estuaries and on muddy shores. They often burrow during the day and feed principally at night, eating any kind of animal food. A length of 5ft. and a weight of 2olb. may be reached. Towards the autumn some eels cease feeding and become silvery; the snout also becomes sharp, the eyes larger and the pectoral fins more pointed. These silver eels descend to the sea, and it has been established by Dr. Johannes Schmidt that they travel across the Atlantic to breed in an area south-east of Bermuda, and die after breeding. The transparent larvae, which have needle-shaped teeth, live near the surface of the ocean, and as they spread out across the Atlantic grow from about iomm. to 75mm. long in about 24 years; the full-grown larvae occur off the Atlantic coast of Europe and in the western Mediterranean during the summer; they cease feeding, lose their larval teeth, shrink in depth and length, and change into the elvers, or little eels, which enter rivers in large numbers during the winter and spring. Scale investigations have shown that male eels assume their breeding dress 4-5 to 81 years after the elver stage, when they are 12 to 2oin. long, and female eels usually after 61 to 84 years, when they are 14 to 2 6in. long; but larger females 3 f t. long have lived I0- to 124 years since the elver stage. The silver eels have the flesh full of fat, and in the most important fisheries they are intercepted on their way to the ocean, as on the Bann, which runs out of Lough Neagh. Denmark has valuable eel fisheries, and at Commachio, on the Adriatic, eels are farmed in extensive brackish lagoons, the natural supply of elvers replenishing the stock. Schmidt's researches are of great economic importance, showing that for a particular fishery it is useless to allow silver eels to escape, as plenty from other regions will reach the breeding place. The American eel (Anguilla chrysypa) differs from the European eel chiefly in the fewer vertebrae, 104 to 1 1 o instead of to 1 I 8 ; it breeds in an area overlapping the breeding area of the European species, but extending westwards from it. It has a shorter larval history, the elvers being one year old instead of three; this difference keeps the species distinct, for if larvae of the American eel travel east they change into elvers in the middle of the Atlantic, and those of the European eel going west reach America as small larvae. Other species of Anguilla are from Japan, Indian ocean and western Pacific. (See FISHES.) (C. T. R.) or GLASS-WRACK (Zostera), the name applied to certain salt-water plants, growing on gently sloping shores in temperate regions. The lower part of the stem is creep ing, the branches growing upwards and dividing. The leaves are long and narrow. Two of the six species are British and three occur off the shores of North America. The pollen grains have the same specific gravity as water, so that they float at any depth. Zostera belongs to the family Potamogetonaceae, which also includes the pond-weeds (q.v.).