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Fishes - Electric Eel

Region: South America

Class: Osteichthyes

Order: Cypriniformes

Family: Electrophoridae

Genus: Electrophorous

Scientific Name: Electrophorus electricus

Description: Eel-like fish (not a true eel) with electric organs; dorsal and ventral fins absent; anal fin very long, united with caudal fin to form a single fin which does not extend on to the dorsal surface of the body. Scales absent. Colouration uniform olive brown, underside of head and throat of adult is brilliant orange; eyes shining green. Length: up to 2.9 metres

Distribution: Northern part of South America. Greatest prevelance in the Amazon Basin.

Habitat: Shallow, muddy pools along creeks and rivers.

Food: Lives on freshwater shrimp as a subadult, changing later to fishes and frogs. The electric eel is toothless and swallows food whole.

Reproduction and Development: Practically nothing is known about the breeding. They disappear from their usual Amazonian haunts during the breeding season. Later, when they return, one of the parents takes care of the young until they are 10 to 15 cm. (4-6 ins.) in length. They have not yet been bred in captivity.

Adaptations: The electric eel has markedly degenerate gills that play no significant part in its respiration. The uptake of oxygen occurs in the mouth, which is almost entirely lined with paillae (protuberances) that provide a large total surface area for gas exchange. Comparatively little carbon dioxide is released through the mouth; most of it is discharged into the water by way of the skin and the vestigial gills. Experiments have shown that the electric eel is responsive to the oxygen content in the air. When it is subjected to air that is low in oxygen, it speeds up its breathing efforts; when the air is abnormally high in oxygen, the fish's breathing slows down. In all fishes, the electric organs are derived from muscle cells. The thin, flattened cells of electric organs are known as electroplaques. Each cell is imbedded in a transparent gelatinous material. In the electric eel, the organ is arranged in columns of electroplaques which run longitudinally and make up a large portion of the animal's mass. All the viscera lie in the general region of the head (can be about 1/5th of the body length). The electroplaques along the body of an electric eel discharge simultaneously (within a period of 3 milliseconds). Power is released by the central nervous system (voltage as well as intensity). Although the charge lasts only two or three thousandths of a second, it can be repeated up to 150 times an hour without visible fatigue on the part of the eel. Lying motionless in the water, the eel is usually electrically inert but when it begins to move, it emits small direction finding impulses at a frequency of about 50 per second.

Threats: The electric eel has no enemies other than man and is among the most feared fish in South America.

Status: Common

References: Animal Life Encyclopedia Vol. 1 and 2. Dr. Bernard Grzimek Scientific American Magazine. Oct. 1968. Article by Kjell Johansen