(strictly) Electrophorus electricus, a species of fish resembling an eel (though not related) that is capable of generating powerful electric shocks. / (broadly) Any species of the genus Electrophorus.

A snake-like fish, reaching between 60 cm and 1.5 m in length, Anguilla anguilla.

(simile, colloquial) So slippery that it is almost impossible to hold. / (idiomatic, simile, colloquial) Very crafty or cunning.

A species of eel, Anguilla japonica, found in Japan, Korea, China, Taiwan, and Vietnam, as well as the northern Philippines.

An eel-like deep-sea fish, Eurypharynx pelecanoides, the only known member of the genus Eurypharynx and family Eurypharyngidae, which is rarely seen by humans, although occasionally caught in fishing nets.

Any of the subfamily Heterocongrinae in the conger eel family Congridae, which live in burrows on the sea floor.

Aplatophis chauliodus, burrow-dwelling eels native to the Gulf of Mexico and the Caribbean Sea.

An air-breathing species of fish (Monopterus albus) found in East and Southeast Asia.

Panturichthys mauritanicus, a species of mud eel.

Scolecenchelys castlei, a species of snake eel found off the coast of New Zealand.