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(also Apodes), an order of fish (the eels) of the superfamily Teleostei. The body, which measures up to 3 m in length and may weigh up to 65 kg, is snakelike and usually scaleless. The dorsal and anal fins are long and often fused with the reduced tail fin, while the ventral and sometimes pectoral fins are absent. The eel develops through metamorphosis, beginning life as a translucent, leaf-shaped larva, or leptocephalus, that is entirely different from the adult eel. There are 22 families, embracing 350 species.
Eels are mainly marine fish, living in warm seas. Only one family lives in fresh water, and the remaining families are sometimes called marine eels. Most marine eels live in shallow water, where they stay hidden in rock clefts and coral reefs or in burrows made in the bottom. Members of the order are mainly predators. Certain species of the family Congridae make vertical burrows in sand. They live in large social groups, forming “eel gardens.” Some, such as the family Synaphobranchidae, inhabit depths of 3,000–4,000 m.
Freshwater eels, which belong to the family Anguillidae, live in fresh water from the immature stage until they reach sexual maturity and enter the open sea for spawning. The single genus, Anguilla, includes ten species that are found in the basins of the Atlantic, Indian, and Pacific oceans. Best known is the European eel (Anguilla anguilla), which inhabits fresh waters of Europe from the basin of the White Sea to the Black Sea, as well as North Africa. Usually the females head upstream, while the males continue to feed in river mouths. The eels are voracious predators that hunt at night. After living in a river or lake from five to 25 years, they swim down to the sea and, after covering a distance of 4,000–7,000 km, spawn in the Sargasso Sea at depths of 400 m and water temperatures of 16°-17°C. After spawning, the eels die, while the larvae drift with the currents to the coasts of Europe for 2½ to three years. After attaining a length of 75 mm, the larvae undergo metamorphosis and turn into 65-mm-lohg elvers that enter rivers. Freshwater eels are an important food fish.
REFERENCESNikol’skii, G. V. Chastnaia ikhtiologiia. Moscow, 1971.
Zhizn’ zhivotnykh, vol. 4, part 1. Moscow, 1971.
V. M. MAKUSHOK